The Comparison Study of Current Control Techniques for Active Power Filters

Transcription

1 Vol:, No:2, 2 The Compars Study of Current Ctrol Technques for Actve Power Flters T. Nargrt, K-L. Areerak and K-N. Areerak Internatal Scence Index, Electrcal and Computer Engneerng Vol:, No:2, 2 waset.org/publcat/436 Abstract Ths paper presents the compars study of current ctrol technques for shunt actve power flter. The hysteress current ctrol, the delta modulat ctrol and the carrer-based PWM ctrol are csdered n the paper. The synchrous detect method s used to calculate the reference currents for shunt actve power flter. The smulat results show that the carrer-based PWM ctrol technque provdes the mnmum %THD value of the source currents compared wth other comparable technques after compensat. However, the %THD values of all three technques can follow the IEEE std Keywords hysteress current ctrol, delta modulat current ctrol, pulse wdth modulat ctrol, shunt actve power flter, synchrous detect. P I. INTRODUCTION OWER cnected nlnear loads can generate the harmcs nto the systems. Theses harmcs cause a lot of dsadvantages such as loss n transmss lnes and electrc 38V Hz v sc n v sb V dc sa sb sc S S3 S S2 S4 S6 SAPF L f L f L f a b c 6-pulse devces, protectve devce falures, and short-lfe electrc equpments n the system []. Therefore, t s very mportant to reduce or elmnate the harmcs n the system. It s well known that the harmc elmnat va a shunt actve power flter (SAPF) [2] as shown n Fg. provdes hgher effcency and more flexble compared wth a passve power flter. In Fg., the three-phase brdge rectfer feedng resstve and 4 H) behaves as a nlnear load nto the power systems. A synchrous detect (SD) method [3] s used for a harmc detect to calculate the reference currents for the shunt actve power flter. The hysteress current ctrol (HCC) [4], [], the delta modulat ctrol (DMC) [6], [7] and the carrer-based PWM ctrol (CPWM) [8], [9] are csdered for performance compars. The performance ndex for ths compars s %THD of the source currents after compensat. The paper s structured as follows. The overvew of the synchrous detect method s addressed n Sect II. La Lb Lc Current Ctrol Fg. The power system csdered La Lb Load three-phase rectfer Lc SD Harmc Detect v sb v sc 3 4H T. Nargrt, Ph.D. student, School of Electrcal Engneerng, Suranaree Unversty of Technology, Nakh Ratchasma, 3, THAILAND. K-L. Areerak, Assstant Professor, PRU Research unt, PeMC research group, School of Electrcal Engneerng, Suranaree Unversty of Technology Nakh Ratchasma, 3, THAILAND (correspdng author: kgpol@sut.ac.th). K-N. Areerak, lecturer, PeMC research group, School of Electrcal Engneerng, Suranaree Unversty of Technology Nakh Ratchasma, 3, THAILAND. The ccepts of three current ctrol technques are presented n Sect III. The smulat results and dscuss are presented n Sect IV. Fnally, Sect V ccludes the results from the compars study. Internatal Scholarly and Scentfc Research & Innovat (2) 2 7 scholar.waset.org/ /436

2 Vol:, No:2, 2 vsa vsb vsc Vsa V sb V sc vsa vsb vsc La Lb Lc La Lb Lc p a, av sa P eq.(2) 3 p dc p b, av eq.(3) sb LPF eq.() eq.(6) p c, av sc step step2 step3 step4 step Fg. 2 The block dagram of the synchrous detect calculat Internatal Scence Index, Electrcal and Computer Engneerng Vol:, No:2, 2 waset.org/publcat/436 II.THE HARMONIC DETECTION USING SYNCHRONOUS DETECTION METHOD The synchrous detect method to calculate the reference currents of shunt actve power flter s explaned n ths sect. The assumpt of ths method s that the balanced three-phase source currents have to be obtaned after compensat. Therefore, the peak value of source currents (I sa, I sb and I sc ) can be set n (). I sa I I () sb The procedure to calculate the reference currents usng the synchrous detect method can be summarzed as follows: Step : Calculate the three-phase power p ) by: p 3 v sa La sc v sb Lb ( 3 v sc Lc Step 2: Determne the fundamental power of usng low pass flter (LPF) as shown n Fg. 3. p 3 LPF P dc (2) P 3 (P dc )by Fg. 3 The separat of the fundamental power from the three-phase power usng LPF Step 3: Calculate the average actve power for each phase P, P, P ) by : ( a, av b, av c, av P P V V ; k a, b c (3) k, av dc sk tot, The V sa, Vsb and Vsc n (3) are the peak value of threephase source voltages n phase a, b and c, respectvely. The total of peak voltage ( V ) n (3) can be calculated by (4). V tot tot V V V (4) sa sb sc Step 4: Calculate the fundamental source currents for each phase,, ) by: ( sa sb sc where, vsb 2 2v p V ; k a, b c () sk sk k, av sk, and vsc are nstantaneous source voltages n phase a, b and c, respectvely. Step : Calculate the reference currents of shunt actve power flter n each phase (,, ) by: ca cb cc ; k a, b c (6) ck Lk sk, The block dagram of overall procedure to calculate the reference currents usng the synchrous detect method s gven n Fg. 2. III. A. Hysteress Current Ctrol CURRENT CONTROL TECHNIUES HB hysteresscomparator HB hysteress comparator HB hysteress comparator cc Fg. 4 The block dagram of the hysteress current ctrol The hysteress current ctrol (HCC) scheme s based a nlnear ctrol as shown n Fg. 4. The compensatng currents ( ca, cb, cc) n Fg. 4 are compared wth the reference currents (, ) by usng hysteress comparators to ca, cb cb S S2 S3 S4 S S6 Internatal Scholarly and Scentfc Research & Innovat (2) 2 72 scholar.waset.org/ /436

