Modified Grid-Connected CSI for Hybrid PV/Wind Power Generation

Hindawi Publishing CorporationInternational Journal of PhotoenergyVolume 2012, Article ID 381016, 12 pagesdoi:10.1155/2012/381016

Research Article

Modified Grid-Connected CSI for Hybrid PV/Wind PowerGeneration System

D. Amorndechaphon,1 S. Premrudeepreechacharn,1 K. Higuchi,2 and X. Roboam3

1 Department of Electrical Engineering, Chiangmai University, Suthep, Muang, Chiangmai 50200, Thailand2 Department of Electronics Engineering, University of Electro-Communications, 1-5-1 Chofugaoaka, Chofu, Tokyo 182-8585, Japan3 Laboratoire Plasma et Conversion d’Energie (LAPLACE), Institut National Polytechnique de Toulouse, 31071 Toulouse, France

Correspondence should be addressed to D. Amorndechaphon, a [email protected]

Received 8 April 2012; Revised 15 August 2012; Accepted 24 August 2012

Academic Editor: Christophe Menezo

Copyright © 2012 D. Amorndechaphon et al. This is an open access article distributed under the Creative Commons AttributionLicense, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properlycited.

The principle of a power conditioning unit for hybrid PV/wind power generation system is proposed. The proposed power condi-tioner is based on the current source inverter (CSI) topology. All energy sources are connected in parallel with a DC-bus throughthe modified wave-shaping circuits. To achieve the unity power factor at the utility grid, the DC-link current can be controlled viathe wave-shaping circuits with the sinusoidal PWM scheme. In this work, the carrier-based PWM scheme is also proposed to min-imize the utility current THD. The power rating of the proposed system can be increased by connecting more PV/wind modulesthrough their wave-shaping circuits in parallel with the other modules. The details of the operating principles, the system configu-rations, and the design considerations are described. The effectiveness of the proposed CSI is demonstrated by simulation results.

1. Introduction

The steadily increasing energy consumption for the con-ventional energy sources like a fossil-energy-based fuel hascreated much interest in the alternative energy sources. Manyrenewable energy sources are now developed and beingwidely used. These energy sources can be integrated to forma hybrid system which is an excellent option for distributedenergy product. In general, the hybrid systems have betterpotential to provide higher quality and more reliable powerthan the single source systems. Recently, the solar andwind energy are the most commonly used renewable energysources in a hybrid system due to the high efficiency and reli-ability to supply the continuous power to the load or the util-ity grid. The typical hybrid power generation system is shownin Figure 1(a). This system includes the energy sources, DC-DC converters, a DC-AC inverter, and the utility grid. Allenergy sources are connected in parallel to a common DC-AC inverter through their individual DC-DC converters.

Several configurations of hybrid PV/wind power gen-eration systems, applying the various static convertertopologies, have been proposed in the literatures [1, 2].

Previous approaches of the hybrid PV/wind power con-verters were mainly based on voltage source inverter (VSI)topology. One of the commonly used VSI for hybridPV/wind is shown in Figure 1(b). In this topology, all energysources are connected to a common DC-bus through theindividual DC-DC boost converters. The DC-DC convertersare responsible for tracking the maximum power of thewind and PV sources under all operating conditions. Theoutputs of both DC-DC converters are then connected toa single-phase DC-AC inverter. The DC-link voltage will beregulated by the DC-AC inverter with the current-regulatedPWM control to achieve the unity power factor at the utilitygrid. Nowadays VSI has received a lot of attention butthe high switching losses of the switching devices in bothconversion stages are still a major drawback of this topology.To overcome this problem, several power converters basedon the current source inverter (CSI) topology have beendeveloped [3–8]. Compared with the VSI topology, CSItopology has the ability to boost the output voltage withoutan additional boost converter [4, 9]. Therefore, CSI isstrongly suggested for the grid-connected systems which themagnitude of the DC input voltage is lower than the peak

2 International Journal of Photoenergy

DC-DCconverter

DC-DCconverter

DC-DCconverter

DC-ACinverter

DC bus

Utilitygrid

Energysource #1

Energy

source #2

Energy

source #N

(a)

PVarrays

Windturbine

C1

iwind

C2

Lwind

vwind

Swind

DwindC3

T1 T3 iac

vac+

−

ipv

Lpv

vpv

Spv

vdc

T2 T4

+

−

+

−

+

−Utility

grid

Dpv

L f

C f

(b)

