Real time digital simulation of shunt active filter for mitigation of current harmonics with P-Q theory

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1 Vol. 8(6), pp , 11 July, 013 DOI /SRE ISSN Academc Journals Scentfc Research and Essays Full Length Research Paper Real tme dgtal smulaton of shunt acte flter for mtgaton of current harmoncs wth P-Q theory G. VIJAYAKUMAR 1 * and R. ANITA 1 Department of Electrcal and Electroncs Engneerng, K.S.R. College of Engneerng, Truchengode, Tamlnadu, Inda. Department of Electrcal and Electroncs Engneerng, Insttute of Road and Transport Technology, Erode, Tamlnadu, Inda. Accepted 9 July, 013 The man objecte of ths paper s to deelop PI and Fuzzy logc controllers to analyze the performance of nstantaneous acte and reacte power (p-) control strategy for extractng reference currents of shunt acte flters under balanced, un-balanced and balanced non-snusodal condtons. When the supply oltages are balanced and snusodal, then all controllers conerge to the same compensaton characterstcs. Howeer, when the supply oltages are dstorted and/or un-balanced snusodal, these control strateges result n dfferent degrees of compensaton n harmoncs. The p- control strategy wth PI controller s unable to yeld an adeuate soluton when source oltages are not deal. Extense smulatons were carred out; smulatons were performed wth balance, unbalanced and non snusodal condtons. Smulaton results aldate the dynamc behaor of Fuzzy logc controller oer PI controller. The 3-ph 4-wre shunt acte flter system s also mplemented on a real tme dgtal smulator (RTDS Hardware) to further erfy ts effecteness. The detaled smulaton and RTDS Hardware results are ncluded. Key words: Harmonc compensaton, shunt acte flter (SAF), P-Q control strategy, PI controller, fuzzy controller, RTDS hardware. INTRODUCTION Instantaneous acte and reacte theory (p- theory) was ntroduced by Akag, Kawakawa, and Nabae n 1984 (Akag et al., 1984). Snce then, many scentsts Peng (1998), Montero (007), Vodyakho et al. (009), Aredes (1997), and engneers made sgnfcant contrbutons to ts modfcatons n three- phase four-wre crcuts and ts applcatons to power electronc eupment. The p- theory (Akag, 007) based on a set of nstantaneous powers defned n the tme doman. No restrctons are mposed on the oltage and current waeforms, and t can be appled to three phase systems wth or wthout neutral wre for three phase generc oltage and current waeforms. Thus t s ald not only n the steady state but also n the transent state. p- theory needs addtonal PLL crcut for synchronzaton so p- method s freuency arant. Fuzzy logc controllers (Mkkl and Panda, 011) hae generated a great deal of nterest n arous applcatons and hae been ntroduced n the power-electroncs. The adantages of fuzzy logc controllers oer the conentonal PI controller are that they do not need an accurate mathematcal model; they can work wth mprecse nputs, can handle nonlnearty, and may be more robust than the conentonal PI controller. The Mamdan type of fuzzy controller used for the control of APF ges better results compared wth the PI controller, but t has the drawback of a larger number of fuzzy sets and 49 rules (Suresh et al., 011). *Correspondng author. E-mal: jayakumargond@yahoo.com.

