Ashfaq and Tripathi Renewables: Wind, Water, and Solar (2015) 2:7 DOI 10.1186/s40807-015-0007-z

ORIGINAL RESEARCH Open Access

Mitigation of operational losses in matrixconverter fed DFIG for WECS

Haroon Ashfaq* and Surendra Kumar Tripathi

Abstract

With the change in the wind profile, the speed of doubly fed induction generator (DFIG) of wind energy conversionsystem (WECS) changes from super synchronous to sub synchronous range and vice versa. DFIG is operated to generatequality power; hence, power at rotor side is controlled using matrix converter taking power from grid and feeding backpower to the grid depending on the wind profile. Input voltage required to be fed to the rotor side of DFIG is alwayschanging and depends on the speed of the available wind. During the operation when power is fed from grid to rotor ofDFIG, a high-voltage stress continues across the switches of power electronic converter (PEC). In existing topologies of thematrix converter used with the DFIG in WECS, the constant voltage stress at the power electronic switch (PES) is availablewhich causes the higher losses across the switch. This also causes common mode voltage (CMV) which leads to the overvoltage stress. This may cause winding insulation damage and bearing failure of the DFIG. Furthermore, higherdv/dt of CMV raises the leakage current which causes the thermal stress and electromagnetic noise to theequipments installed near the matrix converter. In this paper, the work done is focused on the mitigation ofoperational losses in matrix converter fed doubly fed induction generator for wind energy conversion system.The overall loss in the matrix converter and mitigation of common mode voltage is achieved, which improvesthe overall efficiency and the performance of the wind energy conversion system.

Keywords: Wind energy conversion system; Matrix converter; Doubly fed induction generator; Powerelectronic converter; Common mode voltage

IntroductionIn recent time, the application of power electronic con-verter in wind energy conversion system has increased.This not only increased the penetration of wind powerin power system but also the reliability of operation.Various power converters are reported to be used withdoubly fed induction generator (DFIG) to ensure thecontinuous quality power generation from wind-basedpower-generating unit.The standard power electronic interface used with

DFIG is two back-to-back voltage source inverters (VSI)with an intermediate dc link and capacitor (Merahi andBerkouk 2013). This demands a complicated controlstrategy and bulky dc link capacitor. The output currentwaveforms are deviated from being sinusoidal. Due tobulky electrolytic capacitor, the space occupied by theconverter is more. The other disadvantage of back-to-

* Correspondence: harun_ash@yahoo.comDepartment of Electrical Engineering, Faculty of Engineering andTechnology, Jamia Millia Islamia, New Delhi 110025, India

© 2015 Ashfaq and Tripathi. This is an Open AcLicense (http://creativecommons.org/licenses/bmedium, provided the original work is properly

back converter is that at low frequency, the value of out-put current is low as the current is not equally sharedamong the switches of the converters. The electrolyticcapacitor used as a dc link in back-to-back converterhas deteriorate performance at high temperature, hencethe reliability of converter is not considered to be good(Cardenas et al. 2013; Cárdenas et al. 2013a; Cárdenaset al. 2012; Han et al. 2013).But in recent years, an increasing interest in develop-

ing direct frequency power converter has taken place,like matrix converter, indirect matrix converter, andsparse matrix converter etc. (Merahi and Berkouk 2013).This recently developed silicon based ac-ac converterhas the advantage of sinusoidal input and output currentwithout using passive component in the dc link.Among the entire converters used with DFIGs, the

matrix converter is known to be the universal energyprocessor. Matrix converter is a forced commutated ac-acconverter which requires an array of controlled bidirec-tional power electronic switch (PES) to generate variable

cess article distributed under the terms of the Creative Commons Attributiony/4.0), which permits unrestricted use, distribution, and reproduction in anycredited.

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output voltage based on the wind profile. Due to the appli-cation of matrix converter, the performance improvementof wind energy conversion system has been achieved(Hamane et al. 2012; Pena et al. 2011; Taib et al. 2013).With the increase of the application of power electronicconverter (PEC) in wind energy conversion system, thenet penetration of wind power in power system is increas-ing significantly. In spite of various advantages, the mostlyreported disadvantage is the higher switching losses andconduction losses. Research work is being carried out toestimate the conduction losses and switching losses andtheir relation with switching frequency, modulation tech-niques, current ripple, etc. In various research work car-ried out globally, for reduction of losses, the increasedswitching frequency and a combination of continuous anddiscontinuous modulation with distribution of the clamp-ing segments in accordance to the load phase angle wereproposed (Cárdenas et al. 2013b; Ghatpande et al. 2013;Ghoudelbourk et al. 2012; Yin et al. 2005).The most important characteristics of matrix con-

verter include simple and compact power circuit. It alsohas the capacity to generate the load voltage with arbi-trary amplitude and frequency. Operation at unity powerfactor with sinusoidal input and output currents and re-generation capability is the major advantage. Due tovarious attractive characteristics, the matrix converterhas the reasons for the tremendous interest.The relevant control and modulation methods devel-

oped so far for the matrix converter has been shown inthe Figure 1. The matrix converter control which in-cludes the direct transfer function approach is wellknown as the Venturini method. In this method, the out-put voltage is obtained by the product of the input voltageand the transfer matrix which represents the converter.Another strategy is the scalar method which was devel-oped by Roy; this consists of using the instantaneous volt-age ratio of input phase voltages, which generate theactive and zero states of the converter’s switches. The im-portant solution for the control of matrix converter is