3 Vol:, No:2, 2 Internatal Scence Index, Electrcal and Computer Engneerng Vol:, No:2, 2 waset.org/publcat/436 generate the sx swtchng pulses. These pulses are used to ctrol the IGBTs to turn and turn. The basc ccept of the hysteress current ctrol s shown n Fg.. Accordng to Fg., hysteress band (HB) s the possble boundary of the compensatng current. Ths current swngs between upper and lower hysteress lmts. For example n phase a, f s equal or over than the upper hysteress lmt ( ca HB2) then the comparator output s (S=, S2=). On the other hand, f s equal or less than the lower hysteress lmt ( ca HB2) then the comparator output s (S=, S2=). From ths operatng, the ca can swng nsde the hysteress band followng the reference current ( ca ). Ths reference current can be calculated by the synchrous detect method from sect II. The maxmum swtchng frequency (f s,max ) of IGBTs can be calculated by (7) []. The V dc and L f n (7) are the value of the dc bus voltage and the sze of nductor, respectvely. HysteressBand(HB)= f (7) s, max 2Vdc 9HBLf compensatngcurrent = c reference current = c upper hysteress lmt = c HB/2 lower hysteress lmt = c -HB/2 swtchng pulse Fg. The basc ccept of the hysteress current ctrol B. Delta Modulat Current Ctrol lmtcomparator lmt comparator lmt comparator y y2 y3 D clock D clock D clock CK CK CK Fg. 6 The block dagram of the delta modulat current ctrol S S2 S3 S4 S S6 The delta modulat current ctrol (DMC) s also based a nlnear ctrol as shown n Fg. 6. Form ths fgure, the lmt comparators and D-type flp-flops are appled to generate the swtchng sgnals of sx IGBTs. The ccept of the delta modulat current ctrol technque s smple and easy to mplementat. In Fg. 6 for phase a, f s over than ca s less then the comparator output (y) s. In ctrast, f than ca then y s. Ths output s transferred to D-type flpflop for generatng the swtchng pulses. The output of D-type flp-flop ( or S) s determned by the clock sgnal as shown n Fg.7. When the clock sgnal changes from to, S s set equal to the output of comparator (y). The sgnal S2 or s the opposte state of the swtchng pulse S. The swtchng frequency of delta modulat current ctrol technque s not cstant. The maxmum swtchng frequency (f s,max ) for ths technque can be calculated by (8) [], where f clock s the frequency of the clock sgnal. currentthroughnductor= c referencecurrent= c f 2 (8) s, max fclock output of comparator(y) clock sgnal output of D-type flp-flop(s) Fg. 7 The basc ccept of the delta modulat current ctrol C. Carrer-Based PWM Current Ctrol The carrer-based PWM current ctrol (CPWM) scheme s a lnear ctrol. The block dagram of ths technque s shown n Fg. 8. In ths fgure, the dfference between the reference currents ( ca, cb, cb ) and the compensatng currents ( ca, cb, cc ) are sent to the proportal-ntegral (PI) ctrollers to generate the reference voltages ( u ca, u cb, u cc ). These voltages are compared wth the trangular carrer sgnals by usng the lmt comparators to generate the swtchng pulses of sx IGBTs. Internatal Scholarly and Scentfc Research & Innovat (2) 2 73 scholar.waset.org/ /436

