Trans IMarE, Vol 105. Part 1. pp 23-52
Cycloconverter drives for ship propulsion
* K S S m i t h , BSc(Eng), PhD, AMiEE, *R Y a c a m i n i , BSC, MSC, cEng, MiEE. FIMarE a n d t A C W i l l i a m s o n ,
BSC, PhD, CEng. MIEE
*Department of Engineering. University of Aberdeen and fDepanmeni of Electrical Engineering, UMIST
SYNOPSIS
The Royal Navy are considering,
amongst other options using electrical propulsion,
employ ing variable
frequency
cycloconverters
on the next generation
of anti-submarine
warfare frigates.
The ongoing work in the
Engineering
Department
of Aberdeen University is addressing some of the challenges advanced by electrical propulsion.
This paper
concentrates
on the electrical characteristics
of cycloconverter
drive
systems.
INTRODUCTION
The subject of electrical motor propulsion of ships is one
which is being addressed for future use in both the merchant
and defence fleets. This paper examines the types of drive units
which are being proposed and then sets out to study the system
which at the moment looks to be the strongest candidate for use
in the next generation of Royal Navy frigates. The power
electronic unit considered in most detail is the cycloconverter
driving an induction motor.
The operating principles of the cycloconverter are explained and typical examples of this converter's use to date are
indicated. The advantages offered by this propulsion method
are discussed, as is a method of modelling the cycloconverter
and elecuical machines using a lime domain simulation. Using
these computer models it is possible to predict the performance
of the complete marine propulsion system by including the
synchronous generators, power electronic convener, and the
propulsion motor in the simulation. The computer models are
general purpose and are not restricted to any particular drive
configuration. Different convener connections and motor arrangements can be readily incorporated into the simulation.
This is demonstrated in this paper by examples.
ELECTRICAL PROPULSION OPTIONS
The possibilities of using electrical propulsion rather tiian
gas or steam turbines or diesel sets is not anew idea. During the
1920s and 30s the United States aircraft carriers Lexington and
Saratoga had turbo-electric drives and the cruise liners
Normandie and Scharnhorst were both electrically driven.
However, recent advances in power electronics and elecuical
machine design suggest thai the use of electrical propulsion
will be a cost-effective alternative to the mechanical systems
which are currently most commonly used on vessels. Electrical
propulsion has already gained a foothold in the industry as
drives for large cruise liners and icebreakers.
In the U K , the best known example to date is the much
publicised replacement of the Queen Elizabeth II steam turbines with two dc link inverter systems supplying synchronous
machines which are directly coupled to the propeller shaft.'-The conveners are of the G E C 'synchdrive' design.'"* The
synchdrive is used to provide variable frequency control of the
synchronous motors between 0 and 60 Hz. For cruising the
K S Smith received his BSc(Eng) and PhD degrees
from the University of Aberdeen in 1988 and 1992
respectively. SinceOctot)er 1991 he hasbeen a Lecturer
in Engineering at the Department of Engineering, Aberdeen University, with responsibility for the teaching of
heavy electrical power engineering. His main fields of
interest are the interaction between electrical machines
and power electronic converters on closely coupled ac
systems such a s offshore oil and gas installations and
ships. He has been responsible for harmonic and power
system stability measurements on a number of offshore
installations in the UK sector of the North S e a .
R Yacamini is currently a Senior Lecturer in the
Department of Engineering at Aberdeen University. His
previous experience includes 10 years a s a design
engineer with English Electnc and G E C in the rectifier
and high voltage dc transmission fields. During this time
he made extensive use of physical simulations for
controller design a n d system studies. This industrial
period was followed by five years as a lecturer at UMIST
where he carried out research, using frequency domain
computer programs, into H V D C and reactive compensators. He took up his present post at Aberdeen in 1982
and has been involved in consultancy work for the oil
industry for most of this period. The main thrust in his
research has been to developtimedomain C A D analysis
packages for power electronic applications. H e has
published over 50 papers in this and related fields.
A C Williamson obtained his B S c at the University of
Bristol and then spend 13 years in industry working on
the design and development of a wide range of electhcal
machines with emphasis, towards the end, on large
turbine generators. Since joining UMIST (where he
obtained his PhD and is now a Senior Lecturer) he has
been involved in the development of various powerelectrical machine combinations. Typical applications
have been high s p e e d engine testing dynamometer,
high speed, high power vahable speed drives and windturbine driven alternators.
variable frequency conveners are not used. The convener
accelerates the synchronous machines up to the same frequency as the 60 Hz ship supply and then synchronises its
output with the supply. The synchronous motor is then transferred from the convener to the ac system busbars.
In Northern waters around Canada, Finland, and the CIS,
icebreakers are required to keep waterways ice free during the
23
K S Smith, R Yacamini & A C Williamson
winter months. A number of icebreakers have
now been built or fitted with electrical proI. » 1 BMW diesel
generators
pulsion employing cycloconverters. These
AfI switchboard
Forward switchboard
drives give good performance a l the high
600V
50Hz
power ratings and low speeds which are required for this application. Twelve pulse
cycloconverters have recently been installed
2 . V65MW
2 .9C5kW
on the cruise liners Fantasy (US) and Crystal
Phase controlled
motor generator
thyristor rectifiers
Harmony (Japan) rated at 2 x 14 M W and 2 x
sets
12 M W respectively. This is approaching the
power levels required for the propulsion of
ifcOV 60Hz
ttOVÔOHz
the next generation of antisubmarine warfare
frigates.
Ships supplies
Royce
Ships supplies
G! 2»Rolls
The Royal Navy, in considering the deSpey gas turbirws
sign of futiffe warships, must take into consideration the required military role of warships in a changing political climate, and note
the practices being used by the merchant fleet
2 k V5MW, 750V OC
in the design of ships, as these may be aR)lipropulsion motors
cable to warship design. Frigates, which will
2 « Fixed pitch propellers
form üie backbone of the fleet into the 21st
century, have two major roles. They are required to police international waters and
Fig 1 : CODLAG propulsion system on the Type 23 ASW frigate
maintain free access to trade routes for the
merchant fleet. This is essentially a cruising
exercise requiring low cost propulsion. The
second and major war time activity of the
4 K 20MW
generators
frigate is in submarine detection. A n imporAft switchboard
_Forward_sw|l chboard
tant design feature is therefore to reduce the
I
(
vibration caused by frigate propulsion sysI
tems, as this is transferred to the hull of the
ship and becomes water bcMiie noise which
can be delected by submarines at a consid2x 1MW
2 x U 2MW
motor generator
erable distance. Frigates should ideally crecycloconverters
sets
ate as little water borne noise as possible.
This reduces the possibility of detection and
2 X 1DMW
ttOV 60Hz
fctOV 60Hz
makes it easier in turn to detect the noise
propulsion motors
generated by enemy vessels. One possible
Ships supplies
Ships supplies
method of achieving this, which is currently
being considered, is to adopt electrical propulsion. This will also reduce running costs
Fig 2: General arrangement of an 18 MW electrical propulsion system
and, itisbeUeved, would significantly reduce
the noise signature of vessels.' The reduction
in space required ïot modem electrical machines and advances
in power electronic converter technology makes electrical
propulsion systems a real possibility. Previous designs of
machines and power converters were considered too bulky for
naval use.* It is widely accepted that on the QE2, the onboard
noise levels were reduced following the installation of the
Fig 3: Cycloconverter output waveshape composed of
electrical propulsion system. This is on a ship where the
segments of the line to line voltage on Input side
original steam turbine drives were considered to be quiet. It
should be remembered, however, that the converters used on
the QE2 only operate during docking and slow cruising, and
that audible noise as experienced by the passengers of a cruise
liner is different from the water bcäue noise generated by the
ships propellers.
©
0
Another majcM" advantage which electrical propulsion offers
ship designers is the relative freedom with which the prime
movers and power electronic converters can be located within
the ship structure. The electrical cables linking the generator
switchboard, converter, and propulsion motor are more flexible than the mechanical shafting required for gas turbine
propulsion systems which require linear alignment.
The first of the R N frigates partially to employ electrical
propulsion was the Type 23 Anti-Submarine Warfare (ASW)
frigate using the combined diesel electrical and gas (CODL AG)
24
©
©
0
Fig 4: General arrangement of two Graetz bridges to
form a single phase cycloconverter
Trans IMarE. Vol 105. Part 1. pp 23-52
0-5
Ratio of Output frequency
to Input frequency
Fig 5: Chart showing the harmonic frequencies present in the output
voltage of a single phase cycloconverter
sets have been employed lo isolate the propulsion and ships service busbars. This is unlike
offshore practice where the distortion on the
low voltage system is tolerated and only filtered out if it is found to be absolutely necessary.
The dc motors in the C O D L A G system
operate under quiet cruise conditions for towed
array sonar operation. The output of the converter CŒitains harmonics at six, and twelve
times the supply frequency, superimposed on
the mean dc output level. Additional filtering
is connected between the converter and the
motor to prevent harmonic fluxes in the motor
generating noise on the propeller shaft system. When fast acceleration is required the
gas turbines are used to provide ' sprint' power.
The system load at sea varies from about 1.5
M W at low speeds to about 4.5 M W when
motors are at foil power. The motors continue
to operate at full power when the gas turbines
are in use. The harbour load is 0.4 M W .
The Royal Navy is now considering using
full electrical iM^opuIsion for the next genera-
Fig 6: Primitive model of a three phase induction motor
Fig 7: Primitive model of a three phase, salient pole
synchronous machine
system, illustrated in Fig 1.' Generation is at 600V with two
1.65 M W thyristor rectifiers coupled to the generator busbars.
These supply 1.5 M W dc motors which are directly coupled to
the propeller shaft system. When the rectifiers are in operation
severe commutation notching will occur on the generator
busbar, producing waveshapes similar to those observed on
offshore drilling rigs.* ' If the 440V ship service systems were
supplied through step-down transformers from the600W busbar,
these commutation disturbances would be reflected through
the üansformers and appear throughout the low voltage distribution system. This distortion would exceed the levels allowed
in naval systems. To overcome this problem rotary converter
tion of frigates.'". A 5000t A S W frigate has to achieve a
maximum speed of 30 kn using twin shafts. This requires 18
M W per shaft at 200 rev/min. The design of large dc motors is
practically limited to around 8 M W , and tandem designs using
three or more dc machines are not considered feasible as the
size of the overall propulsion motCH" becomes excessive. It wUl
therefore be necessary to use ac machines to reach the required
power level in conjunction with variable frequency systems
such as cycloconverters. Two alternatives are available for the
ac propulsion motors: either induction (asynchronous) or synchronous machines. Induction machines are considered to be
more rugged and robust, and require less maintenance, as
25
K s Smith. R Yacamini & A C Williamson
unlike the synchronous machine there are no electrical terminals to the rotor requiring the use of slip rings. The air gap of
an induction motor is generally smaller than that of a synchronous machine which will make it less able to withstand shock.
Induction machines are also generally cheaper than synchronous machines. The discussion is therefore ongoing and
manufacturers are now looking at the design of induction
machines with much larger air gaps, which will give the
induction motor the same robusmess as the synchronous
machine for this application. The general arrangement of a
possible full 18 M W electrical propulsion system is shown in
Fig 2.
THE CYCLOCONVERTER
The cycloconverter is a power electronic circuit which
converts an ac input to an ac output at a lower frequency. Unlike
many of the converters commonly in use today, such as the
'synchdrive' mentioned above, this is achieved without using
an intermediate dc link, ie the cycloconverter is a single stage
converter. The cycloconverter is not a new power electronic
circuit The principles of this converter are described in one of
the earliest texts on power electronics." Considerable development work took place in Germany in the 1930s where
cycloconverters were used for unction applications. At this
time the principles of grid control, to give a variable output
Fig 8: General arrangement of a three phase, six pulse,
voltage and frequenc were mastered.'^ The cycloconverter
cycloconverter Induction motor drive
generally found an)lication where low frequency, high power ac drives are required.
Examples include tube mills,'^ '* and railway
traction." More recently the converter has
(A)
been applied successfully to a mine winder,'*
the advances in control techniques giving a
1.3k performance comparable with that of a dc
I.ZJk drive."
UThe basic building block used in the con710struction of the cycloconverter is the six pulse
/
il !
3UU —
J\
A
1'
Graetz bridge. A description of the operation
1
>
asoof this converter can be found in standard
texts on power electronic circuits.'*" The
0r
'
Graetz bridge is normally used either as a
hi
1
1 Ml
1
.33U 1
rectifier or as an inverter, converting an ac
1 V
"
1'
1
1
li
Kl
'
\
input to a dc output or a dc input to an ac
• Siltl A
<
1
1 mi
/
T
pMili
/
.710 output. This is controlled by changing the
1
il"
/
firing instants of the thyristors within the
.|k '
f'
'i
«/
bridge, relative to the three phase supply at
W
'-Hi;
W
•1.21k the bridge ac terminals. It is possible to pro-I.Ik duce a low frequency ac output from what
V V
.|.7)k
,
would normally be considered as the dc ter1 0
2ku
4in
ai»
Hkii
IWki
12(kii
14JIII lOlin
IHIIiii
3IUII Ks)
minals of the bridge by continually changing
the fuing delay angles of the thyristors. The
Fig 9: Simulated currents for the system in Fig 8; solid line Is the
output ac voltage waveshape is then cranmotoring condition, dashed is the generating condition
posed of segments of the input ac line to line
voltage as shown in Fig 3. It is possible with
the cycloconverter to control independentiy
both the frequency and amplitude of the output voltage. A
bridge A switched o f f This can be achieved by blocking the
single six pulse bridge cannot supply both positive and negaüiyristOT gate signals to each bridge at the appropriate time.
tive half cycles of the output current which necessitates tiie use
This is not a trivial problem; determining the correa instant lo
of a second bridge. This leads to the basic six pulse single phase
transfer load current between bridges has been a m^or problem
cycloconverter configuration shown in Fig 4. For this circuit to
for cycloconverter designers.
operate successfully, it is necessary to allow only one bridge to
Three phase cycloconverters are formed by combining
conduct at any time. If üie desired load current is positive,
tiiree individual single jAase units. A number of three jAase
bridge A should be conducting and bridge B switched o f f
COTinections are possible which have differing harmonic efNegative load current should be supplied by bridge B , witii
fects upon both the input and output sides of the converter.
