| Under the call of energy conservation and emission reduction,the research of electric vehicle in the market and new technology has been paid great attention in recent years.As the charging equipment of electric vehicle battery,the performance of vehicle charger has a great influence on the range and charging time of electric vehicle.High efficiency,high power density and wide output voltage are required for on-board charger(OBC)applications.LLC resonant converter has the advantage of achieving zero voltage switching(ZVS)for variable frequency and different load condition.Compared with conventional fundamental harmonic approximation(FHA)method,operation-mode analysis based on the time domain model provides an accurate description on resonant current,voltage and DC gain.In this paper,the efficiency-oriented modified method is proposed based on the operation-mode analysis.The converter inductance ratio,characteristic impedance and transformer turns ratio are optimized and both-side soft switching can be achieved in the high output voltage region.Conduction loss can be minimized by optimizing resonant parameters.Finally,a high efficiency design method is proposed and validated through experiments on a 3.3k W prototype applied in OBC.The prototype of the LLC resonant converter has been tested for dynamic charging voltage(230-430V)with peak efficiency value of 98.5%.When the output power is increased,it is not enough that the single-phase LLC with high ripple rate is close to a filter capacitor.Generally,three-phase interleaved LLC resonant converter is used to reduce the output ripple.In this paper,a high-accuracy time domain analysis is adopted to analyze the effects between three phases in detail.According to the operation mode analysis,transformer’s turn ratio,resonant inductor,magnetic inductor and resonant capacitor are optimized based on the design principle of minimizing the conduction loss.Finally,the MEOM of wide output range LLC resonant converter is proposed and its design results is validated by a 6.6k W prototype with 390-430 V DC input voltage and 240-420 V DC output voltage.Experimental results show the peak conversion efficiency of the prototype is 97.42%.In this paper,considering the special load characteristics of the high-voltage power battery,the design method of the single-phase and three-phase LLC resonant converter for the vehicle charger is proposed.The experimental results have obvious advantages over other methods,and the design results are reasonable and effective. |
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