4 Vol:, No:2, 2 PI ctroller u ca lmtcomparator S S2 Ths value can be desgned by the maxmum order of harmc compent csdered for elmnat. ( c reference voltage u) trangular carrer ( u tr ) PI ctroller u cb lmt comparator S3 S4 PI ctroller u cc lmt comparator S S6 swtchng pulse u tr Fg. 9 The basc ccept of carrer-based PWM current ctrol Internatal Scence Index, Electrcal and Computer Engneerng Vol:, No:2, 2 waset.org/publcat/436 trangular carrer Fg. 8 The block dagram of carrer-based PWM current ctrol The prncple of the carrer-based PWM current ctrol s llustrated n Fg. 9. For example n phase a, f the reference voltage ( u ca ) s over than the trangular carrer voltage ( u tr ) then the comparator output s (S=, S2=). If u ca s less than utr then the comparator output s (S=, S2=). The swtchng frequency of ths technque s cstant and t s equal to the frequency of trangular carrer (f tr ) sgnal [2]. IV. SIMULATION RESULTS AND DISCUSSION The three current ctrol technques descrbed n prevous sect are appled to ctrol the current nject of shunt actve power flter. In Fg., the DC bus voltage (V dc ) and nductor (L f ) values are set to 7 V and 39 mh, respectvely. These parameters are desgned by adaptve tabu search (ATS) method [3]. The hysteress band (HB) for hysteress current ctrol s equal to 4 ma. The clock frequency (f clock ) for delta modulat current ctrol s set to 2 khz and the trangular frequency (f tr ) of carrer-based PWM current ctrol s set to khz. Moreover, k p and k values for carrer-based PWM current ctrol are equal to and, respectvely [4] La ca sa tme(s) (a) The smulat results of hysteress current ctrol (HCC) Internatal Scholarly and Scentfc Research & Innovat (2) 2 74 scholar.waset.org/ /436

5 Vol:, No:2, La ca Internatal Scence Index, Electrcal and Computer Engneerng Vol:, No:2, 2 waset.org/publcat/ sa tme(s) (b) The smulat results of delta modulat current ctrol (DMC) La ca sa tme(s) (c) The smulat results of carrer-based PWM current ctrol (CPWM) Fg. The smulat results of harmc elmnat The smulat results of phase a wth three current ctrol methods are shown n Fg.. The performance ndex n the paper for compars study s the average total harmc dstort (%THD av ). Ths value can be calculated by (9). From the smulat results n Fg., the source currents are hghly dstort waveforms and %THD av of these currents s equal to 2.% as shown n Table I. In the paper, the compensatng currents from shunt actve power flter ( ) nject nto the system at t=.4 s. It can be seen that the source currents after compensat ( sa ) are nearly snusodal Internatal Scholarly and Scentfc Research & Innovat (2) 2 7 scholar.waset.org/ /436