\ V n '
\ iP !
26
\ .
Trans IMarE. Vol 105. Part 1, pp 23-52
modulation process present within the
cycloconverter givesriseto con^)onents which
are neither integer multiples of the input or
the output frequencies. The frequency content of tiie output voltage waveshape of a
cycloconverter is therefore extremely complex, containing a wide range of frequencies.
These can be conveniently represented using
tiie chart shown in Fig 5.
The amplitudes of these harmonic frequencies are a fonction of the output voltage
ratio (the depth of modulation control signal
to the converter) and the load power factor.
Each Une in Fig 5 has associated with it a fixed
amplitude, regardless of the frequency ratio.
When the output frequency of Üie drive is
zero, the harmonics present in the output
voltage waveshape correspond to integer
multiples of the converter pulse number and
2Uii
Hkii
ICiOin
lakii
aKkn l(s)
tiie supply frequency. For example, a six
pulse bridge will contain harmonics of order
FIg 10: Cycloconverter output voltage (motoring condition)
6, 12, 18, etc. This corresponds to the left
hand part of Fig 5, where the families of
harmonics present in tiie cycloconverter
originate. When the output frequency of the
cycloconverter is increased, the second term
in equation (1) becomes non-zero producing
frequencies above and below the harmonic
parents. This is clearly shown in Fig 5. It
should be noted from this chart that at several
distinct values of output frequency, the components given by equations ( 1 ) and (2) will be
of very low or even zero frequency, ie dc
components of voltage. Alternatively tiiey
can produce frequencies very close to, or
exacüy equal to the desired output frequency.
Under tiiese operating conditions, the dc
component could possibly saturate the propulsion motor, or the components close to the
wanted output frequency may produce a pronounced beating effect of the motor current
and voltage waveshapes. It is possible to
derive equations which give the frequency
content of the current supplied to the
16Un
cycloconverter from the ac system. As for the
output voltage waveshape this is also found to
Fig 11 : Cycloconverter output voltage (generating condition)
contain a very wide range of frequencies.
When considering using a cycloconverter
for
a
marine
electrical
propulsion drive a number of questions
Twelve pulse cycloconverter circuits can be formed using four,
must be addressed, including: What effect w i l l the
three phase six pulse bridges.
cycloconverter have on the synchronous machines supplying
For the six pulse, single phase cycloconverter, supplied
the ac system? How severe will die ac voltage distortion be. and
from an infinite busbar, the major harmonics present in the
what oscillating torques will be induced on the shaft of the
output voltage are given by:^°
prime mover? Is tiiere a possibility of the oscillating torque
exciting a torsional resonance of tiie propulsion motw-propelf, = 6 p f . ± ( 2 n + l ) f „
(1)
ler shaft system? Is one cycloconverter configuration better
tiian
another for a particular appücation and how is this
For the twelve pulse converter the harmonics are:
assessed? How will the system perform under abnormal conditions such as semiconductor device failure or unbalanced
f,= 12pf,±(2n+ l)f„
(2)
supply conditions?
where f, is the input frequency, f« the output frequency and f^ Üie
harmonic frequencies.
From these equations it is clear that the output voltage of the
cycloconverter contains a large number of harmonic terms.
The frequencies given by the relationships in equations ( 1 ) and
(2) are not in a mathematical sense true harmonics, as the
Questions such as tiiese can be answered by developing
computer models to simulate complete electrical propulsion
systems and assess the relative advantages and disadvantages
of different converter configurations. For tiiis application C A D
software has been used, which allows different cycloconverter
topologies to be readily assembled and simulated.
27
K S Smith. R Yacamini & A C Williamson
POWER ELECTRONIC
SIMULATION
There is a wide range of computer simulation packages available on the software market which can be ^ p l i e d to the analysis of
power electronic and other similar systems.
In developing a computer model of a complete marine propulsion system it is necessary
to describe electrical machines and power
electronic converters, to be able to change the
arrangement of the components, implement
different control strategies, and also smdy the
effects of abnormal opo^tion on the p o f ormance of the converter.
One such package is the Saba* simulator,
which is marketed as a mixed analogue and
digital simulation package and has been found
particularly useful for this type of application. The simulation process using this package can be divided into three distinct stages,
involving the input of the system data, performing the system analysis, and finally
processing and viewing the results of the
analysis (post-processing).
The input to the simulator consists of a file
describing the system to be analysed. This
netUst file can contain references to otiier
netlists and components which allows full
hierarchical systems to be convenientiy analysed. This feature is particularly useful in
developing models of large complex systems, where each subcomponent can be tested
individually before being inccMporated into
the larger system. When the nethst describing
the system is complete, the simulator is invoked and the netlist information read and
checked for errcx's. If no errors are found the
simulation can proceed. The numerical integration techniques used by this simulator
include first and second csder methods such as
Backward-EulerandTr^zoidal methods. The
post-processor allows the results of the analysis
to be viewed on the computer screen. This takes
the form of waveshapes which is convenient as
itmaintainsanengineaing 'feel' forthesystem
being analysed. Frequency domain spectra can
also be di^layed if required.
IN
r.|
6uk
..1
4 Ilk
-
;uk -
-lOk -4Uk
-
.40k —
.•Ok -
Ô
3kii
(Û11
Util
lUkii
lÀn
l-Âu
ItiÙiii
ilùii
Win
is the generating condition
TUMn Us)
Fig 13: Currents drawn by Individual cycioconvsrters
The unique feature of tiie simulator, which
makes it particularly useful for the simulation of marine
cycloconverter prcpulsion systems, is the ability to define the
characteristics of new components. This is achieved using the
Mast modelling language.'' Mast is very similar to the programming languages C and Fortran and is used to describe the
matiiematical relationships governing the operational characteristics of the desired component. The characteristics of any
system can then be programmed, removing the restrictions
present in the type of simulators which onlyrepresentelectrical
networks. Mechanical quantities can be directly represented in
their own units and not by electrical analogues. The connection
points to the templates which describe components can be
either electrical (x mechanical nodes. Although the simulator
is marketed as an electrical simulate^- this facility allows it to be
used as a mechanical simulator, and where electrical machines
are used as an electro-mechanical simulator.
28
4I11
The programming capabilities of Mast have therefore been
used to develop models which describe the operation of induction and synchronous machines, as well as the controller
present in the cycloconverter. Electrical machines have been
modelled by programming the voltage balance equations of the
phase models of the machines in combination with the relationships describing the dynamics of the rotor system. In the case
of the induction machine, the representation employed in the
simulations is shown in Fig 6.^ The machine consists of three
stator windings (sa, sb, and sc) and three rotor windings (ra, rb,
and rc). The parameters for tiiis model can be calculated from
the fundamental equivalent circuit of the machine. The primitive model of the synchronous machine implemented is shown
in Fig 7. In this representation four windings are shown on the
rotor of the synchronous machine, two in the direct and two in
the quadrature axis." This allows the effects of synchronous
Trans IMarE. Vol 105. Pan 1. pp 23-52
of the stator currents to give torque control,
can also be implemented.
The basic elements of a ship electrical
propulsion system have been modelled; these
can be used to study the different systems
proposed.
POSSIBLE
CYCLOCONVERTER
PROPULSION SYSTEMS
lOka
llUii
Fig 14: Total current drawn from the ac system
aWkii
t(s)
Full electrical propulsion of a 5000t A S W
frigate will require two drives each rated at 18
M W . Present Royal Navy frigate experience
of electric drives is limited to the 1.6 M W dc
drives used in the C O D L A G system. It is
unhkely üiat tiie R N will adopt tiie 18 M W
drive in the fu^t instance; instead it is felt tiiat
a 4 M W drive, combined wifli existing gas
turbine technology in an arrangement similar
to the C O D L A G system, is likely to be used
as a further step towards tiie 18 M W drive.
This smaller drive will itself intixxluce a
number of new design problems to frigate
electrical engineers. These design questions
are related to the topology o f the
cycloconverter and changes to the power
system itself will be required.
In order to reach the power levels required
for electrical propulsion it will be necessary
to increase the voltage of the prime mover
generators from 440/660V to 3.3 k V , 6.6 k V o r
11 kV. Switchgearratedattiiesevoltage levels
is readily available from manufacturers, and
has found extensive use on offshore oil and gas
recovery platforms. It has also been suggested
that it may be advantageous to raise tiie frequency of generation frcan 60-90 Hz.
In designing the 4 M W drive a number of
different options have to be considered. What
should be the pulse number o f the
cycloconverter? Should a tiiree or four wire
connection to die propulsion motor be used?
Fig 15: Motor current waveshape showing the effect of changing from a
Should an induction or a synchronous mafour wire to a three wire connection; dashed is four wire, solid Is three
chine be used? Are some transformer conwire
nections preferable to others? In attempting
to answer these questions a large number of
machine saliency to be included in the simulation if necessary.
different converter configurations must be considered. The
Phase models of electrical machines have been found to be
computer modelling of the cycloconverter drive allows die
more useful than the more widely used two axis models.^
relative merits of different converter topologies to be considUsing the Saber simulator, it was found that the phase model
ered and the performance of the complete electrical propulsion
was more robust and gave shorter run times in many cases. In
system as a single unit to be analysed.
addition using the phase model it is possible to consider the
effects of unbalances within the machine and to show how
these would affect the overall performance of the cycloconverter
SIMULATION RESULTS
drive.
In the contfoller implemented in tiie work described in tiiis
paper an open loop strategy has been employed, based upon die
Cycloconverters and motors
well known inverse cosine control method. The logic required
In order to illusfrate the characteristics of different conto implement this controller, determining tiie thyristor firing
verter topologies, and also demonstrate tiie usefulness of time
instants as weU as die converter group blocking and deblocking
domain simulation as a design tool, waveshapes obtained from
signals, has been written into the simulation using the Mast
tiie simulation for a number of different cycloconverters are
modelling language. Otiier control sfrategies, such as control
presented and discussed.
29
K s Smith. R Yacamini & A C Williamson
The basic building block used in the design of large
cycloconverter drives, as mentioned above, is the six pulse
bridge. Two back to back bridges combined give a
cycloconverter with a single phase output and six bridges can
be used to give a three phase output. Transformers are required
at die input to each phase of die cycloconverter to provide
electrical isolation between phases, if the motor phases are not
isolated. One of the propulsion options being considered is to
use a star connected induction motor. A possible configuration
f o r a 4 M W six pulse drive is therefore shown in Fig 8. A switch,
S W l , is shown in the neutral wire to the motor. For the first set
of simulation results this switch is left closed, giving a four wire
motor connection. It will be shown later that if S W l is opened
to turn the drive into a three wire connection then changes in the
waveshapes associated with the drive will occur. The parameters of the system analysed have not been chosen to model an
existing or planned cycloconverter installation. The purpose of
displaying the waveshapes is to emphasise the possibilities for
analysis offered by the simulation. In the cases presented for
example, the system supply frequency is 50 Hz, rather than the
more normal 60 Hz for a ship, or the 90 Hz suggested for future
installations. The supply frequency, and indeed all the other
parameters of the system including the machine ratings and
reactances, can be conveniently changed to allow the study of
other systems. More importantly from the designer's point of
view, this allows direct comparisons between systems to be
made.
The waveshapes obtained from this simulation are shown in
Figs 8-14. Two conditions are illustrated corresponding to
motoring and generating action in Uie motor with the output
frequency of the drive at 15 Hz. Fortiiemotoring condition üie
mechanical power supplied by the motor is 2.4 M W whilst for
the generating condition üie power is 4.2 M W . The waveshapes
for each of tiiese conditions are shown together on the same
graph to allow direct comparisons in the time domain to be
made between them.
Figure 9 shows the stator currents for the two cases studied.
There is clearly a phase difference present between these
waveshapes. This is required to achieve the reversal of power
flow, as no phase difference is present in the motor line to
neutral voltage as shown in Figs 10 and 11. This is to be
expected as the modulating function to the cycloconverter,
which determines the reference signal to the inverse cosine
controller has not changed. The change in load is achieved by
changing tiie polarity of tiie load torque. It should be noted from
close inspection of Figs 10 and 11 that with the motor generating, the bridges witiiin the cycloconverter spend considerably
more time in inversion than in rectification mode. This is to be
expected since power flow is now from the motor shaft back
tiirough tiie converter to üie ac power system. The torque
waveshape on üie shaft oftiiepropulsion motor is shown in Fig
13. The reversal in tiie sign of torque required to produce a
reversal in power flow is clear. The currents drawn by the
individual cycloconverters are shown in Fig 13. Inspection of
tiiese waveshapes shows that there are, in fact, a wide range of
frequencies present, including frequencies below the supply
frequency. The effect of Üie 120 deg phase displacement
between each of tiie single phase cycloconverters is to reduce
the number of frequencies present in the current waveshape
drawn from the supply system. This waveshape is shown in Fig
14. Although tiie harmonic content is reduced tiiere is still a
wide range of frequencies present, including non-integer and
sub-harmonic terms.
