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A New Method for Determining Reference Compensating Currents of the Three-Phase Shunt Active Power Filter Gary W. Chang Author Affiliation: Depar tment of Elec tric al Engin eerin g, Na- tional Chung Cheng University, Chia-Yi, Taiwan. Abstract: Among various solutions to electric power quality prob- lems, the use of a shunt active power filter (SAPF) has been proven as an effective method to compensate reactive power and to mitigate har- mon ic cur ren ts of nonl inearloa ds.When des igninga SAPF, it is crucia l to generate reference currents for determining actual compensating current injections to the point of common coupling. In contrast to the conventional instantaneous reactive power theory that needs coordi- nat e transformations, the new met hod prop osed in this let ter is to det er- mine reference compensating currents based on the balance of the instantaneous reactive and active power generated in the SAPF. It is shown that the proposed method is suitable for reactive and harmonic power compensation by using a SAPF. In addition to maintaining the sinusoidal source currents, this method also eliminates the need for in- stalling energy storage device for reactive power compensation as well as the dc source for the harmonic compensation in the active power fil- ter. Therefore, a simpler design of the SAPF with the minimal line losses can be expected. Keywords: Activ e power filte r, refer ence compe nsati ng curre nt, instantaneous reactive power theory, coordinate transformation, in- stantaneous power balance. Introduction: The concept of using the SAPF for reactive and har- monic power compensation was introduced more than two decades ago. By measuring the load currents and voltages, the SAPF can inject compensating currents as well as absorb or generate reactive power at the point of common coupling for controlling the harmonics and com- pensating reactive power of the connected load. In 1983, Akagi et al. proposed an innovative approach based on the instantane ous reac tive power theory(i.e., p-q the ory)to compute SAPF reference compensating currents, and this approach inspired the devel- opment of many other p-q theor y-base d metho ds for real izing the SAPF [1], [2]. Willems indicated, however, that the p-q theory is com- plete only in three-phase systems without zero-sequence component [3]. Also, the insta ntane ous react ive power theory-based metho d re- quires coordinatetrans forma tions betwe en the a-b-c coordi nate and the p-q coordinate, which increases the complexity when designing the SAPF controlle r. Mor e rec ent ly, Peng et al.propos ed a the ory tha t gave a gen era liz ed def inition of theinsta nta neous rea cti ve powe r in the a-b-c coordi nate [4]. Alt hough Pen g’s approach does not nee d the coordi nat e transformation, it requires an additional function for instantaneous re- active power vector calculation in the SAPF controller. Based on the instantaneous reactive power space vector defined in [4] and the con - cept of instantaneous power balance, the author of this letter presents a direct method for determining the SAPF reference compensating cur- rents. The proposed method is valid for both sinusoidal/nonsinusoidal and balanced/unbalanced three-phase power systems. Instantaneous Power Balance Method: Figure 1 shows the sche- matic diagram of a typical three-phase four-wire SAPF compensating system. The three-phase instantaneous active power consumed by the load is IEEE Power Engineering Review, March 2001 63 Figure 1. The schematic diagram of the three-phase SAPF compensation Figure 2. Source voltage, source currents before and after compensation at each phase ( v k , i lk , i sk , k a b c = , , )
