Design Of Modified LLC Resonant Converter With Wide Output Range

High-frequency power electronics technology has always been an important development direction of power electronics.As the operating frequency increases,the power density can be effectively improved,and the switching losses will also be increased undesirably.In order to resolve the conflict between high frequency and switching losses,the soft-switching technology is born out.As a result of that,the LLC resonant converter has received a lot of attention and application owing to its easily soft-switching characteristics.With the rapid development of new energy generation?electric vehicles and telecommunications,the converters are required to realize wide-range voltage gain and high efficiency at the same time.However,the traditional LLC resonant converter can perform well only around the resonance point and is mainly suitable for a narrow voltage gain.In this paper,the improvements and optimization design of traditional LLC resonant converters have been analyzed and studied for wide range of output voltage and power occasions.In this paper,a variable-mode control strategy has been adopted for traditional LLC circuit structure.This so-called variable-mode control strategy consists of Pulse Frequency Modulation in Full-bridge(FB PFM)?Phase Shift Modulation in Full-bridge(FB_PSM)and Pulse Frequency Modulation in Half-bridge(HB PFM).With this strategy,the wide-range output voltage can berealized without broadening the operating frequency range.Apart from that,an optimal parameters design method which aims to maximize the magnetizing inductance on the condition that the requirements of wide-range output voltage and primary MO SFETs' soft-switching are met has been put forward.Based on the traditional LLC circuit structure,an novel interleaved LCLC resonant converter with Pulse Frequency Modulation plus Phase Shift Modulation(PFPPS)has been presented.The equivalent magnetizing inductance can be adjusted by varying operating frequency,which is beneficial to realization of wide voltage gain and high overall frequency.And the output voltage range can be further expanded by adjusting the phase between modules at resonance point.It can be found out that the same gain range can also be realized in the case of wide load range by simplified time domain analysis.In addition,an optimal parameters design method that maximizes the magnetizing inductance and limits the voltage of resonant capacitance is also proposed to improve overall efficiency and system reliability.At last,the 10kW LLC resonant converter with variable-mode control strategy and interleaved LCLC resonant converter are designed and set up separately to verify the above control strategy,topological structure and parameters optimization design methods.