An Energy Stored Quasi Z Source inverter for Photovoltaic Application

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1 IOSR Journal of Electrcal an Electroncs Engneerng (IOSR-JEEE) e-issn: ,p-ISSN: , olume 9, Issue 2 er. (Mar Apr. 24), PP An Energy Store Quas Z Source nverter for Photovoltac Applcaton K.Dnesh Kumar, D.Arun Prasa 2,2 Anna Unversty henna, 6 25, Ina,2 Department of Electrcal & Electroncs Engneerng,,2 PSNA ollege of Engneerng & Technology, Dngul, na Abstract: The quas-z-source nverter (qzsi) wth battery operaton can balance the stochastc fluctuatons of photovoltac (P) power njecte to the gr/loa. Ths work proposes a new topology of the energy-store qzsi to overcome ths savantage an elvers the contnuous power to the gr/loa. The operatng characterstc of the propose soluton s analyze n etal an compare to that of the SPWM an TPWM. Two strateges are propose wth the relate esgn prncples to control the new energy-store qzsi when apple to the P power system. They can control the nverter output power an manage the battery power, smultaneously. The quas-z-source nverter (QZSI) s a sngle stage power converter erve from the Z-source nverter topology, employng an mpeance network whch couples the source an the nverter to acheve voltage boost an nverson. The voltage boost an nverson, an energy storage are ntegrate n a sngle stage nverter. The valty of the propose P system s prove by expermental results, showng an effcent metho for the energy-store P power generaton. Keywors: Energy storage, Photovoltac(P) power generaton, Power converson, Quas-Z-Source Inverter (QZSI), Snusoal an Trapezoal PWM. I. INTRODUTION The worlwe-nstalle photovoltac (P) power capacty shows nearly an exponental ncrease ue to ecreasng costs an to mprovements n solar energy technology. Power converter topologes employe n the P power generaton systems are manly characterze by two or sngle stage nverters [] []. The snglestage nverter s an attractve soluton ue to ts compactness, low cost, an relablty. However, ts conventonal structure must be oversze to cope wth the we P voltage varaton erve from changes of rraaton an temperature. The two-stage nverter topology apples a boost c/c converter to mnmze the requre klovolt ampere ratng of the nverter an boost the we-range nput voltage to a constant esre output value. However, the swtch n the c/c converter wll ncrease the cost an ecrease the effcency. The Z-source nverter (ZSI) presents a new sngle stage structure to acheve the voltage boost/buck character n a sngle power converson stage, whch has been reporte n applcatons to P systems [3]. Ths type of converter can hanle the P c voltage varatons over a we range wthout overratng the nverter. As a result, the component count an system cost are reuce, wth mprove relablty ue to the allowe shoot through state. Recently propose quas-z-source nverters (qzsi) have some new attractve avantages more sutable for applcaton n P systems [3] [6]. Ths wll make the P system smpler an wll lower cost, because of the followng [6]: ) the qzsi raws a constant current from the P panel, an thus, there s no nee for extra flterng capactors; 2) the qzsi features a lower component (capactor) ratng; an 3) the qzsi reuces swtchng rpples seen by the P panels. In aton, the ntermttent an unscheule characterstcs of solar power lmt the applcablty of P systems. Therefore, much of the lterature suggests the aton of an energy storage system (ESS) to work n conjuncton wth P power generaton to make ts output power contnuous, stable, an smooth [5] [8]. Moreover, when apple as a gr-connecte system, t mplements other mportant auxlary servces normally prove by specal an expensve equpment (electrcal power qualtycontrol, loa peak eman control, etc.) [2], [8], [9]. Most of the exstng ESS technologes employ a brectonal c/c converter to manage the batteres [5], [6], [8], whch makes the system complex, ncreases ts cost, an ecreases ts relablty. Pulse Wth Moulaton s a powerful technque for controllng analog crcuts wth a power sent to a loa. Duty cycle s efne as the rato of (ton/t), where T s the pero n secons. There are a several PWM technques whch are beng employe for verse applcatons, a few of them beng snusoal, square wave, trapezoal, star-case, elta, elta-sgma, space vector, harmonc njecton, thr harmonc PWM technques. PWM technques am at provng better controllable output voltage along wth reucton of harmoncs. The project eals wth the comparson of harmonc analyses performe by some of the PWM technques usng FFT tool of Smulnk n MATAB, unertakng a few of them, thereby nferrng that whch technque s the best one among them. 85 Page

