GaN-based MHz-LLC Resonant Converter with High Voltage Gain for Solar Energy Integration

This paper presents the design and analysis of an MHz and high voltage step-up LLC resonant converter using Gallium Nitride devices with high efficiency and high power density for solar energy integration. Both frequency and phase shift modulation strategies have been used for the control of the LLC resonant converter to regulate the output voltage while achieving a wide output power range operation from full-load to no-load. The switching frequency modulation is used for high-load operation and phase shift modulation is applied for light-load operation. The steady-state analysis of the LLC resonant converter considering higher-order harmonics is proposed in this paper to achieve accurate modeling of the converter dc gain and waveforms. The presented accurate steady-state modeling considering harmonics can significantly benefit the analysis, design, and control of the LLC resonant converter. In addition, the high-frequency transformer design and detailed converter loss analysis are presented in this paper. The presented work achieves zero-voltage switching for wide input voltage and output power ranges. Simulation results at different operating points are provided to validate the improved accuracy of the proposed steady-state modeling approach compared with the fundamental harmonic approximation method. Experimental results on a 1 MHz, 1 kW LLC resonant power converter hardware prototype with an input voltage range of 36 V - 60 V and an output voltage of 400 V are provided to validate the proposed analysis and modulation strategies with an efficiency of 95.5%.