Figure 1: Hybrid PV/wind generation system—(a) general structure of typical hybrid system and (b) hybrid system based on VSI topology.

ipv i1idcIpv iinv iac

i1 idc iinv iac

vac

Utilitygrid

vpvipv

i2iwindIwind

0 π 2π 0 π 2π 0 π 2π 0 π 2π0 π 2π

0 π 2π 0 π 2π

i2iwind vwind

Currentwave

shaper

Currentwave

shaper

UnfolderLow-pass

filter

+

−

+

−

+

−

(a)

i1idc

Ipv

Iwind

0 π

0 π

2π

0 π

Ipv

Iwindi2

iinv Ipv

Iwind

0 π

+

(b)

Figure 2: Conceptual expression of the proposed current sharing technique—(a) simplified block diagram and (b) current waveforms forshowing the part shared by each energy source.

of utility voltage. In addition, CSI generally features simpleconverter structure and reliable short-circuit protection.Furthermore, the application of CSI for hybrid PV/windgrid-connected system has not been reported in the previouspublications.

In this paper, a modified grid-connected CSI for hybridrenewable energy systems consisting of PV and wind is pro-posed. The details of the operation principle and the systemconfiguration are also discussed. The simulation setup hasbeen carried out to verify the system performance of theproposed ideas under the different scenarios.

2. Operating Principles

2.1. Overview Concept of the Proposed System with DC-LinkCurrent Sharing Technique. In this section, the overview ofthe proposed hybrid PV/wind power generation system asshown in Figure 2 can be introduced. The proposed systemconsists of two constant current sources ipv and iwind, twocurrent wave-shaping circuits (can be named as DC-DCchopper), an unfolding circuit, and a low-pass filter. Twoconstant current sources are connected in parallel to acommon DC-bus through their own current wave-shapingcircuits. Both wave shaping circuits, operating in the sameswitching frequency, are used to perform the PWM outputcurrents i1 and i2 at a DC-bus. In order to supply activepower to the utility grid, the DC-link current idc is controlledto be in phase with the utility voltage vac. Therefore, the unity

power factor can be achieved. The unfolding circuit is used toproduce a unipolar pulse-width modulation (PWM) currentiinv by setting the direction of a PWM current idc at a DC link.At the last stage, low-pass filter is connected to eliminate thehigh-frequency harmonic components in a unipolar PWMcurrent iinv before injected to the utility grid.

In Figure 2(b), the waveforms of i1, i2, idc, and iinv inthe block diagram in Figure 2(a) are shown. According toKirchhoff ’s current law (KCL), it can be seen that the PWMcurrent at a DC-bus idc is the sum of output currents fromthe two wave-shaping circuits i1 and i2, respectively. Hence,the instantaneous DC-link current idc can be determinedby idc = i1 + i2. In addition, the magnitude of idc can befound by summing the magnitude of i1 and i2 (Idc = Ipv +Iwind), respectively. As a result, the magnitude of idc can beindependently controlled by two constant current sources ipv

and iwind, respectively.

2.2. Circuit Configuration and Control Strategy. Figure 3(a)shows the circuit topology of the proposed grid-connectedCSI for hybrid PV/wind power generation. The circuit dia-gram differs from that of a VSI in Figure 1(b) by the absenceof a DC-link capacitor C3. The proposed circuit is composedof two wave-shaping circuits, a thyristor-based H-bridgeinverter, and CL low-pass filter. Input renewable energysources, PV and wind, are connected to a common DC-bus through their own wave-shaping circuits. The proposedsystem control scheme is also illustrated in Figure 3(b).

International Journal of Photoenergy 3

PVarrays

Windturbine

C1

iwind

C2

Lwind

vwind

Swind

Dwind

T1 T3 iac

vac

ipv

Lpv

vpv

Spv

T2 T4

Utilitygrid

i1

i2

idc

Dpv

iinv

+

−

+

−+

−

L f

C f

(a)

Absolute

MPPT

MPPTWind

vac

ipv

vpvKpv

irpv

K1

vcr

Pcal

PV

irwKwind

0 π 2π

0 π 2π

0 π0 π

0 π0 π

+−

+−

+−

vm

vm,pv vS,pv

vm,wind

vS,windωm

vT1, vT4

vT2, vT3

(b)

Figure 3: Proposed grid-connected CSI for hybrid PV/wind power generation—(a) power converter scheme and (b) system control scheme.