2 An Energy Store Quas Z Source nverter for Photovoltac Applcaton 86 Fg.. Exstng qzsi wth battery for P power generaton Wthout requrements of any atonal c/c converters or components, the qzsi was frst propose for P power generaton system. But the solar rraaton an the P panel s temperature change ranomly, the c-lnk peak voltage wll fluctuate accorngly. So, the atonal backup s neee lke battery to supply the contnuous power to the loa. Ths paper ams to resolve the aforementone problems, analyze all possble schemes of the energy-store qzsi, compare ther benefts an lmtatons, an fn a new topology more preferable to applcaton n the P power system. II. PROPOSED TOPOOGY Fg.2. Energy-store qzsi wth battery Fg. shows just one of the qzsi topologes, f the battery s connecte n parallel wth the capactor 2 there s scontnuous moe wll occur urng battery scharge. As a counterpart, we connect the battery n parallel to the capactor, leang to a new topology n Fg. 2. They have common ponts: ) there are three power sources/consumers,.e., P panels, battery, an the gr/loa, an 2) as long as controllng two power flows, the thr one automatcally matches the power fference, accorng to the power equaton Where Pn,Pout an PB are the P panel power, output power of the nverter an the battery power respectvely. The power Pn s always postve because the P panel s sngle rectonal power supply, PB s postve when the battery elvers energy an negatve when absorbng energy, an Pout s postve when the nverter njects power to the gr. Moes of operaton: Smlar to the exstng qzsi operatng prncple [3], the system n Fg. 2 also has two operatng moes n the contnuous conucton moe (M). (a) 86 Page

3 An Energy Store Quas Z Source nverter for Photovoltac Applcaton 87 (b) Fg.3. Two operatng moes n them. (a) Shoot through Moe. (b) Non shoot through Moe. ) Shoot through moe: Ths moe wll make the nverter short crcut va any one phase leg, combnatons of any two phase legs, an all three phase legs n Fg. 2, whch s referre to as the shoot through state [3]. As a result, the oe Dzs turne off ue to the reverse bas voltage. Its equvalent crcut s shown n Fg. 3(a). Durng ths tme nterval, the crcut equatons are presente as follows: Where, an enote the currents of nuctors an 2 an the battery, respectvely;,, an enote the voltages of capactors an 2 an the P panel, respectvely; enotes the capactance of capactors an 2; an enotes the nuctance of nuctors an 2. 2) Non shoot through moe: Ths moe wll make the nverter operate n one of the sx actve states an two tratonal zero states, whch are referre to as the non-shoot-through state [5]. ontnuous current flows through the oe an ts equvalent crcut urng ths tme nterval, the crcut equatons are presente as follows: (6) (7) (9) Where, s the loa current gong to the nverter. TABE I OMPARISON OF URRENT BEHAIOR FOR TWO INDUTORS Input an output power relaton Battery power Inuctor currents Shoot through moe Non shoot through moe 87 Page

4 An Energy Store Quas Z Source nverter for Photovoltac Applcaton 88 Page 88 III. State Space Analyss To stuy the behavor of any system, moelng an smulaton are very essental. State-space analyss s a popular an useful approach for moelng any non-lnear an tme varant system. Shoot through moe: From equatons (2) to (5) X= n B () Non shoot through moe: From equatons (6) to (9) X = x + n b () Inverter system moel: We efne as the tme nterval for Moe I an as the tme nterval for Moe II, wth a swtchng cycle T. The shoot-through uty rato s then efne as, an T = +. Usng the state space average metho, from () an (), the nverter s state space equaton s, X= ) ( ) ( ) ( ) ( x+ ) ( ) ( n B (2) Wherex s the state varables,.e., At the steay state, the left se of (2) s zero. Therefore, the average voltages an currents have the relatonshps From the above equatons we get, (3) (4) (5) (6) The D lne peak oltage Therefore the D peak voltage wll be, (7) The voltage of capactor wll be approxmately equal to the battery voltage f the voltage rop on the battery s nternal resstance s gnore. Thus, from (3), (4), an (6), the c-lnk peak voltage wll be

