A Dynamic Smooth Transition Control Integrated With Hybrid Modulation for Wide Output Voltage Range Bidirectional CLLC Resonant Converters

The objective of this paper is to propose a dynamic smooth transition control integrated with hybrid modulation for wide output voltage range bidirectional CLLC resonant converters. Traditionally, the pulse frequency modulation (PFM) technique is adopted for CLLC resonant converters. However, under the low output voltage and light load condition, the PFM control might be failed because of the parasitic effect under high frequency operation. To solve this issue, the phase shift modulation (PSM) can be included to achieve wide output voltage range and full load operation. Therefore, the hybrid modulation integrated with PFM and PSM is utilized in this paper. Moreover, in order to suppress the voltage fluctuation and to reduce the response time during the mode switching transient, a dynamic smooth transition control (DSTC) is proposed in this paper. The proposed control can be implemented by the digital signal processor (DSP) without adding extra circuit and components. Finally, a 2kW prototype CLLC resonant converter is built to verify the performance and feasibility of the proposed circuit and control strategy. Experimental results show that the peak circuit conversion efficiency is 96.7%, whereas the improvement of the voltage fluctuation and the transient response time during the mode switching are equal to 50% and 42%, respectively.