On the DC-side of the inverter, the DC chokes Lpv andLwind are required to provide the smooth and continuousDC currents ipv and iwind, respectively. Chopper switchesSpv and Swind can be controlled to shape the constant inputDC current ipv and iwind to be the PWM currents i1 and i2,respectively, at a DC-bus. To achieve the unity power factorat the utility grid, the utility current iac is required to besinusoidal and in phase with the utility voltage vac. Thus thevoltage vac will be rectified to establish a full-wave rectifiedsinusoidal signal vm, where K1 is an absolute gain. In thesame time, the maximum power point tracker (MPPT) canbe used for tracking the maximum power of PV and wind bymultiplying the reference signal vm with the MPPT referenceof each energy source irpv and irw to produce the modulatingsignal vm,pv and vm,wind, respectively. In PV array, an MPPTalgorithm is used to determine the optimal operating pointirpv. The optimal current irpv is calculated and tracked frommeasured valued of PV voltage vpv and PV current ipv.Similarly, for the wind turbine, the extracted power of thewind turbine Pcal and wind speed ωm are measured. Theoptimal point irw can be provided by the MPPT controller.In both energy sources, Kpv and Kwind are the constant gainof the MPPT controller of PV and wind, respectively.

To obtain the control signal of chopper switches vS,pv andvS,wind, the modulating signals vm,pv and vm,wind are comparedwith a triangular-shaped carrier waveform vcr of the switch-ing frequency fsw. The instantaneous DC-link current idc canbe obtained by the summation of i1 and i2. The H-bridgeinverter operates in synchronism with the utility grid and iscontrolled to provide a unipolar PWM current iinv. The zero-crossing circuit is used to generate the control signal of H-bridge inverter vT1, vT2, vT3, and vT4. Switches T1 and T4 areturned on in the positive half-cycle of the grid voltage vac,whereas T2 and T3 are turned on in the negative half cycle. Itcan be observed that the inverter current iinv is obtained byunfolding the DC-link current idc. At the last stage,Cf and L f

form the low-pass filter which attenuates the high frequencycomponents in the inverter output current iinv.

The principle of the PWM scheme for the proposedCSI is illustrated in Figure 4. For the proposed modulationscheme, two modulating waves vm,pv and vm,wind are required.Both modulating waves are of the same frequency and

1vcr

i1

idc

i2

iinv

2π0

0

0

0

0

π

Ipv

Iwind

Ipv + Iwind

iinv1

Ipv + Iwind

vm,pv

vS,pv

vm,wind

vS,wind

vT1, vT4

vT2, vT3

Figure 4: Steady-state waveforms of the proposed grid-connectedCSI for hybrid PV/wind system.

synchronize with the utility grid but the magnitudes Vm,pv

and vm,wind are different. The modulating waves vm,pv andvm,wind are compared with a common triangular carrier wavevcr, generating two gating signals vS,pv and vS,wind for chopperswitches Spv and Swind, respectively. It should be notedthat the fundamental-frequency component of the invertercurrent iinv can be expressed as iinv1 as shown in Figure 4.

2.3. Inverter Mode of Operation. In order to understand theoperation details of the proposed grid-connected CSI inFigure 3(a), the equivalent circuit is illustrated in Figure 5.This circuit can be subdivided into two configurations, theinput DC-side and the output AC-side, respectively.

For a simplify analysis in each interval of the circuit, thefollowing conditions are assumed.

(I) The input voltage sources vpv and vwind and DCchokes Lpv and Lwind can be considered and modeled


i1 idc idc

Ipv

Iwind

iac

vac

i2

Swind

Dwind

T1 T3Spv

T2 T4

Dpv

Vdc Idc

+−

+

−

Figure 5: Simplified equivalent circuit of the proposed system.

i1 idc

Ipv

Iwind

i2

Swind

Dwind

Spv

Dpv

Vdc

+

−

(a)

i1 idc

Ipv

Iwind

i2

Swind

Dwind

Spv

Dpv

Vdc

+

−

(b)

Figure 6: DC-side operation—(a) vm < vcr and (b) vm > vcr.

as the constant current sources Ipv and Iwind, respec-tively.

(II) The output voltage at the DC-side can be assumed tobe a constant DC voltage source Vdc.

(III) The input current at the AC-side can be assumed tobe a constant DC current source Idc.

(IV) All semiconductor switches in the DC-side and theAC-side are operated at the switching frequency ( fsw)and the grid frequency ( fline), respectively.

