Two-Loop Controlled Buck-SEPIC Converter for Input Source Power Management

A two-loop digital control strategy is proposed for load distribution on a two-input integrated buck-SEPIC converter-based dc-dc power conversion system. The proposed control strategy involves two decoupled control loops: one for low-voltage source (LVS) current control and the other for dc load voltage regulation. A discrete-time model of the proposed converter is established, and then, the relative gain array theory (RGA) of multi-input-multi-output control systems is applied to establish feasible combinations of input and output quantities, as well as control and power distribution quantities, for achieving optimal load allocation to input sources. The computed RGA number for diagonal pairing is close to one, for most of the frequencies of interest, indicating the optimal choice of controlling load voltage v(o) with duty ratio d(1) and LVS current i(g) with duty ratio d(2). Digital voltage-and current-mode controllers are designed using discrete-time z-transfer functions. The closed-loop integrated converter performance is verified as matching the theoretical predictions. The experimental measurements are in agreement with the analytical results, thus validating the proposed digital load distribution control concept.