Figure 1 Matrix converter modulation and control methods.

achieved from the use of pulse width modulation (PWM)technique which was previously developed for voltagesource inverters. The simplest approach is to use carrier-based PWM techniques. A very elegant and powerful so-lution currently in use is to apply space vector modulation(SVM) in matrix converters. An alternative solution is dir-ect torque and flux control, which has also been proposedfor the speed control of an ac machine driven by thematrix converter. Various modern techniques, such aspredictive control, have recently been proposed for thecurrent and torque control of ac machines using matrixconverter. The control strategies based on PWM methodswhich allow for output voltage regulation while maintain-ing unity power factor on the input side have been appliedto different kinds of matrix converters, as has been re-ported in various research papers (Venturini 1980; Royand April 1989; Lopez Arevalo et al. 2010; Yoon and Sul2006; Casadei et al. 2002; Ormaetxea et al. 2011; Xiao andRahman 2009; Vargas et al. 2008a; Vargas et al. 2008b;Rodriguez et al. 2010).The space vector approach is based on the instantan-

eous space vector representation of input and outputvoltages and currents. The SVM technique for matrixconverter has the inherent capability to achieve full con-trol of both the output voltage vector and the instantan-eous input current displacement angle. The matrixconverter using SVM technique has a reduced resonancein the input filter. Carrier-based PWM method does nottake care of the quality of the input current originatestrong resonances in the input filter.In this paper, due to the abovementioned factors, the

space vector modulation technique is adopted with matrixconverter for wind energy conversion system. Higherswitching loss is the major drawback of the matrix con-verter application. Also, the wind profile changes, and theswitching and conduction of engaged PEC is also affected.In this paper, a modified matrix converter topologyusing space vector modulation is proposed which havelow conduction losses and switching losses. In addition,

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the voltage stress across the semiconductor devices ofpower converter is also reduced even though the windprofile is fluctuating. The proposed topology also re-duces common mode voltage (CMV) hence low ther-mal stress on the winding of DFIG. This approach hasthe advantages like low switching and conductionlosses, mitigation of common mode voltage, and overallimprovement in the efficiency and the performance ofthe wind energy conversion system. For this purpose,the virtual dc link voltage of the modified convertertopology is controlled according to the speed of DFIGand is kept at value of required rotor voltage. In thispaper, the change in virtual dc link voltage with windprofile is proposed. In the proposed work, the dc linkvoltage is controlled on the basis of corresponding windprofile.

MethodsAnalysis and review of matrix converter performanceApplication of matrix converter with suitable maximumpower point tracking (MPPT) technique with DFIG ofwind energy conversion system (WECS) improves theperformance. Continuous observation of DFIG speed isperformed and close loop feedback is to be obtained.Matrix converter connected between the rotor of DFIGand grid fed power to the rotor of DFIG during sub syn-chronous operation. During super synchronous oper-ation condition, the power is fed to the grid from rotorof DFIG is known as slip power recovery. During the op-eration when power is fed from grid to rotor of DFIG, ahigh-voltage stress continues across the switches of PEC(Ugalde-Loo et al. 2013; Blaabjerg et al. 2012; Garcésand Molinas 2012; Ashfaq and Tripathi 2012; Soufi et al.2013). Hence high dc voltage exists; this is also a factorresponsible for the CMV. The CMV causes the overvoltage stress to the winding insulation of DFIG and in-creased thermal losses. CMV is dependent on the virtualdc link voltage of the proposed power electronic con-verter. If the virtual dc link voltage of the proposed con-verter is changed, the CMV will also change (Lee andSul 2001; Swamy et al. 2001; Wei et al. 2004; Holmes1996; Lee et al. 2010; Yue et al. 2006; Arifujjaman 2013;Ponmani and Rajaram 2013). Requirement of rotor volt-age also varies with respect to slip value which is gov-erned by the wind characteristics.Matrix converter employed with WECS accommodates

any input and output power factor independent of eachother. This also controls the switching and injection ofharmonics in the system which arises due to gusts inavailable wind (Ghatpande et al. 2013). Losses are re-duced in the proposed work by applying the vectormodulation and clamp switching strategy. This is con-trolling the virtual dc link voltage and eliminating the

voltage stress across the PES. Modulation strategy isbased on the space vector modulation.The rotor voltage of DFIG depends on the operating

slip, stator voltage, and the stator to rotor turn ratio.Therefore, the required virtual dc link voltage alsochanges with the slip. Thus, more the deviation fromthe synchronous speed, higher is the virtual dc linkvoltage value.The proposed system shown in Figure 2 having two

subsections of proposed matrix converter engaged inpower control, the current source rectifier (CSR) andVSI, their role interchanges as power flows from grid torotor or vice versa. Wind speed sensor is employed tocontinuously monitor the speed of wind turbine. Thecorresponding slip calculation on the basis of currentoperating speed is performed by the slip calculator unitconnected in the proposed system. On the basis of inputobtained from monitoring system, the required rotorvoltage calculation is performed by rotor voltage calcu-lator unit. All this input is fed to the control unit to de-termine the SVM strategy and pulse generation forcontrolled operation. This regulates the virtual dc linkvoltage which fluctuates due to gusts or variation in thewind profile depending on the geographical and envir-onmental conditions.

