SPEEDAM 2006
International Symposium on Power Electronics,
Electrical Drives, Automation and Motion
SyntegraTM – Next Generation Traction Drive System,
Total Integration of Traction, Bogie and Braking Technology
J. Germishuizen*, A. Jöckel*, T. Hoffmann**, M. Teichmann**, L. Löwenstein***, F. v.Wangelin***
* Siemens AG, Automation&Drives, Large Drives, Traction, Vogelweiherstr. 1-15, D-90441 Nürnberg (Germany)
** Siemens Transportation Systems GmbH & Co. KG, Eggenberger Str. 31, A-8021 Graz (Austria)
*** Siemens AG, Transportation Systems, Group Technology, W.-v.-Siemens-Str. 67, D-91052 Erlangen (Germany)
Index Terms - Motor Design, Drives, Direct Drives,
Permanent Magnet Machines, Traction, Bogie, Rail
Vehicles, Integration, Braking Technology.
I. INTRODUCTION
Today, metro or commuter trains with underfloor
traction equipment use a traction drive system consisting
of a 3-phase IGBT inverter, feeding 2...4 induction
motors with a power rating of 120…300kW. For torque
transmission from the traction motor to the wheelset, a
gear unit is required for the induction motor, entailing the
following drawbacks for the customer:
• investment cost
• energy losses
• maintenance cost
• possible oil leakage
• noise caused by gear unit.
Furthermore, despite of its many and well-known
advantages, the induction traction motor also shows some
drawbacks:
• very high short circuit torque – leading to oversized
mechanical drive train
• quite low stray inductance – giving rise to inverter
induced torque ripple and noise in the low speed
region
• rather high losses in the rotor – making it difficult to
design a completely closed traction motor with a water
cooled stator.
For torque transmission, there are two major types for
the design of the coupling and mechanical drive train:
• semi-suspended drive with an axle-hung gear unit and
a traction motor being mounted in the bogie frame;
both are connected via an oil-greased tooth-coupling
1-4244-0194-1/06/$20.00 ©2006 IEEE
• totally suspended drive with a motor integrated gear
unit, both being mounted in the bogie frame; torque is
transferred to the wheelset via a cardan hollow shaft
coupling containing rubber elastic elements.
In both cases, the coupling needs investment, space,
adjustment and maintenance. Additionally, the number of
bearings to maintain is rather large.
The goal of the presented innovation is to replace this
complex drive system by a very simple gearless traction
drive system based on a high-torque permanent magnet
(PM) motor. The basic concept of the drive system has
been developed for a high-speed train application [1] and
is now adopted for a totally integrated drive for a metro
or commuter train.
II. BASIC SPECIFICATION OF THE DRIVE SYSTEM
Most important data of the drive specification are the
torque and power rating, the given space and the max.
DC link voltage of the traction inverter.
A. Torque-Speed-Diagram
Metros and commuter trains have a typical
acceleration performance between 1.1 and 1.3m/s2.
Depending on the number of driven wheelsets and the
wheel diameter, the basic torque-speed-diagram is shown
in fig.1.
6
Torque T (kNm)
Abstract--The state-of-the-art drive system of today’s
metro or commuter trains with underfloor traction
equipment consists of a 3-phase IGBT inverter, feeding two
or four induction traction motors in parallel. For torque
transmission from the traction motor to the wheelset, a gear
unit is required for the drive. As a rather radical
innovation, this paper presents a completely new gearless
drive system for future metros or commuter trains called
SyntegraTM based on a permanent magnet traction motor.
The paper reports on the electrical and mechanical design of
the traction motor, the braking concept, the integration into
the bogie, the manufacturing and some test results of the
laboratory test bench.
5
P Braking = 300kW
4
3
P Driving = 150kW
2
1
0
0
100
200
300
400
500
Speed n (rpm)
600
700
Fig. 1. Torque-speed characteristic for one driven wheelset.
Typically for metro trains, the driving and braking
torque is basically the same, while the braking power
rating equals double of the traction power rating.
