three phase matrix converter based traction...

THREE PHASE MATRIX CONVERTER BASED TRACTION

TRANSFORMER

K.V.Divya Sree#1, SK.Ruksana#2

Assistant professor#1of Department of EEE-Vasavi collage of engineering , Hyderabad ,TS ,India.

M.Tech student#2 in power systems and power electronics ,Department of EEE , Vasavi collage of engineering,

Hyderabad ,TS ,India.

Abstract—A new system/topology based on power electronic transformer is proposed in this project. Proposed Power

Electronic Transformer shall install in the electric traction substation and regulates the voltage to the train of that section

crossing to it. Proposed power electronic transformer has several advantages over the solid-state transformer presently in use

in the traction substatoions.PET consists of a High-frequency transformer with three phase matrix converter to step-up

frequency on its primary and another three phase matrix convert to step-down the frequency on its secondary sides

respectively. PET involves advantages say Reduced size and volume of the transformer , Reduced cost and copper savings,

Reduced losses.etc.Three phase Matrix converter is employed on both the primary and secondary side of the transformer. Its

control is accomplished by Space vector modulation technique at both the primary and secondary side of the PET. Matrix

converter having several advantages of Direct AC-AC conversion without intermediate stage conversion, Bi-directional power

flow capability, Controllable output voltage and frequency has been verified.

Keywords— Electric Traction. Matrix converter ,Power electronic transformer, Power conversion, Space vector modulation.

I.INTRODUCTION

The basic layout of the project has been depicted in fig 1.Which describes the proposed power electric transformer

for electric traction system.It includes a High frequency transformer with a power electronic device Matrix

converter at both of its primary and secondary sides with input and output filters constituted as a power electronic

transformer. Matrix converter connected at both the input and output side of a high frequency transformer is

controlled by space vector modulation technique[1].This project has been motivated by several electrification

railway systems .Few locomotives use solid state 50hz step down transformer which is bulkier and requires

considerable space which reduces its performance and voltage fluctuations[2].As the frequency of operation of the

transformer in the electric traction substation is low say 50hz ,the size of the transformer increases which results in

its bulkier size.The voltage requirement for the catenary is 25kv 50hz AC ,but this may vary from 18kv to 30kv

because of poor regulation at the traction substation or incorrect configurations of the transformer etc. The above

mentioned drawbacks of a low frequency solid state transformer which is under operation presently can be

overcome by employing a high frequency transformer in the electric traction substation.Some locomotives use

multiple transformers amd multiple converter of different configurations to run in different supply systems.It

requires on board extra heavy equipment and in some cases interruptions may occur in train operation.

Therefore,Power electric transformer was designed to be installed in the electric traction substation to provide

suitable AC power supply for the train that crosses the rail sector.The matrix converter used in this dissertation at

both the primary and secondary sides of the high frequency transformer has important advantages such as;simplified

algorithm control,maximum voltage transfer ratio without adding third harmonic componrent in the output voltage

of the system[3].Currently, matrix converters may be used in electrical substations to regulate grid voltages[4],

regulation of power flow in high power transmission grids[5],in the renewable energy applications where they

provide the electrical connection between the power generator and the electric grid [6],in the transportation industry

ranging from the aerospace sector to the railway sector.Besides the low distortion of the input and output

waveforms,the lower weight and volume of the matrix converters on compared with the other conventional

converters and the bi-directional power flow capability of the matrix converter has the significant advantages in the

transportation sector[7],which allows regenerative braking.

International Journal of Scientific Research and Review

Volume 7, Issue 4, 2018

ISSN NO: 2279-543X

http://dynamicpublisher.org/302

Figure:1:Power Electronic Transformer for Electric Traction

The need for power factor controlled devices are not needed as three phase matrix converter with svm technique

provides controllable power factor.