6 Vol:, No:2, 2 Internatal Scence Index, Electrcal and Computer Engneerng Vol:, No:2, 2 waset.org/publcat/436 waveform. From Table I, the %THD av of these currents for hysteress current ctrol (HCC), delta modulat current ctrol (DMC) and carrer-based PWM current ctrol (CPWM) are equal to 3.67% 4.39% and 3.32%, respectvely. %THD av = 2 %THD k k a, b, c In Table I, the results after compensat usng CPWM technque can provde the mnmum %THD av compared wth HCC and DMC technques. It means that the CPWM technque s the best method for the proposed system to ctrol the current nject of shunt actve power flter. However, the %THD av values of three technques can be satsfed under IEEE Std TABLE I THE PERFORMANCE COMPARISON OF CURRENT CONTROL TECHNIUES %THD av of source current %THD av before compensat %THD av after compensat 3 Current ctrol technques HCC DMC CPWM 2.% 3.67% 4.39% 3.32% V. CONCLUSION Ths paper presents the compars study of three current ctrol approaches for shunt actve power flter. The hysteress current ctrol, the delta modulat ctrol and the carrerbased PWM ctrol are selected to csder the performance compars. The synchrous detect method s appled to calculate the reference currents for shunt actve power flter. The compars results show that the carrer-based PWM ctrol technque s the best method to obtan the mnmum %THD av after compensat. However, the %THD av values of all three technques can follow the IEEE std ACKNOWLEDGMENT Ths work was supported by Suranaree Unversty of Technology (SUT) and by the ce of the Hgher Educat Commss under NRU project of Thaland. REFERENCES [] IEEE Std , IEEE Recommended Practces and Requrements for Harmc Ctrol n Electrcal Power Systems, 993. [2] F. Zhuo, J. Yang, J. Hu, and Z. Wang, Study Actve Power Flter used n Three-Phase Four Wre System, Proceedngs of the Power Electrcs and Mot Ctrol Cference, vol.3,pp. 37-4, 2. [3] C. E. Ln, C.L. Chen, and C. L. Huang, Current Compensat for Unbalanced Three-phase Systems Usng Synchrous D Journal of Electrcal Power System Research, vo.26, pp. 63-7, 993. (9) [4] M. Kale, and E. Ozdemr, A Novel Adaptve Hysteress Band Current Ctroller for Shunt Actve Power Flter, IEEE Cference Ctrol Applcats,CCA 23, pp.7-82, 23. [] L. Jun, and W. Dazh, Study and Smulat of a Novel Hysteress Current Ctrol Strategy IEEE Internatal Cference Intellgent Computat Technology and Automat, pp.36-39, 29. [6] P. D. Zogas Delta Modulat Technque n Statc PWM IEEE Transacts ndustry applcats, vol. IA-7, no.2, pp , 98. [7] M. A. Rahman, J. E. uacoe, and M. A. Choudhury IEEE Transacts power electrcs, vol. PE-2, no.3, pp , 987. [8] J-H Km, and S-K. Sul, -Based PWM Method for Three- Phase Four- IEEE Transact Power Electrcs, vol.9, no., pp. 66-7, 24. [9] A. I. Maswood, and E. Al-Ammar, Analyss of a PWM Voltage Source Inverter wth PI Ctroller under N-deal cdts IEEE Cference IPEC-2, pp.93-98, 2. [] D.M.E. Ingram, ess Current IEEE Internatal Cference Power Electrcs and Drve Systems, pp , 997. [] J. W. Kmball, P. T. Kren, and Y. Chen, Hysteress and Delta Modulat Ctrol of Cverters Usng Sensorless Current Mode IEEE Transacts power electrcs, vol. 2, no. 4, pp. 4-8, 26. [2] D. Chen and S. Xe, Revew of the ctrol strateges appled to actve power flters IEEE Internatal Cference Electrc Utlty Deregulat, Restructurng and Power Technologes (DRPT24) pp ,24. [3] T. Nargrt, K-L. Areerak and A. Srkaew, Desgn of an Actve Power Flter usng Adaptve Tabu Search Proceedngs of the 8 th WSEAS Internatal Cference Artfcal Intellgence, pp , 29. [4] L. Moran, P. Godoy, R. Wallace and A new current ctrol strategy for actve power flters usng three PWM voltage source nverters, IEEE Power Electrcs Specalsts Cference, PESC '93, pp. 3-9, 993. T. Nargrt receved the B.Eng, and M.Eng degrees n electrcal engneerng from Suranaree Unversty of Technology (SUT), Thaland, n 28 and 2, In now (2), studyng n Ph.D degree n electrcal engneerng of SUT. He has been a member of Power ualty Research Unt (PRU) n the School of Electrcal Engneerng, SUT. Hs man research nterests nclude actve power flter, harmc elmnat, ntellgence ctrol system and AI applcat. K-L. Areerak receved the B.Eng, M.Eng, and Ph.D. degrees n electrcal engneerng from Suranaree Unversty of Technology (SUT), Thaland, n 2, 23, and 27, respectvely. Snce 27, he has been a lecturer and Head of Power ualty Research Unt (PRU) n the School of Electrcal Engneerng, SUT. He receved the Assstant Professor n Electrcal Engneerng n 29. Hs man research nterests nclude actve power flter, harmc elmnat, artfcal ntellgence applcats, motor drve, and ntellgence ctrol systems. K-N. Areerak receved the B.Eng. and M.Eng degrees from Suranaree Unversty of Technology (SUT), Nakh Ratchasma, Thaland, n 2 and 2, respectvely and the Ph.D. degree from the Unversty of Nottngham, Nottngham, UK., n 29, all n electrcal engneerng. In 22, he was a lecturer n the Electrcal and Electrc Department, Rangst Unversty, Thaland. Snce 23, he has been a Lecturer n the School of Electrcal Engneerng, SUT. Hs man research nterests nclude system dentfcats, artfcal ntellgence applcats, stablty analyss of power systems wth cstant power loads, modelng and ctrol of power electrc based systems, and ctrol theory. Internatal Scholarly and Scentfc Research & Innovat (2) 2 76 scholar.waset.org/ /436