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 PWL-MCT controller over traditional modulation approaches, and the strong efficiency improvement achievable at voltage conversion ratios away from the nominal one.