Together with the maximum braking voltage, this
requirement marks an important requirement for the
electromagnetic design of the traction motor.
S2 - 23
Authorized licensed use limited to: TONGJI UNIVERSITY. Downloaded on April 07,2024 at 06:18:52 UTC from IEEE Xplore. Restrictions apply.
B. Mechanical Drive Concept
The mounting space for a gearless traction drive is
given between the wheels of the wheelset. So basically,
the track gauge, the worn wheel diameter and the ground
clearance limit the space for the gearless traction motor.
In our case, the vehicle is designed for standard gauge of
1435mm.
Another important point is the type of the drive train.
Fully suspended drives need a flexible coupling between
motor and wheelset and allow only for a smaller outer
diameter of the stator. Since maximum speed of the metro
vehicle is only 80km/h, an axle-mounted unsuspended
traction drive will not lead to excessive wheel-rail contact
forces and thus is going to be the most economic
solution. Fig. 2 shows the schematic longitudinal cross
section of the gearless drive arrangement.
Fig. 2. Schematic longitudinal cross section of the gearless drive.
C. Supply voltage limits
The traction drive is being fed from low voltage of
750V DC. In driving, the DC voltage may drop down to
500V, in braking the voltage can rise up to 1000V.
III. ELECTROMAGNETIC DESIGN
Based on the given basic requirements, the main
dimensions of the traction motor can be fixed concerning
the maximum outer diameter of the stator housing and,
together with the housing design, the stator lamination.
Respecting the diameter of the supporting wheelset shaft,
the diameter of the rotor hollow shaft can be determined.
For a high-torque permanent magnet motor, a rather
high number of poles is suitable, enabling the magnetic
yoke of stator and of rotor to become quite thin. This
maximises the rotor diameter increasing the torque of the
motor to the needed value.
For the design of the permanent magnet rotor, a design
with surface mounted magnets was chosen. Here, the
permanent magnets are glued onto the rotor surface and
fixed by a glass fiber bandage. As the rotational speed of
the rotor is very low, the bandage can be designed quite
thin.
As the flux distribution in base speed region or flux
weakening condition is rather complex to calculate,
numerical 2D FEM was used to obtain the required
current and the flux density values for a given torque.
The stator lamination carries a conventional form coil
winding with an insulation system of thermal class 200.
Due to the high pole pitch, the end windings become
short making the machine very compact.
IV. MECHANICAL DESIGN
Following the electromagnetic design, the mechanical
design "packages" the active parts of the machine. The
stator housing is made out of an iron cast piece with
rectangular cross-section and the axial water tubes being
drilled in the four corners. Water cooling is an additional
feature to make the motor more compact.
The wheelset carries a rotor hollow shaft which is
shrinked stiffly on the two ends. The rotor hollow shaft
itself carries the magnets, finally fixed by a glass fiber
bandage.
V. BOGIE INTEGRATION
In parallel to the traction drive development, a
completely new bogie concept for metros and commuter
trains was designed.
Compared to conventional traction drives the gearless
traction drive can be completely integrated in the bogie.
The outcome of that is:
• Due to the coaxial traction motor construction the
space requirement of the traction drive is minimised.
• All tractive effort and traction torque is transferred
directly from one traction motor of a bogie to the
second. From this traction motor there is a direct link
to the vehicle body using a pair of rods. Due to this
direct connection the bogie frame is almost free of
tractive effort.
• If the bogie has wheelsets with inboard bearings, the
bearings of the axle-mounted gearless motor and the
motor bearings can be integrated. In this case, the
driving wheelset has only two bearings.
• Self-evidently, the design of the bearing system has to
take the additional mechanical constraints and the
temperature rise into account.
As a result the high integration level leads to lower mass
of the bogie. Compared to a conventional traction drive,
not only the gear unit, but also the couplings of the drive
are completely eliminated.
VI. REALISATION AND TEST RESULTS
Due to the encouraging results of the paper studies, it
was decided to build several prototypes of the SyntegraTM
traction motors not only for the test bench, but also to
verify them in a prototype vehicle.
