Design and Simulation of Matrix Converter for Wind Turbine Coupled Permanent Magnet Synchronous Generator

8/20/2019 Design and Simulation of Matrix Converter for Wind Turbine Coupled Permanent Magnet Synchronous Generator

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IPASJ International Journal of Electrical Engineering (IIJEE) Web Site: http://www.ipasj.org/IIJEE/IIJEE.htm

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Volume 3, Issue 8, August 2015 ISSN 2321-600X

Volume 3, Issue 8, August 2015 Page 23

ABSTRACT

Variable speed permanent magnet synchronous generators are often used to extract electrical energy from wind energy for low

rating power generation for microgrid or islanded grid applications. Due to variation of wind speed the frequency and

amplitude of induced voltage also changes. This problem can be overcome by using either a back-to-back converter or a matrix

converter. Unlike conventional back to back converter, matrix converter does not require any energy storing element like

capacitor or battery storage. The elimination of bulky capacitor in matrix converter results in reduced size, weight, space of the

converter part and increases the reliability. Losses in matrix converter are less as compared to back to back converter, as it is

having one stage energy conversion, where the later has two stage energy conversions. The matrix converter requires only one

controller unlike the back-to-back converter which requires two controllers, one at the inverter side and another at the rectifier

side. The use of a matrix converter with permanent magnet synchronous generator leads to a gearless, compact, and reliable

structure with little maintenance which is superior for low-power microgrid applications.

Keywords: Matrix converter, permanent-magnet synchronous generator (PMSG), pulse width modulation(PWM),

variable-speed wind generator.

1.INTRODUCTION

In recent few years the power generation through wind-turbine has been increased worldwide drastically. Particular

interest has been increased on distributed generation through small wind-turbines because of their advantages like:

lower impact on the landscape, lower noise level, grid codes and national laws imposing simpler grid connection and

higher feed-in tariffs and capability to work in island-mode for isolated communities [1]. Variable speed wind energy

conversion systems are now a day most popular because these are capable of extracting higher power and hence posses’

higher efficiency by the use of MPPT algorithm [2]. In double fed induction generators speed of generator should be

maintained within a certain limit and that is achieved by connecting the turbine and generator through gear box which

sometimes suffers from faults and hence its reliability gets affected and also it increases the maintenance of the

system[3]. But in case of permanent magnet alternator the turbine and the alternator can be coupled directly for

variable speed operation. The elimination of gear box arrangement increases the reliability of the overall system.

Permanent magnet alternator does not require any reactive power for its excitation;

hence it has a higher power factor and efficiency than other machines [4]. PMSG can run at lower speed with higher

number of pole without compromising the efficiency and hence gear box can be eliminated [5]. But the challenge inintegrating the turbine generator set with grid or microgrid or islanded grid is the variable frequency and amplitude of

induced voltage due to variation of wind speed. This problem can be overcome by either back-to-back converter or

matrix converter. In back to back converter the induced voltage of variable amplitude and frequency is first converted to

dc through a converter and again converted back to ac voltage of desired amplitude and frequency through an inverter.

The generator side quantities such as generator speed and torque are controlled by the converter near the generator so

that maximum power can be achieved from wind and the converter near the grid controls the grid side quantities such

as voltage, active and reactive power flow to grid, improves the stability of the system and quality of power and

maintains the dc link capacitor voltage at constant value. A matrix converter is a direct ac to ac converter that can

convert ac voltage of variable amplitude and variable frequency to ac voltage of fixed amplitude and fixed frequency

which does not require any energy storage element like capacitor or battery storage. In the absence of bulky energy

storing element, reduces the size, cost and weight of the converter and also improves the reliability of the system.

Matrix converter has some drawbacks like large number of switches, complex modulation technique and four step

switching of bidirectional switches. These problems are solved by high speed digital signal processors with great

performance [6]. Hence now matrix converter with small packed module has became a suitable alternative to the

conventional converter for it advantages like higher reliability, sinusoidal voltage and current, improved power factor.

Thus the combination of matrix converter and PMSG with multiple poles gives greater performance for low power local

Design and Simulation of Matrix Converter for

Wind Turbine Coupled Permanent MagnetSynchronous Generator

Priyabrata Nayak , KanhuCharan Patra , Pradeep Kumar

Department of Electrical Engineering, NIT Calicut


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load and microgrid applications [7]. Unlike conventional converter, both the generator side quantities as well as the

grid side quantities are controlled simultaneously in matrix converter. As it does not require any reactive power, this

reactive power can be used to feed local load to control voltage at grid or microgrid. Different modulation techniques

are there for matrix converter such as Alesina and Venturini method, space vector modulation (SVM) method andsingular value decomposition (SVD) modulation technique [9]-[11]. The block diagram representation of PMSGconnected to load through matrix converter is shown in Figure 1.

