ISSN 1009 3095 Journal of ,Z17ejiang University(SCIENCE) V. 1, No. 4, P. 394 - 397, Oct. - Dec., 2(XX) http://www, chinainfo, gov. crYperiodical; http://www, zju. edu. ca; http://lib, zju. edu. ca/English; http://www, zjupress, corn - 394 A NEW STRUCTURE OF SERIAL HYBRID ACTIVE POWER FILTER FOR HIGH POWER APPLICATION" CHEN G u o - z h u ( [ ~ , l ~ ) t , LU Z h e n g - y u ( ~ - ~ - ) , QLAN Z h a o - m i n g ( $ ~ , ~ ] ) ( Electrical Institute of Zhejiang University, Hangzhou, 310027, China) "I"E-mail: [email protected] Received Aug.28, 1999; revision accepted Apr. 15,2000 Abstract: This paper proposes a new structure of serial hybrid active power filter which can reduce the power rating of the active power filter dramatically, and has good performancefor ham~nic suppression. The principle and designing rides are analyzed, rllae proposed structure is rational and feasible for high kVA applications. Simulation rexsultsare presented too. Key words: activepower filter, harmonics, power conditioning, power quality Document code: A CLC ntmfl~r: TM714 INTRODUCTION To cope with the more and more serious harmonic problems mainly caused by power electronic equipment application, various kinds of active filters have been proposed and put into field applications recently. Among them, a Serial Hybrid Active Power Filter ( S H A P F ) as shown in Fig. 1 (exclude the dotted box) is particularly attractive due to its low cost, good performance, multi-function and small rating serial active power filter ( A P F , typically 5 % of the l o a d ) . It presents a resistance k to harmonic current and a low resistance to fundamental component (Chen et a l . , 1998; Peng et al. , 1988) However, it is clear that when the system power rating is high, the Voltage Source Inverter ( V S I ) , the APF, has to deliver not only the harmonic power but certain amount of fundamental power components too. This causes high demand for a large power rating of VSI. It is difficult to protect the APF inverter too due to its serial structure. These actually limit the SHAPF application. }'or this reason, only one power system application in U. S. A has been reported ( Bhattacharga et al. , 1995). PRINCIPLES AND ANALYSIS with notch impedance character is proposed (Fig. 1 ) for preventing current coupled from the main circuit from impacting on the VSI. By detailed design, it acts as a sink for the fundamental current and voltage from the main side and the APF inverter respectively. Where, PPF1 is the fundamental frequency tuned L - C branch proposed by this paper; PF is a set of passive filters, such as 5th, 7th and so on, and a high pass one; Vc, Vr are the output voltage vectors of the APF and VSI respectively; Z r is the equivalent impedance of VSI including a low pass filter. In Fig. 1 hereafter V, I , Z represent voltage, current and impedance of the branches ; Subscripts S , L , F , r and p represent the branches source, load, PF, VSI and PPF1 respectively. 1. Design considerafiorts For the aim that most fundamental current coupled from the main side sink into PPF1 and without causing high fundamental voltage or increasing harmonic current supplied by the VSI, it has to comply with the following conditions: I Zp(co0) I = R < : I Zr(CO0) I I /p(CO0) " Zp(co0) I"--~ Lsl x COo x ls(COo)/n---"O I Zp(CO h ) I::~-I JCOh X Lsl + Zl(COh) 13~1 Zr(COh) I (1) A fundamental frequency tuned L-C filter 9 Projectsupportedby DELTA~ience. Technologyand FMucationI~velopmentFoundationfor PowerEl~tronicsof China. A NEW STRUCTURE OF SERIAL HYBRID ACTIVE POWER FILTER 395 [ Vc ( (oo ) = I , ( (oo ) " j(Oo L2 + I t ( ( o 