Study On Application Of APFC In Electric Vehicle Charger

In recent years,with the continuous progress of power electronic technology, lots of power electronic equipments are accessed to the power grid,which brings to the power gird a range of serious problems.As the most important part of power electronic equipment, the quality of power supply will greatly affect the performance of electrical equipment.Since the birth of switch-mode power supplies,it has brought great convenience.Because of the nonlinear and low power factor, a lot of harmonic is ejected to the power grid, which leads to a distortion of input current waveforms and a serious harmonic polution of power grid day by day. APFC technique can reduce the harmonic content of input current, improve the switching power supply power factor, so it has attracted more and more attention. Combing the 3500W electric vehicle charger project, the main Boost converter and UC3854 controller which is based on CCM control are studied.Three common current control modes, the characteristics and the problems of the output ripple and the input harmonics are studied.For the DC/DC level, a small signal model of the LLC resonant converter is established by using the fundamental frequency component method, and the small signal model and the DC gain function are obtained. The parametric design of the resonant converter is further studied by analyzing the variation of the DC gain function.A large number of parameters for the main circuit and control circuit are calculated.The main circuit includes the boost inductance and the output capacitor calculation,The control circuit includes the peak current limiting circuit and the feed forward filtering circuit.A simulation is made via using SIMetrix software and the simulation results have reached the preset index.Then, small signal model of the main circuit and control circuit respectively has been made to get the complete small signal model of the system. According to the optimization mathematical model of voltage loop and current loop compensation network, In order to gain margin and phase margin constraints, using the genetic Algorithm,parameters on the voltage loop and current loop compensation network is optimized.The stability of voltage ring and current loop is improved,The suppression ability of current loop to the noise and the suppression of the voltage loop to ripple gain are enhanced.On this basis, circuit design and debugging has been completed. The experimental results show that the circuit designed in this paper can get an a stable DC output voltage of 400V, the input current can strictly follows the input voltage,the circuit of power factor is improved.Then it improved the topology of the main circuit, with simple structure, high step-up ratio with tapped inductor APFC circuit, and effectively solved the problem of power switch tube impact current and the diode junction temperature.Finally, the circuit parameters of the LLC resonant converter is designed and the simulation is made via using SIMetrix software to verify the feasibility of the calculated data.