Constant Frequency Modulation Strategy for DAB-LLC Sigma Converter to Achieve Voltage Regulation with Wide ZVS Range

The bidirectional converter based on DAB-LLC Sigma structure, merging the high efficiency of LLC with the superior controllability of DAB, has attracted intensive research attention in recent years. In order to accomplish voltage regulation and soft switching in a wide range, two constant frequency modulation strategies based on different sub-converters regulating voltage are presented in this paper. For the control strategy of DAB voltage regulation, a hybrid modulation strategy is studied in this paper, which can realize soft switching in a full load range. For the control strategy of LLC voltage regulation, a centrally symmetric PWM control is applied to LLC to regulate voltage and DAB operates at single phase shift (SPS) modulation to implement auxiliary power regulation. And the feasibility of these strategies is confirmed through results.