The prototype motors were built in the normal
manufacturing sites in Nürnberg using proven design
production engineering:
• standard form coil winding insulation class 200
• standard steel lamination sheets
• motor housing and bearing housing made from iron
cast blanks.
For the prototype motors, magnetized magnets had to
be handled and had to be glued manually onto the rotor
surface – a rather time consuming labour. After the
application of the bandage, the rotor was put into an oven
S2 - 24
Authorized licensed use limited to: TONGJI UNIVERSITY. Downloaded on April 07,2024 at 06:18:52 UTC from IEEE Xplore. Restrictions apply.
As the rotor temperature in operational service is yet
unknown and the PM flux linkage is temperature
dependent, two lines are drawn for the cold rotor in blue
and the warm rotor in red respectively.
The most important feature is the drive efficiency
which is shown in fig. 5, also calculated from the
measured motor parameters. The stator winding losses
are calculated for a winding temperature of 150°C
according to IEC60349 standard.
Drive efficiency K
to cure the resin of the bandage. Finally, the magnetized
rotor was inserted into the stator.
For testing, a very detailed test programme was
elaborated including the following steps:
• no-load tests with open terminals
• short circuit tests
• no-load tests at sinusoidal voltage supply
• heat run tests at sinusoidal voltage supply
• heat run tests at inverter feeding
• overspeed tests.
A. Measurement Results
In this paragraph, some exemplary results of the
performed type tests are presented. First, an oscilloscope
plot of the induced voltage at no-load (open terminals) is
shown in fig. 3.
Klemmenspannung [U ,s]
600 600
525
375
300
225
Induction Motor
Induction Motor + Gear
20
40
60
Vehicle speed v (km/h)
80
100
Fig. 5. Drive efficiency at full load (driving operation).
150
75
VW i1
0
75
150
225
300
375
450
600
PM Motor, rotor cold PM Motor, rotor warm
0
450
UVi1
1,00
0,98
0,96
0,94
0,92
0,90
0,88
0,86
0,84
0,82
0,80
525
600
0.05
0.04
0.03
0.02
0.01
0.05
0
0.01
0.02
0.03
ti1
0.04
0.05
0.05
Fig. 3. Terminal voltage at no-load (open terminal) test.
Based on the no-load and the short circuit test, the
motor parameters were identified which are
• Resistance of the stator winding Rs
• Flux linkage of the PM rotor at no-load <p
• Motor inductance in d-axis Ld
• Motor inductance in q-axis Lq (only from FEM)
From this, the characteristic curves of the drive can be
evaluated. In fig. 4 the motor phase current at full load
(driving condition) is shown in comparison to the
standard induction motor, for the same DC link voltage.
The data for the PM motor are compared not only to a
standard induction motor, but also to a complete drive
including the gear unit for which a constant efficiency of
97% is assumed.
It can be seen, that the PM traction drive reaches
values up to 94% efficiency which is a remarkable
performance for a 150kW traction drive. At partial load
being very important for traction drives, the efficiency
difference to the standard drive system should be even
larger. Next step will be a loss calculation assuming a
complete realistic drive cycle to determine the LCC
benefit for the customer due to lower energy
consumption.
VII. TRACTION INVERTER AND CONTROL DESIGN
The inverter of the SyntegraTM drive system is a three
phase inverter with IGBT modules. As the current rating
of the PM traction motor is comparable to the induction
motor, the IGBT modules do not need to be oversized.
Fig. 6 shows the scheme of the main circuit.
Motor current I s (A)
300
PM Motor, rotor warm
250
Induction Motor
200
150
PM Motor, rotor cold
100
50
0
0
20
40
60
80
Vehicle speed v (km/h)
100
Fig. 6. Syntegra drive system main electrical circuit.
Fig. 4. Motor phase current at full load (driving operation).
Switching frequencies of the IGBT inverter can be also
kept at the same value as for the induction machine.