2 140 Sc. Res. Essays Fgure 1. Basc compensaton prncple. Though seeral control technues and strateges (Salmeron and Herrera, 006) had deeloped but stll performance of flter n contradctons, these became prmarly motaton for the current paper. Present paper manly focused on two controllers.e., fuzzy and PI. Addtonally we deeloped a flter wth nstantaneous acte and reacte power (p-) method whch s promnent one wth ths we analyzed the performance of flter under dfferent man oltages. On obserng fuzzy controller shows some superor performance oer PI controller. To aldate current obseratons, Extense smulatons were performed and the detaled smulaton and RTDS Hardware results are ncluded. COMPENSATION PRINCIPLE The acte power flter s controlled to draw/supply the compensatng current Rodrguez (009). f from/to the load to cancel out the current harmoncs on AC sde and reacte power flow from/to the source there by makng the source current n phase wth source oltage. Fgure 1 shows the basc compensaton prncple of the acte power flter and t seres as an energy storage element to supply the real power dfference between load and source durng the transent perod. When the load condton changes the real power balance between the mans and the load wll be dsturbed. Ths real power dfference s to be compensated by the DC capactor. Ths changes the DC capactor oltage away from the reference oltage. In order to keep satsfactory operaton or the acte flter, the peak alue of the reference source current must be adjusted to proportonally change the real power drawn from the source. Ths real power charged/dscharged by the capactor compensates the real power dfference between the consumed by the load and that of suppled by the source. If the DC capactor oltage s recoered and attans the reference oltage, the real power suppled by the source s supposed to be eual to that consumed by the load agan. INSTANTANEOUS ACTIVE AND REACTIVE POWER (P-Q) METHOD The control algorthm block dagram for p- method s depcted n Fgure. The three-phase source oltages ( sa, sb, sc ) and load currents ( La, Lb, Lc ) n the a-b-c coordnates are algebracally transformed to the α-β coordnates usng Clarke s transformaton. In ths method (Mkkl and Panda, 011), a set of oltages ( a, b, c ) and currents (a, b, c) from phase coordnates are frst transferred to the 0αβ coordnates usng Clark transformaton: V V V 0 C a b c 0 C La L Lc ; (1)

3 Vjayakumar and Anta 141 Fgure. Control method for Shunt current compensaton based on p- theory C () Where C s the so called transformaton matrx and Generalzed nstantaneous power, p(t) lc c lb b la a lc lb la c b a P. (3) The p- formulaton defnes the generalzed nstantaneous power, p(t), and nstantaneous reacte power ector, (t) n terms of the α-β-0 components as (4) (5) Where ; (6) p p (7) (8) Where. In the new coordnates system, the nstantaneous power has two components: the zeroseuence nstantaneous real power, P0, and the nstantaneous real power due to poste and negate seuence components, ) ( ) ( ) ( t P t p t P (9)

4 14 Sc. Res. Essays Fgure 3. Reference current extracton wth conentonal p- method wth PI controller. Fgure 4. Conentonal PI controller. P ( t) (10) P t) ( (11) Usng the aboe euatons and consderng the orthogonal nature of ectors and the reference source current n the αβ0 frame s deler no zero-seuence acte power s0ref = 0 (so that the zero-seuence component of the oltage at the PCC does not contrbute to the source power). The reference source current n the α-β-0frame s therefore (13) (1) sref sref sref P P 0 L L (14) The objecte of the p- strategy s to get the source to ge only the constant acte power demanded by the load In addton, the source must Constructon of PI Controller Fgures 3 and 4 show the nternal structure of the control