The results of passing the lime domain data, present in tiie
waveshapes presented above, through a Fourier analysis programme with a resolution of 5 Hz, produced tiie frequencies
30
Rg 16: Primitive model of an induction motor with a
double wound stator
Fig 17: General arrangement of a six pulse
cycloconverter supplying a double wound stator
induction motor
shown in Tables I and II. for the motoring and generating
conditions respectively. The corresponding harmonic spectra
are shown in Appendix 1 for the motoring condition.
Inspection of Tables I and II shows tiiat the harmonics
present in the output voltage waveshape of üie cycloconverter
agree with those which would be obtained using equations (1 )
and (2), which are based on a frequency domain calculation.
The simulations do have the advantage of showing actual
waveshapes which the previous analysis does not show. The
waveshapes obtained from the simulation also include üie
effects of commutation overlap and the iniercoupling that is
present between tiie cyclcoconvertcrs. These effects are ignored in the frequency domain calculation. The wanted output
frequency is 15 Hz, and sideband frequencies appear at odd
Trans IMarE. Vol 105. Pan 1. pp 23-52
I
3tn
I
•Uli
I
6Uii
I
Hkn
I
lUkii
I
I3in
1
Mn
I
Idlkn
I
ItUn
3Xkii ih
Fig 18: General arrangement of a six pulse cycloconverter supplying a
double wound stator induction motor
^
Jkn
i
-Uli
I
6an
!
8Uii
1
lUkn
1
Okn
1
l*ka
1
IfiOra
1
IWm
2UUn t(s)
Fig 19: Voltage across one stator phase of the double wound motor
multiples of 15 Hz above and below the supply frequency times
the converter pulse number, ie 300 Hz. Sidebands also appear
cenffed around600 Hz. For example, sidebands cenu-ed around
300 Hz appear at 285 Hz and 315 Hz, and also at 255 Hz and
345 Hz.
Harmonic currents flow in the stator winding of die machine
at tiie frequencies present in the output voltage w a v e s h ^ . The
15 Hz wanted component produces the mean dc component of
tOTque whilst the harmcMiic currents give rise to harmonic
components of torque. The largest harmonic torque is at 300
Hz. This harmonic torque is independent of the output frequency of the cycloconverter drive. The frequency of this
component is determined by tiie frequency of tiie supply
system and the converter pulse number, and does, in fact.
appear at the same frequency at which the
sidebands present in the cycloconverter output voltage are centred, ie at the product of six
timestiiesupply frequency andtiieccmverter
pulse number. This torque is produced by the
action of the pairs of sideband current harmonics centred around this frequency. The
wanted component of current at 15 Hz produces a flux wave in the air gap of the propulsion motor which is of positive phase
sequence. The first pair of sidebands occur at
285 Hz and 315 Hz. The current at 285 Hz
produces a flux wave which rotates in the
same direction as the 15 Hz flux wave, ie the
285 Hz flux wave is also of positive phase
sequence. The flux associated with the
component at 315 Hz will rotate intiieopposite
direction to that at 285 Hz and is therefore of
negative phase sequence. The contribution of
these components to the mean value of torque
is negligible. They do however combine to
produce a harmonic pulsating torque at 300
Hz. A similar argument can be applied to tiie
otiier sidebands centred around 300 Hz. A
harmonic torque also spears at 600 Hz,
which is produced by the sideband current
harmonics centred around this frequency.
The currents drawn by the individual
cycloconverters are very rich in harmonics.
Inspection of Tables I and II reveals some
large components, eg 20 Hz of 45.46 % and
80 Hz of 25.84 % for the motoring condition.
Due to the transformer ccmnections employed
and the 120 deg phase shift present at tiie
output of each individual cycloccaiverter,
many of these harmonics have their amplitude significantiy reduced intiiecurrent drawn
from the ac supply system. For example, die
COTiponents at 20 Hz and 80 Hz discussed
above are reduced to 1.03 % and 0.72 % in die
supply current. It should be noted that tiie
harmonics generally associated with a six
pulse converter, ie 5th, 7tii, U t h , 13tii, etc,
are present in both the ac system supply
current and the current to the individual
cycloconverters. The amplitude of these
COTiponents on the ac supply side and on die
cycloconverter input are tiie same. No significant attenuation of these components
occurs.
If the switch S W l in Fig 8 is opened, this
has an effect on die current supplied to the
propulsion motor. The current waveshapes obtained for the
motoring condition studied previously witii the switch closed,
and tiiat witii the switch open, are shown togetiier in Fig 15.
There is clearly a significant difference between the two
w a v e s h ^ s . This effect is due to the output voltage of tiie tiiree
phase cycloconverter containing frequencies which are of zero
phase sequence. Currents at tiiese frequencies can only flow if
tiiere is a neutral connection to die motor. These components
are tiierefore present in tiie earlier waveshapes where the
switch S W1 is closed but are absent when it is opened. It should
be noted, however, tiiat die presence or absence of zero
sequence currents in tiie supply to tiie motor does not affect tiie
elecfromagnetic torque produced bytiiemachine. This is due
to die zero sequence components producing no air gap mmf.
31
K S Smith. R Yacamini & A C Williamson
Zero sequence currents can therefore only
flow in the stator winding (if a neutral wire is
present), and consequentiy the impedance of
the induction motor is smallor to components
of zero phase sequence as the rotor is not
included in the zero sequence equivalent
circuit"-^
A n alternative design for the propulsion
motor would be to use an induction machine
witii a double wound statw winding. The
primitive phase model of such a motor is
shown in Fig 16, in which the two sets of
stator windings are displaced by 30 deg electrical, and each phase winding is supplied by
a single phase cycloconverter. The 30 deg
phase shift present in the stator windings has
the effect of cancelling a large number of the
harmonic mmfs present in the air g ^ of the
machine, and so reduces the ripple present in
I
i
i
I
i
I
!
6Un
Kin
UKkn
13Jm
\43a\
160m
I8O111
ZXkn l(s)
3lh
4kii
the induced machine electromagnetic torque.
This can be illusu-ated by the results obtained
Fig 20: Machine torque for double wound motor
from the computer simulation ior the system
shown in Fig 17, which features such a motor.
The current supplied to the motor is shown
in Fig 18. This waveshape is not signiflcantiy
different from that drawn by the three phase,
three winding motor shown in Fig 9. The
motor line to neutral voltage is shown in Fig
19. This waveshape is seen to contain more
high frequency terms due to the increased
number of converters supplied from a common busbar. The effects of commutations
taking place in other converters are present
from the connection at the point of common
coupling. Intarcoupling effects between the
six stator windings of the machine are also
present
The most significant diffCTcnce between
the three phase machine and the six phase
machine lies in the torque shown in Fig 20.
Comparison of this waveshape with Fig 12
clearly shows that the ripple component is
reduced. (Note that the dc value between the
two cases is different.) The cycloconverter
—!
1
1
1
i
1
1
I
I
3Jni
-till
fiUn
Bkn
Ittkn
12Un
14Cini
160m
IHm
aXkn t(s)
input current shown in Fig 21 is broadly
similar to that of Fig 13 as would be expected.
Fig 21: Current drawn by an Individual cycloconverter
The current drawn from the ac system is
shown in Fig 22 which displays less harmonic
distortion than die earlier case of F i g 14.
content of the torque is reduced, as are the harmonics present
These general observations on the time domain waveshapes
in tiie current waveshape from the ac system.
are confirmed by inspection of tiie results obtained from
Fourier analysis shown in Table III.
Ships generators
The frequencies present in tiie motor voltage and the motor
In the earlier sections the effects of the cycloconverter upon
current for the double wound machine and the earlier tiiree
the propulsion motor, and especially tiie torque produced by
phase machine are almost identical in both frequency and
the motor, have been considered in detail. Large cycloconverter
amplitude. The current drawn from the ac system contains less
drives, if applied to ships, will have a significant effect upon tiie
hamionics tiian tiie earlier case; the side bands previously
synchronous generators which supply the system. The
centred around tiie 50 Hz fundamental are significantiy reduced. It should be noted that the harmonics characteristic of
cycloconverter propulsion system on a frigate would, in fact,
a six pulse drive, ie the 5th and 7th, are not eliminated as they
be tiie largest single load on tiie frigates electrical system. A n
would be with a twelve pulse converter. They are, however,
understanding of the possible detrimental effects of the drive
reduced using the double wound stator.
on the alternators is therefore required.
The characteristics of non-linear loads, such as diode and
From the waveshapes and tables of harmcmics presented, it
thyristor bridges, on die performance of synchronous mais apparent tiiat the cycloconverter drive with a double wound
chines has been studied previously
These works show that
stator on the propulsion motor offers a number of advantages
for wound rotor machines which do not display the effect of
over a three phase machine. Most significantiy tiie harmonic
32
Trans IMarE. Vol 105. Pan 1. pp 23-52
akii
lakii
IHkii
3irkii l(s)
Fig 22: Total current drawn from the ac system
(N .,1
12.3k .
ent system components, are included automatically in tiie time domain simulation.
Figure 23 shows tiie torque on tiie shaft of
tiie alternator when the cycloconverter is running. This waveshape is seen to be rich in
harmonics, which are tabulated m Table IV
and also shown graphically in Appendix I.
The most significant of these is at 300 Hz (30
%), produced by tiie action of the 5ti3 and 7ti3
harmonic currents, drawn by the
cycloconverter, which flow in the alternator
stator. It should also be noted tiiat tiiere are a
number of lower frequencies present in this
waveshape some of which have relatively
large amplitudes, forexamplea 15 Hzcomponent of 3.8 % and 30 Hz of 6.8 %. There is
clearly a possibiüty of these or other such low
frequencies exciting a resonance of the prime
mover-altemator rotor system, careful consideration of which will be required. The
current flowing in die stator windings is shown
in Fig 24. It should be noted that the amphtudes of the frequencies present in this
waveshape are not significantiy different from
those obtained using tiie earher simpler representation of the supply system by an emf
behind a fixed inductance. If Üüie simulation
had been perfOTmed with a synchronous machine displaying more significant sahency
this would not have been the case.
The simulation results given in this section
have shown tiiat tiie Saber time domain simulation package has been developed to model a
range of cycloconverters and electrical machines, and used to perform system calculations for the complete electrical propulsion
system as one unit, not as separate parts. The
interaction between the constituent parts of
the system is therefore maintained in tiie
simulation.
akii
2U(kn l(s)
CONCLUSIONS
Fig 23: Torque on the shaft of an aKemator supplying a three phase, six
pulse 4 MW cycloconverter drive
sahency, tiie machine can be represented by an emf behind a
fixed reactance. For a machine which does display saliency, tiie
ccHnmutating reactance is no longer constant and a more
ccMnplex machine model is required. The foil phase model
discussed in the section on power electmoic simulation is
therefore used in the ship propulsion simulations to represent
the alternator supplying the cycloconverter drive.
T o demonstrate the complete simulation o f the
cycloconverter propulsion system, \he synchronous machine
model was combined with tiie earher six pulse cycloconverter
supplying a three (^ase three winding induction motor. The
signals which this simulation provides, in addition, to those
obtained eariier, are the electromagnetic torque on tiie shaft of
the alternator, the currents flowing in the damper windings and
also the terminal voltage of the machine. With tiiis simulation
the effects of tiie time varying commutating reactance of tiie
alternator and all the intercoupling present between the differ-
In tiiis paper, tiie operating principles of
the cycloconverter have been discussed. This
converter spears at tiie moment to be tiie
most hkely candidate for use in the next
generation of Royal Navy frigates, should tiie Navy adopt ac
elecuical propulsion. It has been demonstrated that it is now
possible to analyse the complete electrical propulsion system,
including die synchronous generators, cycloconverters and tiie
propulsion motors which may be found on future marine
installations. As a design tool this computer simulation is
extremely useful. The way in which the parameters of one
system building block affecttiieperformance of another can be
readily calculated. The computer simulation is not restricted to
any one particular converter configuration and can tiierefore be
used to assess die advantages and disadvantages of different
electrical propulsion system arrangement.
The computer models have been achieved using tiie Saber
simulator, tiius taking advantage of a modem computer aided
engineering software package. Of particular importance is tiie
Mast modelling language, which can be used to describe die
operating characteristics of new components which may not be
33
K S Smith. R Yacamini tSc A C
Williamson
available in the system library. This has been
used particularly in tiiis work to define die
characteristics of electrical machines which
supply and fed from the power electronic
converters. The hierarchical nature of tiie
simulation package allows the different components of the system to be developed separately and tiien added into the complete system simulation. This also allows the system
topology to be readily changed. The ability to
simulate mixed electro-mechanical systems
has been emphasised. This ability is being
extended at Aberdeen University into the
analysis of motor noise generation and the
behaviour of shaft systems and propellers.
The results obtained from a number of
different system studies have been used to
illustrate the usefulness of this metiiod for
analysing the performance characteristics of
different cycloconverter systems.
