Harmonic compensation characteristics of active power filters to nonlinear loads based on impedance analysis

In this paper, the harmonic compensation characteristics of APFs to nonlinear loads are investigated by a circuit equivalent method based on impedance analysis. It is found that the ac-side harmonic current of voltage source type nonlinear load (VSNL) will be amplified seriously when it is compensated by shunt APF, and the ac-side harmonic voltage of current source type nonlinear load (CSNL) will be amplified when compensated by series APF. The harmonic amplification effect is the main factor to restrict the application of APFs to different kind of nonlinear loads in all circumstance. Methods to diminish the harmonic amplification effects based on altering load´s equivalent impedance are derived. Due to the duality property of shunt APF and series APF, simulation and experiment are carried out only for shunt APF harmonic compensating system, and the results verify the correctness of the analysis and validity of the propose method.