Five step-low frequency switching active power filter for network harmonic compensation in substations

This paper presents the performance evaluation of an active power filter that uses a five-step current source inverter. The use of a multi-step inverter implies lower frequency switching, thereby allowing the introduction of higher power switching devices. The control filter uses a frequency domain approach in which line current harmonics are extracted using an FFT routine. A compensating current related to the harmonic components of the load current is generated. This compensating current is injected at the point of common coupling to cancel the load current distortion. The algorithm used to generate the compensating function is presented and the system's ability to reduce current harmonics with lower frequency switching is demonstrated through simulations and a low power prototype.