0 ) " j(oo M Source Vs ls Vc zp((oo) E / = I t ( ( o 0 ) " j(ooLl + I s ( ( o o ) " j(ooM tlt(a~o) + Ip((oo) = /r((o0) ~ 0 (3) VSI Z, t'-" v~ ""l Z, Nolinar load Hg. Zr Proposed serial hybrid active power filter (SHAPF) for high power application Where (o0, cob are fundamental and harmonic frequencies; Zp ( o-,0 ) is impedance of the PPF1 tuned L - C branch ; n is the transformer ratio; R is the equivalent resistance of the tuned PPF1; Lsl is the primary leakage induc "tance of the transformer. Z1 (cob) is the equivalent impedance to harmonics of the transformer converted from the main side. Here I j(oh x Lsl I>>1 ZI ((oh) I is usually tenable for the main source and the PF. By using Equation ( 1 ) , the current of the inverter (VSI) can be calculated as: I~ = I , ( ( o 0) + / r ( C O h ) Zp((o0) + Zp((o0) + Zr((oo) ls((o~ L((oh) Zr((oh) 4- Z ( ( o h ) 4- Z p ( ( o h ) 9 + g M i n:ll 2. The harmonic suppression performance An equivalent circuit ( F i g . 2 ) was used to investigate the transfer function H I (j(o) 9 Equations ( 3 ) and ( 4 ) for fundamental ( COo) and Equation ( 5 ) for harmonics ((oh) can be derived as follows: For fundamental _ n Fig.2 The equivalent circuit of proposed SHAPF we can get V~ H, (fioo) = Zp((oo) I~- = nz (4) For harmonics V~((oh) = I s ( ( o h ) " j(oh " Lz + / t ( ( o h ) " j(ohM " (Zr + (oh " L1) + G - Mwh It((oh) (2) Where Zr is the output current and voltage of the Current Controlling Voltage Source ( C C V S ) , that is the VSI, controlled by residual harmonic current of the source branch ( Is ((oh) with gain G. Ir is the current supplied by the VSI . Equation ( 2 ) shows that the fundamental current component flowing into/out of the VSI is almost eliminated if Zp ( COo) I ~z I Z , ( COo) 9 ! ! i V~h = G 9 I s ( ( o h ) " I r Is(cOb) 9 M(oh ///jwhLsl /r((oh) Is = /r((oh) = Zr((.Oh) 4- (-oh " L 1 Is(oh) v~ Ht (j(oh) -- l,h G - Mooh M 9 (oh = Zr(COh) + (oh " LI Using + (ohL2, M ---- ~ / L 1 L 2 and LI = n 2 9 L2 H1(j(oh) - G _ K n (5) From Equations ( 4 ) and ( 5 ) , we can conclude : This structure SHAPF has the same transfer function for harmonics control as that reported in literature ( P e n g et a l . , 1988; Bhattacharya et a l . , 1 9 9 5 ) . It acts as a harmonic isolator with equivalent resistance K . SHAPF with extremely low resistance to fun- 396 CHEN Guozhu, LU Zhengyu et al. damental current can be produced by proper design. 1988, S. Bhattacharya et a l . , 1995). lOOo;oo 3. The rating and protection of the VSI -100.00 L 100.00, The three phase APF-VSI's rating is determined by S, = 1 V r Ixl I r Ix3 -100 00 l / ~ ' " ' ~ \ 300.00 . . . . . . (6) /~ -300.08 1000 Here V~h : G - I~ ( C-Oh ) , and L is given by Equation ( 2 ) . To achieve the same system suppression performance, residual harmonic current I~ ( cos ) , under the conditions of Equation ( 1 ) , we can find that the first term of Equation ( 2 ) is Zp ( ) reduced by Zp ( coo ) + Z r( coO ) ' while the sec- _ r t ~ -10.08 - - - 48o.0o 48o.08 508.08 Time (ms) 108.00 - - 0.08 -100.00 100.00 ..< ond term is almost constant in the application of the proposed S H A P F . What is more, the first 0.00, term of the Equation (2) is usually m u c h larger 4 0.00 ~ , . / ' ~ ~ - ~ ~ F ~ , / ~ - f ' ~ _ f%J than the second term in a conventional S H A P F -10.08 460.00 480.00 500.00 ( Zp --~ ~ ). That is to say that the rating of the Time (ms) VSI without this structure is mainly fundamental, Fig. 3 SHAPF harmonic suppression simulation F r o m t o p to bottom: s o u r c e c u r r e n t 1~ , hind c u r r e n t and it is sharply reduced by the proposed l L , inverter output voltage Vm~(V~) , inverter S H A P F . Also, the S~ is reduced dramatically. current I~(1~) ( a ) Conventional SHAPF; ( b ) With the PPFI providing a fundamental SHAPF with proposed structure channel for the main coupled current, this S H A P F structure can easily protect the VSI from From Fig. 4, we can see that the VSI fundao v e r - current, and can provide uninterrupted mental current is greatly reduced from 6 . 