2.3.1. DC-Side Operation. For the one switching period, theoperation of the converter in the DC-side can be divided intotwo stages. The equivalent circuit for each stage is shownin Figure 6 and its key waveforms are depicted in Figure 4.Assuming that the modulating signals for energy sources canbe defined as vm,pv = vm,wind = vm. The operation processesof the DC-side are specified as follows.

Stage 1 (vm < vcr). When vm < vcr, chopper switches Spv

and Swind are on, chopper diodes Dpv and Dwind are off, theinput DC currents Ipv and Iwind flow through Spv and Swind,respectively. The current Ipv and Iwind cannot flow throughthe diodes Dpv and Dwind, leading to i1 = i2 = 0. According toKCL, the DC-link current idc can be considered as consistingof the sum of diode currents i1 and i2. That is,

idc(t) = 0. (1)

Stage 2 (vm > vcr). When vm > vcr, chopper switches Spv andSwind are off, chopper diodes Dpv and Dwind are on, the input

DC currents Ipv and Iwind flow to the load through Dpv andDwind, respectively, resulting in i1 = Ipv and i2 = Iwind. Similarto the first stage, the DC-link current idc is obtained as

idc(t) = Ipv + Iwind. (2)

The DC-link current idc for all stages can be rewritten interm of the switching states as follows:

idc(t) = Ipv

[1− dpv

]+ Iwind[1− dwind], (3)

where dpv and dwind are the switching states of the chopperswitches Spv and Swind, respectively. The switching statesdpv = 1 and dwind = 1 if vm < vcr (in stage 1); otherwise 0(in stage 2).

2.3.2. AC-Side Operation. In Figure 7, the equivalent circuitin the AC-side is shown. The AC utility voltage can beexpressed by vac = Vac · sin(ωt), where Vac is the peak ofutility voltage. The operation of this side consists of twostages during the switching cycle. The operation can bedescribed as follows.

Stage 1 (vac > 0). When vac > 0, the inverter switches T1 andT4 are on, T2 and T3 are off, the input DC current Idc flows tothe grid through T1 and T4, respectively. Then the AC utilitycurrent iac equals to Idc.

Stage 2 (vac < 0). The inverter switches T1 and T4 are off, T2

and T3 are on, when vac < 0. The DC current Idc flows to thegrid through T2 and T3, respectively, resulting in the utilitycurrent iac to be equal to −Idc.


idc

iac

vac

T1 T3

T2 T4

Idc

+

−

(a)

idc

iac

vac

T1 T3

T2 T4

Idc

+

−

(b)

Figure 7: AC-side operation—(a) vac > 0 and (b) vac < 0.

Therefore, the utility current iac can be defined as

iac(t) ={idc(t); sin(ωt) ≥ 0

−idc(t); sin(ωt) < 0.(4)

It should be noted that the low-pass filter is notconsidered in this analysis. Hence, the PWM output currentiinv is equal to the utility current iac (iinv = iac).

2.4. PWM Current Analysis. From the PWM scheme inSection 2.2, the analysis of harmonic components in the pro-posed CSI can be performed. The mathematical expressionof the PWM currents i1 and i2 can generally be expressed asfollows [3]:

i1(t) = mpvIpv

2· |sin(ωt)|

+∞∑

k=1

Ipv

πk· sin

[kπmpv|sin(ωt)|

]· cos(kωst).

i2(t) = mwindIwind

2· |sin(ωt)|

+∞∑

k=1

Iwind

πk· sin[kπmwind|sin(ωt)|] · cos(kωst),

(5)

where k = the number of kth harmonic component; ω� ωs;ω = 2π fline and ωs = 2π fsw; mpv = Vm,pv/Vcr and mwind =Vm,wind/Vcr; mpv and mwind are the modulation index of PVand wind sources, respectively; Vm,pv and Vm,wind are thepeaks of modulating signals for PV and wind sources vm,pv

and vm,wind, respectively; Vcr is the peak of the triangularcarrier waveform vcr. Equations (5) are valid to 0 ≤ mpv ≤ 1and 0 ≤ mwind ≤ 1, respectively.

The DC-link current idc can be found from

idc(t) = i1(t) + i2(t). (6)

Thus,

idc(t) = 12

(mpvIpv + mwindIwind

)· |sin(ωt)|

+∞∑

k=1

Ipv

πk· sin

[kπmpv|sin(ωt)|

]· cos(kωst)

+∞∑

k=1

Iwind

πk· sin[kπmwind|sin(ωt)|] · cos(kωst).

