A Constant Frequency Constant Duty Cycle Soft Startup Control Method with Energy Limitation Features for CLLC Converters

CLLC converter has great application prospect in bidirectional charging of electric vehicles. Aiming at the problem of large current pulse when CLLC converter starts, a soft start control strategy with frequency reduction and constant duty cycle is proposed. Firstly, the analytical expression of the converter is given by using the operation mode analysis, and the working process of the converter is reflected by solving the state equations. Then, the constraint conditions are set based on the voltage and current tolerance of the device, and the optimal control parameters of the soft-start are obtained with the fastest start speed as the optimization objective. Finally, the feasibility of the control strategy is verified by simulation. Under the condition of 100V input voltage, the no-load start experiment is carried out on the prototype, and the current surge is greatly suppressed, and the soft start control target is realized.