Fig 24: Current flowing in the motor windings of an alternator connected
to a 4 MW cycloconverter drive
ACKNOWLEDGEMENTS
The authors would like to acknowledge the Science and
Engineering Research Council for providing funding and M r D
Bain. Reprographics Section, Department of Engineering.
Aberdeen University, for preparing illustrations.
REFERENCES
1. J B Borman. T h e electrical propulsion system of tiie
QE2: some aspects of the design and development'.
G E C Publication No 3493-353.
2. P Bloom, 'QE2 goes diesel electric'. Modern Power
Systems (USA). Vol 6, No 9, pp 19-23 (1986).
3. D Finney, 'The synchdrive - a synchronous motor
variable speed drive system', GEC Journal for Industry.
Vol 5, No 3, pp 108-114 (October 1981).
4. D Finney. 'Synchdrive converters for high voltage
motors', GEC Journal for Industry, Vol 7, No 1, pp 2530 (February 1983).
5. W J Levedhal, "Integrated ship machinery systems re\/isiied\NavalEngitu;ersJournal,pp93-0\
(May 1989)
6. J V JoUiff and D LGreene, 'Advanced integrated electric
propulsion: a reality of tiie eighties'. Naval Engineers
Journal, pp 232 - 254 (April 1982).
7. E J Greer, 'Electrical power engineering in modem
surface warships'. GEC Review, Vol 2, No 3, pp 151157(1986).
8. K S Smitii and R Yacamini, 'Commutation voltage
spikes on isolated offshore power systems', Proc 24th
Universities Power Engineering Conference, Belfast, pp
417-420 (September 1989).
9. R Yacamini, L Hu and R Fallaize, 'Calculation of
commutation spikes and harmonics on offshore platfomis'. lEE Proc, Vol 137, Pt B , No 1 (January 1990).
10. P TNonon and M Murphy, 'Realising the potential - f u l l
electric propulsion of surface warships'. RINA International Symposium on the Future of Surface Warships,
London (June 1990).
34
11. H Rissik, The Fundamental Theory of Arc Converters,
Chapman and Hall Ltd (1939).
12. R Feinberg, 'Frequency changing using mercury arc
mutators', y / f f , pp 531-543 (1939).
13. E Blauenstein. 'The first gearless tube mill', BrownBoveri Review, Vol 3, pp 96-105 (1970).
14. J Langer. 'Static frequency changer supply system for
synchronous motors driving tube mills'. Brown-Boveri
Review, Vol 3, pp 112-119 (1970).
15. W Faust, 'Static frequency changers for 16 2/3 c/s
railway networks' Brown-Boveri Review, pp 519-525
(August 1964).
16. D G Taylor, 'Squirrel cage induction motor cycloconverter drive at Wearmouth Colliery ' A ' pit friction
winder. Part 1. Development of drive system for winder
application', Afm/>2^ Technology,pp 4-9 Oanuary 1988).
17. D M Cross, 'Squirrel cage induction motor cyclo-convertcr drive at Wearmouth Colliery ' A ' pit friction
winder. Part 2, Drive control and regulating system'.
Mining Technology, pp 11-15 (January 1988).
18. C W Lander. Power Electronics, McGraw-Hill (1987).
19. J G Kassakain, M F Schlecht and G C Verghese, Principles of Power Electronics, Addison-Wesley (1991).
20. B R Pelly. Thyristor Phase Controlled Converters and
Cycloconverters, Wiley, New York (1971 ).
21. MAST reference manual (Ver 3.01), Analogy Ltd.
Beaverton, Oregon, U S A (1990).
22. A K De Sarkar and G J Berg, 'Digital simulation of tiiree
phase induction rc\oiors\IEEEPAS, Vol PAS 89, No 6,
pp 1031-1037 (July 1970).
23. P C Krause, Analysis of Electric Machinery, McGrawHill, New York (1986).
24. B Adkins and R G Harley, The General Theory of Alternating Current Machines, Chapman and Hall (1975).
25. A C Williamson, 'The effects of system harmonics upon
machines'. International Conference on Harmonics in
Power Systems, UMIST, Manchester, England (1981).
26. G C Jain, 'The effect of voltage waveshape on tiie
performance of a three phase induction motor', IEEE
Trans IMarE. Vol 105. Pan 1. pp 23-52
27.
28.
29.
30.
Trans Power Apparatus arui Systems, Vol PAS-84, pp
561-566.
W J Bon wiek and V H Jones, 'Performance of a synchronous generatOT witia a bridge rectifier', Proc lEE, V o l
133, Pt C, No 6, pp 1338-1342 (September 1972).
W J Bon wiek and V H Jones, 'Rectifier loaded synchronous generatOTS with damper windings', Proc lEE, Vol
120, No 6, pp 659-666 (June 1973).
W J Bonwick 'Voltage waveform distortion in synchronous generators witii rectifier loading', Proc lEE, Vol
127, No 1, pp 13-19 (January 1980).
S Moriyasu and C Uenosono, ' A n analysis of tiie charactOTstics of a synchronous machine connected to a dc
link', Archiv für Electrotechnic, Vol 69, pp 111-120
(1986).
APPENDIX 1
FREQUENCY DOMAIN SPECTRA
The following section contains tiie frequency domain spectra (Figs 25-32) for some of the waveshapes presented in the
section cm simulation results. The spectra have been presented
to supplement die tables of harmonics (Tables I-IV) referenced in the text
APPENDIX 2
SIMULATION VERIFICATION
At the time of writing this paper tiie information available
in tiie public domain regarding tiie types of cycloconverter
systems and the parameters for the drives proposed for warship
propulsion is extremely limited. As no cycloconverter propulsion for frigates currentiy exists, verification of the computer
model against a real system is not possible.
As the simulator has a modular approach to developing
submodels of the various components which comprise the
cycloconverter drive, it has been possible to test each of these
individually and compare the performance of tiie submodel
with the results of tests published previously for these items.
This approach has been used to verify the accuracy of the
induction and synchronous machine submodels with both
sinusoidal and distorted busbar waveshapes. Assistance of a
technical nature on the modelling of modem cycloconverters
was received from M r Derek Taylor of C E G E L E C , Rugby.
Comparisons in botii tiie time and frequency domains, between
site measured and simulated waveshapes for the cycloconverter
output voltage and currents, gave confidence in the ability of
the simulation to model correctiy a cycloconverter. The
assistance of M r Taylor in this exercise is gratefully acknowledged.
35
K s Smith. R Yacamini & A C Williamson
Table I: Fourier analysis for motoring condition
T a b l e No 1
255 0
.00
.00
10.73
20.40
.00
260 0
2.84
3.20
.00
.00
.00
265 0
.00
.00
.00
.00
.00
270 0
.00
.00
.00
.00
.00
Motor
275 0
.00
.00
.00
,88
.00
Current Current Current Voltage Torque
280 0
.62
8.86
.00
.00
.00
Motoring
Freq
0.0
36
Syscem
.56
Cyclo
Condition
Motor
Motor
.86
.00
.00
285 0
.00
.00
6.76
29.66
.00
100.00
290 0
.00
2.53
.00
.00
.00
5.0
.00
.00
1.09
.00
2.28
295 0
.00
.00
.00
.51
.00
10.0
1.45
6.58
.00
.00
3.34
300 0
.00
.00
.00
.00
8.29
15.0
.00
.00
100.00
100.00
2.91
305 0
.00
.00
.00
.00
.00
20.0
1.03
45.46
.73
.00
3.28
310 0
.00
4 .48
.00
.00
.00
25.0
.88
.00
1.25
.00
2.09
315 0
.00
.00
4.37
20.73
.00
30.0
2.13
1.21
.64
.00
1.92
320 0
.73
4.61
.00
.00
.00
35.0
1.54
.00
1.17
.91
.82
325 0
.00
.00
.00
.00
.00
40.0
1.99
3.49
.55
.00
1.33
330 0
.00
.00
.00
.00
.00
45.0
1.31
.00
8.14
3.25
.00
335 0
.00
.00
.00
.00
.00
50.0
100.00
100.00
.53
.00
.60
340 0
1.21
1.39
.00
.00
.00
55.0
1.08
.52
.89
.54
.00
345 0
.00
.00
2.07
5.50
.00
60.0
1.12
.95
.00
.00
.00
350 0
5.10
5.22
.00
.00
.00
65.0
1.37
.00
.74
.00
.00
355 0
.00
.00
.00
.00
.00
70.0
2.69
2.93
.00
.00
.00
360 0
.00
.00
.00
.00
.00
75.0
1.14
.00
2.80
3.19
.00
365 0
.00
.00
.00
.00
.00
80.0
.72
25.86
.00
.00
.00
370 0
.00
.79
.00
.00
.00
85.0
.93
.55
.00
.67
.00
375 0
.00
.00
.00
.00
.00
90.0
.53
.66
.00
.00
.99
380 0
.00
3.67
.00
.00
.00
95.0
.69
.55
.00
.00
.00
385 0
.00
.00
.00
1.05
.00
100.0
.72
.90
.00
.00
.00
390 0
.00
.00
.00
.00
.00
105.0
.00
.52
2.15
3.10
.00
395 0
.00
.00
.00
.00
.00
110.0
.72
8.68
.00
.00
.00
400 0
.00
.67
.00
.00
.00
115.0
.00
.00
.00
.64
.00
405 0
.00
.00
.00
1.B2
.00
120.0
.00
.00
.00
.00
.00
410 0
.00
.90
.00
.00
.00
125.0
.56
.00
.00
.79
.00
415 0
.00
.00
.00
.50
.00
130.0
.68
1.90
.00
.00
.00
420 0
.00
.00
.00
.00
.00
135.0
.57
.00
2.58
2.76
.00
425 0
.00
.00
.00
.52
.00
140.0
2.76
3.27
.00
.00
.00
430 0
.00
1.70
.00
.00
.00
145.0
.00
.00
.00
.64
.00
435 0
.00
.00
.00
2.14
.00
150.0
.00
.00
.00
.00
.00
440 0
.72
.86
.00
.00
.00
155.0
.00
.00
.00
.55
.00
445 0
.00
.00
.00
.00
.00
160.0
1.83
2.31
.00
.00
.00
450 0
.00
.00
.00
.00
.00
165.0
.00
.00
1.41
2.73
.00
455 0
.00
.00
.00
.00
.00
170.0
.78
2.04
.00
.00
.00
460 0
3.22
3.24
.00
.00
.00
175.0
.00
.00
.00
.00
.00
465 0
.00
.00
1.04
3.77
.00
180.0
.00
.00
.00
.00
.00
470 0
.00
.70
.00
.00
.00
185.0
.00
.00
.00
.00
.00
475 0
.00
.00
.00
.76
.00
190.0
.52
11.31
.00
.00
.00
480 0
.00
.00
.00
.00
.00
195.0
.00
.00
1.70
4 .44
.00
485 0
.00
.00
.00
.68
.00
200.0
.00
1.91
.00
.00
.00
490 0
.00
4.83
.00
.00
.00
205.0
.00
.00
.00
.00
.00
495 0
.00
.00
.88
6.71
.00
210.0
.00
.00
.00
.00
2.53
SOD 0
.00
.80
.00
.00
.00
215.0
.00
.00
.00
.60
.00
505 0
.00
.00
.00
.00
.00
220.0
.00
23.71
.00
.00
.00
510 0
.00
.00
.00
.00
1.56
225.0
.00
.00
3.69
12.33
.00
515 0
.00
.00
.00
.60
.00
230.0
.56
1 .54
.00
.00
.00
520 0
.00
4.46
.00
.00
.00
235.0
.00
.00
.00
.00
.00
525 0
.00
.00
1.64
13.45
.00
240.0
.64
.00
.00
.00
.00
530 0
.00
1.12
.00
.00
.00
245.0
.00
.00
.00
.00
.00
535 0
.00
.00
.00
.00
.00
250.0
14.30
14.80
.00
.00
.00
540 0
.00
.00
.00
.00
.00
Trans IMarE. Vol 105. Part 1. pp 23-52
Table I: Fourier analysis for motoring condition (cont)
545.0
.00
.00
.00
.88
.00
835.0
.00
.00
.00
.72
550.0
4.20
4 .27
.00
.00
.00
840.0
. 00
.00
.00
.00
.00
555.0
.00
.00
1.38
6.18
.00
845.0
.00
.00
.00
.00
.00
560.0
1.76
1.86
.00
.00
.00
850.0
1.61
1.67
.00
.00
.00
565.0
.00
.00
.00
.67
.00
855.0
.00
.00
.57
3.61
.00
570.0
.00
.00
.00
.00
.00
860.0
1.69
1.69
.00
.00
.00
575.0
.00
.00
.00
.55
.00
865.0
.00
.00
.00
.00
.00
580.0
.00
2.92
.00
.00
.00
870.0
.00
.00
.00
.00
.00
585.0
.00
.00
.54
5.21
.00
875.0
.00
.00
.00
.92
.00
590.0
.00
2.07
.00
.00
.00
880.0
.00
1 .80
.00
.00
.00
595.0
.00
.00
.00
.00
.00
885.0
.00
.00
.00
.95
.00
.00
600.0
.00
.00
.00
.00
1.15
890.0
.00
.92
.00
.00
.00
605.0
.00
.00
.00
.62
.00
895.0
.00
.00
.00
.00
.00
.00
610.0
.00
2.11
.00
.00
.00
900.0
.00
.00
.00
.00
615.0
.00
.00
.55
5.10
.00
905.0
.00
.00
.00
.81
.00
620.0
.00
2.56
.00
.00
.00
910.0
.00
1.24
.00
.00
.00
625.0
.00
.00
.00
.00
.00
915.0
.00
.00
.00
4.03
.00
630.0
.00
.00
.00
.00
.00
920.0
.00
1.36
.00
.00
.00
.00
635.0
.00
.00
.00
.52
.00
925.0
.00
.00
.00
.96
640.0
.96
.85
.00
.00
.00
930.0
.00
.00
.00
.00
.00
645.0
.00
.00
.85
4.60
.00
935.0
.00
.00
.00
.00
.00
650.0
2.34
2.48
.00
.00
.00
940.0
.85
1.63
.00
.00
.00
655.0
.00
.00
.00
.65
.00
945.0
.00
.00
.00
4.04
.00
660.0
.00
.00
.00
.00
.00
950.0
1.03
1.08
.00
.00
.00
665.0
.00
.00
.00
.58
.00
955.0
.00
.00
.00
.87
.00
670.0
.77
1 .00
.00
.00
.00
960.0
.00
.00
.00
.00
.00
675.0
.00
.00
.51
4.65
.00
965.0
.00
.00
.00
.00
.00
.00
680.0
.00
1.34
.00
.00
.00
970.0
1.03
.61
.00
.00
685.0
.00
.00
.00
1.12
.00
975.0
.00
.00
.00
2.10
.00
690.0
.00
.00
.00
.00
.00
980.0
.00
1.37
.00
.00
.00
695.0
.00
.00
.00
.00
.00
985.0
.00
.00
.00
.00
.00
700.0
.00
1.86
.00
.00
.00
990.0
.00
.00
.00
.00
.00
705.0
.00
.00
.00
4 .47
.00
995.0
.00
.00
.00
.00
.00
710.0
.00
1 .34
.00
.00
.00
1000.0
.00
1.72
.00
.00
.00
715.0
.00
.00
.00
.00
.00
.00
720.0
.00
.00
.00
.00
725.0
.00
.00
.00
.00
.00
730 .0
.00
2.07
.00
.00
.00
735.0
.00
.00
.54
5.94
.00
.00
740.0
.74
.91
.00
.00
745.0
.DO
.00
.00
.00
.00
750.0
.00
.00
.00
.00
.00
755.0
.00
.00
.00
1 .56
.00
760.0
2.15
2.17
.00
.00
.00
765.0
.00
.00
.78
4.33
.00
770.0
.00
.00
.00
.00
.00
775.0
.00
.00
.00
1.11
.00
780.0
.00
.00
.00
.00
.00
785.0
.00
.00
.00
.84
.00
.00
790.0
.00
1 .80
.00
.00
795.0
.00
.00
.00
3.96
.00
800.0
.00
.95
.00
.00
.00
805.0
.00
.00
.00
.00
.00
810.0
.00
.00
.00
.00
.51
815.0
.00
.00
.00
.00
.00
820.0
.00
2.04
.00
.00
.00
825.0
.00
.00
.00
2.27
.00
830.0
.00
1.13
.00
.00
.00
Table prepared using a Fourier analysis with a
resolution o f 5 H z .
