Analysis of Unit vector and Proportional-Resonant Current Controller for Harmonic Compensation in a Hybrid Active Power Filter

Active filtering of electric power has now become a mature technology for harmonic and reactive powercompensation in ac networks. This paper proposes a combination of low- and high frequency hybrid active power filter (APF) to operate in parallel for better performance. The individual hybrid Active Power Filter is a series combinationof passive filter with the corresponding voltage source inverter. The dc links of both inverters are connected in parallel, and the voltage of this dc link is maintained by the low-frequency inverter (LFI). The low-and high-frequency inverterseliminate lower and higher order harmonics respectively. In addition, it is possible to design the LFI such that it canalso compensate the reactive power of the load. The individual passive filter of the hybrid topology is designed to takecare of specific order of harmonics that are predominant in the load. In order to make the supply currents sinusoidal, an effective harmonic compensation method is developed with the aid of a conventional proportional-integral (PI) and vector PI controllers. The absence of the harmonic detector not only simplifies the control scheme but also significantly improves the accuracy of the APF, since the control performance is no longer affected by the performance of the harmonic tracking process. Furthermore, the total cost to implement the proposed APF becomes lower, owing to the minimized current sensors and the use of a four-switch three-phase inverter. Despite the simplified hardware, the performance of the APF is improved significantly compared to the traditional control scheme. Index Terms-- active power filter (APF); PI controllers AND Shunt Active Power filter