power sector
K.V.KANDASAMY, SARAT KUMAR SAHOO,
S.PRABHAKAR KARTHIKEYAN
A Technology Review on Matrix Converter
Matrix Converter (MC) is mostly useful in high power energy generation system like wind
energy, solar energy, Unified Power Quality Control (UPQC) systems. Such circuits are easily
adaptable where critical power situation occurs. Moreover these types of circuits are versatile
with less component and low power loss capability. This type of circuit not only used in power
generation systems and also used in various industries application. With wide variety of usage
and importance, matrix converter still modified further to meet the requirement in the field of
energy.
I
n recent years, efficient control of AC
Signals in terms of voltage and frequency is much required due to technology advancement in industries. In past
decades such controlling techniques were
tedious and complex, the voltage and frequency could not vary simultaneously. So a
less complex circuit with low loss and better output is mandatory.
K.V.Kandasamy, Assistant Professor at Velammal Engineering College, Chennai. Pursuing Ph.D. at Vellore Institute of Technology (VIT) University.
Dr. Sarat Kumar Sahoo, Associate Professor in the
School of Electrical Engineering, VIT University.
Dr. S.Prabhakar Karthikeyan, Associate Professor in
the School of Electrical Engineering, VIT University.
less number of switches with unique control as shown in fig 1.
Fig.1. General Direct Matrix Converter
Among most of the converter in AC-AC
converters, matrix converter is one of better converter due to the versatile nature of
the converter. Matrix converter is an alternative to AC-DC-AC converter which uses
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Fig.2. Practical Matrix Converter
The matrix converter is a forced commutated single stage converter with an
array of mxn bidirectional power switches
connected directly from m-phase input
to n-phase output produce variable output voltage with unrestricted frequency.
The matrix converter comes just for the
replacement of cycloconverter. The matrix converter output can be obtained by
proper modulation technique. Since matrix
converter uses only switches it transfer the
energy without DC-link and large energy
storage elements. The key feature in a MC,
it is the fully controlled four quadrant operation due to bidirectional switch, which
allows high frequency operation.
History of Matrix Converter
In early 1930’s, the single stage AC to AC
converter was introduced. The purpose of
AC to AC converter is to change frequency
and voltage arbitrarily. Later the term has
been changed into cycloconverter with
some modification also called as frequency
changer with direct coupling.
Even though cycloconverter has some
advantage like single step energy converter, no dc link and less amount of reactive
coil and capability of switch off during enenergética
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power sector
ergy. It does have some of the drawback
like maximum output frequency could not
exceed the frequency of input voltage, low
PF (Power factor) high and varying reactive
power. Then in 1939, Zavalishm .D.A. proposed and supplement cycloconverter by
artificial commutation.
In 1964 Schonung and Stermmler, proposed triangular wave carrier based sinusoidal PWM for three phases. Then SVM
(Space Vector Modulation) method was
modified further by many others. In later
1980’s more research work was carried out
on power converter and controlled devices. A new topology was introduced named
3√2
matrix converter.
This was first mentioned
π
by Alesina and Venturini. This replaces a
back to back cycloconverter which uses
more number of thryrsitor switches. The
matrix converter was introduced for replacement of ac-dc-ac converter to avoid
power converter stage.
Pfaf, Westcha and Wick 1982 propose
a new strategy of modulation technique
called space vector modulation. Later it was
proposed with small modification by Huber and Borojevic 1995, Altun and Sunter
2003; Shephered and Zhang 2004, Sunter
and Altun 2005; Arevalo 2008: Bradaschia
et al 2009: Cardenas et al 2009, Arevalo et
al 2010, Vargas et al 2009 and 2010.
Advantages of Matrix Converter
Matrix converter receives more attention
by researchers due to the following advantages :
• Simple Circuit with Unique Component
• Compact power circuit with variable
amplitude and frequency control.
• Operate nearly unity power factor
• Bidirectional power flow
There are only few type of frequency converter that are available. The Fig 3 represent the different variety of such converter.
In each type the frequency is either increased or decreased.
AC-DC-AC Converter
An AC-DC-AC converter consists of an either controlled or uncontrolled converter,
inverter and a small DC link capacitor connected between converter and inverter
stage. The converter is connected to the
input supply and the load is connected on
inverter side. If current flow through the
DC link is continuous then the Vrms value
becomes
V i.e 1.35V.
Fig.4. Circuit representation of D.C Link Converter
Cycloconverter
Cycloconverter is a device which converts
frequency from one to another in integral
multiples. (Fo= n Fi (or) Fo = Fi/n, (n=1, 2,
3……n), where n is the integral multiple).
Fig.5 Three Phase Cycloconverter α2 =180-α1
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Application of Cycloconverter
The most common applications of cycloconverter are
• Speed Control of drives
• Induction Heating
• Slip-power recovery Scherbius
• Variable-speed drives
• Constant-frequency (VSCF) power
generation for air-craft 400Hz power
supplies
In the above Fig 6 α1 and α2 are the
firing angle of the positive and negative
group respectively. Some of the advantages of the cycloconverter are direct frequency conversion without any intermediate
stage, operates at any power factor, capable of regeneration and the disadvantages
that are large number of thyristors are required in cycloconverter, Complex control
circuitry, Output frequency is limited to integral multiples of input frequency.
Usually polypropylene capacitor will be
connected for the DC link supplied to AC
component. Since polypropylene size is
smaller the overall size of the circuit is reduced and the life time of the whole circuit
is increased for conformist design.