5 An Energy Store Quas Z Source nverter for Photovoltac Applcaton 89 Analyss an omparson: Accorng to () an (3), n Fg. 2, the followng can be observe. ) If,, an, the battery s schargng. 2) If,, an, the battery s chargng. 3) If,, an, the battery wll not have energy exchange. Fg. shows sgnfcantly fferent performances because the average currents of ts two nuctors an battery have the followng expresson: Table I summarzes both crcuts current behavors, whch presents nverse current relatonshps for the two nuctors when the battery charges an scharges. In aton, the new topology n Fg. 2 works n the M, f (9) Durng Moe II; otherwse, t works n the DM f urng Moe II. In steay state, the average current of capactor s zero, an (2) wll become The power equaton shoul satsfy the followng nequalty: It shows that the system represente n Fg. 2 always operates n the M urng battery chargng ue to,,, an. However, the schargng battery s lmte by (2) an (22) to ensure that the system n Fg. 2 operates n the M. It s notceable that (22) wll be true f (2) s met, but (2) may not be true f (22) s met, because the nstantaneous current nfluences the oe current of the Z-source network. The current may be ecrease to zero urng Moe II, whch causes the oe to turn off. Thus, the DM occurs even f the average currents or powers meet (2) or (22). For Fg., t wll work n the M, f In steay state, the average current of capactor 2 s zero, an (23) wll become, The power equaton wll satsfy the followng nequalty: It shows that the system represente n Fg. always operates n the M urng battery chargng ue to,, an. However, the schargng battery s lmte by (23) an (25) to ensure that the system n Fg. operates n the M. The nstantaneous current nfluences the oe current of the Z- source network. Thus, (25) wll be true f (23) s met, but (23) may not be true f (25) s met. The DM occurs f the current s less than zero urng Moe II. From (24), Fg. 4 s rawn to show the battery scharge power rato over the nverter output power an the lmtaton of nverter output power for Fg.. The battery maxmumschargng power s lmte n Fg. 4(a), whch causes a lmte nverter output power n Fg. 4(b). A DM occurs f the battery schargng power excees ts lmtaton curve, whch lmts the P power generaton performance of thesystem n Fg.. I. Snusoal An Trapezoal Pwm The snusoal PWM technque s very popular for nustral converters. In the SPWM technque, where a trangular carrer wave of frequency fc s compare wth the funamental frequency f snusoal moulatng wave. The trapezoal PWM s an avance technque for nverters an converters. In the TPWM tech- 89 Page

6 An Energy Store Quas Z Source nverter for Photovoltac Applcaton 9 nque, where a trangular carrer wave of frequency fc s compare wth the trapezoal moulatng wave. The same carrer wave can be use for all three phases. The followng are some major concerns then comparng the two PWM technques:. ow swtchng losses.. Goo utlzaton of D power supply that s to elver a hgher output voltage wth the same D supply.. Goo lnearty n voltage an or current control. v. ow harmoncs contents n the output voltage an or currents, especally n the low-frequency regon. Boost control of QZSI: The voltage gan G of the Z-source nverter can be expresse as, (26) (27) Where B s the boost factor an M s the moulaton nex, Where s shoot through uty cycle, Where s the peak value of the output phase voltage, s the nput c voltage, M s the moulaton nex, an B sthe boost factor etermne by the shoot-through tme nterval( ) over a swtchng cycle (T), or the shoot-through uty rato. (29) Fg.6. Sketch map of smple boost control In orer to reuce the volume an cost of the Z-source network, we nee to elmnate the lowfrequency current rpple by usng a constant shoot-through uty rato. In SB, there are fve moulaton curves: two shoot through envelop sgnal p an n, an three moulatng reference snusoal sgnal a, b an c. The ampltue of shoot through envelop sgnal shoul be greater than or equal to peak value of moulatng snusoal reference sgnal. By comparng c sgnal wth the hgh frequency trangular carrer, shoot through swtchng pulses are generate. The three phase moulatng reference sgnals are compare wth hgh frequency trangular sgnal to prouce the swtchng pulses. These two sgnals are compare by a comparator. Therefore when trangular sgnal s greater than upper envelope p or less than lower envelope n, the crcut enters nto ST state. Because the boost factor s etermne by the shoot-though uty cycle, as expresse n (27), the shootthrough uty cycle Fg.5 Sketch map of smple boost control. 9 Page