37
K s Smith. R Yacamini & A C Williamson
Table II: Fourier analysis for generating condition
Table
38
2
255 0
.00
.00
8.87
18.36
.00
260 0
1.83
2.19
.00
.00
.00
265 0
.55
1.41
.00
.00
.00
270 0
.00
.00
.00
.95
.00
Motor
275 0
.00
.00
.00
.00
.00
Current Current Current Voltage Torque
280 0
.00
7.71
.00
.00
.00
285 0
.00
.00
2.77
12.45
.00
.00
Generating
Freq
No
system
Cyclo
Condition
Motor
Motor
.0
.00
00
6.12
.00
100.00
290 0
.00
3.31
.00
.00
5.0
1.36
4 81
2.85
.00
1.58
295 0
.00
.50
.00
.00
.00
10.0
.00
6 28
2.62
.00
1.53
300 0
.00
.00
.00
.79
3.95
15.0
.00
00
100.00
100.00
3.16
305 0
.00
.75
.00
1 .14
.00
20.0
2.00
51 61
1.88
.00
1.21
310 0
.00
4.30
.00
.00
.00
25.0
.56
2 55
1.54
.00
.97
315 0
.00
.00
2.65
13.31
.00
30.0
.65
1 52
5.28
2.10
1.55
320 0
.00
6.09
.00
.00
.00
35.0
2.98
8 84
.89
.82
.58
325 0
.00
.00
.00
.00
.00
40.0
3.66
3 57
.71
.00
.00
330 0
.00
.00
.00
.58
.00
45.0
.92
2 13
.99
.69
.83
335 0
.00
.57
.00
.00
.00
50.0
100.00
100 00
.78
.00
.00
340 0
1.25
1.47
.00
.00
.00
55.0
1.60
3 70
.78
.57
.00
345 0
.00
.00
2.22
6.46
.00
60.0
.73
1 98
3 .90
2.49
.54
350 0
4.28
4.38
.00
.00
.00
65.0
1.53
4 80
.66
.00
.00
355 0
.00
.00
.00
.68
.00
70.0
1.60
00
.54
.00
.00
360 0
.00
.00
.00
.00
.00
75.0
.00
1 13
2.35
1.80
.00
365 0
.00
.60
.00
.00
.00
80.0
.76
22 52
.00
.00
.00
370 0
.00
1.25
.00
.00
.00
85.0
.82
2 82
.00
.00
.00
375 0
.00
.00
.76
4.29
.00
90.0
.00
51
3.03
2.83
1.46
380 0
.00
2.40
.00
.00
.00
95.0
1.02
3 75
.00
.50
.00
385 0
.00
.50
.00
.57
.00
100.0
.00
1 29
.00
.00
.00
390 0
.00
.00
.00
.00
.52
105.0
.00
72
.82
1.02
.00
395 0
.00
.00
.00
.00
.00
110.0
.00
8 35
.00
.00
.00
400 0
.00
.98
.00
.00
.00
115.0
.59
2 24
.00
.00
.00
405 0
.00
.00
.00
3.54
.00
120.0
.00
00
2.24
3 .05
.00
410 0
.00
1.06
.00
.00
.00
125.0
.86
2 81
.00
.62
.00
415 0
.00
.78
.00
.00
.00
130.0
.74
2 22
.00
.00
.00
420 0
.00
.00
.00
.00
.00
135.0
.00
00
1.13
1.42
.00
425 0
.00
.56
.00
.00
.00
140.0
3 .04
2 12
.00
.00
.00
430 0
.00
3 .17
.00
.00
.00
145.0
.00
1 72
.00
.00
.00
435 0
.00
.00
.84
4.03
.00
150.0
.00
00
1 .60
3 .05
.00
440 0
.00
.68
.00
.00
.00
155.0
.63
2 21
.00
.00
.00
445 0
.00
.86
.00
.51
.00
160.0
4.08
3 88
.00
.00
.00
450 0
.00
.00
.00
.98
.00
165.0
.00
00
1.65
1.47
.00
455 0
.00
.53
.00
.68
.00
170.0
.93
1 51
.00
.00
.00
460 0
4.75
4.92
.00
.00
.00
175.0
.68
1 91
.00
.00
.00
465 0
.00
.00
1.55
7.17
.00
180.0
.00
00
1.11
2.73
.00
470 0
.64
1.10
.00
.00
.00
185.0
.52
1 70
.00
.00
.00
475 0
.00
.00
.00
.71
.00
190.0
.00
13 42
.00
.00
.00
480 0
.00
.00
.00
1.81
.00
195.0
.00
60
1.73
4.48
.00
485 0
.00
.54
.00
.00
.00
200.0
.00
1 69
.00
.00
.00
490 0
.00
4.56
.00
.00
.00
205.0
.84
2 31
.00
.63
.00
495 0
.00
.00
.86
6.84
.00
210.0
.00
68
.84
2.50
2.36
500 0
.00
.00
.00
.00
.00
215.0
.00
77
.00
.00
.00
505 0
.00
.00
.00
.00
.00
510 0
.00
.00
.00
220.0
.65
22 89
.00
.00
.00
1.83
1.15
225.0
.00
75
3.80
14.90
.00
515 0
.00
.00
.00
.52
.00
230.0
.57
2 69
.00
.00
.00
520 0
.00
3.47
.00
.00
.00
235.0
.00
98
.00
.00
.00
525 0
.00
.00
.55
5.75
.00
240.0
.00
62
.59
1.67
.00
530 0
.00
2.43
.00
.00
.00
245.0
.00
74
.00
.00
.00
535 0
.00
.00
.00
.00
.00
250.0
11.25
11 15
.00
.00
.00
540 0
.00
.00
.00
1.87
.00
Trans IMarE. Vol 105. Part 1. pp 23-52
Table II: Fourier analysis for generating condition (cont)
545.0
.00
.00
.00
.51
.00
835 0
.00
.00
.00
.00
.00
550.0
2.97
2.76
.00
.00
.00
840 0
. 00
.00
.0.".
.68
.00
555.0
.00
.00
.77
3.55
.00
845 0
.00
.00
.00
.82
.00
560.0
3.03
2.86
.00
.00
.00
850 0
1.25
1.10
.00
.00
.00
565.0
.00
.00
.00
.62
.00
855 0
.00
.00
.00
.00
.00
570.0
.
.00
.00
1.76
.00
860 0
1.08
1.04
.00
.00
.00
575.0
.00
.00
.00
.56
.00
865 0
.00
.00
. 00
.00
.00
580.0
.00
2.74
.00
.00
.00
870 0
.00
.00
.00
.64
.00
585.0
.00
.00
.00
.80
.00
875 0
.00
.00
.00
.00
.00
590.0
.00
2.27
.00
.00
.00
880 0
.00
1.80
.00
.00
.00
595.0
.00
.00
.00
.00
.00
885 0
.00
.00
.00
.00
.00
600.0
.00
.00
.00
1.60
.00
890 0
.00
1.03
.00
.00
.00
605.0
.00
.00
.00
.00
.00
895 0
.00
.00
.00
.00
.00
610.0
.00
2.07
.00
.00
.00
900 0
.00
.00
.00
.71
.00
615.0
.00
.00
.00
4.10
.00
90S c
.00
.00
.00
.61
.00
620.0
.00
1.88
.00
.00
.00
910 0
.00
.58
.00
.00
.00
625.0
.00
.00
.00
.00
.00
915 0
.cc
.00
.00
1.00
.00
630.0
.00
.00
.00
.99
.00
920 0
.00
.92
.00
.00
.00
635.0
.00
.00
.00
.75
.00
925 0
.00
.00
.00
.00
.00
640.0
.98
.00
.00
.00
.00
930 0
.00
.00
.00
.92
.00
645.0
.00
.00
.56
2.17
.00
935 0
.00
.00
.00
.00
.00
650.0
1.82
1.88
.00
.00
.00
940 0
.72
2.19
.00
.00
.00
655.0
.00
.00
.00
.00
.00
945 0
.00
.00
.00
3.41
.00
660.0
.00
.00
.00
.00
.00
950 0
.98
.78
.00
.00
.00
665.0
.00
.00
.00
.00
.00
9S5 0
.00
.00
.00
.60
.00
670.0
1.45
1.88
.00
.00
.00
960 0
. i
.00
.00
1.04
.00
675.0
.00
.00
.00
3.01
.00
965 0
.00
.00
.00
.00
.00
680.0
.00
1.37
.00
.00
.00
970 0
1.39
.83
.00
.00
.00
685.0
.00
.00
.00
.89
.00
975 0
.00
.00
.00
2.10
.00
690.0
.00
.00
.00
.00
.00
980 0
.00
1.25
.00
.00
.00
695.0
.00
.00
.00
.00
.00
985 0
.00
.00
.00
.00
.00
700.0
.00
2.40
.00
.00
.00
990 0
.00
.00
.00
.00
.00
705.0
.00
.00
.00
3.24
.00
995 0
.00
.00
.00
.00
.00
710.0
.00
1.34
.00
.00
.00
1000 0
.00
1.49
.00
.00
.00
715.0
.00
.00
.00
.00
.00
720.0
.00
.00
.00
.81
.00
725.0
.00
.00
.00
.72
.00
730.0
.00
2.75
.00
.00
.00
735.0
.00
.00
.00
4.81
.00
740.0
.00
1.01
.00
.00
.00
745.0
.00
.00
.00
.51
.00
750.0
.0
.00
.00
.55
.00
755.0
.00
.00
.00
.00
.00
760 .0
1.39
1.40
.00
.00
.00
765.0
.00
.00
.66
4.59
.00
770.0
1.15
1.33
.00
.00
.00
775.0
.00
.00
.00
.00
.00
.00
.00
.76
.00
.00
.00
.52
.00
780.0
785.0
. G .1
790.0
.00
1.72
.00
.00
.00
795.0
.00
.00
.00
1.97
.00
800.0
.00
1.50
.00
.00
.00
805.0
.00
.00
.00
.B !
.00
810.0
.00
.00
.00
.69
.00
815.0
.00
.00
.00
.G0
.00
820.0
.oc
1.17
.00
.00
.00
825.0
.00
.00
.00
2.61
.00
830.0
.00
1.56
.00
.00
.00
Table prepared using a Fourier analysis with a
resolution o f 5 H z .