(7)

According to (4) the inverter output current iinv can beobtained by the operating of the unfolding circuit. Hence,the inverter output current iinv can be expressed in terms ofits harmonic components as

iinv(t) = 12

(mpvIpv + mwindIwind

)· sin(ωt)

+∞∑

k=1

Ipv

πk· sin

[kπmpv sin(ωt)

]· cos(kωst)

+∞∑

k=1

Iwind

πk· sin[kπmwind sin(ωt)] · cos(kωst).

(8)

Under the conditions of Ipv = Iwind and mpv /=mwind, thewaveform of the inverter output current iinv and its harmoniccontents in (8) can be shown in Figure 8. It can be observedthat the waveform of the inverter current iinv is close to aunipolar PWM waveform. We can consider at the conditionsof Ipv = Iwind = I and mpv = mwind = m, the current iinv

simplified as follows:

iinv(t) = mI · sin(ωt)

+∞∑

k=1

2Iπk· sin[kπm sin(ωt)] · cos(kωst).

(9)

From this result, the PWM inverter current iinv can be shownin Figure 9(a). This waveform is similar to a unipolar PWMwaveform. Figure 9(b) shows the harmonic spectrum of theinverter current iinv. It can be seen that the current has


0.08 0.085 0.09 0.095 0.1

Time (s)

−5

−10

0

5

10

(a)

0 1000 2000 3000 4000 5000

0

2

4

6

8

Frequency (Hz)

(b)

Figure 8: PWM output current waveform iinv and harmonic content of the proposed circuit operating at mpv /=mwind, Ipv = Iwind, fline =50 Hz and fsw = 1 kHz.

0.08 0.085 0.09 0.095 0.1

Time (s)

−5

−10

0

5

10

(a)

0 1000 2000 3000 4000 5000

0

2

4

6

8

Frequency (Hz)

10

(b)

Figure 9: PWM output current waveform iinv and harmonic content of the proposed circuit operating at mpv = mwind, Ipv = Iwind, fline =50 Hz, and fsw = 1 kHz.

harmonics at the multiples of the switching frequency, thatis, at fsw, 2 fsw, and so on. The harmonics of significantmagnitudes also appear in the side bands of the switchingfrequency and its multiples.

2.5. Carrier-Based PWM Scheme. In order to reduce theharmonic distortion in the inverter output current iinv, acarrier-based PWM scheme can be proposed. In general,this scheme can be classified into two categories: phase-shifted and level-shifted modulations. In this paper, a phase-shifted modulation is only studied and applied to the pro-posed hybrid PV/wind power systems. Normally, the hybridPV/wind system may be connected in parallel more than twoenergy sources. The n energy sources require n triangular car-rier signals. For the phase-shifted multicarrier modulation,the carrier waves for each module vcr,pv and vcr,wind are ofsame amplitude and frequency, but there is a phase shift φcr

between any the adjacent carrier waves, given by

φcr = 360◦

n. (10)

For the proposed hybrid PV/wind system as shown inthe Figure 3(a), there are two energy sources for system.The modulating signals vm,pv and vm,wind have the samefrequency but the amplitude is different depending on theMPPT signals of each module. According to (10), the phaseshift φcr between each carrier wave vcr,pv and vcr,wind is 180◦.The gate signals vS,pv and vS,wind are generated by comparing

1

i1

idc

i2

iinv

2π0

0

0

0

0

π

Ipv

Iwind

Ipv + Iwind

iinv1Ipv + Iwind

vcr,pv vcr,windvm,pv

vS,pv

vm,wind

vS,wind

vT1, vT4

vT2, vT3

Figure 10: The steady-state waveforms of the proposed phase-shifted PWM multicarrier modulation.

the modulating wave vm,pv and vm,wind with the carrier wavesvcr,pv and vcr,wind, respectively. The principle of the proposedphase-shifted modulation for the hybrid PV/wind systemcan be shown in Figure 10. The inverter operates under theconditions of Ipv = Iwind = I and mpv = mwind = m.


0.08 0.085 0.09 0.095 0.1

Time (s)

−5

−10

0

5

10

(a)

0 1000 2000 3000 4000 5000

0

2

4

6

8

Frequency (Hz)

10

(b)

Figure 11: PWM output current waveform iinv and harmonic content of the proposed circuit with phase-shifted modulation operating atIpv = Iwind, mpv = mwind, fline = 50 Hz, and fsw = 1 kHz.

