Modified hysteresis control with minor loops for single-phase full-bridge inverters

An efficient online PWM (pulsewidth modulation) control method for single-phase full-bridge inverters is proposed. The conventional hysteresis control method has good dynamic responses, but the switching frequencies are high because it does not optimize switching patterns. Full-bridge inverters can generate +E, -E, and 0 (zero) levels where E is an input DC voltage level. The hysteresis control method does not utilize maximum freedom and it selects the output only among two levels (+E and -E). The method selects the optimum output among the three levels (+E, -E, and 0) instantaneously. The control circuit of the proposed method is very simple. Whereas the conventional hysteresis control has only one hysteresis comparator, the proposed method has two hysteresis comparators (wide and narrow loops). When a reference signal goes up, the wide-loop output becomes high and the inverter output is +E, or 0 according to the narrow-loop output. When a reference signal goes down, the wide-loop output becomes low and the inverter output is -E or 0. The method is validated to optimize the output level instantaneously and to reduce the switching times. >