39
K S Smith. R Yacamini & A C Williamson
Table III: Fourier analysis for double wound motor
Table No 3
255.0
.00
.00
5.41
23.25
.00
260.0
.00
1.92
.00
.00
.00
265.0
.00
.00
.00
.86
.00
270.0
.00
.00
.00
.00
.00
Motor
275.0
.00
.00
.00
.00
.00
Current Current Current Voltage Torque
280.0
.00
3.13
.00
.00
.00
285.0
.00
.00
1.74
24.79
.00
Double
Freq
40
System
Wound M o t o r
Cyclo
Motor
Motor
.0
.00
.00
.00
.00
IOC .00
290.0
.00
5.87
.00
.00
.00
5.0
.00
.00
.00
.00
.00
295.0
.00
.00
.00
.70
.00
10.0
.98
5.18
.00
.00
.00
300.0
.00
.00
.00
.00
.00
15.0
.00
.00
100.00
100.00
.00
305.0
.00
.00
.00
.99
.00
20.0
.00
58.62
.00
.00
.00
310.0
.00
1.85
.00
.00
.00
25.0
.00
.00
.00
.00
.00
315.0
.00
.00
1.47
24.27
.00
30.0
.00
.00
.00
.00
.00
320.0
.00
8.21
.00
.00
.00
35.0
.00
.00
.00
.00
.00
325.0
.00
.00
.00
1.85
.00
40.0
.00
.79
.00
.00
.00
330.0
.00
.00
.00
.00
.00
45.0
.00
.00
6.03
5.06
.00
335.0
.00
.00
.00
.76
.00
50.0
100.00
100.00
.00
.00
.00
340.0
.00
1.02
.00
.00
.00
55.0
.00
.00
.00
1.40
.00
345.0
.00
.00
1.80
10.55
.00
60.0
.00
.00
.00
.00
.00
350.0
2.41
2.65
.00
.00
.00
65.0
.00
.00
.00
.00
.00
355.0
.00
.00
.00
.00
.00
70.0
.71
.52
.00
.00
.00
360.0
.00
.00
.00
.00
.00
75.0
.00
.00
4.06
5.05
.CO
365.0
.00
.00
.00
.88
.00
80.0
.00
23.92
.00
.00
.00
370.0
.00
.58
.00
.00
.00
85.0
.00
.00
.00
1 .34
.00
375.0
.00
.00
1.02
7.06
.00
90.0
.00
.00
.00
.00
.00
380.0
.00
2.51
.00
.00
.00
95.0
.00
.00
.00
.00
.00
385.0
.00
.00
.00
.86
.00
100.0
.00
.00
.00
.00
.00
390.0
.00
.00
.00
.00
.00
105.0
.00
.00
2.72
5.69
.00
395.0
.00
.00
.00
1.56
.00
110.0
.83
8.01
.00
.00
1)0
400.0
.00
.50
.00
.00
.00
115.0
.00
.00
.00
2.16
.00
405.0
.00
.00
.54
4.87
.00
120.0
.00
.00
.00
.00
.00
410.0
.00
1.10
.00
.00
.00
125.0
.00
.00
.00
.94
00
415.0
.00
.00
.00
.00
.00
130.0
.54
.65
.00
.00
OC
420.0
.00
.00
.00
.00
.00
135.0
.00
.00
1.35
3.52
00
425.0
.00
.00
.00
1.15
.00
140.0
.00
3.35
.00
.00
00
430.0
.00
1.83
.00
.00
.00
145.0
.00
.00
.00
.00
00
435.0
.00
.00
.00
3.64
.00
150.0
.00
.00
.00
.00
00
440.0
.00
.00
.00
.00
.00
155.0
.00
.00
.00
1.50
00
445.0
.00
.00
.00
.83
.00
160.0
.00
2.21
.00
.00
00
450.0
.00
.00
.00
.00
.00
165.0
.00
.00
.98
2.91
00
455.0
.00
.00
.00
1.30
.00
170.0
.72
1.19
.00
.00
00
460.0
.00
4.00
.00
.00
.00
175.0
.00
.00
.00
.00
00
465.0
.00
.00
.54
4.41
.00
180.0
.00
.00
.00
.00
00
470.0
.00
.00
.00
.00
.00
185.0
.00
.00
.00
1.27
00
475.0
.00
.00
.00
.63
.00
190.0
.00
9.78
.00
.00
00
480.0
.00
.00
.00
.00
.00
195.0
.00
.00
1 .00
4.10
00
485.0
.00
.00
.00
.70
.00
200.0
.00
.00
.00
.00
00
490.0
.00
5.89
.00
.00
.00
205.0
.00
.00
.00
1.33
00
495.0
.00
.00
.63
6.91
.00
210.0
.00
.00
.00
.00
00
500.0
.00
.64
.00
.00
.00
215.0
.00
.00
.00
1.03
00
505.0
.00
.00
.00
.64
.00
220.0
.00
23.58
.00
.00
00
510.0
.00
.00
.00
.00
.00
225.0
.00
.00
2.13
8.84
00
515.0
.00
.00
.00
.71
.00
230.0
.00
.00
.00
.00
00
520.0
.00
1.84
.00
.00
.00
235.0
.00
.00
.00
.00
00
525.0
.00
.00
.74
6.13
.00
240.0
.00
.00
.00
.00
00
530.0
.00
1.56
.00
.00
.00
245.0
.00
.00
.00
1.07
00
535.0
.00
.00
.00
.00
.00
250.0
6.88
7.65
.00
.00
00
540.0
.00
.00
.00
.00
.00
Trans IMarE. Vol 105, Pan 1. pp 23-52
Table III: Fourier analysis for double wound motor (cont)
545.0
.00
.00
.00
.76
.00
835 .0
.00
.00
.00
1.13
.00
550.0
1.48
1.62
.00
.00
.00
840 .0
.00
.00
.00
.00
.00
555.0
.00
.00
.00
3.05
,00
845 .0
.00
.00
.00
.63
.00
560.0
.00
3.04
.00
.00
.00
850 .0
.55
.56
.00
.00
.00
.00
565.0
.00
.00
.00
.00
.00
855 .0
.00
.00
.00
1.47
570.0
.00
.00
.00
.00
.00
860 .0
.00
.96
.00
.00
.00
575.0
.00
.00
.00
.83
.00
865 .0
.00
.00
.00
.00
.00
580.0
.00
.89
.00
.00
.00
870 .0
.00
.00
.00
.00
.00
585.0
.00
.00
.00
2.71
.00
875 .0
.00
.00
.00
.00
.00
590.0
.00
3.18
.00
.00
.00
880 .0
.00
.00
.00
.00
.00
595.0
.00
.00
.00
1.11
.00
885 0
.00
.00
.00
2.59
.00
600.0
.00
.00
.00
.00
.00
890 0
.00
.73
.00
.00
.00
605.0
.00
.00
.00
.63
.00
895 0
.00
.00
.00
.74
.00
610.0
.00
.00
.00
.00
.00
900 0
.00
.00
.00
.00
.00
615.0
.00
.00
.00
7.58
.00
905.0
.00
.00
.00
.59
.00
620.0
.00
1.43
.00
.00
.00
910 0
.00
.00
.00
.00
.00
625.0
.00
.00
.00
.67
.00
915 0
.00
.00
.00
3.25
.00
630.0
.00
.00
.00
.00
.00
920 0
.00
.00
.00
.00
.06
635.0
.00
.00
.00
1.05
.00
925 0
.00
.00
.00
1.17
.00
640.0
.00
.00
.00
.00
.00
930 0
.00
.00
.00
.00
.00
645.0
.00
.00
.00
2.50
.00
935 0
.00
.00
.00
1.45
.00
650.0
.84
.88
.00
.00
.00
940 0
.00
.51
.00
.00
.00
655.0
.00
.00
.00
.00
.00
945 0
.00
.00
.00
1.39
.00
660.0
.00
.00
.00
.00
.00
950 0
.00
.00
.00
.00
.00
665.0
.00
.00
.00
1.20
.00
955 0
.00
.00
.00
.70
.00
670.0
.00
.53
.00
.00
.00
960 0
.00
.00
.00
.00
.00
675.0
.00
.00
.00
.00
.00
965 0
.00
.00
.00
1.03
.00
680.0
.00
.75
.00
.00
.00
970. 0
.66
.00
.00
.00
.00
685.0
.00
.00
.00
.73
.00
975. 0
.00
.00
.00
1.25
.00
690.0
.00
.00
.00
.00
.00
980. 0
.00
.51
.00
.00
.00
695.0
.00
.00
.00
1 .19
.00
985. 0
.00
.00
.00
.65
.00
700.0
.00
1.14
.00
.00
.00
990. 0
.00
.00
.00
.00
.00
705.0
.00
.00
.00
1 .40
.00
995. 0
.00
.00
.00
1.46
.00
710.0
.00
.00
.00
.00
.00
715.0
.00
.00
.00
.00
.00
720.0
.00
.00
.00
.00
.00
725.0
.00
.00
.00
.53
.00
Table prepared using a Fourier analysis with a
resolution of 5 H z .
730.0
.00
1.91
.00
.00
735.0
.00
.00
.00
6.16
.00
740.0
.00
.00
.00
.00
.00
745.0
.00
.00
.00
.66
.00
750.0
.00
.00
.00
.00
.00
.00
755.0
.00
.00
.00
1.12
.00
760.0
.00
1.72
.00
.00
.00
765.0
.00
.00
.00
6.20
.00
770.0
.67
.72
.00
.00
.00
.00
775.0
.00
.00
.00
.58
780.0
.00
.00
.00
.00
.00
785.0
.00
.00
.00
.64
.00
790.0
.00
.76
.00
.00
.00
795.0
.00
.00
.00
7.86
.00
.00
800.0
.00
.96
.00
.00
805.0
.00
.00
.00
1.35
.00
810.0
.00
.00
.00
.00
.00
.00
815.0
.00
.00
.00
.00
820.0
.00
.66
.00
.56
.00
825.0
.00
.00
.00
2.75
.00
830.0
.00
1.48
.00
.00
.00
41
K S Smith. R Yacamini & A C Williamson
Table IV: Fourier analysis for simulation including alternator
Table
No
4
ulation including
alternator
Freq
5.40
9.68
255 .0
.00
.00
260.0
1.13
1.89
265.0
.00
.00
.77
270 .0
.00
.00
2.36
.62
.94
1 .00
System
System
Machine
275.0
.00
.00
.84
Voltage
Current
Torque
280.0
.00
.63
1.30
285.0
.00
.00
1.33
.c
.00
.00
100.00
290 .0
.00
.00
.84
5. 0
.00
.00
2.28
295 .0
.00
.00
.00
10 . ii
.00
1.77
3.16
300 .0
.00
.00
30.64
15 . 0
.00
.00
3.82
305 .0
.00
.00
.00
20
.00
3.19
2.98
310 .0
.00
.00
.72
25 . 0
.00
.00
1.43
315 .0
.00
.00
.87
30 .0
.00
1.06
6.84
320 .0
.00
.74
.66
35 . 0
.00
1.75
.97
325 .0
.00
.00
.00
40 . c
.00
1.54
1.49
330 .0
.00
.00
1.55
45 . 0
.00
1.00
1.55
335 .0
.00
.00
.00
100.00
100.00
1.09
340 .0
.94
1.18
.00
55 . c
.00
.90
.55
345 .0
.00
.00
.00
60 . 0
.00
1.32
2.96
350 .0
2.92
3.90
.00
c5 . c
.00
1 .45
.00
355 .0
.00
.00
.00
70 . 0
.00
1.50
.90
360 .0
.00
.00
1.07
75 .0
.00
.00
1.01
365 .0
.00
.00
.00
80 . c
.00
1.54
.69
370 ,0
.00
.51
.00
85
.00
.00
.00
375 ,0
.00
.00
.00
90 .0
.00
.52
6.96
380 ,0
.00
.00
.00
95 .c
.00
.57
.00
385 .0
.00
.00
.00
100 .0
.00
.00
.62
390 ,0
.00
.00
3 .74
50 . -
42
250 .0
105 .0
.00
.00
.70
395 .0
.00
.00
.00
110 .0
.00
.81
.54
400 .0
.00
.00
.00
115 . 0
.00
.00
.00
405 ,0
.00
.00
.00
120 .0
.00
.00
1.77
410 .0
.00
.00
.00
125 .0
.00
.00
.00
415 ,0
.00
.00
.00
1 tc.0
.00
.69
.00
420 ,0
.00
.00
.68
135 .0
.00
.00
.55
425 .0
.00
.00
.00
140. .0
.73
2.45
.00
430 ,0
.00
.00
.00
145, .0
.00
.00
.00
435 .0
.00
.00
.00
I5i; ,0
.00
.00
.94
440 ,0
.00
.50
.00
155 .0
.00
.00
.00
445 ,0
.00
.00
.00
160 ,0
.00
.97
.00
450 ,0
.00
.00
.00
165 .0
.00
.00
.00
455 .0
.00
.00
.00
170 .0
.00
.00
.00
460 .0
2.56
2.56
.OC
175 . 0
.00
.00
.00
465 .0
.00
.00
.00
180 .0
.00
.00
1.39
470 ,0
.00
.00
.00
185 . c
.00
.00
.00
475 ,0
.00
.00
.00
190 ,0
.00
.00
.00
480 ,0
.00
.00
.87
195 .0
.00
.00
.00
485 .0
.00
.00
.00
200 .0
.00
.00
.00
490 ,0
.00
.00
.00
205 . Ü
.00
.00
.00
495 .0
.00
.00
.00
210 .'!