7 A to power supply to the load when the VSI faults. 0 . 3 6 A with the proposed structure. The losses, This was one of the difficulties limiting the SHAPF actual application formerly ( S . Bhatta7.00 charya, 1 9 9 5 ) . ] - - 5.25 SIMULATION RESULT 3.50 1.75 To test the aforementioned rules and principles, a detailed simulation was done over the set of parameters below. Load rating 50 kVA/380V 3 ~ ; Transformer ratio n = 1 0 : 1 ; PPF1 branch: 0.0t] O.O0 Q co" 138'uF) ~ ' (a) 5,25 350 1.75 5o Some results are shown as follows: Fig. 3 shows us that the new structure SHAPF has the same good performance for harmonic suppression as the harmonic suppressor systems reported in literature ( F . Z. Peng et al. , 500.00 7.00 J Zp = 0 . 2 + j ( co . 3 O m H - 250.00 Frequency (Hz) 0 0 0 ~ . J x0.00 A /% 250.00 Frequency (Hz) (b) F i g .4 VSI current speclrmn (a) conventional SHAPF; (b) proposed SHAPF A NEW STRUCTURE OF" SERIAL HYBRID ACTIVE POWER FILTER which are square functions of the c u r r e n t , s h a r p ly drop down. A l t h o u g h the harmonic current of the VSI is increased a little, it is not very serious. Especially in higher power system this small increase can be i g n o r e d . If this structure S H A P F is applied to higher power rating s y s t e m , for a 10 MVA s y s t e m , for example, the rating of the VSI can be r e d u c e d from the typical 5 0 0 k V A to 20 - 30 k V A . W h i c h is valuable in practical applications. CONCLUSIONS The new structure serial S H A P F a n d its designing rules are p r e s e n t e d in this p a p e r . A n a l y sis and simulation results showed that this S H A P F has good p e r f o r m a n c e for h a r m o n i c suppression. It is simpe but c a n reduce the A P F inv e r t e r ' s power rating and r e d u c e e n e r g y losses and cost significantly. The new S H A P F c a n give highly reliable protection against harmonic currents. It is suitable for high power a p p l i c a t i o n . 397 References Akagi H.. H . , Fujita, 1995. A New Power Line Conditioner for Harmonic Compensation in Power Systems, IEEE - PWRD, 10(3) : 1570 - 1575. Bhattacharya S., Divan D . M . , 1995. Design and Implementation of a Hybrid APF, In: APEC' 1995 Conference Record, USA.p. 189 - 195. Cheng PoTai, Bhattacharga S., Divan D. M., 1996. Hybrid Solution for Improving Passive Filter Performance in High Power Applications, In: APEC'96 Conference Record, USA, p.911 - 917. Chen Guo'Aau, Lu Zhenggu, Qian 7~aaoming, 1998. A Hybrid Solution to Active Power Filter for the Purpose of Harmonic Suppression and Resonance Damping, In: Prec. of Power Con' 98 Beijing, China, p. 1 5 4 2 1546. Chen Guozhu, l_a Zhengyu, Qian Zhaoming, 1999. rllae harmonic pollution report of the industry adjustable speed system , In : Proc. of the national 5th EMC conference ( '99EMC Beijing), China. p. 210 - 216 (In Chinese , with English abstract). Fujita H., Akagi H., 1990. A Practical Approach to Harmonic Compensation in Power Systems, In : IEEE - IAS Annual Meeting, Conference Record, USA. p. 11071112. Peng F . Z . , Akagi H., Nabae A., 1988. A New Approach to Harmonic Compensation in Power System, In: IEEE - IAS Conference Record, p. 874 - 880.