Stability analysis of harmonic compensation system under weak grid conditions

Detecting the load currents is a basic control method of paralleled active power filter (PAPF). The stability and compensation effect of the system would be influenced by the interactions of the load, weak grid and the paralleled active power filter (PAPF), when the load can´t be equivalent to an ideal harmonic current source. The impedance models are established to analyze the stability of the system, and the relationship between the interactions and the stability is discussed using the Nyquist criterion. A compound control scheme is proposed based on virtual impedance control and changing compensation rate, which can ensure the stability and the compensation effect of the system with sacrificing smaller capacity of APF. Simulation results are presented to verify the validity of analysis results.