The inverter PWM current iinv can be expressed in terms ofFourier series as [3]

iinv(t) = mI · sin(ωt)

+∑

even k

2Iπk· sin[kπm sin(ωt)] · cos(kωst).

(11)

The inverter output current waveform iinv based on phase-shifted multicarrier modulation is shown in Figure 11(a),and its spectrum is also illustrated in Figure 11(b). Theoperating conditions are Ipv = Iwind = I , mpv = mwind =m, fline = 50 Hz, and fsw = 1 kHz. The inverter currenthas harmonics and sidebands at the multiple of the twiceswitching frequency, that is, 2 fsw, 4 fsw, and so on. It is clearthat the current waveform is formed by five current steps: 2I ,I , 0, −I , and −2I , resulting in a further reduction in THD.

3. Design Consideration

3.1. Input DC Choke Design. Large inductors Lpv and Lwind

are used in the DC-side of the inverter, which make the inputvoltage sources vpv and vwind appear as the constant DC cur-rent sources Ipv and Iwind. When the chopper switch is turnedon, the inductor current rises and the energy is stored inthe inductor. If switch is turned off, the energy stored in theinductor is transferred to the AC-side through the diode andthe inductor current falls. To design the value of this induc-tor, the inductor stored energy must be considered. When theswitch is turned on, the energy stored in the inductor is

EL = 12LI2 = PdcTon, (12)

where L = choke inductance, Pdc = average input power atDC-side, T = switching period, Ton = T/2 = turn-on time,and I = average input current. The choke inductance can beexpressed as

L = Pac

ηI2 fsw, (13)

where η = converter efficiency, Pac = η · Pdc = averageoutput power at AC-side, and fsw = switching frequency.

Table 1: Simulation parameters.

Output-rated power Pac = 1000 W

PV source current Ipv = 5 A

Wind source current Iwind = 5 A

Utility grid voltage vac = 220 Vrms

Utility grid frequency fline = 50 Hz

Chopper switching frequency fsw = 3 kHz

Input inductor for PV converter Lpv = 13 mH

Input inductor for wind converter Lwind = 13 mH

Low-pass filter inductor Lf = 4 mH

Low-pass filter capacitor Cf = 2μF

3.2. Output Low-Pass Filter Design. In order to reduce thehigh-frequency harmonics in the PWM output current iinv

of the grid-connected inverter, a low-pass filter is needed.Passive low-pass filters are normally used as L, LC, CL, andLCL filters. In this paper, a simple CL low-pass filter ischosen. A detailed analysis is not considered in this paper.Following the design procedure of [10], the inductor L f andcapacitor Cf can be found through the following equations:

L f = Vac

Pac2π fsw,

Cf = 0.332π fswL f

,

(14)

where Vac is the amplitude of the grid voltage vac.

4. Results and Discussion

To verify the proposed grid-connected CSI for hybridPV/wind system with a simple current-sharing technique,the simulation setup has been designed and carried out withPSIM. It should be noted that the MPPT operating for PVand wind energy is not studied in this paper. The circuitparameters are shown in Table 1. The PV and wind energysources vpv and vwind and input DC chokes Lpv and Lwind aremodeled by DC current sources Ipv and Iwind, respectively.

Figure 12 confirms the principle of PWM strategy for theproposed CSI operating under the condition of mpv = 0.9and mwind = 0.4. The gate signals for all switches in CSI vS,pv,


0

0.2

0.4

0.6

0.8

1

vcrvm,pv vm,wind

(a)

0

0.2

0.4

0.6

0.8

1

v S,p

v

(b)

0

0.2

0.4

0.6

0.8

1

v S,w

ind

(c)

0

0.2

0.4

0.6

0.8

1

v T1,v

T4

(d)

0.08 0.085 0.09 0.095 0.1

Time (s)

0

0.2

0.4

0.6

0.8

1

v T2,v

T3

(e)

Figure 12: PWM switching strategy (top to bottom) vm,pv, vm,wind, vcr, vS,pv, vS,wind, vT1, vT4, vT2, and vT3.

−5

−10

0

5

10

i1

i2

(a)

−5

−10

0

5

10

idc

(b)

−5

−10

0

5

10

vac

iinv

(c)

0.08 0.085 0.09 0.095 0.1

Time (s)

−5

−10

0

5

10

iac

(d)

Figure 13: Operation of the system under the conditions of mpv = mwind, Ipv = Iwind, fline = 50 Hz and fsw = 3 kHz (top to bottom) i1, i2, idc,iinv, vac, and iac.


