Quasi-fixed-frequency Digital Modulation Control Of High-power LCC Resonant Converter

Resonant soft switching technology is the key technology for achieving high efficiency and high power in power systems,and it is also one of the hotspots in the field of switching power supplies.LCC resonant converters are usually used in high-voltage and low-current applications,and have a wide input/output range,which makes them one of the more mature topologies used in resonant soft-switching technology.In order to reduce the range of resonant current and switching frequency and apply to low-voltage and high-current occasions,it is necessary to perform characteristic analysis and control design for the LCC resonant converter system to improve system performance.According to the working principle of LCC resonant converter,this paper has completed the theoretical modeling and characteristic analysis,control system design,simulation and technical implementation of LCC resonant converter.Simulation and experimental results show that when the LCC resonant converter adopts the proposed design scheme,which has the advantages of high power density,small size,wide operating range,small switching frequency variation range,and simple control.Aiming at the quasi-fixed-frequency digital modulation control of the high-power LCC resonant converter,this paper focuses on the following aspects:1.Combined with the basic working principle of the LCC resonant converter,the working conditions for achieving stable soft switching are derived.The mathematical model is established using the fundamental wave approximation method and the extended function method,which lays a theoretical foundation for subsequent system characteristic analysis and parameter design.2.Combined the characteristics of the fixed-frequency phase-change modulation control method and the variable-frequency phase-phase modulation control method,a quasi-fixedfrequency modulation control method is derived.The proposed method expands the voltage gain and Zero Voltage Switching(ZVS)range of the LCC resonant converter through cooperative linear control of switching frequency and phase.Not only does the LCC resonant converter working in continuous conduction mode have accurate and stable output voltage,but also guarantees the ZVS conduction of the primary side full bridge switch in a wide operating range.Under the premise of better working performance and higher efficiency,the switching frequency is linearly changed in a small range,which is convenient for the design and optimization of magnetic components.3.The whole system design and implementation of LCC resonant converter is completed,including the design of main power circuit,auxiliary power supply,control circuit,switch driver circuit and software system.The design adheres to the principles of reasonable layout,compact size,simple and convenient,mature and reliable,and low cost.On the basis of reducing the complexity of the system,the miniaturized module power supply with high power density is realized.Finally,the accuracy and effectiveness of the proposed quasi-fixed-frequency modulation control method and design method are verified by simulation and experimental results of LCC resonant converters under different input voltages and output powers.