A New Method for Determining Reference Compensating Currents of the Three-Phase Shunt Active Power Filter Gary W. Chang Author Affiliation: Department of Electrical Engineering, 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- monic currents of nonlinear loads. When designing a SAPF, it is crucial 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- nate transformations, the new method proposed in this letter is to deter- 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: Active power filter, reference compensating current, 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 instantaneous reactive power theory (i.e., p-q theory) to compute SAPF reference compensating currents, and this approach inspired the devel- opment of many other p-q theory-based methods for realizing 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 instantaneous reactive power theory-based method re- quires coordinate transformations between the a-b-c coordinate and the p-q coordinate, which increases the complexity when designing the SAPF controller. More recently, Peng et al. proposed a theory that gave a generalized definition of the instantaneous reactive power in the a-b-c coordinate [4]. Although Peng’s approach does not need the coordinate 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 abc = , , )