Robust Control Methodologies For dc/dc PWM Converters Under Wide Changes in Operating Conditions

In this paper, a comparative study on the subject of robust control of dc/dc PWM converters is presented. Considering a wide range of possible changes for the converter’s operating conditions, robust control of dc/dc PWM converters using some state of the art robust controllers i.e., ∞ H , μ , and fuzzy controllers is studied. The system under study is a CUK converter as a non-linear, variable structure, and non-minimum phase plant with complex and potentially chaotic behavior. The results confirm successful performance of the ∞ H and μ controllers in providing wonderful robustness to even wide changes in the operating point. The results also prove that in compare with the ∞ H , the μ controller can by far provide superior results. As will be shown, while the results are quit interesting, the ability of such linear controllers is restricted to the situations where a linear model for the under study system is considered. They may fall down to control the exact physical system, especially where the large signal behavior of the converter is studied. To overcome the aforementioned issues, a simple robust fuzzy controller accompanied with a non-linear / time varying feed-forward controller is proposed. The results clearly prove the relative superiority of fuzzy controller design framework, which lead to a non-linear controller, to overcome the stability issues of the complex dc/dc converters. Key-words: dc/dc Converter, Instability, Chaos, Robust Control, Fuzzy Controller, ∞ H Controller, μ Controller, State Space Averaging, Cuk Converter. Nomenclature: Vref: X: V: D: Y: X0: Vs: D0: V0: z: v: d: y: S(s), T(s), R(s): G(s): Reference voltage of converter Converter’s State vector Input voltage Duty cycle Output voltage State vector at operating point Nominal input voltage Duty cycle at operating point Output voltage at operating point Deviation of state vector Deviation of input voltage Deviation of duty cycle Deviation of output voltage Sensitivity, complementary sensitivity , and additive robustness functions Transfer function of the plant K(s): W1 , W2, W3 :