.00
.00
3 .80
500 .0
.00
.00
.00
215
.00
.00
.00
505 .0
.00
.00
.00
220 .0
.00
.58
.00
510 .0
.00
.00
10.72
225 .0
.00
.00
.00
515 .0
.00
.00
.00
230 .0
.00
.56
.00
520 ,0
.57
.00
.00
235 .0
.00
.00
.00
525 .0
.00
.00
.00
240 . Ü
.00
.00
.78
530 ,0
.00
.00
.00
245 . 0
.00
.00
.00
535 .0
.00
.00
.00
Trans IMarE. Vol 105. Pan l.pp
23-52
Table IV: Fourier analysis for simulation including alternator (cont)
540.0
.00
.00
1.15
830.0
.00
.00
.00
545.0
.00
.00
.00
835.0
.00
.00
.00
550.0
2.46
1.97
.00
840.0
.00
.00
.58
555.0
.00
.OC
.56
845.0
.01)
.00
.00
560.0
2.09
1.77
.52
850.0
1.14
.61
.00
565.0
.00
.00
.00
855.0
.00
.uu
.00
570.0
.00
. o:
1.63
860.0
2.21
1.18
.00
575.0
. 00
.00
.00
865.0
.00
.00
.00
580.0
.00
.00
.00
870.0
.00
.00
.67
585.0
.00
.00
.00
875.0
.00
.00
.00
590.0
.00
.00
.00
880.0
.00
.00
.00
595.0
.00
.00
.00
885.0
. C')
.00
.00
600.0
.00
.00
6.99
890.0
.00
.00
.00
605.0
.00
.00
.00
895.0
.00
.00
.00
610.0
.00
.00
.00
900.0
.00
.00
2.44
615.0
.00
.00
.00
905.0
.00
. 0 (]
.00
620.0
.00
.00
.00
910.0
.00
.00
.00
625.0
.00
.00
.00
915.0
.00
.00
.00
630.0
.00
.00
.00
920.0
.00
.00
.00
635.0
.00
.00
.00
925.0
.00
.00
.00
640.0
.61
.00
.00
930.0
.00
.00
.00
645.0
.00
.00
.00
935.0
.00
.00
.00
650.0
1.96
1.41
.00
940.0
.00
.00
.00
655.0
.00
.00
.00
945.0
.00
.00
.00
660.0
.00
.00
.00
950.0
1.13
.55
.00
665.0
.00
.00
.00
955.0
.00
.00
.00
670.0
.88
.61
.00
960.0
.00
.00
.00
675.0
.00
.00
.00
965.0
.00
.00
.00
680.0
.00
.00
.00
970.0
1.79
.82
.00
685.0
.00
.00
.00
975.0
.00
.00
.00
690.0
.00
.00
1 .36
980.0
.00
.00
.00
695.0
.00
.00
. 00
985.0
.00
.00
,00
700.0
.00
.00
.00
990.0
.00
.00
.59
705.0
.00
.00
.00
995.0
.00
.00
,00
710.0
.00
.00
.00
715.0
.00
.00
.00
720.0
.00
.00
2.41
725.0
.00
.00
.00
730.0
.1)0
.00
.00
735.0
.00
.00
.00
740.0
.00
.00
.00
745.0
.00
.00
.00
750.0
. n
Q
.00
.00
755.0
. 'J :
.00
.00
760.0
2.66
1.58
.00
765.0
.Ù0
.00
.00
770.0
.75
.00
.00
775.0
.01)
.00
.00
780.0
.00
. CO
.52
.00
785.0
.C0
.CO
790.0
.00
.00
.00
795 .0
.00
. 00
.00
800.0
.00
.00
.00
.00
.00
810.0
.00
.00
5.95
815.0
.00
.00
.00
820.0
. i:
.00
.00
825.0
.00
.00
.00
805.0
Table prepared using a Fourier analysis with a
resolution of 5 H z .
43
K S Smith. R Yacamini
A C Williamson
MAG(%)
20-
18-^
Reference:
Table 1
Signai:
ac system current
16-^
14-^
12
J
10^
4-^
2-^
200
400
600
800
i
Ik
• 111., 111. ..111.,
1.2k
1.4k
JUl
1.6k
IIIII
I i l II
1.8k
II II
iLiL
2k
f(Hz)
Fig 25: Frequency spectra of harmonics present in the ac system current for motoring condition (see Fig 14 and Table I)
MAG(%)
55-
50-^
Reference:
Tabic 1
Signal:
cycloconverter input current
45-4
40—^
35-J
30-J
25-^
20-^
15^
10_J
5-4
idiJi
200
400
1 I N I il ll II li 1.1[ ll II li II II il |i II I. IIIIII \lli 11 11 II .1II i| Il II u II .. II [I . .1II • • l.^l. • I I 1 . . .11
600
800
Ik
1.2k
1.4k
1.6k
1.8k
2k
2
f(Hz)
Fig 26: Frequency spectra of harmonics present in the cycloconverter input current (see Fig 13 and Table I)
44
Trans IMarE. Vol 105. Pan 1. pp 23-52
MAG(*)
60 -
55
Reference:
Table 1
Signal:
motor stator voltage
50-1
45 —
40-
35-
30-
25-
20-
1.6k
1.8k
2k
f(H7,)
Fig 27: Frequency spectra of harmonies present in the motor stator voltage (see Fig 10 and Table I)
MAG(^Ç-)
40-
Reference:
Table 1
Signal:
motor stator current
35-^
30-^
20-J
10-J
5-^
-i—„J< à i h
200
400
600
800
Ik
.2k
1.4k
].6k
1.8k
2k
r(Mz)
Fig 28: Frequency spectra of harmonics present in the motor stator current (see Fig 9 and Table I)
45
K S Smith. R Yacamini & AC
Williamson
MAG(%)
30-
27.5
-
Reference:
Sicnal:
25-
22.5
Table 1
motor electromagnetic torque
-
20-
17.5
-
15
-
1 2.5 —
10-
7.5
-
5-
2.5
-
0
J-X
200
600
Ik
800
1.2k
1.4k
1.6k
2k
1,8k
f(Hz)
Fig 29: Frequency spectra of harmonics present in the motor electromagnetic torque (see Fig 12 and Table I)
MAG(%)
20-
18 J
Reference:
Table 4
Signal:
ac system voltage
16 . J
14-^
10-4
8-^
2-^
A
200
400
600
800
Ik
1,2k
1,4k
1.6k
1.8k
2k
2.2k
2.:
Fig 30: Frequency spectra of harmonics present In the ac system voltage (see Table IV)
46
f(H7.)
Trans IMarE. Vol 105. Part 1. pp 23-52
MAG(%)
20-
Reference:
Table 4
Sienal:
ac system current
18-4
16
14
12-^
10 J
6-^
4-4
2-^
À. A
200
400
600
-* M
. . Ai
t -
A-
- g
T
.4k
800
1
1.6k
• •• 1
2k
1.8k
f(Hz)
Fig 31 : Frequency spectra of harmonics present In the ac system/alternator atator windings (see Fig 24 and Table IV)
MAG(%)
50-
45 J
Reference:
Table 4
Signal:
alternator torque
40-4
35
J
30 J
25-J
20-^
15
10-^
5-^
V ^ W i
0
MAG(%) : f ( M z )
200
400
600
800
h. II
i
Ï
1.2k
1.4k
V
1.6k
•
1.8k
2k f ( H z )
(.3)1 o r
Fig 32: Frequency spectra of harmonics present In the electromagnetic torque of the alternator (see Fig 23 and Table IV)
47
K S Smith. R Yacamini &AC
Williamson
Discussion
C d r N A Haines (Royal Naval Engineering College,
Manadon)
1. The authors have mentioned in their paper that their Saber
simulations have been able to model both the
cycloconverters and the generators and motors in the
proposed propulsion system. With specü"ic regard to the
motors and generators, I wonder if they could explain
more fully the type of ac machine models used, ie d-q
models, phase models or equivalent circuit models. In
addition, could they please explain how they obtained
representative ac machine parameters for their chosen
models, and how sensitive the accuracies of die simulations
are to diese parameter values?
2.
In their paper, the authors have shown in Fig 17 two six
pulse cycloconverters feeding a double wound stator
induction motor. 1 wonder if the authors could comment
on the advantages they see in employing this type of
converter/motor arrangement in preference to a single 12pulse converter with a conventional singly-wound stator
induction motor.
• K S Smith, • R Yacamini and t A C Williamson (•University
of Aberdeen and t U M I S T ) The authors thank Cdr Haines for
his question which addresses the problems associated widi
modell ing electrical machines and obtaining parameters for the
machines. Three methods are available to model the electrical
machines in the proposed cycloconverter propulsion system.
These are two-axis (or d-q) models, phase models, and
equivalent circuit models. All three methods have previously
been used by the research group at Aberdeen University.
Experience has shown diat die phase model is the most
convenient forihis type of simulation. The phase model allows
the effects of zero-sequence currents and voltages to be correctly
calculated as well as allowing unbalances within the electrical
machine to be analysed. Equivalent circuit models give the
machine impedances at different frequencies. As such they
belong to the realm of frequency rather than time domain
analysis.
The simulation is based upon the voltage balance and rotor
dynamic equations for the induction machine and synchronous
machine primitive models shown in Figs 6 and 7 of the paper
These equations are solved in the time domain using a time
stepping integration technique. For the induction machine, this
gives a six by six impedance matrix and for the synchronous
machine a seven by seven matrix. For the double wound
induction machine (see Fig 16 of the paper) a nine by nine
matrix is obtained. Some of the inductances in the matrix are
time varying, due to the rotation of die rotor, which requires
that the impedance matrix is recalculated at each time step. The
use of a two-axis machine representation would considerably
reduce the size of the matrices and remove the necessity to
recalculate the impedance matrix at each time step. However
in order to link the machine model with the cycloconverter
model a phase to two-axis and two-axis to phase conversion
would be required in the simulation. It has been found üiat
implementing this conversion within Mast, the programming
language used by Saber produced computer run times which
exceed those of the full phase model. For this reason phase
models are our preferred method of representing machines.
The machine parameters used in the simulations are based
upon the standard parameters available from manufacturers.
For the induction motor the single phase equivalent circuit
48
with the rotor parameters referred to the stator is used. From
this the mutual inductances between stator phases, rotor phases,
and stator and rotor phases required for the voltage balance
equations can be determined. For the synchronous machine,
the standard direct axis and quadrature axis reactances and time
constants are used to determine the self inductances and mutual
inductances for the windings of the primitive synchronous
machine model shown in Fig 7 of the paper
The accuracy of the parameters available for elecuical
machines is generally poor, and the authors acknowledge that
a simulation is only as accurate as die parameters used. For this
reason is it necessary when performing case studies, to run the
simulations using a range of parameters within the tolerances
set by the manufacturers? In a computer simulation, exact
agreement between measured and simulated responses is unlikely to be obtained. The value of computer simulation does
not lie in determining the exact response of a system. Its
usefulness lies in the ability to study the performance of a
system around a particular operating point, and to assess die
effects of changes upon die system performance.
The principal advantage of the double wound winding over
the single wound winding for die induction motor stator when
supplied from six pulse cycloconverters, is that the 5th and 7th
harmonic fluxes produced by the abc and uvw windings cancel
each other out, removing the characteristic 6th harmonic from
the rotor electromagnetic torque. The 6th harmonic torque
would be present in a single wound motor supplied from a six
pulse cycloconverter A single 12 pulse cycloconverter with a
conventional single wound stator induction motor would also
be free from the 6th harmonic torque. Although this suggests
that there is no particular advantage to be gained from the use
of the double wound machine, from an operational point of
view some advantages do exist. For example, it would be
possible to carry out maintenance on the converters which
supply the uvw windings, whilst the motor continues to operate
(on reduced power), on the abc windings.
C d r C G Hodge (Royal Navy, Foxhill, Bath). 1 presume that
the digital simulation of the electrical system used fixed values
of inductance. The graphs of harmonic content of the voltage
and current waveforms produced by the simulation could be
used to calculate the harmonic impedance of the machine. If
this is done. I believe it would show a fundamental impedance
üiat could be related to the synchronous impedance of the
machine; and harmonic impedances that could be related to a
u^sient impedance and their harmonic number Can the
auüiors explain how simulation based on a fixed value of
inductance can produce results which exhibit variable inductance levels?
* K S Smith, *R Yacamini and t A C Williamson (*University
of Aberdeen and t U M I S T ) Cdr Hodge's question is closely
related to that of Cdr Haines. As suggested, we have
subsequently calculated the harmonic impedance of the
synchronous machine using the current and voltage spectra
obtained from the time domain simulation. For this particular
exercise the machine's direct axis parameters were set to Xj =
1.5 pu, Xd- " 0.3 pu, and Xj. = 0.1 pu, on an S base of 6 M V A ,
at a rated voltage of 6.6 k V . Using the Fourier post-processor
gave the following amplitudes (peak values) for the 6k + 1
hamionics present in the alternator voltage and current
waveshapes when supplying a six pulse cycloconverter (the
Trans IMarE. Vol 105. Part 1. pp 23-52
voltage is line to line). From this die harmonic
impedance at each harmonic number can be
Harmonic
determined (see Table I).
n
From these impedance calculations it
would appear that the synchronous reac1
5
tance of the machine is 11.49 ohms, and that
7
the impedance to the harmonics is approxi11
mately given by 1.3n, where 1.3 is the
13
average value of die impedances in the last
17
column of the table (ignoring die funda19
mental) and n is the appropriate harmonic
number Convening these to per-unit gives
a synchronous reactance of 11.48/7.26 =
1.58 pu, and a harmonic impedance of 1.3n/7.26 = 0.18n pu.