TABLE-1-PARAMETERS

S.NO PARAMETER RANGE

1. INPUT VOLTAGE 66/110/132/220 KV

2. INPUT FREQUENCY 50hz

3. PRIMARY TPMC OUTPUT

VOLTAGE ANFD

FREQUENCY

132kv,1000hz

4. PRIMARY OF HIGH

FREQUENCY TRANSFORMER

132kv,1000 hz

5. SECONDARY OF HIGH

FREQUENCY TRANSFORMER

25kv,1000hz

6. SECOMDARY TPMC OUTPUT 25kv,50hz



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II.THREE PHASE MATRIX CONVERTER

Matrix converter is a device which converts AC input supply to the required variable AC supply with desired

voltage magnitude and desired frequency without any intermediate conversion process.It is an power electronic

device with a higher switching frequency that guarantees a variable frequency in the output voltage .whereas in case

of an DC link converter which converts AC-DC-AC voltage requires more components as diode

rectifier,filters,charge-up circuits and a bulkier dc link capacitor.But not needed in case of a three phase matrix

converter as it an direct single stage conversion converter.It uses bi-directional controlled switches to achieve

automatic conversion of power supply from AC-AC.Three phase matrix converter provides an alternate for the

PWM voltage rectifier.Three phase matrix converter provides an sinusoidal input and output waveforms with

minimal higher order and no sub-harmonics components in its waveform.It has an inherent bi-directional power

flow capability and input power factor can be fully controlled.It has a maximum input-output voltage transfer ratio

of limited 87% for a sinusoidal input and output waveform which is a drawback for the matrix converter.It requires

more semiconductor devices than conventional AC-AC indirect power frequency converters,since there are no

mono-lithic uni-directional switches are available directly,two igbts with diodes connected in parallel to it has been

employed for the purpose of bi-directional power flow.Three phase matrix converter is sensitive to the disturbances

of the input voltage system.It consists of nine bi-directional switches as depicted in the figure 2.This arrangement

allows the matrix converter to be connected to any of the three input phases to any of the three output phases.

Figure:2: three phase matrix converter

Three phase matrix converter can theoretically assume 512 different switching states combinations in its operation

but not all the switching states can be completely utilized.Without taking into consideration of the control technique

employed for the three phase natrix converter,the switching states combinations must satisfy two basic rules which

are as follows,assuming that the matrix converter is supplied by a voltage source and feeding an inductive load,



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1.input phases of the matrix converter never be short-circuited.

2.output currents of the matrix converter should not be interrupted.

(1)

Hence,from a practical point of view these rules imply that one and only one bi-directional switch per output phase

must be switched ON at any instant of time.With this constraint employing to the three phase matrix converter ,only

27 switching combinations are permitted.

Figure:3:bidirectional switch

Fig 3 shows a bi-directional switch where switch S1a conducts for the downward current direction shown as switch

S1b conducts for an upward current direction shown.Since no mono lithic bidirectional switches are under research

presently ,two IGBT’s connected in anti-parallel with a diode parallel to it is employed as a bidirectional switch for

the three phase matrix converter.The commutation technique employed in this technique was soft switching

commutation as the commutation was a drawback for the three phase matrix converter.

III.SPACE VECTOR MODULATION TECHNIQUE

Modulation strategies for three phase matrix converter involves duty cycle matrix approach and space vector

approach. Among them duty cycle matrix approach includes alesina-venturini modulation,optimum AV method and

scalar modulation method. Space vector approach includes direct space vector and indirect space vector approach

method.All the techniques mentioned above are effectively applied to the control of three phase matrix converter.By

zero crossing detection of the input phase voltage, a Conventional space vector modulation technique is used as

shown in the figure 4 a).A balanced input voltage with a rated value is assumed.

Figure 4 b) shows six voltage space vectors of an three phase matrix converter output voltage and its

synthesis.where 0,I,II,III,IV,V,and VI represents the six active voltage vectors and V0 and V7 represents zero

vectors.



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Figure:4:a)Line to line output voltage vector b) space location of vectors c)representation reference vector

With the theoretical assumption that the switching frequency is much higher than the input frequency , it is possible

to define the reference vector as,

(2)

The reference vector of the line to line output voltage describes a circular trajectory in the plane and it is being

synthesized with the space vectors as shown in the figure 4 c).The similar procedure can be adopted for the current

vectors also. With the assumption that the switching frequency is much higher than the input frequency,the reference

current vector can be represented as the,

(3)



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From the above equations,duty cycles can be calculated by trigonometric analysis.The resultant modulation requires

four non-zero vectors and a null vector.For the input current and output voltage modulation,the switching times for

each vector can be obtained by multiplying the cycle factors at each instant which are as follows.

