Research On The High-efficiency Charger Of Electric Vehicle

Under the dual pressures of energy crisis and environmental pollution, more and more countries begin to promote new energy vehicles, mainly in the plug in hybrid electric vehicles (PHEVs) and battery electric vehicles (BEVS). With the development of electric vehicles, car charger is also receiving more and more attention. With high reliability, high efficiency and high power density, electric vehicle charger and its control method have become a hot research topic.According to the requirements of the electric vehicle charger, car charger studied in this paper adopts a cascade circuit structure with the interleaved boost power factor correction (PFC) circuit and LLC circuit. The Boost PFC in the first-stage uses staggered parallel structure, which can not only reduce the high frequency ripple of input current, reduce the harmonic distortion rate, but also reduce the current stress of power devices and do help to the selection of switching tube. The second-stage employs the LLC circuit which is independently controlled.thus achieving the zero voltage switching (ZVS) of switches tube in the primary side within full load range, achieving the zero current switch (ZCS) of rectifier diodes on the secondary side when working frequency is less than the resonant frequency, and improving the adaptive ability to battery charge characteristics.In order to improve the efficiency and power density, the LLC circuit is set with a higher resonant switching frequency. Also, in order to avoid the analog signal distortion, as well as realize the complex control and communication function, the design of the first-stage and second-stage circuits in the car charger in this paper adopt the digital control, using a digital signal processor (DSP). Voltage and current signals collected by the conditioning circuit enter into the AD sampling port of the digital control chip, and the PI regulator is adopted with this digital control chip.The switching frequency is changed according to results of calculation, thus meeting the different requirements of voltage and current in the process of DC charging lithium iron phosphate battery.In this paper, a 3kWexperimental prototype platform is built, whose experiments are full-digital control. The experimental results verify the effectiveness and validity of the analysis. When operating at full load, the harmonic distortion rate of AC input current is reduced, the power factor reaches 0.99, and the efficiency of the whole machine reaches 95%.