Figure 1 Block diagram representation of PMSG connected to load through MC

2.PM SYNCHRONOUS GENERATOR

Different type of generators, such as dc generator, induction generator and synchronous generator, can be used to

extract electrical energy from wind by connecting it with wind turbine. Themain advantage of synchronous generator is

that it does not draw reactive power from grid and its output reactive power can be controlled by its field excitation

control and the reactive power can be used for reactive power compensation or to improve voltage profile of power

system. Permanent magnet synchronous generators have some advantages over electrically excited synchronous

generator are:

It has higher efficiency.

Power loss is less as there is no requirement of dc excitation.

In absence of field current, the thermal stability of PMSG increases.

No requirement of slip ring and brushes resulting in higher reliability and less maintenance.

High power to weight ratio.

However, permanent magnet synchronous generators have some disadvantages like:

Cost of the material for permanent magnet is high.

Manufacturing is difficult.

At higher temperature the permanent magnet gets demagnetized.

Permanent magnet synchronous generators are more attracting due to the improvement of magnetic characteristics and

the reduction of the cost of permanent magnet. A permanent magnet synchronous generator with suitable converter for

variable speed operation gives very good performance. PMSGs are the most suitable option for wind power generation

at the offshore due to the improvement of PM, reduction of the PM material and the power electronics converters [8].

2.1Permanent magnet synchronous generator modeling

The voltage equations of PMSG as shown in Figure 2 are given by

The electromagnetic torque equation is given by

The generated voltage and current waveforms of the PMSG for different wind speed are shown in Figure 2.


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Figure 2 Voltage and Current waveform of generator for different wind speed.

From Figure 3, it can be noticed that, the generated voltage of PMSG is varying with the variation in wind speed.

Various parameters of generators for different wind speed are listed in Table 1.

Table 1: Voltage, frequency, power and rotor speed for different wind speed.

3.MATRIX CONVERTER

Matrix converter is a converter that can convert a voltage waveform of fixed frequency and fixed amplitude to a voltage

waveform of desired amplitude and frequency or vice versa and it does not require any dc link or energy storing

element like conventional back-to-back converter, hence results a converter of smaller size, cost, weight and higherreliability.

The input and output voltage and current of matrix converter are related to each other through an array of bidirectional

switches of IGBT that are arranged in a matrix form such that any phase at the output can be generated from any phase

of input.

For m*n phase matrix converter the number of bidirectional switches required are m*n, where m is the number of

phases at the input side and n is the number of phases at output side of matrix converter. Hence three phase to three

phase matrix converter total 9 bidirectional switches are required.

Figure 3 Three phase to three phase matrix converter [6].

Wind Speed

(M/Sec)

Line to Line

Voltage (volts)

Frequency

(Hz)

Rotor Speed

(rad/sec)

Active

Power (kW)

Reactive

Power

(kVAR)

7 245 38.5 105 5.4 140

9 312 43.2 130 6.95 180

12 390 50 152 8.5 270

14 438 55.8 174 10.8 420

16 487 62.2 205 14.28 580


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The function of each IGBT based bidirectional switches can be given by

There are two switching option for each switch i.e. on or off. Therefore for nine switches we have = 512 switching

combinations.

But the matrix converter for this application has some restrictions like

i.e. at any time only one switch from each group can be switched on in order to prevent short circuit at the input

terminal. Therefore considering this restriction, the 3* 3 matrix converter for this application has 27 switching

combinations.

The output voltage and current of matrix converter are obtained from the input voltage and current of matrix converter

and hence the relationship between the output voltage and current of matrix converter and the input voltage and current

of matrix converter are related to each other by the following relation:

Switching function of matrix S can be developed by the equation 3 and 4 if the desired output voltage and the input

current are known.

Matrix converter is a combination of bidirectional switches arranged in matrix form that can convert a voltage

waveform of fixed frequency and fixed amplitude to a voltage waveform of desired amplitude and frequency or vice

versa and does not require any dc link or energy storing element. The working principle of matrix converter is tocalculate the duty cycle and accordingly produce switching pulses of very high frequency for the bidirectional switches

to obtain the output voltage of desired low frequency.

3.1 Flow chart of modulation method

Space vector pulse width modulation method has been used for the modulation of the matrix to generate the pulses for

the bidirectional switches of the matrix converter. The flow chart of the modulation method described above is shown

in Figure 4.

Figure 4 Flow chart of matrix converter modulation method


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4.RESULTS

4.1Frequency control ofmatrix converter

50 Hz is taken as the reference frequency for the modulation of matrix converter.

Figure 5 Output voltage of matrix converter for input voltage of different frequencies.

The matrix converter is connected to controllable voltage source and voltage of frequency 30 Hz up to 0.1 sec and

frequency of is 60 Hz from 0.1 sec to 0.2 sec are given as input signal to the matrix converter and the output voltage of

matrix converter is of 50 Hz for the entire time.

