Varying Switching Frequency Control for Current-Fed Dual-Active Bridge DC-DC Converter with Constant Flux Density Change for Transformers

For current-fed dual-active bridge bidirectional dc-dc converters, a PWM plus dual phase shifted (PPDPS) control with varying switching frequency was proposed. To prevent magnetic core saturation, the flux density change of the transformer is kept constant in spite of the battery voltage and the load. The detailed loss breakdown was implemented by comparing with the conventional PPDPS with fixed switching frequency. With the proposed control, zero voltage switching performance is better with lower battery voltage and the conversion efficiency can be improved compared with fixed switching frequency control. The closed loop control implementation was given in detail. Both the steady state and dynamic response with different battery voltages are good. The effectiveness of the proposed control is verified by the experimental results of a 2.4-kW laboratory prototype.