S2 - 25
Authorized licensed use limited to: TONGJI UNIVERSITY. Downloaded on April 07,2024 at 06:18:52 UTC from IEEE Xplore. Restrictions apply.
Nevertheless, torque and current ripple as well as inverter
induced noise emission are lower due to the larger
inductance of the PM machine.
The IGBT inverter is water cooled, and the cooling
circuit is therefore thermally combined with that of the
traction motor. The main difference with the state-of-theart traction inverter for induction motors is the need for a
single-drive configuration, i.e. each motor must be fed by
its own inverter. This fact is increasing the cost for the
drive system. However, additional advantage as increased
adhesion utilization lower vibration and arbitrarily chosen
wheel diameters of different wheelsets can be offered to
the customer.
In case of a permanent inverter fault, the PM traction
motor must be separated from the inverter by mechanical
switchgear. This is done for two main reasons:
• it has to be made sure that the PM machine does not
supply any continuous current to the inverter in case of
a fault
• the PM machine has lower losses at no-load than at
short circuit conditions.
In this cut-out mode, normal metro passenger driving
cycle can be performed for the cut-out PM motors
without water cooling.
Torque control of a PM synchronous machine does not
differ too much from that of an induction machine. While
the inner control circuits for the torque and the flux
producing current components stay basically identical,
the field orientation itself has to be adapted. In case of an
induction machine, field orientation refers to the rotor
flux space phasor. In case of a synchronous machine,
field orientation is reduced to a rotor angle orientation,
normally requiring a rotor position encoder.
Robust traction drives cannot be equipped with very
complex and sensible sensors for rotor position
measurement. Therefore, an observer has been adopted to
estimate rotor position from the given values of current
and DC link voltage signal.
VIII. NEW BRAKING TECHNOLOGY
Opposite to induction machines, PM machines
generate an intrinsic braking torque if connected to an
adequate ohmic resistance. This feature of the PM
machine enables a fundamental change of the existing
braking concept of metros and trains.
It is state-of-the-art to use an electro-dynamic (ED)
regenerative brake for service brakes and a fully-fledged
electro-pneumatic (EP) friction brake for all kinds of
emergency brakes. Both are completely independent
systems. The friction brake is put into operation each
time an emergency brake is requested, even when the ED
brake is fully functional. The friction brake requires a lot
of components for compressed air production, storage,
distribution and system control. Therefore minimal
failure rates are demanded for each component.
With the use of the PM machine the fully-fledged
electro-pneumatic friction brake is intended to be
substituted. This means a wide reduction or even the
removal of the pneumatic braking system.
•
•
•
•
Positive effects are
reduction of wear (abrasion)
noise reduction
reduction of dust caused by brake shoe wear
less maintenance
The goal is to perform all braking requirements service brakes and emergency brakes - with the ED
brake. A new secondary brake system, a safe electric
brake, will be established instead of the EP brake. A
brake control will be adopted to detect a malfunction of
the ED brake in case of emergency brakes, e.g. by
nominal / actual value comparison, and to switch to the
safe electric brake.
The safe electric brake only consists of the
components shown in fig. 7:
• PM traction motor
• 3-phase brake resistor
• contactor to cut off the converter
• contactor to connect the brake resistor
Fig. 7. PM machine with 3-phase brake resistor and contactors.
Cutting off the converter is necessary to protect the
converter and to eliminate any influence of the microprocessor controlled traction drive system during
emergency braking.
Because of the few components a rise of availability
can be achieved. The lay-out with one brake system per
wheelset leads to an increased redundancy. To get the
acceptance for the safe electric brake a rating into risk
class IV "negligible" according to European Standard
EN 61508 for the failure of the safety brake function of
the vehicle must be reached. Depending on the train
configuration the required failure rates of each
component can be determined.
The characteristics of the braking torque curve can be
set via adjusting the resistance. Its maximum torque is
defined by the motor data. As shown in fig. 8 the
maximum torque can be moved along the speed axis by
variation of the ohmic brake resistance RB. A lower
resistance moves the maximum torque to lower speeds
and vice versa.
