A Nested-loop Control Strategy for a Bidirectional Ćuk Inverter

This paper presents a nested loop control strategy for a bidirectional Ćuk inverter. The Ćuk converter is a high order, non-linear power converter and as such, controlling the converter to achieve good and dynamically robust behavior can be difficult. Existing solutions to this problem include sliding mode and current control strategies; although these solutions work, they suffer from complexity in design, implementation and limited compensation. The solution presented in this paper analyses the coupling capacitor, as the primary energy transfer element, and uses its power transfer during the different states of the converter, to decouple the control loop into a nested current loop and outer voltage loop; with low order, linear plants that can be compensated for using classical control theory. This also solves the non-linearity due to the duty cycle without deriving an average model. The control will be shown to cope with both AC and DC reference voltages with variable point operation. As illustrated by the simulated and experimental results, the control strategy can compensate for sudden load changes, short circuits and non-linear loads - changes that sliding mode and current control cannot compensate for.