5 Vjayakumar and Anta 143 Fgure 5. Proposed fuzzy nference system. crcut. The control scheme conssts of PI controller, lmter, and three phase sne wae generator for reference current generaton and generaton of swtchng sgnals. The peak alue of reference currents s estmated by regulatng the DC lnk oltage. The actual capactor oltage s compared wth a set reference alue (Akag, 1996). The error sgnal s then processed through a PI controller, whch contrbutes to zero steady error n trackng the reference current sgnal. The output of the PI controller s consdered as peak alue of the supply current (I max ), whch s composed of two components: 1) fundamental acte power component of load current, and ) loss component of APF; to mantan the aerage capactor oltage to a constant alue. Peak alue of the current (I max ) so obtaned, s multpled by the unt sne ectors n phase wth the respecte source oltages to obtan the reference compensatng currents. These estmated reference currents (Isa*, Isb*, Isc*) and sensed actual currents (Isa, Isb, Isc) are compared at a hysteress band, whch ges the error sgnal for the modulaton technue. Ths error sgnal decdes the operaton of the conerter swtches. In ths current control crcut confguraton, the source/supply currents Isabc are made to follow the snusodal reference current Iabc, wthn a fxed hysteretc band. The wdth of hysteress wndow determnes the source current pattern, ts harmonc spectrum and the swtchng freuency of the deces. The DC lnk capactor oltage s kept constant throughout the operatng range of the conerter. In ths scheme, each phase of the conerter s controlled ndependently. To ncrease the current of a partcular phase, the lower swtch of the conerter assocated wth that partcular phase s turned on whle to decrease the current the upper swtch of the respecte conerter phase s turned on. Wth ths one can realze, potental and feasblty of PI controller. CONSTRUCTION OF FUZZY LOGIC CONTROLLER Fgure 5 shows the nternal structure of the control crcut. The control scheme conssts of fuzzy controller (Krawanch and O Connell, 004) lmter and three phase sne wae generator for reference current generaton and generaton of swtchng sgnals. The peak alue of reference currents s estmated by regulatng the DC lnk oltage. The actual capactor oltage s compared wth a set reference alue. The error sgnal s then processed through a fuzzy controller, whch contrbutes to zero steady error n trackng the reference current sgnal. A fuzzy controller conerts a lngustc control strategy nto an automatc control strategy, and fuzzy rules are constructed by expert experence or knowledge database (Jan, 00). Frstly, nput Error E and change n Error hae been placed of the angular elocty to be the nput arables of the fuzzy logc controller. Then the output arable of the fuzzy logc controller s presented by the control Current Imax. To conert these numercal arables nto lngustc arables, the followng seen fuzzy leels or sets are chosen as: NB (negate bg), NM (negate medum), NS (negate small), ZE (zero), PS (poste small), PM (poste medum), and PB (poste bg) as shown n Fgure 6 (Table 1). The fuzzy controller s characterzed as follows: 1) Seen fuzzy sets for each nput and output. ) Fuzzfcaton usng contnuous unerse of dscourse. 3) Implcaton usng Mamdan s mn operator. 4) De-fuzzfcaton usng the centrod method. The bock dagram of Fuzzy logc controller s shown n Fgure 7. It conssts of blocks fuzzfcaton Interface, Knowledge base, decson makng logc and defuzzfcaton. RTDS HARDWARE Ths smulator was deeloped wth the am of meetng the transent smulaton needs of electromechancal dres and electrc systems whle solng the lmtatons of tradtonal real-tme smulators whch s shown n Fgure 8. It s based on a central prncple: the use of wdely aalable, user-frendly, hghly compette commercal products (PC platform, Smulnk ). The real-tme

6 144 Sc. Res. Essays Fgure 6. (a) Input arable E membershp functon. (b) Input change n error normalzed MF. (c) Output I max normalzed MF. Table 1. Rule base. (de/dt)/e NB NM NS Z PS PM PB NB NB NB NB NB NM NS Z NM NB NB NB NM PB Z PS NS NB NB NM PB Z PS PM Z NB NM PB Z PS PM PB PS NM PB Z PS PM PB PB PM PB Z PS PM PB PB PB PB Z PS PM PB PB PB PB

