A Constant Current Control Method With Improved Dynamic Performance for CLLC Converters

The capacitor-inductor-inductor-capacitor ( CLLC ) converter is a promising topology for bidirectional power conversion applications, such as hydrogen or battery energy storage systems and bidirectional pulsing current charging or heating for electric vehicle (EV) batteries. For these applications, high dynamic constant current control is required. In this article, a novel constant current control method with improved dynamic performance over the conventional proportional-integral (PI) method is proposed for the CLLC converter. In constant current control, the charging and discharging process of the output capacitor determines the dynamic performance. A state trajectory model is proposed for the CLLC converter and is employed to analyze the transient process in the resonant tank. Based on the analysis, a novel dead-band-based control method for the constant current control is proposed. The proposed method can directly and effectively control the charging and the discharging process of the output capacitor, which the conventional PI control method cannot do. As a result, the dynamic performance is improved. The correctness of the proposed state trajectory model, the state trajectory analysis, and the effectiveness of the proposed constant current control method are verified by experiments. Experimental results show that the response time of the proposed method is reduced by more than 50% compared with that of the conventional PI method, with no overshoot.