Proposed control system overview for stable operationWind profile continuously changes with respect to time;hence, the controlling of matrix converter employedwith DFIG in WECS also varies accordingly. Due to thisincrease in on loss, off loss and conduction loss in powerelectronic switch and CMV effect in DFIG are observedwith fluctuations in wind profile. CMV may cause ma-chine winding insulation failure and bearing deterior-ation. To reduce the CMV, small and medium positiveline to line voltage is employed to generate dc link volt-age in rectifier stage, and suitable zero vector is chosenduring inverter stage. Hence, the virtual dc link voltageof the converter is controlled to neutralize the impact ofvariation in wind velocity.Since the required rotor voltage always changes with

the slip value, hence, the required rotor current keepschanging and depends on the required rotor voltage dueto the gusts and fluctuations in the available wind. Inthe proposed scheme (as shown in Figure 3), the virtualdc link voltage is controlled referring the wind profile.Hence, on the basis of wind profile, the output voltageof the matrix converter connected to grid side is con-trolled and the suitable switching strategy developed isemployed. To control the operation of matrix converter,various control and modulation techniques like spacevector modulation, direct torque control, singular valuedecomposition modulation, input power factor compen-sation, etc. are used. Space vector modulation technique

Figure 2 Simplified representation of proposed system.

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is employed here. With the application of the proposedstrategy of controlling the dc link voltage, both supplyand rotor side voltage and current are obtained sinus-oidal. Virtual dc link voltage is controlled in such a waythat the voltage stress across the switches remains aslow as possible which will help in reducing the on losses,off losses, and the conduction losses in the power electronic

Figure 3 Proposed wind energy conversion system control.

switches. This also controls the CMV and reduces the ther-mal stress on the DFIG rotor windings.On the basis of the rotor speed, the slip value is calcu-

lated and the corresponding instantaneous rotor voltageis calculated. This instantaneous rotor voltage value iscompared with the previous recorded rotor voltage. Thecompared value and the virtual dc link voltage are fed to

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the controlling unit. On the basis of the voltage andcurrent signals, the modulation control signals are gen-erated to control the matrix converter.As seen from the Figure 3, the virtual dc link voltage

and rotor voltage signals are fed to the controlling unit.The signal from controlling unit and Vc value is used togenerate the reference voltage signal to be fed to themodulation control signal unit. Similarly, the second PIcontroller is used to generate the reference current sig-nal to be fed to the modulation control signal unit. Themodulation control signal unit generates the signal to befed to the space vector modulation unit on the basis ofreceived reference voltage and reference current signals.The space vector modulation unit processes the signalreceived from the modulation control signal unit andthe signal from the rotor voltage calculator. The signalsgenerated from space vector modulation unit control theswitching and operation of the matrix converter which isa major contribution by this paper. Since the large dis-turbances and noise is expected due to variable windprofile, hence, the forced oscillations and steady-state er-rors are eliminated in this process.Current and voltage at the output side are controlled

by controlling the duty cycle of the switches. The rela-tions between voltage and current are justified by follow-ing equations:

VABC ¼ S:Vabc ð1Þ

Iabc ¼ ST :IABC ð2Þ

Where VABC = output voltageVabc = input voltage

Figure 4 Control with space vector modulation.

IABC =output currentIabc = input current

S ¼S11 S12 S13S21 S22 S23S31 S32 S33

24

35

S11 - S33 is duty cycle of corresponding switches ofmatrix converter.

Proposed modulation and switching scheme for matrixconverter operationProposed MC topology is an equivalent combination ofan input virtual rectifier and the output virtual inverterconnected to a virtual dc link. Virtual rectifier is con-trolled as classical current source rectifier and virtual in-verter as the classical voltage source inverter. BidirectionalCSR is cascaded to VSI without any intermediate energystorage element physically present. The intermediate volt-age is ‘virtual dc link voltage.’Selections of modulation strategy and switching pat-

tern of PEC also have impact on the output power qual-ity which is a major concern in the wind based powergeneration.Proposed scheme for the control with space vector

modulation is shown in Figure 4. The proposed schemefor the control of virtual dc link voltage is shown inFigure 5 and its corresponding space vector diagram ofthe CSR is shown in Figure 6. The space vector modu-lation is based on the instantaneous space vector repre-sentation of input and output voltage and current spacevector as discussed in Figure 3. There are 27 allowedstates in a matrix converter taking in account the input

Figure 5 Proposed scheme for virtual DC link voltage control.