7 Vjayakumar and Anta 145 Fgure 7. Block dagram of fuzzy logc controller (FLC). Fgure 8. RT-LAB smulator archtecture.

8 146 Sc. Res. Essays smulator conssts of two man tools: a real-tme dstrbuted smulaton package (RT-LAB) for the executon of Smulnk block dagrams on a PC-cluster, and algorthmc toolboxes desgned for the fxed-tmestep smulaton of stff electrc crcuts and ther controllers. Real-tme smulaton and Hardware-In-the- Loop (HIL) applcatons are ncreasngly recognzed as essental tools for and electrcal systems. Smulator archtecture Block dagram and schematc Interface The present real-tme electrc smulator s based on RT LAB real-tme, dstrbuted smulaton platform; t s optmzed to run Smulnk n real-tme, wth effcent fxedstep solers, on PC Cluster. Based on COTS nonpropretary PC components, RT LAB (Forsyth P 004) s a modular real-tme smulaton platform, for the automatc mplementaton of system-leel, block dagram models, on standard PC s. It uses the popular MATLAB/Smulnk as a front-end for edtng and ewng graphc models n block-dagram format. The block dagram models become the source from whch code can be automatcally generated, manpulated and downloaded onto target processors (Pentum and Pentum-compatble) for realtme or dstrbuted smulaton. Smulator confguraton The RT-LAB smulator conssts of One or more target PC s (computaton nodes); one of the PCs (Master) manages the communcaton between the hosts and the targets and the communcaton between all other target PC s. The targets use the REDHAT real-tme operatng system. One or more host PC s allowng multple users to access the targets; one of the hosts has the full control of the smulator, whle other hosts, n read-only mode, can recee and dsplay sgnals from the real-tme smulator. I/O s of arous types (analog n and out, dgtal n and out, PWM n and out, tmers, encoders, etc.). I/O s can be managed by dedcated processors dstrbuted oer seeral nodes. SIMULATION AND RTDS RESULTS Fgures 9a and 9b show the performance of Shunt acte flter under balanced snusodal oltage condton wth PI controller and real tme smulaton. It s obsered from the load current waeform harmoncs are njected by the non lnear loads, and een though the nterrupton occurs (Fgure 9a shows) the source current s stll snusodal by the PI p- controller. It reduces the harmoncs up to.15% of THD as per IEEE-519 standard. Dynamc behaor of the system s mproed consecutely by addng the fuzzy logc controller. It s obsered from waeform Spectrum 1.7% of THD as shown n Fgure 9c. The performance of Shunt acte flter under unbalanced snusodal oltage condton s show n Fgures 10a and 10b. The source current s stll snusodal een though the oltage changes occur n the nput sde. It s obsered from the waeform that the harmoncs current s compensated and source current s made snusodal as stpulated by IEEE519 standard. The termnal oltage s mantaned to the reference oltage by adjustng the reacte power njecton. Fgures 10a and 10b show that under un-balanced snusodal oltage condton, THD for p- method wth PI Controller usng Matlab smulaton s 4.16% and usng Real tme smulaton hard ware s 4.3%; THD for p- method wth Fuzzy Controller usng matlab smulaton s.98% as shown n Fgure 10c and usng RTDS Hard ware s 3.7% as shown n Fgure 10d. Smlarly performance of Shunt acte flter under balanced non-snusodal oltage condton as shown n Fgures 11a and 11b. THD for p- method wth PI Controller usng Matlab smulaton s 5.31% and usng RTDS Hard ware s 5.41%; THD for p- method wth Fuzzy Controller usng Matlab smulaton s 3.85% and usng RTDS Hard ware s 4.15% as shown n Fgure 11c and 11d. Consdered the load s changed to two phase load and also the load currents are absence between 0. and 0.5 s. These loads are appled agan at 0.5 s respectely. The neutral current s shown n Fgure 1a wthout the compensaton and Fgure 1b shows that after compensaton. The THD comparson s shown n Fgure 13 under dfferent oltage transent. Conclusons In the present paper two controllers are deeloped and erfed wth three phase four wre system. Een though two controllers are capable to compensate current harmoncs n the 3-phase 4-wre system, but t s obsered that Fuzzy Logc controller shows some dynamc performance oer Conentonal PI controller. PWM pattern generaton based on carrer less hysteress based current control s used for uck response. Addtonally, on contrast of dfferent control strateges; p- control strategy s used for obtanng reference currents n the system, because n ths strategy, angle θ s calculated drectly from man oltages and enables operaton to be freuency ndependent ther by technue aods large numbers of synchronzaton problems. It s also obsered that DC oltage regulaton system ald to be a stable and steady-state error free system was obtaned. Thus wth fuzzy logc and p- approach a noel shunt acte flter can be deeloped. The 3-ph 4-wre SHAF system s also mplemented on a Real Tme Dgtal Smulator to further erfy ts effecteness. Essental smulaton and RTDS Hardware results are presented to aldate the performance of shunt acte flter.

