Adaptive feedforward and feedback control schemes for sliding mode controlled power converters

A major disadvantage of applying sliding mode control to dc/dc converters is that the steady-state switching frequency is affected by line and load variations. This is undesirable as it complicates the design of the input and output filters. To reduce switching frequency deviation in the events of line and load variations, an adaptive feedforward control scheme that varies the hysteresis band according to the change of line input voltage and an adaptive feedback control scheme that varies the control parameter (i.e., sliding coefficient) according to the change of the output load are proposed. This paper presents a thorough investigation into the problem and the effectiveness of the proposed solutions. In addition, methods of implementing the proposed adaptive control strategies are discussed. Experimental results confirm that the adaptive control schemes are capable of reducing the switching frequency variations caused by both line and load variations.