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short circuit output open circuit restraints. Out ofthese, 24 states are active vectors and 3 states are zerovector. Out of these 24 states of active vector, 18 statesare stationary vector and 6 states are rotating vector.Therefore, in 27 possible switching configurations, 21are applied in which 18 switching configurations de-termine an output voltage vector and input currentvector having fixed directions. The 18 switching con-figurations determine the space vector as shown inFigure 6. The remaining 3 switching configurationsdetermine zero input current and output voltage vec-tor. Switching pattern is defined on the basis of thescalar comparison of input phase voltage and the in-stantaneous value of the desired output voltage whichdepends on the DFIG operation profile. At any givensampling time, the voltage vector and current dis-placement angle are known as reference quantity. Thecontrol of the input side can be obtained by control-ling the phase angle value of the current vector. Thecurrent and voltage vectors are generated by referring

Figure 6 Proposed space vector diagram of input CSR.

the duty cycle which is determined by phase of outputvoltage and input current vector references.Proposed space vector diagram shows the sector defi-

nitions and commutation sequence to obtain the virtualdc link voltage. Table 1 shown below defines the se-quence of switches to be clamped and modulated. Upperswitch of any one phase is kept at ON state and thelower switches of remaining phases are modulated. Thisgives the multiple dc link voltage values as per the re-quirement. The magnitude of virtual dc link voltage isdefined by modulated switch.The converter is controlled by modulating the CSR

with always one upper switch and one lower switch on.The upper and lower switches are from the same inputphase which gives the freewheeling state to dc; this givesthe minimum average dc voltage. To get the maximumaverage dc link voltage, the switches are selected fromthe different phases.The modulated switches and virtual dc link voltage over

a period is controlled using proposed switching andmodulation strategy. The proposed technique ensures theproper selection of zero space vectors in the inverter stagewhich is resulting in the significant reduction in the peak

Table 1 Proposed switching combination and virtual DClink voltage

Sextant Clampedswitch

Modulatedswitches

Virtual DClink voltage

1 R Y’ W’ vRY vRW

2 W’ R Y vRW vYW

3 Y W’ R vYW vYR

4 R’ Y W vYR vWR

5 W R’ Y’ vWR vWY

6 Y’ W R vWY vRY

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value of common mode voltage. The reduction of peak

value of CMV is achieved up to 1 ffiffi3

p.

times of the CMV

obtained in conventional techniques of control.In the proposed work, the modulation technique used

involves the six switching pattern with changes and alsoclamps the output phase which is having the major abso-lute current. By adopting this technique, the decrementin the switching losses and increment in the converterefficiency is achieved.In Table 1, the sequence of clamed switch and modu-

lated switches is defined to determine the virtual dc linkvoltage. Determination of phase voltages as shown inFigure 5 is defined as follows.Voltage across the switch R is given as:

VR ¼ Vm cosθR ð3ÞWhere Vm = input voltage amplitude and θR is phase

angular displacement.Similarly, the voltage across the switch Y is given as:

VY ¼ Vm cosθY ð4ÞWhere Vm = input voltage amplitude and θY is phase

angular displacement.And the voltage across the switch W is given as:

VW ¼ Vm cosθW ð5ÞWhere Vm = input voltage amplitude and θW is phase

angular displacement.Thus:

VR þ VY þ VW ¼ 0 ð6ÞFigure 7 gives the reference phasor crossing over dur-

ing transition of sextant as proposed in Table 1. Pro-posed sequence of replacement of states for peaksampling and through sampling is defined in such a waythat distortion of the waveform be null or minimum

Figure 7 Proposed sampling scenario during sextant transition.

possible. At point ‘a’ as shown in Figure 7, sextant transi-tion occurs from sextant6 to sextant1. At point ‘b’, thefirst carrier peak is obtained and the switch transitionoccurs; moving further at point ‘c’ , the carrier peak valueis achieved. Section between ‘b’ and ‘c’ causes the narrowswitching pulses which may cause the malfunctioning ofthe PES. Therefore, the value of δb is minimized in theproposed work. At point ‘d,’ again, the switching transi-tion takes place as occurred at point ‘b’ hence at point‘e,’ the sextant transition occurs and is repeated so on topoints ‘f ’ , ‘g’ , ‘h’ , etc.Narrow pulse is avoided by controlling the value of δb

and is done in the proposed work. To minimize theswitching losses, CSR is commutated at points ‘b,’ ‘d,’ ‘f,’‘h,’ and so on as dc link current is null or minimum atthese points.

Proposed loss mitigation technique for matrix converterMatrix converter operates at higher frequency to im-prove the output characteristics. Since the virtual dc linkvoltage also varies with respect to the wind profile as therequired rotor side voltage in the DFIG varies, this in-creases the application of high switching frequency tokeep the voltage and current sinusoidal; hence, the switch-ing losses are more due to gusts and variable characteris-tics of wind. Switching losses are required to be reducedfor performance enhancement. In case of the forced com-mutation, the losses are high. In this paper for the reduc-tion of the losses and increase of switching frequency, acombination of the continuous and discontinuous modu-lation and distribution of the clamping segment in accord-ance to the load phase angle is proposed.Conduction losses in the PES are the function of

collector current (IC) and the collector emitter voltage(VCE) (www.datasheetarchive.com/matrix%20conver-ter-datasheet.html; www.datasheets.org.uk/bidirectio-nal%20switch%20igbt%20matrix%20c;

Figure 9 WECS prototype using DFIG with matrix converter.

