Dithering for sliding mode control of DC/DC converters

The implementation of sliding mode controllers for power electronic converters needs the use of a suitable strategy in order to maintain the switching frequency finite and possibly constant. This objective can be obtained by replacing the ideal relay characteristic of the sliding controller with a variable hysteresis band. In this paper we show that the same objective can be also achieved by injecting a high frequency signal at the input of the relay. Recent results on the averaging of dithered switching systems are exploited in order to show the effectiveness of the proposed approach and to provide insights for the design of shape and parameters of the signal to be injected. Dither is shown to play an important role for stability and robustness of the controlled converter. Simulations on boost and buck DC/DC converters confirm the expected results.