Precise control strategy of dual-mode flyback DC/DC converter

Abstract

Flyback converters (FBCs) have been widely used in portable fuel-cell power systems since they feature step up/down ability, galvanic isolation between the input and output, and low cost. As the input/output voltage of the FBC varies, it may operate either in discontinuous-conduction mode (DCM) or in continuous-conduction mode (CCM). Since different modes of the FBC result in different dynamics, it is difficult to stabilise the converter operating in both modes. To solve the problem, the authors propose a controller that can control a dual-mode FBC whether it operates in DCM or in CCM. The proposed controller is composed of a dual-mode feed-forward control unit and a feed-back control unit based on the common Lyapunov function. The dual-mode feed-forward control signal is utilised to reduce the burden on the common Lyapunov function-based feed-back controller that must function well despite variable system dynamics. The closed-loop system guarantees global exponential stability and provides a fast transient response as the operating mode of the FBC switches between DCM and CCM. When constructing the proposed controller, they use the large-signal nonlinear averaged model of the dual-mode FBC and consider the parasitic components. Experimental tests were conducted to validate the proposed control scheme.