0 5 10 15 20 25 30 35 400

20

40

60

80

100

120

140

160

180

Percentage change in current

Per

cent

age

chan

ge in

loss

On loss

Off loss

Conduction loss

Figure 8 Relation between percentage change in loss with respect to load current of DFIG.

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www.alldatasheet.com; www.igbt.cn/UserFiles/Suppor-t_IGBT/file_057.pdf; pdf.datasheetcatalog.com/data-sheet/…/mXyzxuz.pdf; www.datasheetarchive.com):

VCE ¼ Aþ B:IC þ C:IC2 ð7Þ

Losses in the converter are due to switch on, switchoff, and conduction of the switches. The turn on loss ofthe PES depends on various parameters like on time,voltage across the switch, resistance, etc. Similarly, theoff and conduction losses are also dependent on above-mentioned parameters as well as the switching frequen-cies. The abovementioned parameters are determined onthe basis of wind profile and characteristics.Thus, the conduction losses Pcond are dependent on

the switch parameters and are defined as:

Pcond ¼ 1T

ZtoþT

to

VCE :IC :dt ð8Þ

Energy dissipated Esw in each switching action of PES:

Esw ¼ fk1:IC2 þ fk2:IC ð9Þ

Where fk1 and fk2 are considered to be nonlinear func-tion of blocking voltage and the type of switching lossesconsidered.Switching losses are determined by the instantaneous

value of dc link voltage and current which varies withwind characteristics. In the proposed work, these lossesare minimized by providing lowest and the second lar-gest input line to line voltage for the formation of theconverter virtual dc link voltage.In the case of the traditional control strategy, the dc

link voltage is kept constant. Therefore, the calculatedconduction and switching losses are high as demonstratedfrom above equations. These losses are dependent on thevoltage value. In the case of the proposed work, the virtualdc link voltage is changing as per the required rotor

voltage governed by the wind profile. Therefore, the netloss component decreases which results in the effi-ciency enhancement of the converter. In comparison tothe traditional method, the loss component is low inthe proposed method which depends on the loadcurrent as shown in Figure 8. The net reduction of 32%in loss component is achieved using the proposed tech-nique of virtual dc link voltage control.In the proposed work, the magnitude of virtual dc

link voltage is controlled on the basis of wind profile.This value keeps changing with respect to the windprofile, hence the voltage stress across the PES alsokeeps changing. DFIG is forced to operate at speed nearto synchronous. Hence on losses, off losses, conductionlosses, and the energy dissipated in the switching actionare also minimized by controlling the value of VCE and IC.

0 5 10 15 20 25 300

5

10

15

20

25

30

Percentage change in slip

Per

cent

age

chan

ge

in v

irtu

al d

c lin

k vo

ltag

e

Figure 10 Relation between virtual dc link voltage and slip of DFIG.

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In the proposed work, the virtual dc link voltage iscontrolled to reduce the loss component simultaneouslythe CMV also changes. With the change in the CMV,the total harmonic distortion (THD) also gets effected. Itis found that this is a kind of trade off between the rmsvalue of CMV and THD of input current. The harmonicmitigation is achieved as the design filters connectedwith the matrix converter ensures that no harmonics areintroduced to the system and provide the unity powerfactor with no harmonic current injection. This insuresthe maximum possible harmonics mitigation.It is found that if the virtual dc link voltage is con-

trolled and kept low when high rotor voltage is not re-quired, the load current will also change accordingly. Ascalculated from equation number 7, 8, and 9, the net op-erational losses will reduce down. In the proposed work,the virtual dc link voltage is kept low when possible.This reduces the voltage stress across the power electronic

Figure 11 Virtual DC link voltage.

switches; as a result, the operational losses are reduced.This is achieved using the proposed modulation andswitching scheme discussed in the paper.

Results and discussionThe work proposed in the paper is for a grid interactiveWECS, hence to validate the proposed topology, modu-lation strategy and control of power electronic con-verter shown in Figure 3 is simulated using MATLAB/simulink. To verify the proposed performance improve-ment of WECS, the following system configuration issimulated. DFIG with Pg = 1.5 MW, Rs = 0.012Ω, Rr =0.021Ω, Ls = Lr = 0.0137 H, M = 0.0135 H, J = 50 kg m2,p = 2, f = 0.00071 Nms/rd, Vg = 690 V is simulated usingproposed matrix converter with parameters as Pmax =7.5 kW, VCES = 1,200 V, Ic_nom = 35A having input filterparameters CF = 4.7 μF (305 V), LF = 1.6 mH (16 A), Rd =33Ω (11 W), Rpu = 47Ω (11 W, 220 V) and clamp circuit

Figure 12 Common mode voltage (traditional method).

