PWM and PFM Hybrid Modulation Scheme for Dual-input LLC Resonant Converter

This paper proposes a pulse-width-modulation (PWM) and pulse-frequency-modulation (PFM) hybrid modulation scheme to minimize the light load switching loss of a dual-input LLC resonant converter for photovoltaic (PV) applications. The converter voltage gain is controlled by adjusting the duty cycle at light load and varying the operating frequency at heavy load. Zero-voltage-switching (ZVS) is realized in all primary switches and zero-current-switching (ZCS) is achieved in secondary diodes over the entire range of source voltages and load conditions. In addition, voltage stress across switches does not exceed the input PV voltage. The dual-input LLC converter with proposed control scheme was established in L Tspice+PSIM softwares to analyze the performance. A 500-W dual-input LLC prototype was built to experimentally demonstrate the performance of the proposed hybrid modulation scheme. The input voltage range was selected to be 25 V to 50 V with an output voltage regulated at 200 V DC. Experimental results are closely matching the simulation results. With the proposed modulation scheme, the converter light load efficiency can be improved by maximum 6% while maintaining the conversion efficiency above 90% for the entire power range.