A frequency adaptive strategy for composite current controller of Shunt Active Power Filters

Shunt Active Power Filters (APFs) are effective to eliminate harmonic current generated by nonlinear load. Many current control strategies including composite controller are proposed but the current control performance when grid frequency fluctuates is rarely discussed. This paper presents a frequency adaptive strategy for composite controller which can change sampling frequency of the controller automatically to track the grid frequency, so that excellent grid current compensating performance can be obtained in spite of grid frequency variation. To obtain both high compensation precision and fast dynamic response, the current composite control system includes an external repetitive control loop and an inner PI control loop. The frequency adaptive capability is achieved by the use of a special phase-locked loop. Simulation and experimental results verify the validity and feasibility of the schemes proposed by this paper.