Transient DC Bias and Current Impact Effects of High-Frequency-Isolated Bidirectional DC-DC Converter in Practice

This paper presents the transient dc bias and the current impact effects of a high-frequency-isolated bidirectional dc-dc converter (IBDC) in practice because the theoretical premise in the steady process cannot be satisfied strictly in the transient process. The transient characterizations of IBDC under the steady phase-shift (SPS) strategy are analyzed comprehensively, and the corresponding model is modified for all of the transient processes in the same and different power flows. Due to the existence of the dc bias, the current model in the transient process is different from the traditional model in the steady process, and the models are different with different operating conditions. On this basis, a transient phase-shift (TPS) strategy is proposed to improve the transient performance of the SPS strategy. Unlike in the SPS strategy, the voltages of the transformer are symmetrical in the TPS strategy, which causes that the voltage-time product of the transformer voltages is zero during a switching period, then eliminates the transient dc bias and improves the current impact, and further increases the response speed of the transient process effectively. Finally, comprehensive experiments verify the theoretical analysis.