S2 - 26
Authorized licensed use limited to: TONGJI UNIVERSITY. Downloaded on April 07,2024 at 06:18:52 UTC from IEEE Xplore. Restrictions apply.
With the use of additional capacitances Ck connected
in parallel to each resistor the speed-dependent inductive
load can be compensated and a further torque increase is
possible.
R B || CK
• three phase gearless PM traction motors, completely
enclosed and water cooled [4, 5]
• total integration of the traction motors into a new
bogie concept avoiding the coupling and even the
bearings for the traction motor
• use of the PM machine for a safe electric emergency
brake (disruptive braking technology).
P Braking
RB / 2
The braking concept represents the safe electric brake
in a very simple design. For future applications it is
considered to develop circuits or control systems, which
• can vary the braking resistance to create a constant
braking torque for all speeds,
• enable to use the existing brake resistor with chopper
operation.
Torque
short circuit
RB
0
100
200
300
400
Speed [rpm]
500
600
700
Fig. 8. Torque-speed-characteristic for different values of the brake
resistance RB and with capacitance Ck in parallel.
Compared to the service brake curve there is a lack of
braking torque at low speeds. Braking torque lacking
power can easily be delivered by small mechanical
brakes, which are needed anyway to hold the vehicle at
standstill. At speeds lower than 150rpm no important
energy conversion occurs. The important range for
braking is at speeds above 150rpm, where train velocity
is high and full braking power is required.
The paper reports on the electrical and mechanical
design of the motor, the inverter, the braking concept, the
integration into the bogie, the manufacturing and some
test results of the laboratory test bench. In the meantime,
two SyntegraTM bogies have been integrated in a test
vehicle and are being tested in the Siemens test center in
Wildenrath (PCW).
ACKNOWLEDGMENT
The development of the gearless drive system was
kindly supported by the "Bayerisches Staatsministerium
für Wirtschaft, Infrastruktur, Verkehr und Technologie"
in Munich.
IX. CUSTOMER ADVANTAGES
The novel totally integrated gearless drive system
SyntegraTM offers the following advantages to customers:
• higher efficiency of the traction motor
• no gear energy losses
• no gear maintenance
• no gear noise
• oil-free drive system
• no traction motor fan noise
• reduced noise of the traction motor caused by inverter
feeding
• reduced noise of the traction motor by rather low
motor speed
• no coupling adjusting or maintenance
• only two bearings per driven wheelset
• reduced total mass of the total bogie
• reduced rotating mass of the driving wheelsets
• reduced maintenance of the mechanical braking
system.
REFERENCES
[1] Jöckel, A.; Knaak, H.-J.: INTRA ICE – A Novel Direct
Drive System for Future High-Speed Trains. International
Conference on Electrical Machines ICEM 2002, Brugge,
September 2002.
[2] Palik, F.: Entwicklung der elektrischen ŠKODALokomotive der Dritten Generation, Baureihe 85EO.
Elektrische Bahnen 88 (1990), Vol. 12, pp. 436-441.
[3] Palik, F.; Kurbasow, A.S.: Elektrischer Bahnantrieb ohne
Getriebe. Elektrische Bahnen 89 (1991), Vol. 2, pp. 66-70.
[4] Koch, Th.; Binder, A.: Permanent magnet synchronous
direct drive for high speed trains. Proceedings of
Electromotion ‘01, Bologna 2001, pp. 287-292.
[5] Koch, Th.; Binder, A.: Energy saving with high speed
trains propelled by direct permanent magnet synchronous
drive. Proceedings of the PCIM, Nürnberg 2001.
X. CONCLUSIONS
As a rather radical innovation, this paper presents a
completely new gearless drive system for future metros
or commuter trains called SyntegraTM. Basically, for a rail
car with four driven wheelsets it consists of the following
components:
• 4 single-drive three phase inverters with water cooled
IGBT modules
S2 - 27
Authorized licensed use limited to: TONGJI UNIVERSITY. Downloaded on April 07,2024 at 06:18:52 UTC from IEEE Xplore. Restrictions apply.