4.2Voltage control of matrix converter

220 V (rms) has been taken as the reference voltage for the matrix converter modulation.

Figure 6 Output of matrix converter for different input voltage at different time.

Closed loop control of voltage is shown in Figure 6. The magnitude of input voltage is 280 V (rms) up to 0.1 sec and

530 V (rms) between 0.1 sec to 0.2 sec is given to the matrix converter through controllable voltage source and the

output voltage of matrix converter is 220 V (rms).4.3MC withwind turbine coupled PMSG

Simulink diagram of three phase load connected to the wind turbine coupled permanent magnet synchronous generator

through matrix converter is shown in Figure 7. Here the phase voltages of generated output of turbine generator set is


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measured through three phase measurement unit and the reference voltage and frequency are taken from grid. From

this actual voltage and reference signals switching pulses are generated through PWM modulation method and the

pulses are given to the matrix converter.

Figure 7 Simulink model of PMSG connected to load through matrix converter.

Figure 8 The input and output voltage of MC with filter for different wind speed.

Different wind speeds are applied to the turbine of the turbine generator model. At the wind speed of 12 m/sec, the

voltage is 220 V (rms) and the frequency is 50 Hz and at the wind speed of 9 m/s, the voltage is 175 V (rms) and the

frequency is 43 Hz and at the wind speed of 16 m/sec the voltage is 280 V (rms) and frequency is 62 Hz.. Connectingthis turbine generator model to matrix converter the voltage is stabilized to 219 V (rms) and frequency to 50 Hz

irrespective of the input voltage and frequency as shown in Figure 8.

4.4 Performance of matrix converter with variable wind speed

Figure 9 Variable wind speed


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Figure 10 The input and output voltage of Matrix Converter

The wind speed of time 5 min has been taken as shown in Figure 9 and given as input to the turbine of turbine

generator model. As the wind speed is varying the generated voltage of PMSG is also varying as shown in Figure 10.

The generated output voltage of PMSG is given as input to the matrix converter and the output voltage at the output or

load side of matrix converter is of fixed amplitude and frequency at rated values which is fed to the three phase load as

shown in Figure 10.

5.CONCLUSION

The wind turbine and permanent magnet synchronous generator are simulated in MATLAB for different wind speed

and the voltage, frequency, active and reactive power, electromagnetic torque and rotor speed of the generator are

plotted. The output voltage and frequency of PMSG are stabilized to rated values with Matrix Converter with pulsewidth modulation technique. Sinusoidal output current is achieved through Matrix converter. With matrix converter the

bulky capacitor is eliminated, thus resulting in a converter with less weight, space and cost. As it is a one stage energy

conversion system, the losses also reduced.

REFERENCES

[1]

Natalia Angela Orlando, Marco Liserre, Rosa Anna Mastromauro, and Antonio Dell’Aquila, “A Survey of Control

Issues in PMSG-Based Small Wind-Turbine Systems,” IEEE Transactions On Industrial Informatics, Vol. 9, No.

3, August 2013.

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[3] H. Polinder, F. F. A. van der Pijl, G. J. de Vilder, and P. J. Tavner, “Comparison of direct-drive and geared

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IEEE Trans. Ind. Electron., vol. 54, no. 1, pp. 660–670, Jan. 2007.

[6]

P. W.Wheeler, J. Rodríguez, J. C. Clare, L. Empringham, and A. Weinstein “Matrix converters: A technology

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[7]

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[8]

M. E. Haque, K. M. Muttaqi, and M. Negnevitsky, "Control of a standalone variable speed wind turbine with a

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[9]

Alesina and M. G. B. Venturini, “Analysis and design of optimum amplitude nine-switch direct AC-AC

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[11]

H. Hojabri, H. Mokhtari, and L. Chang, “A generalized technique of modeling, analysis and control of a matrix

converter using SVD modulation technique.” IEEE Trans. Ind. Electron., vol. 58, no. 3, pp. 949–959, Mar. 2011.

AUTHOR

Priyabrta Nayak received his B-Tech degree in Electrical Engineering from Bijupatnaik University of Technology,

Orissa in 2012 and M Tech degree from NIT Calicut, Kerala, India in Power Systems Specialization in 2015.

KanhuCharan Patra received the B-Tech in Electrical and Electronics engineering from National institute of

science and technology, Berhampur and M-Tech degree in Electrical engineering from National institute of

technology (NIT) Calicut, Kerala

Pradeep Kumar received his B Tech degree in Electrical and Electronics Engineering from Maharaja Agrasen

Institute of Technology, New Delhi in 2012 and M Tech degree from NIT Calicut, Kerala, India in Power Systems

Specialization in 2015.

Design and Simulation of Matrix Converter for Wind Turbine Coupled Permanent Magnet Synchronous Generator

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