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parameters as Cclamp = 2 × 270 μF (450 V), Rclamp = 2 × 47KΩ (10 W). The control and modulation of the proposedmatrix converter is done using SVM technique.The abovementioned system is also validated with the

help of a prototype of wind energy conversion systemusing DFIG with matrix converter as shown in Figure 9.Variable frequency drive (VFD) controlled inductionmotor is used as a wind turbine emulator. A two channel50 MHz digital oscilloscope of RIGOL make (DS1052Emodel) is used for observation and measurement of re-sults. The DFIG used in the experimental setup has fourpoles with rated power of 3.7 kW. The rated current andvoltage are 7.5 A and 415 V, respectively.The simulation results prove that the proposed tech-

nique achieves the objective of controlling the virtual dclink voltage to reduce the losses in the operation of

Figure 13 Common mode voltage (proposed method).

matrix converter significantly. In the proposed work, thePEC is replaced by the modified matrix converter withcontrol of virtual dc link voltage as per the DFIG oper-ation profile. It has been observed that net losses of theconverter are reduced. Figure 10 represents the relationbetween change in slip with respect to required change invirtual dc link voltage of the modified matrix converter. Itis analyzed and concluded from the simulation results thatthe on loss, conduction loss, and off loss component in-creases with increase of current. This is validated withhelp of equation number 9 and simulation result repre-sented in the Figure 8.Voltage required across the rotor of DFIG is wind pro-

file dependent, hence the current required also varies.Net power loss is minimized by controlling the virtualdc link voltage as per the requirement. Reduction in on

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1-2

-1.5

-1

-0.5

0

0.5

1

1.5

2

Time (sec)

Cur

rent

(pu

)

Figure 14 Matrix converter input current (traditional method).

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losses, off losses, and conduction losses is achieved andis found that the net loss reduction of 32% is achievedby controlling the virtual dc link voltage using proposedSVM technique in comparison to PWM technique with-out virtual dc link voltage control.As shown in Figures 3 and 4 of proposed wind energy

conversion system control, the SVM technique is usedto control the virtual dc link voltage. As per the analysisfrom the various papers, the level of voltage stress intraditional method reaches up to 1,100 V and above. It isalso found that this value varies with change in themodulation index which is reported to vary from 0.4 to1. In the proposed method, it has been reduced on thebasis of wind profile. The virtual dc link voltage value isvaried from 300 to 750 V in the proposed method asshown in Figure 11. In case of large wind profile distur-bances, the value is reaching up to 1,200 V for smallduration and stabilizes to the low value. As the DFIG isoperating near the synchronous speed, the stress isfound to be minimum and changes with respect to thedeviation from synchronous speed. The acceptable level

Figure 15 Matrix converter input current (proposed method).

may vary up to 20% to 30% above the rated value whichdepends on the rating of DFIG and the power electronicconverter (i.e., matrix converter).The magnitude of the required virtual dc link voltage

is controlled on the basis of wind profile and DFIG oper-ation, i.e., slip value. Figure 11 gives the simulation re-sults representing the corresponding value of virtual dclink voltage with respect to time. Virtual dc link voltageof the proposed modified matrix converter topology iscontrolled referring the wind profile. When DFIG is op-erating near to the synchronous speed, the requiredvalue of the virtual dc link voltage is null or the leastminimum. With the variation of the wind speed with re-spect to time which results in the deviation of DFIG op-eration from synchronous speed, the required virtual dclink voltage changes as shown in Figure 11.Figures 12 and 13 represent the common mode volt-

age values in traditional topology and proposed modifiedmatrix converter topology, respectively. It is found thatthe peak value of CMV in proposed work is reduced asshown in Figure 13. Hence, the CMV also controlled

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1-2

-1.5

-1

-0.5

0

0.5

1

1.5

2

Time (sec)

Cur

rent

(pu

)

Figure 16 Matrix converter output current (traditional method).

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and reduction in the peak is achieved by controlling thevirtual dc link voltage using proposed SVM. It is foundthat common mode voltage peak value is reduced to44% (as a percentage of CMV with respect to proposedand PWM technology) by selecting the zero space vectorin the inverter stage using proposed SVM technique incomparison of using PWM technique.Figures 14 and 15 represent the matrix converter in-

put current waveform with traditional topology andproposed modified matrix converter topology, respect-ively. Figures 16 and 17 are representing the outputcurrent waveform with traditional topology and pro-posed modified matrix converter topology, respectively.It is observed that the input current waveform and outputcurrent waveform obtained with the proposed modi-fied matrix converter topology is sinusoidal and dis-tortion free.The input and output current waveforms of proposed

modified matrix converter topology show no significantdeterioration. Although minor deterioration in both in-put and output current waveforms is observed at initialinstant, but it is found to be improving very fast asshown in the result. Comparing Figures 14 and 15 for in-put current, it is found that the performance is improved.

Figure 17 Matrix converter output current (proposed method).

Similarly for output current, the improvement can be rec-ognized by comparing Figures 16 and 17. This is achievedusing proposed technique; hence, improved power qualityis achieved. It is observed that for reduced virtual dc linkvoltage operation, the input current ripple is slightly higherthan the current ripple when maximum virtual dc link volt-age is generated. This has been taken in account while de-signing of the input filter. Designed filters connected withmatrix converter ensure that no sub-harmonics are intro-duced to the system and provide unity power factor atline side with no harmonic current injection. This en-sures the variable wind speed operation of DFIG withmore reliable and economical performance. It is alsoobserved that input and output current of the matrixconverter are at unity power factor. Harmonic contentis largely minimized and the power quality is improved.Thus, there is a significant improvement in the per-formance of matrix converter, DFIG and overall windenergy conversion system.

