Modeling and Decoupled Control of a Non-isolated High Step-up/down Bidirectional DC-DC Converter

Bidirectional DC-DC converters play a very important role in energy storage systems. High voltage conversion ratio, high efficiency and economy are challenging issues for the research and development of advanced bidirectional DC-DC converters. In this paper, the modeling and control of a new non-isolated high step-up/down bidirectional DC-DC converter is studied. This converter is a combination of buck-boost and dual-active-half-bridge converter. It features wide-range high voltage conversion ratio and high efficiency due to full soft switching. However, the circuit coupling causes troubles in control stability. For instance, in island boost mode, oscillation easily occurs if output voltage of high-pressure is still directly regulated by shifted phase. Hence A dynamically accurate enough model is required for analysis and more stable control method is needed. For the modeling, scholars have made some research on calculating power delivered by the transformer with its series inductor current, but they have not taken the series inductor current as a state variable in full frequency domain. Such methods achieve good outcomes in steady-state, but are at a cost of dynamic inaccuracy more or less. In this paper, an average modeling technique which considers transformer series inductor current as a state variable in full frequency domain for dynamic accuracy is proposed. A decoupled control is also proposed to achieve a leap in stability. Simulation and experiment results are also presented to verify the proposed average model and the decoupled control.