7 An Energy Store Quas Z Source nverter for Photovoltac Applcaton 9. Smulaton Stuy The smulaton results for the QZSI output voltage, current an FET analyss of SPWM an TPWM s shown n the fgure below. Fg.7. Output voltage an Output current whle the system operates n SPWM. out=6v, Iout=.A wth n=2v an =.2 Fg.8. Output voltage an Output current whle the system operates n TPWM. out=2v, Iout=.A wth n=2v an =.2 Fg. 9. FET analyss of SPWM(THD=3.6%) 9 Page

8 An Energy Store Quas Z Source nverter for Photovoltac Applcaton 92 Fg.. FET analyss of TPWM (THD=5.39%) I. oncluson In ths research work, a novel topology for an energystore qzsi has been propose to overcome the shortcomng of the exstng solutons n P power system. The theoretcal analyss, smulatons results presente n ths work clearly emonstrate the propose energy-store qzsi wth snusoal an trapezoal pwm technque. The battery operaton can balance the fluctuatons from P panel an supply the contnuous power to the gr/loa whenever P panel cannot generate the power ue to some low rraaton. There are three power sources/consumers,.e., P panels, battery, an the gr/loa. As long as controllng two power flows, the thr one automatcally matches the power fference. So, recently propose energy store quas-z-source nverters (qzsi) have some new attractve avantages more sutable for applcaton n P systems. Ths wll make the P system smpler an wll lower cost. Reference [] J. havarra, D. Bel, F. Gunjoan,. Meza, an J. Negron, Energybalance control of P cascae multlevel gr-connecte nverters for phase-shfte an level-shfte pulse-wth moulatons, IEEE Trans. In. Electron., vol. 6, no., pp. 98, Jan. 23. [2] D. nnkov, I. Roasto, R. Strzeleck, an M. Aamowcz, Step-up D/D converters wth cascae quas-z-source network, IEEE Trans. In. Electron., vol. 59, no., pp , Oct. 22. [3] G. Petrone, G. Spagnuolo, an M. tell, An analog technque for strbute MPPT P applcatons, IEEE Trans. In. Electron., vol. 59, no. 2, pp , Dec. 22. [4] D. nnkov an I. Roasto, Quas-Z-source-base solate D/D converters for strbute power generaton, IEEE Trans. In. Electron., vol. 58, no., pp. 92 2, Jan. 2. [5] D. nnkov an I. Roasto, Quas-Z-source-base solate D/D converters for strbute power generaton, IEEE Trans. In. Electron., vol. 58, no., pp. 92 2, Jan. 2. [6] ] F. Braascha, M.. avalcant, P. E. P. Ferraz, F. A. S. Neves, E.. os Santos, an J. H. G. M. a Slva, Moulaton for threephase transformerless Z-source nverter to reuce leakage currents n photovoltac systems, IEEE Trans. In. Electron., vol. 58, no. 2, pp , Dec. 2. [7] W. an X. He, Revew of nonsolate hgh-step-up D/D converters n photovoltac gr- connecte applcatons, IEEE Trans. In. Electron., vol. 58, no. 4, pp , Apr. 2. [8] Q.Tran, T.hun, J. Ahn, an H.-H. ee, Algorthms for controllng both the D boost an A output voltage of Z-source nverter, IEEE Trans.In. Electron., vol. 54, no. 5, pp , Oct. 27. [9]. J. Gajanayake, D. M. lathgamuwa, an.. Poh, Development of a comprehensve moel an a multloop controller for Z- source nverter DG systems, IEEE Trans. In. Electron., vol. 54, no. 4, pp , Aug. 27. [] M. Shen, J. Wang, A. Joseph, F. Z. Peng,. M. Tolbert, an D. J. Aams, onstant boost control of the Z source nverter to mnmze current rpple an voltage stress, IEEE Trans. In. Appl., vol. 42, no. 3, pp , May/Jun Page