ConclusionsThe proposed work in this paper is replacing the powerelectronic converter with modified matrix converter withcontrol of virtual dc link voltage as per the DFIG operation

Ashfaq and Tripathi Renewables: Wind, Water, and Solar (2015) 2:7 Page 13 of 14

which is wind profile dependent. The net power converterlosses have been reduced even with higher switching fre-quency. Reduced converter losses lower the thermalstresses across the switches. The common mode voltagepeak value also decreases regardless of the output fre-quency. The inverter mode switching sequence affects theCMV, but the effect is not significant. Due to reducedCMV peak value, the leakage current through parasitic cap-acitor between stator core and stator winding reducesresulting in low thermal stress in DFIG windings. Mitiga-tion of operational losses in matrix converter fed doublyfed induction generator for wind energy conversion systemis achieved. The overall performance of the wind energyconversion system improves and ensures the reliable andquality power delivery to the connected grid with fluctuat-ing wind characteristics.

Competing interestsThe authors declare that they have no competing interests.

Authors’ contributionsHA significantly contributed in conception and design of the paper. SKTcontributed in the acquisition of data. HA carried out the analysis andinterpretation of data and drafting of manuscript with inclusion ofintellectual contents. SKT worked toward the drafting and analysis. HA andSKT are responsible for final approval, accountability, and accuracy.

AcknowledgementsAuthors thankfully acknowledge the Department of Electrical Engineering,Jamia Millia Islamia, New Delhi, India for providing the infrastructure facilitieslike, labs, computer, softwares, internet and journal accesses, etc. to carry outand support our research work.

Received: 23 September 2014 Accepted: 26 January 2015

ReferencesArifujjaman, M. (2013). Reliability comparison of power electronic converters for

grid-connected 1.5kw wind energy conversion system. Renewable Energy,57, 348–357.

Ashfaq, H., Tripathi, S. K. (2012) Performance Improvement of Wind EnergyConversion System using Matrix Converter. IEEE 5th India InternationalConference on Power Electronics (IICPE), 1–5.

Blaabjerg, F, Liserre, M, & Ke, M. (2012). Power electronics converters for windturbine systems. IEEE Transactions on Industry Applications, 48(2), 708–719.

Cárdenas, R, Peña, R, Wheeler, P, Clare, J, & Juri, C. (2012). Control of a matrixconverter for the operation of autonomous systems. Renewable Energy,43, 343–353.

Cardenas, R, Pena, R, Alepuz, S, & Asher, G. (2013). Overview of control systemsfor the operation of DFIGs in wind energy applications. IEEE TransactionsonIndustrial Electronics, 60(7), 2776–2798.

Cárdenas, R, Peña, R, Wheeler, P, Clare, J, Muñoz, A, & Sureda, A. (2013a). Control of awind generation system based on a Brushless Doubly-Fed Induction Generatorfed by a matrix converter. Electric Power Systems Research, 103, 49–60.

Cárdenas, R, Peña, R, Clare, J, Wheeler, P, & Zanchetta, P. (2013b). A repetitivecontrol system for four-leg matrix converters feeding non-linear loads. ElectricPower Systems Research, 104, 18–27.

Casadei, D, Serra, G, Tani, A, & Zarri, L. (2002). Matrix converter modulationstrategies: a new general approach based on space-vector representation ofthe switch state. IEEE Transactions Industrial Electronics, 49(2), 370–381.

Garcés, A, & Molinas, M. (2012). A study of efficiency in a reduced matrixconverter for offshore wind farms. IEEE Transactions on Industrial Electronics,59(1), 184–193.

Ghatpande, O., Corzine, K., Fajri, P., Ferdowsi, M. (2013). Multiple Reference FrameTheory for Harmonic Compensation via Doubly Fed Induction Generators. IEEEPower and Energy Conference (PECI), 60–64. doi: 10.1109/PECI.2013.6506035

Ghoudelbourk, S., Bahi, T., Mohammedi, M. (2012). Improving the Quality ofEnergy Supplied by a Doubly-Fed Induction Generator. 2nd InternationalSymposium on Environment Friendly Energies and Applications (EFEA), 437–442.

Hamane, B, Benghanemm, M, Bouzid, AM, Belabbes, A, Bouhamida, M, & Draou,A. (2012). Control for variable speed wind turbine driving a doubly fedinduction generator using Fuzzy-PI control. Energy Procedia, 18, 476–485.

Han, Y, Kim, S, Jung-Ik, H, & Lee, WJ. (2013). A doubly fed induction generatorcontrolled in single-sided grid connection for wind turbines. IEEE Transactionson Energy Conversion, 28(2), 413–424.

Holmes, DG. (1996). The significance of zero space vector placement forcarrier-based PWM schemes. IEEE Transactions on Industry Applications,32, 1122–1129.