Considering the parameters which were inidally input to the
simulation, it would appear that the time domain simulation
predicts that the impedance to the fundamental corresponds to
die direct axis synchronous reactance (Xj = 1.5 pu), and that die
impedance to harmonics corresponds to (x^. + \g)l2. This is in
agreement with the suggestions made by Cdr Hodge.
Table I shows that the time domain simulation can display
the phenomenon described as 'variable inductance levels'. We
do not agree with this description. The table shows the variation of machine reactance with frequency (the resistive component is ignored). These reactances have been obtained by
converting die current and voltage waveshapes produced by
the time domain simulation into the frequency domain, and
then calculating the impedance in the frequency domain.
In time domain analysis, reactance has no meaning. The
voltage balance equations are expressed in terms of resistances,
inductance, and instantaneous rate of change of current. It
should be noted, however, that some of the mutual inductances
in the synchronous machine model vary with rotor angular
position. These time varying inductances can therefore be
described as 'variable inductances'. The term 'direct axis
reactance' is an unfortunate one. This expresses the machine
impedance at a particular rated frequency; perhaps when
dealing with time domain analysis the term 'direct axis inductance' would be more appropriate.
M Murphy ( C E G E L E C Projects Ltd, Rugby) Thank you
once again to die authors for their very interesting paper
following closely on the heels of an earlier contribution at the
Institute. I have two questions:
1. The ripples shown in the ac motor currents (Fig 9 of the
paper) represent those achieved in die first generation
designs and later motors have much lower ripples. However, the machine torque shows a cyclic ripple (Fig 12 of
the paper) which is not observed on a real system. Can the
authors explain this?
2. How do the ac harmonics and resultant ac voltage (supply
side) compare wiüi a six pulse dc drive? Has any work
been done to explore the optimum relationships for motor
pole number, motor frequency and ac supply frequency
which may optimise the quality of ac supply waveforms?
• K S Smith, •R Yacamini and t A C Williamson (•University
of Aberdeen and tUMIST) The auüiors Üiank Mr Murphy for
his kind comments and also for setting us two challenging
questions.
We understand from our discussions with drive manufacturers, diat it is now possible to design induction motors for
cycloconverter applications which have leakage inductances
which are larger than additional designs. Limiting die starting
current for direct on-line starting is not a problem with
cycloconverter drives. This increased leakage inductance will
Table I: Harmonic impedance calculations
Voltage
(V)
Current
(A)
Impedance Z
(ohms)
9027.27
509.94
266.22
206.76
175.34
112.74
114.20
785.22
75.83
30.57
15.52
11.05
4.74
4.26
11.49
6.72
8.71
13.25
15.86
23.78
26.81
Z/n
(ohms)
11.49
1.34
1.24
1.20
1.22
1.39
1.41
limit the amplitude of the motor current ripple. In the simulation results presented in the paper, the motor parameters chosen
for the simulation are based on 'first' generationmotor designs.
The motor torque shown in Fig 12 of the paper is actually the
air gap electromagnetic torque. The torque delivered to the load
through the motor shaft coupling differs from this due to die
inertia of the rotor die ripple in the torque producing a small
speed variation. The air gap elecu-omagnetic torque cannot be
measured directly and we assume that the torque waveshape
observed by M r Murphy is in fact measured at the motor
coupling. This is illustrated using the simulation shown in Figs
1 a and 1 b overleaf. The electromagnetic torque and load torque
are shown along with the small variations in the rotor speed.
Another feature of real systems which is not present in die
simulation is the closed loop speed controller. Modem drives
use a vector controller to control the torque produced by the
motor, by controlling the motor line currents. We would
suggest that the torque control loop will have sufficient bandwidth to damp low frequency ripple. We are currently investigating this effect.
In answer to the second question, for a traditional six pulse
dc drive, the current harmonics injected into the ac system
correspond to die characteristic 5di, 7di, l l ü i . 13di, etc harmonics. The amplitude of the current depends upon the load
characterisücs and the speed of the dc machine (which determines die back emf). Speed conu-ol is achieved by varying the
converter firing angle which controls the voltage applied to the
armature of die machine (assuming constant field excitation).
The frequencies present in the line current do not change with
converter firing angle (assuming the dc current has no ripple
component, and that the commutation overlap angle is small)
nor does their amplitude relative to die fundamental component. An earlier paper illustrates the waveshapes obtained from
site measurements and the Saber simulation for dc drives (see
Ref 1 overleaO.
With a six pulse cycloconverter drive, the current harmonics
injected into the ac system include the same characteristics
harmonics and in addiuon modulation product frequencies.
The frequency of the side-bands is a function of the converter
output frequency, and it is diese components which giveriseto
die presence of frequencies which are neither harmonics or
subharmonics of die fundamental frequency. The convener
input transformer connections also influence the frequencies
present in the ac line current. The complete family of frequencies present in the line current can therefore be divided into two
groups: those due to the modulation process, and those which
are circuit dependent. These harmonic frequencies are discussed at length by Pelly (see Ref 2 overleaf).
For a cycloconverter with a balanced three phase output, the
first sideband terms to appear in die family of frequencies is die
fundamental supply component modulated by six times die
output frequency. The amplitude of this component is usually
less than 4% of die fundamental. The conuibution made to the
49
K S Smith. R Yacamini & A C Williamson
Electromagnetic torque
500
Load
torque
420
J
0
\
I
\
I
L
10
Time (s) x10-2
15
20
Fig la: Variation of torque with time
450
C 5
Shaft speed
440
X
«-1
^
TD
430
S
420
Q.
(/î
ro
410
400
10
Time(s) xlO"^
Fig 1b: Variation of shaft speed with time
50
15
20
Trans IMarE. Vol 105, Pan 1. pp 23-52
distortion of the line current is limited, and does not therefore
present any appreciable subharmonic load to die input system,
if this system can be regarded as infinite. The distortion of the
input current wave is determined substanually by the circuitdependent harmonic components. With circuits of sufficiently
high pulse number it is possible to obtain current waveshapes
with very low distortion. It is claimed by Pelly that for three
phase cycloconverters supplied from large ac systems, the
distortion of the input current waveform is generally less than
that of the input current waveform of a rectifier, with the same
pulse number supplying a dc output. The resulting ac voltage
distortion for a cycloconverter drive is therefore less than for
the dc drive. It should be noted, however, üiat subharmonic
frequencies will be present in the ac line current, which will
produce low frequency torques on the rotor of a ship's alternator.
The work carried out at Aberdeen University has not considered in detail the optimum relationships for motor pole pair
number, motor frequency, or ac supply frequency. However it
is interesting to consider here the possible advantages offered
by increasing the ac supply and motor frequencies. Traditional
cycloconverter designs would limit the output frequency to
around one third of the input frequency. In die case of a 60 Hz
system, diis would give a maximum cycloconverter output
frequency of 20 Hz. In order to produce the required 200 rev/
min shaft speed, a motor with six pole pairs would be required.
If the ac system frequency is increased to 90 Hz, the upper
operating frequency of the cycloconverter becomes 30 Hz.
This would require a motor widi twelve pole pairs. At this
higher operating frequency, the impedance of the motor (assuming the same inductances) to the characteristic
cycloconverter harmonics is increased, reducing the current
ripple and improving die electomagnetic torque waveshape. If
die maximum output frequency is further increased, beyond
the traditional limit to 60 Hz, a motor widi 18 pole pairs is
required. At this higher operating frequency the advantage of
higher machine imp)edance is further enhanced, again reducing
the harmonics present in the motor line current. Raising the ac
system supply frequency from 60 to 90 Hz, also will increase
the impedance of the alternators, decrease die amplitude of the
supply current harmonics and so improve the ac system voltage. An optimisation study would dierefore appear attractive.
References
1. R Yacamini. Lihua Hu and ID Stewart. 'Electric drives on ships
and oil platfomis". Trans IMarE. Vol 104, Part 4 (1992).
2. B R Pelly, Phase Controlled Converters and
Cycloconverter,
Wiley. New York (1971).
Professor J O Flower (Department of Engineering,
University of Warwick) This has been a most interesting
presentation, on a fascinating topic, by the audiors, and diere
are a number of questions I should like to ask. It is unclear to
me, bodi from reading die paper and from listening to the
lecture, as to the interplay between the Sabre and die Mast
software used in the simulations. Please may I have some
further explanations? Further, I should be most interested to
know why die authors make special mention of die BackwardEuler and the Trapezoidal integration routines for this
application. Is it merely that, for this integration problem, first
and second order methods are accurate enough and, thereby,
the integration process can be speeded up to some considerable
extent?
During the simulations I wonder how long the process took
to settle down to give, for example, the steady state waveforms
such as those shown in Fig 14 of the paper Since it is stated, in
the paper that there are frequencies present which are neither
harmonics nor subharmonics of the fundamental frequency,
then we have an aperiodic waveform; is this a problem? The
ingredients of these problems are those which can lead to
chaotic behaviour; have the audiors noted any evidence of this
in their results?
1 was a little surprised to see that there is interest in power
supply frequencies up to 90 Hz. I wonder why this is seen as
advantageous. These higher frequencies will certainly lead to
higher losses, although, to compensate, it should be possible to
raise die power-to-weight ratio of the machines. This presumably might be desirable in die confined space of a frigate.
Would the authors comment on this, please?
Just a comment to finish with. M r Yacamini told us about
his ambition for including propeller and ship dynamics in
future work; a laudable ambition and 1 look forward to learning
of diis work in due course. However, we have also heard this
evening of the difficulties of obtaining electrical machine
parameters for simulation purposes. I fear diese difficulties
will be nought compared with the problem of obtaining data on
marine propellers under transient conditions.
• K S Smith, •R Yacamini and t A C Williamson (•University
of Aberdeen and tUMIST) The authors diank Professor
Flower for his comments. The software used for the analysis is
called Saber. This name is applied to the complete simulation
system. Mast is a programming language which is used to
supply information about die characteristics of components
which constitute the system. A compilation process converts
die Mast programme into code which die Saber executable file
can interpret. This is then used to set up the maüices which
describe the system to be anal ysed. When tlii s stage i s completed,
die analysis of the system can proceed. The integration
algorithms available within the Saber simulator are restricted
to the first and second order Backward-Euler and Trapezoidal
methods. The software vendors have advised us that higher
order methods are generally not suitable when analysing
complex systems, and so they are not made available in Saber,
which is essentially a general purpose equation solver.
The question of settling down time is an interesting one.
Approximately Is of simulation time is required to ensure diat
die transient associated with the initial point of the simulation
has decayed. As the cycloconverter produces frequencies which
are neitlier harmonics or subharmonics of the supply frequency, a very long period may be required before the
waveshapes repeat themselves. If, however, the input and
output frequencies do remain constant, then a definite period
associated with the lowest frequency generated can be identified. For example, if the ac supply system frequency is 50 Hz
and the converter output frequency is 15 Hz, then the lowest
frequency present in the converter waveshapes will be at 5 Hz.
If the questioner would not allow the term 'steady-state' to be
applied until the lowest frequency present has repealed itself in
the waveshape, then perhaps we should use die term 'quasisteady-staie' to describe die waveshapes presented in die
paper If the computer simulation was allowed to run for
sufficient time, 'steady-state' waveshapes would be obtained.
The waveshapes produced by the simulation therefore have a
define period, and are not aperiodic. We have seen no evidence
of chaotic behaviour in our simulations.
The possible advantages of using power supply frequencies
up to 90 Hz, have been discussed in response to M r Murphy's
question. High frequency generation at 400 Hz is common on
aircraft, and it has been considered for use on isolated offshore
oil and gas installations (see Ref 1 overieaf).This paper shows
that the biggest advantage in terms of reduced weight occurs
51
K S Smith, R Yacamini Je A C Williamson
when the operating frequency is raised from 50 Hz (or 60 Hz)
to 200 Hz. This gives a weight saving of 30%. Beyond this
frequency diere is a diminishing return, a frequency of 400 Hz
producing a saving of 32%. To the audiors ' knowledge no work
has been carried out to investigate the suitability of generation
at 200 Hz for frigate applications.
We thank Professor Flower for his comments on our 'laudable ambition '. We feel however diat the si mulations of the size
and complexity that we are presently carrying out would not
have been possible even two or three years ago. Recent improvements in software design and the capability of small
52
computers have made this possible. We also feel that recent
advances in data acquisition systems and information technology allow us to dream about simulating the transient behaviour
of complete ship propulsion systems. After all, that is what is
expected of us who live in ivory towers.
Reference
1.
R Yacamini. D A Hitchens and J C de Oliveira. 'Weight
reduction in offshore electrical power modules by running the
system at higher frequencies'. Proc 5th International Symposium on Offshore Engineering. Vol 5. pp 739-752. Federal
University of Rio de Janeiro, Brazil (September 1985).