Direct and indirect SMC control schemes for DC-DC switching converters

Two different approaches employed to design a sliding mode controller for buck DC-DC converters are presented. The first approach, called direct SMC, adopts the conventional sliding mode control (SMC) with hysteresis method to reduce the switching frequency, in which the output of the SMC controller is applied directly to the power switch. The second approach, called indirect SMC, is based on the modified integral variable structure control (MIVSC), in which the output of the SMC controller is applied to the PWM. The two schemes are compared by simulations and experiments. The results show that the indirect SMC control scheme exhibits better load disturbance rejection than the direct SMC control scheme