Filter technique of variable frequency speed control system

This paper introduces a novel digital approach applied to a three-phase four-wire active power filter, which is made up of a three-phase four-leg voltage source converter. The controller just detects main current and DC side capacitor voltage and duty cycle of the switches can be calculated simply. This controller has fewer measurement, higher robustness and simpler calculation as comparing to traditional controllers. Simulation results verify that the active power filter with proposed controller can compensate the harmonics effectively.