−5

−10

0

5

10

i1

i2

(a)

−5

−10

0

5

10

idc

(b)

−5

−10

0

5

10

vac

iinv

(c)

0.08 0.085 0.09 0.095 0.1

Time (s)

−5

−10

0

5

10

iac

(d)

Figure 14: Operation of the system under the conditions of mpv = mwind, Ipv < Iwind, fline = 50 Hz and fsw = 3 kHz (top to bottom) i1, i2, idc,iinv, vac, and iac.

−5

−10

0

5

10

i1

i2

(a)

−5

−10

0

5

10

idc

(b)

−5

−10

0

5

10

vac

iinv

(c)

0.08 0.085 0.09 0.095 0.1

Time (s)

−5

−10

0

5

10

iac

(d)

Figure 15: Operation of the system under the conditions of mpv > mwind, Ipv < Iwind, fline = 50 Hz and fsw = 3 kHz (top to bottom) i1, i2, idc,iinv, vac, and iac.

vS,wind, vT1, vT2, vT3, and vT4 are also shown in Figure 12.Figures 13, 14 and 15 show the simulated waveform for theproposed CSI, operating under the different conditions, (a)mpv = mwind and Ipv = Iwind; (b) mpv = mwind and Ipv < Iwind;(c) mpv > mwind and Ipv < Iwind. The following can beobserved.

(a) The two different currents i1 and i2 can be combinedto produce the current idc at a DC-bus.

(b) The amplitude of idc can be determined by IDC =Ipv + Iwind. The magnitude of i1 and i2 can beindependently controlled by the output power ofeach energy source.

(c) The unfolding circuit has two complementary switchpairs (T1, T4 and T2, T3) switching at line frequency50 Hz. The unipolar PWM current iinv is performedby unfolding the DC-link current idc.


−5

−10

0

5

10

i1

i2

(a)

−5

−10

0

5

10

idc

(b)

−5

−10

0

5

10

vac

iinv

(c)

0.08 0.085 0.09 0.095 0.1

Time (s)

−5

−10

0

5

10

iac

(d)

Figure 16: Operation of the system under the conditions of mpv > mwind, Ipv < Iwind, fline = 50 Hz and fsw = 20 kHz (top to bottom) i1, i2,idc, iinv, and iac.

−5

−10

0

5

10

i1

i2

(a)

−5

−10

0

5

10

idc

(b)

−5

−10

0

5

10

vac

iinv

(c)

0.08 0.085 0.09 0.095 0.1

Time (s)

−5

−10

0

5

10

iac

(d)

Figure 17: Simulated waveforms of the hybrid PV/wind system with phase-shifted PWM operating under the conditions of mpv = mwind,Ipv = Iwind, fline = 50 Hz and fsw = 20 kHz (top to bottom) i1, i2, idc, iinv, vac, and iac.

(d) The waveform of the grid current iac is close to sinu-soidal with low THD. The low amount of harmonicdistortion is due to the elimination of high-orderharmonic contents by the filtering effect of CL low-pass filter.

Figure 16 shows the simulated waveforms for the pro-posed CSI, operating at higher switching frequency. It can beobserved that the proposed converter can produce a smooth

AC current at the utility grid with low harmonic compo-nents. The waveforms of the proposed grid-connected CSIfor hybrid PV/wind system with phase-shifted multicarriermodulation are shown in Figure 17. It can be noted that theinverter output current waveform iinv is formed with fivecurrent levels.

In higher power applications, the increasing of outputpower rating of a hybrid PV/wind power generation systemis required. It can be achieved by connecting more PV/wind


PVarrays

PVarrays

Windturbine

iwind

i1 idcipv1

vpv1

Lpv1

Cpv1

Spv1

Dpv1

T1 T3

T2 T4

iinv iac

i2 vac

vwind Utilitygrid

ipv2

vpv2

Lpv2

Cpv2Spv2

Dpv2

i3

DC bus

+

−+

−+

−

+

−+ −

L f

C fDw1

Lw1

Sw1

Cw1

Figure 18: Extension energy sources for increasing the output power of the proposed hybrid PV/wind system.