Lee, HD, & Sul, SK. (2001). Common-mode voltage reduction method modifyingthe distribution of zero-voltage vector in PWM converter/inverter system. IEEETransaction on Industry Applications, 37(5), 1732–1738.

Lee, MY, Wheeler, P, & Klumpner, C. (2010). Space-vector modulated multilevelmatrix converter. IEEE Transactions on Industry Applications, 57(10), 3385–3394.

Lopez Arevalo, S, Zanchetta, P, Wheeler, P, Trentin, A, & Empringham, L. (2010).Control and implementation of a matrix-converterbased AC-groundpower-supply unit for aircraft servicing. IEEE Transactions Industrial Electronics,57(6), 2076–2084.

Merahi, F, & Berkouk, EM. (2013). Back-to-back five-level converters for windenergy conversion system with dc-bus imbalance minimization. RenewableEnergy, 60, 137–149.

Ormaetxea, E, Andreu, J, Kortabarria, I, Bidarte, U, Martinez-de-Alegria, I, Ibarra, E,& Olaguenaga, E. (2011). Matrix converter protection and computationalcapabilities based on a system on chip design with an FPGA. IEEETransactions Power Electronics, 26(1), 272–287.

pdf.datasheetcatalog.com/datasheet/…/mXyzxuz.pdfPena, R, Cardenas, R, Reyes, E, Clare, J, & Wheeler, P. (2011). Control of a doubly

fed induction generator via an indirect matrix converter with changing dcvoltage. IEEE Transactions on Industrial Electronics, 58(10), 4664–4674.

Ponmani, C, & Rajaram, M. (2013). Compensation strategy of matrix converter fedinduction motor drive under input voltage and load disturbances usinginternal model control. International Journal of Electrical Power & EnergySystems, 44(1), 43–51.

Rodriguez, J., Kolar, J., Espinoza, J., Rivera, M., Rojas, C. (2010). Predictive torqueand flux control of an induction machine fed by an indirect matrix converter.IEEE ICIT Proceedings, 1857–1863.

Roy, G, & April, G-E. (1989). Cycloconverter operation under a new scalar controlalgorithm. 20th Annual IEEE Power Electronics Specialists Conference Proceeding,1, 368–375.

Soufi, Y, Bahi, T, Lekhchine, S, & Dib, D. (2013). Performance analysis of DFIM fedby matrix converter and multi level inverter. Energy Conversion andManagement, 72, 187–193.

Swamy, MM, Yamada, K, & Kume, T. (2001). Common mode current attenuationtechniques for use with PWM drives. IEEE Transaction on Power Electronics,16(2), 248–55.

Taib, N, Metidji, B, & Rekioua, T. (2013). Performance and efficiency controlenhancement of wind power generation system based on DFIG using three-level sparse matrix converter. International Journal of Electrical Power & EnergySystems, 53, 287–296.

Ugalde-Loo, CE, Ekanayake, JB, & Jenkins, N. (2013). State-space modeling of windturbine generators for power system studies. IEEE Transactions on IndustryApplication, 49(1), 223–32.

Vargas, R, Rodriguez, J, Ammann, U, & Wheeler, P. (2008a). Predictive currentcontrol of an induction machine fed by a matrix converter with reactivepower control. IEEE Transactions Industrial Electronics, 55(12), 4362–4371.

Vargas, R, Ammann, U, Rodriguez, J, & Pontt, J. (2008b). Predictive strategy tocontrol common-mode voltage in loads fed by matrix converters,”. IEEETransactions Industrial Electronics, 55(12), 4372–4380.

Venturini, M. (1980). A new sine wave in sine wave out, conversion techniquewhich eliminates reactive elements. Powercon Proceeding, 7, E3/1–E3/15.

Wei, S, Zargari, N, Wu, B, & Rizzo, S. (2004). Comparison and mitigation ofcommon mode voltage in power converter topologies. IEEE IndustryApplications Conference, 3, 1852–1857.

www.alldatasheet.comwww.datasheetarchive.comwww.datasheetarchive.com/matrix%20converter-datasheet.htmlhttp://www.datasheetarchive.com/pdf/Datasheets-SW17/DSASW00331822.htmlwww.igbt.cn/UserFiles/Support_IGBT/file_057.pdf

Ashfaq and Tripathi Renewables: Wind, Water, and Solar (2015) 2:7 Page 14 of 14

Xiao, D., Rahman, F. (2009). An improved DTC for matrix converter drives usingmulti-mode ISVM and unity input power factor correction. 13th EPE Proceeding,1–10.

Yin, Q, Russel, JK, Thomas, AN, & Lu, H. (2005). Analytical investigation of theswitching frequency harmonic characteristic for common mode reductionmodulator. IEEE Industry Applications Conference, 2, 1398–1405.

Yoon, YD, & Sul, SK. (2006). Carrier-based modulation technique for matrixconverter. IEEE Transactions Power Electronics, 21(6), 1691–1703.

Yue, F, Wheeler, P, & Clare, J. (2006). Relationship of modulation schemes for matrixconverters (pp. 266–270). Dublin, Ireland: IET PEMD Conference Proceeding.

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