An Adaptive Hysteresis Current Control Based on Unipolar PWM for Active Power Filters

This paper presents a new adaptive hysteresis current control based on unipolar pulse width modulation with magnitude and time errors. Variable switching frequency due to fixed hysteresis bands known as a drawback of hysteresis method used in power system applications which generates sub-harmonics and low order harmonics and affects the quality of the power systems. Adaptive hysteresis band is a classical method to control the switching frequency. Several issues and solutions have been discussed and proposed in this paper to keep the switching frequency constant when the current error is close to zero for the unipolar modulation. Magnitude and time error signals are to control the load current and the inverter voltage level change respectively; which are the main issues to implement the adaptive current control based on unipolar modulation. Simulations have been carried out to verify the proposed adaptive hysteresis band controller and the results are presented and discussed in this paper.