Research On LLC Resonant Converter For Electric Vehicle Charging Machine Applications

Increasing the operating frequency of the power converter circuit can effectively reduce the volume of the magnetic element and consequently improve converter power density can be improve. However, with a rise in the frequency of switching, converter switching losses increase accordingly, which seriously hampers the efficiency of the converter. To solve the problem of serious switching losses, the utilization of soft-switching technology is needed in the converter. Compared with conventional resonant converter, LLC resonant converter can realize ZVS in wide output voltage range or even the whole load range, thus reducing the switching losses effectively at high frequencies. In addition, LLC resonant converter can achieve ZCS for secondary rectifier diodes, solve the problem of the diode reverse recovery and reduce the EMI.A 400V input,600V to 750V output LLC full-bridge resonant converter is designed in this paper, which will be applied to new energy electric vehicle charging machine adopting three modules in parallel output with a total output power of 10kW. This application, as a result, satisfies the demands of electric vehicle charging small size, high efficiency and fast charging. First, this paper introduces the resonant converter classification and the outstanding advantages of LLC full-bridge resonant converter. To meet the need of subject, it also identifies the circuit topology of LLC full-bridge resonant converter. Then, it establishes the LLC equivalent circuit through a fundamental analysis. At the same time, the gain characteristics and the operating principle of the circuit are analyzed within different frequency ranges. LLC parameter design and circuit performance are researched in wide output voltage ranges to get the optimized parameter design method. On this basis, the paper identifies the parameters of high-power, high efficiency and wide output voltage range of LLC full-bridge resonant converter through a large number of calculations. And it utilizes SIMETRIX to build a closed-loop simulation circuit and verify the feasibility of the LLC full-bridge resonant converter parameters.Finally, the LLC full-bridge resonant converter control system is designed, including the isolation circuit voltage sampling, the sampling circuit isolation circuit, driver circuit, protection circuit, etc.. This paper adopts digital control program, using TMS320F2808 as a control chip in the control unit, and all functions of LLC full-bridge resonant converter are achieved by programming for DSP. And the paper gives a solution to some detailed problems. Based on the theoretical analysis, a lOkW electric vehicle charging machine prototype is designed. Moreover, an analysis of the results of the experiment further validates the correctness of theoretical analysis and the feasibility of the design method.