(4)

After the calculation of the duty cycles,it is the next step to determine the order the vectors applied to the matrix

converter inorder to ensure the control of output voltage and input current.The selection of vectors applied to the

matrix converter shall be governed by few priorities,which includes reduced harmonic distortion of the input current

or reduced number of commutations of the switches.Based on the above mentioned constraints,the vectors to be

used in the modulation process are as follows.

TABLE-2-Matrix converter’s vectors to be used in the modulation process



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Based on the output voltage and input current reference ,the duty cycles are calculated.A sawtooth carrier wave of

frequency 5khz is compared with the duty cycles inorder to know the time period of the vectors as depicted in the

figure 5.Based on the analysis of the table 2 and figure 5 ,vectors are applied to the three phase matrix converter.

Figure:5:Modulation process used to select the space vectors and time interval they are applied

IV.HIGH FREQUENCY TRANSFORMER

A high frequency transformer transfers electric power at desired high frequency greater than 1khz of frequency.Its

size depends on the power to be transferred and also on its frequency of operation.The mechanical size and the

frequency of the transformer are inversely proportional to each other.For a given supply voltage,the flux density in a

transformer core is inversely proportional to supply frequency and cross-sectional area of the core.So, as the

frequency is increased ,for the same power level and voltage the cross-sectional area of the transformer core is

reduced with reduced number of turns.

V.SIMULINK MODEL

Figure:6: simplified schematic of the SST model



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VI.SIMULATED RESULTS

The power electronic transformer in this dissertation was implemented in MATLAB/Simulink Software inorder to

evaluate the performance of the system under 50hz operating scenario.Three phase matrix converter input voltage

and current without filter is shown in figure 7 and the total harmonic distortion of the input current is shown in

figure 8.

Figure:7:input voltage and current without filtering

Figure:8:THD of input current with no filter



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Figure 9 shows the input voltage and current waveforms after the filtering with figure 10 depicting the THD values

of the input current after filtering with almost minimum third harmonics.

Figure:9:input voltage and current after filtering

Figure:10:THD of input current after filtering



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Figure 11 shows the output voltage of the primary side three phase matrix converter which steps up the frequency

from 50hz to 1khz.Whereas,figure 12 depicts the three phase voltage and current at 1000hz frequency which is fed

as an input to the high frequency transformer.

Figure:11:R,Y,B phases of output voltages of TPMC

Figure:12:three phase voltage and current of primary TPMC

Figure 13 a) shows the primary voltage and current of the high frequency transformer. Whereas, figure 13 b) shows

the secondary side voltage and current of the high frequency transformer.



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a)transformer primary voltage and current

b) transformer secondary voltage and current

fig:13:transformer primary and secondary voltage and current

Figure 14 shows the output voltages of a three phase matrix converter at the secondary side steps down the

frequency from 1khz to 50hz without a filter.

Fig:14:secondary side TPMC output voltages without filter



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Figure 15 shows the load voltage and current with a filter , whereas the figure 16 shows the THD of the output

voltage which depicts the reduced third harmonic content.

Fig:15:load voltage and current with filter

Fig:16:THD of load voltage

VII.CONCLUSIONS

The power electronic transformer has been tested in the MATLAB/Simulink software with good results.The output

load voltage and currents are of good voltage and current limits with reduced third harmonic component.The

reputation of the technique used is of great importance as both the input currents and output voltages are

sinusoidal.It is possible to conclude that the work achieved the proposed objectives .



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ACKNOWLEDGMENT

I take this opportunity to extend my profound thanks and deep sense of gratitude to god and my family for giving me

the opportunity and strength along with patience to undertake this work. I am also grateful to our professors for the

kind encouragement and constant support extended in completion of this work. I am also thankful to all those who

have incidentally helped me, through their valuable guidance ,co-operation and unstinted support during the course

of my project.

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