Abstract：In this paper, an asymmetrical phase-shift (APS) control for the series-parallel (LCC-type) resonant converter was proposed. A pulse width modulation (PWM) and phase-shift combined modulation scheme was implemented to achieve two independent control variables, which introduced additional degrees of freedom in control. The steady-state characteristics of the converter were analyzed including output power, zero-voltage switching (ZVS) operation and resonant current. This analysis demonstrates that different combinations of duty cycle and phase shift angle can achieve the same output power, leading to distinct root mean square (RMS) resonant currents and affecting ZVS operation. An efficiency optimization strategy based APS control was then proposed to deliver a specific output power with minimized RMS resonant current while maintain ZVS. As such, the efficiency of the converter is improved in a wide load variation range. The theoretical analysis and the validity of the proposed method has been verified by the results of simulation and a 1.9kW prototype.
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2017, Vol. 32 