9 Vjayakumar and Anta 147 Fgure 9. 3ph 4wre shunt acte flter response wth p- control strategy under balanced snusodal usng. (a) PI wth matlab; (b) PI wth RTDS hardware; (c) Fuzzy wth matlab; (d) Fuzzy wth RTDS hardware.

10 148 Sc. Res. Essays Fgure ph 4wre shunt acte flter response wth p- control strategy under un-balanced snusodal usng. (a) PI wth Matlab; (b) PI wth RTDS hardware; (c) Fuzzy wth matlab; (d) Fuzzy wth RTDS hardware.

11 Vjayakumar and Anta 149 Fgure 11. 3ph 4wre Shunt acte flter response wth p- control strategy under Non-snusodal usng. (a) PI wth matlab; (b) PI wth RTDS hardware; (c) Fuzzy wth matlab; (b) Fuzzy wth RTDS hardware.

12 150 Sc. Res. Essays (a) (b) Fgure 1. (a) Neutral current wthout compensaton. (b) Neutral current after compensaton.

13 Vjayakumar and Anta 151 Fgure 13. THD for p- control strategy wth PI and fuzzy controllers usng Matlab and RTDS hardware. REFERENCES Akag (007). Instantaneous Power Theory and Applcatons to Power Condtonng. IEEE Press/Wley-Inter-Scence Akag H (1996). New Trends n Acte Flters for Power Condtonng. IEEE Trans. Ind. Appl. 3(6): Akag H, Kanazawa Y (1984). Instantaneous Reacte Power Compensators Comprsng Swtchng Deces wthout Energy Storage Components. IEEE Trans. Ind. Appl. 0(3): Aredes M (1997). Three-Phase Four-Wre Shunt Acte Flter Control Strateges. IEEE Trans. Power Electron. 1(): Forsyth P (004). Real Tme Dgtal Smulaton for Control and Protecton System Testng. IEEE Proc. Power Electron. Specalsts Conf. 1: Jan SK (00). Fuzzy Logc Controlled Shunt Acte Power Flter for Power Qualty Improement. IEEE Proc. Electrc Power Appl. 149(5): Krawanch P, O Connell RM (004). Fuzzy Logc Control of an Acte Power Lne Condtoner. IEEE Trans. Power Electron. 19(6): Mkkl S, Panda AK (011). Instantaneous Acte and Reacte Power and Current Strateges for Current Harmoncs Cancellaton n 3-ph 4Wre SHAF wth Both PI and Fuzzy Controllers. J. Energ. Power Eng. 3(3): Mkkl S, Panda AK (011). SHAF for Mtgaton of Current Harmoncs Usng p- Method wth PI and Fuzzy Controllers. Eng. Technol. Appl. Sc. Res. 1(4): Montero MIM (007). Comparson of Control Strateges for Shunt Acte Power Flters n Three-Phase Four-Wre Systems. IEEE Trans. on Power Electroncs. (1):9-36. Peng Z (1998). Harmonc and Reacte Power Compensaton Based on the Generalzed Instantaneous Reacte Power Theory for Three- Phase Four-Wre Systems. IEEE Trans. Power Electron. 13(5): Rodrguez P (009). Current Harmoncs Cancellaton n Three-Phase Four-Wre Systems by Usng a Four-Branch Star Flterng Topology. IEEE Trans. Power Electron. 4(8): Salmeron P, Herrera RS (006). Dstorted and Unbalanced Systems Compensaton wthn Instantaneous Reacte Power Framework. IEEE Trans. Power Del. 1(3): Suresh M, Panda AK, Suresh Y (011). Fuzzy Controller Based 3Phase 4Wre Shunt Acte Flter for Mtgaton of Current Harmoncs wth Combned p- and Id-I Control Strateges. J. Energ. Power Eng. 3(1):43-5. Vodyakho O, Chrs M, Senor C (009). Three-Leel Inerter-Based Shunt Acte Power Flter n Three-Phase Three-Wre and Four-Wre Systems. IEEE Trans. Power Electron. 4(5):