−5

−10

0

5

10

i1

i2

i3

(a)

−5

−10

0

5

10

idc

(b)

−5

−10

0

5

10

vac

iinv

(c)

0.08 0.085 0.09 0.095 0.1

Time (s)

−5

−10

0

5

10

iac

(d)

Figure 19: Simulated waveforms of the multimodules hybrid PV/wind system with phase-shifted PWM operating under the conditions ofmpv1 = mwind = mpv2, Ipv1 = Iwind = Ipv2, fline = 50 Hz and fsw = 20 kHz (top to bottom) i1, i2, i3, idc, iinv, vac, and iac.

modules in parallel with the other modules through theirown DC-DC chopper to a common DC-bus. The config-uration of multimodules PV/wind system with all modulesconnected in parallel is shown in Figure 18. The waveformsof the converter can be shown in Figure 19.

5. Conclusion

A grid-connected inverter for hybrid PV/wind power gener-ation system was proposed. The proposed inverter was basedon the current source inverter (CSI) topology. A number ofissues were investigated, including the simple current sharingtechnique, the inverter configuration, operating principle,PWM strategy technique, PWM current analysis, and designconsideration. The emphasis of this paper was on the newpower converter scheme, where the operating analysis was

discussed in details. The proficiency of the proposed inverterwas accessed through the computer simulation under the dif-ferent operation conditions. The performance of the pro-posed CSI was confirmed by the simulation results.

Acknowledgments

This work is supported in part by Thailand Research Fund(TRF) through the Royal Golden Jubilee Ph.D. programunder Grant no. PHD/0166/2550, by the French Govern-ment’s contribution to the RGJ-Ph.D program, and by theEnergy Policy and Planning Office (EPPO), Ministry ofEnergy, Thailand. This work is also supported by NationalResearch University (NRU) Project from Office of the HigherEducation Commission of Thailand.


References

[1] Y. M. Chen, Y. C. Liu, S. C. Hung, and C. S. Cheng, “Multi-input inverter for grid-connected hybrid PV/wind powersystem,” IEEE Transactions on Power Electronics, vol. 22, no. 3,pp. 1070–1077, 2007.

[2] C. Liu, K. T. Chau, and X. Zhang, “An efficient wind-photovoltaic hybrid generation system using doubly excitedpermanent-magnet brushless machine,” IEEE Transactions onIndustrial Electronics, vol. 57, no. 3, pp. 831–839, 2010.

[3] P. G. Barbosa, H. A. C. Braga, M. C. B. Rodrigues, and E. C.Teixeira, “Boost current multilevel inverter and Its applicationon single-phase grid-connected photovoltaic systems,” IEEETransactions on Power Electronics, vol. 21, no. 4, pp. 1116–1124, 2006.

[4] Y. Chen and K. Smedley, “Three-phase boost-type grid-con-nected inverter,” IEEE Transactions on Power Electronics, vol.23, no. 5, pp. 2301–2309, 2008.

[5] N. Vazquez, H. Lopez, C. Hernandez, E. Vazquez, R. Osorio,and J. Arau, “A different multilevel current-source inverter,”IEEE Transactions on Industrial Electronics, vol. 57, no. 8, pp.2623–2632, 2010.

[6] R. T. H. Li, H. S. H. Chung, W. H. Lau, and B. Zhou, “Useof hybrid PWM and passive resonant snubber for a grid-connected CSI,” IEEE Transactions on Power Electronics, vol.25, no. 2, pp. 298–309, 2010.

[7] B. M. T. Ho and H. S. H. Chung, “An integrated inverter withmaximum power tracking for grid-connected PV systems,”IEEE Transactions on Power Electronics, vol. 20, no. 4, pp. 953–962, 2005.

[8] G. Ertasgin, D. M. Whaley, N. Ertugrul, and W. L. Soong,“Implementation and performance evaluation of a low-costcurrent-source grid-connected inverter for PV applications,”in Proceedings of the IEEE International Conference on Sustain-able Energy Technologies (ICSET ’08), pp. 939–944, November2008.

[9] M. Kazerani, Z. C. Zhang, and B. T. Ooi, “Linearly controllableboost voltages from tri-level PWM current-source inverter,”IEEE Transactions on Industrial Electronics, vol. 42, no. 1, pp.72–77, 1995.

[10] B. Bouneb, D. M. Grant, A. Cruden, and J. R. McDonald, “Gridconnected inverter suitable for economic residential fuel celloperation,” in Proceedings of the European Conference on PowerElectronics and Applications, p. 10, September 2005.

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