Frequency Converter
Fig.3. Block diagram of Various Frequency Converter
quired, then three sets of three phase to
single-phase circuits are interconnected is
shown in the Fig 5.
The cycloconverter categorized into step
up and step down cycloconverter. These
converter is also categorized into naturally
commutated cycloconverter (NCC) and
forced commutated cycloconverter (FCC).
When three phase frequency output is re-
Fig.6 Voltage and Current of Cycloconverter
An additional inductor is used to limit
the circulating current due to increase in
output voltage and frequency which cause
deforms of waveform Fig 6 represents the
output voltage deforms with an increase in
output voltage and frequency, most general application of cycloconverter are three
phase high power, low speed synchronous
machine drives and speed control of induction motor drives.
Direct Matrix Converter
The direct matrix converter shown in Fig
1 is one which converts AC to AC voltage with variable frequency using suitable PWM technique. Matrix converter
have the ability to regenerate power and
restrain input current and output voltage
harmonics. Usually the matrix converter
voltage will not exceed 87% of its input
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power sector
proposed by Venturini, but 100% can
achievable using other techniques. The
bi-directional switches must be capable of
permitting current flow in either directions
shown in fig 2.
So, unswervingly the output voltages
will be generated from the input voltages.
Due to the limitation of sampling rate over
input to output frequency the maximum
output voltage is equal to √3/2 of the maximum input voltage this is an inherent limit
of matrix converter. The switches in MC
should be switched ON in such a way that
input is never short circuited and output
must not be open circuit, because of the
inductive nature of the load.
The power filter (Rf, Lf, Cf) located at the
input side of the converter produces almost sinusoidal source current and avoid
generation of overvoltage. These filters
provides series and parallel resonance for
the load circuit. The series resonance is
for any harmonic coming from supply and
parallel resonance for harmonics generated due to switching of converters. Due to
presence of capacitor and inductive nature
of load current, only one switch of each
column can be closed. The mathematical
module of MC is given below
Sij (t) =
on
{ 1,0, Switch
Switch off
Where, vo, vi, ii and io are voltage and
current of output and input vector respectively. T(Sij) is the instantaneous transfer
matrix of the DMC
(
SAa SBa SCa
SAc SBc SCc
SAb SBb SCb
)
The above equation is used to evaluate
the output voltage and input current using suitable triggering of matrix switches,
output voltage. The matrix combination
switching is given in transfer matrix.
Various Matrix Converter
Matrix converter mainly classified as direct
and indirect matrix converter. Indirect matrix converter uses the above technique of
AC-DC-AC. These Indirect matrix converters further classified based on the Complexity, Functionality and Usage for particular applications.
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Fig 7. MC based UPFC control
Sliding mode-based direct power control
Matrix Converter (DPC-MC) controllers have
zero steady-state errors and no overshoots,
good tracking performance, and fast dynamic responses. When compared to linear
PI controller Slide mode control are simpler
to implement and require less processing
power. Due to technological advances in
power electronics devices and high end
processors, matrix converters attain best result using proper control schemes like predictive control, ANN(artificial Neural Network), Fuzzy, Genetic algorithm for future
power converter applications.
Some few indirect type matrix converter
are
• Sparse Matrix Converter
• Very Sparse Matrix Converter
• Inverting Link Sparse Matrix Converter
• Ultra Sparse Matrix Converter.
Fig.8. Wind Turbine Driving Matrix Converter
vo = T(Sij) * vi
ii = (Sij)T*io
T(Sij) =
In Recent year’s huge
investment are made
in renewable energy
resources for the
replacement of existing
energy source like
thermal, nuclear, hydro
etc. Many developed
countries are more
focussing on higher
energy demands to meet
the future requirement
by taking advantage of
the abundant energy in
wind, solar and other
renewable energy
Area of Applicability
These days, Unified Power Flow Control
(UPFCs) is the one of the most powerful
flexible ac transmission systems (FACTS)
devices. The UPFC is nothing but the combination of a static synchronous compensator (STATCOM) and a static synchronous
series compensator (SSSC) which shares a
common dc capacitor link.
The minimum energy storage capability
of matrix allow independent reactive control on the UPFC shunt and series converter sides. Conventional UPFC controllers do
not have robustness. Despite of conventional UPFC method
Matrix converter UPFC (MC-UPFC) are
ability to control the full range of power
outage show in Fig 7. Recent nonlinear
approaches use better tuning control like
PI control method. So tuning of PWM using these techniques adopted to meet the
requirement. Still, there is possibility of
further improvement in the dynamic response of UPFCs, using nonlinear robust
controllers.
In Recent year’s huge investment are made
in renewable energy resources for the replacement of existing energy source like
thermal, nuclear, hydro etc. Many developed
countries are more focussing on higher energy demands to meet the future requirement
by taking advantage of the abundant energy
in wind, solar and other renewable energy
The U.S. has targeted about 20% of the
electricity produced in 2030 to be from wind
energy. Now a day’s doubly fed induction
machines or converter-driven synchronous
machines are used to generate power above
1MW. Some of the largest unit’s currently
available off-shore applications are built
on the direct drive synchronous machine.
Matrix converter is one of the best suit for
such applications. Since matrix converter is
a bidirectional converter it used for both sub
and super synchronous of wind turbine. Fig
8 shows basic connection of grid to wind
turbine using converter. Matrix converter is
replaced with these converters to meet better requirement of the wind turbine 7
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