Robust control of DC/DC PWM converters: a comparison of H∞, μ, and fuzzy logic based approaches

In this paper small and large signal responses and robust control of DC/DC PWM converters are investigated. The system under study is a CUK converter as a nonlinear and variable structure plant with a very complex and chaotic behavior. Results obtained from applications of the H_∞ and μ, and fuzzy controllers are presented and discussed. They show successful application of the H_∞ and μ controllers in providing an excellent robust stability and performance against the changes in the input DC voltage of the converter where the nominal averaged and linearized model of the converter is used and only small signal study is the goal. The results showed that the μ controller can provide a response which is lower conservative and more robust (in the sense of stability and/or performance). It has been shown that the under study system can be unstable and chaotic at large signal conditions where the above mentioned robust but linear controllers are used. A robust fuzzy logic based controller with a nonlinear and time varying feedforward controller has been proposed and it has been shown that it can provide an excellent response and robust performance against the changes in the converter input voltage and/or load resistance while the startup transient response of the converter is studied.