Bidirectional DC/DC Converter Based on Interleaved Parallel Buck/Boost Cascades CLLLC

In this paper, a two-stage bidirectional DC/DC converter is suggested to handle the energy transfer for electric vehicles between high-voltage and low-voltage batteries. The converter enables bidirectional power transfer, a broad range of input voltage, and a high ratio of voltage. The front stage adopts the bidirectional CLLLC resonant converter, which possesses excellent soft switching characteristics because of its symmetrical structure in both forward and reverse directions. Open-loop fixed frequency control is used in the forward direction to set the working frequency of the switching transistors near the resonance frequency, and the voltage and current double closed loop control is employed to achieve a constant voltage ratio and efficient power transmission in the reverse direction. The rear stage adopts an interleaved parallel bidirectional Buck/Boost converter, and the interleaved parallel structure helps to lessen the output current ripple. The duty cycle secondary distribution method is used on the basis of the voltage and current double closed loop control to regulate the output voltage and make the converter operate stably. The principle and characteristics of the bidirectional DC/DC converter are analyzed, and by modeling and experimentation, the theoretical analysis's viability and correctness are confirmed.