Variable-band hysteresis current controllers for PWM voltage-source inverters

Hysteresis current controllers having fixed bands are used in inverters of high-performance ac drives. The switching frequency of such controllers varies over the fundamental period of the modulating signal. The maximum switching frequency (MSF) of these controllers is high. To limit the MSF within the limit of inverter switches, fixed carrier lockouts are usually incorporated. The incorporation of carrier lockouts causes current distortion, and load currents do not confine within the predetermined band. In this paper, two new controllers are proposed. One is a mixed-mode controller of sinusoidal band added to a fixed band, and the other is an equidistant-band current controller. Performances of the proposed controllers are compared with the performances of the conventional fixed-band and sinusoidal-band controllers.