A Low-Complexity Trajectory Controller for Reduced Conduction Losses in Series-Resonant Dual Half-Bridge Converters

This paper describes a low-complexity trajectory controller for near-optimal minimization of conduction losses in series-resonant, dual half-bridge converters (SR-DHB). The technique builds on the concept of minimum current trajectory (MCT) of a resonant converter, and formulates a piecewise-linear approximation of the MCT (PWL-MCT) for an SR-DHB topology, which can be implemented digitally via standard arithmetic operations. The low-complexity realization of such technique makes it suitable to be easily implemented in a commercial microcontroller, or even inside a custom-designed digital IC, depending on the target application requirements. Even more importantly, the MCT-based control trajectory can be formulated independently of the converter parameters, resulting in a control approach of the broadest applicability. When equipped with such simple trajectory controller, the SR-DHB converter becomes an efficient, controllable bidirectional dc-dc power unit, which can be employed in a number of scenarios, including dc power distribution systems and battery-to-battery power interfaces. Compared with traditional phase shift modulation, the proposed trajectory controller yields higher efficiency at intermediate-to-light load levels, and equal efficiency at heavy load. Furthermore, the proposed PWL-MCT concept can be implemented to accommodate wide variations in the converter voltage conversion ratio, making the resulting power unit versatile and voltage-programmable. The proposed approach is validated on a 800 W, 200 V-to-145 V, SR-DHB converter prototype. Efficiency comparisons are discussed highlighting the benefits of the PWLMCT controller over traditional modulation approaches, and the strong efficiency improvement achievable at voltage conversion ratios away from the nominal one.