AC/DC Converter In DC Charging System Of Electric Vehicles And Battery Equalization Technology

The environmental pollution caused by national economic development has seriously affected people's life.Electric vehicles have the advantage of low-carbon environmental protection,which is conducive to reducing pollution,and electric vehicles successfully spread must have advanced charging technology as a basis,so the study of DC charging system has far-reaching significance and wide application prospects.This dissertation studies the AC/DC converter in DC charging system as the core.On this basis,a new type of battery equalization circuit is designed to enhance the consistency of remaining battery pack during charging process.The main research is as follows.In this dissertation,the working principle of PWM rectifier is analyzed firstly,and the mathematical model of three-phase voltage source PWM rectifier in three-phase stationary symmetric coordinate system is established after selecting the main circuit of three-phase half-bridge topology,then its mathematical model in two-phase stationary vertical coordinate system and two-phase synchronous rotation coordinate system are derived by coordinate transformation.The principle of LCL filter is studied in detail.The stability of LCL filter is analyzed by the frequency domain characteristic curve of transfer function and passive damping method is used to suppress the resonant point.According to the mathematical model in the two-phase synchronous rotation coordinate system of rectifier and system performance requirements,a direct current control strategy based on grid voltage orientation is used to realize feedforward decoupling of inner current loop to eliminate coupling items and interference,so as to achieve the active shaft and reactive power of independent current control.The design of double closed-loop control system is completed,and the design of PI regulator is introduced in detail according to the requirements of control system performance.The principle and implementation of Space Vector Pulse Width Modulation(SVPWM)are deeply studied.In order to eliminate the hidden dangers caused by the inconsistency of remaining electric quantity in electric vehicle battery pack during charging process,an equalization circuit based on the topology of flyback transformer is designed,and the LCD absorption circuit is applied to transformer power switch branch to reduce the voltage spike caused by leakage inductance.The principle and working modes of the circuit are analyzed,and it is proved that the power switch can realize soft switch function at switch moment by formula derivation.Finally,the effective control strategy is developed.A 12 kW experimental system is completely designed.The main parameters of hardware part are calculated and a variety of circuits are designed.The control logic and program flow charts of software part are designed.Then,a simulation model is built in MATLAB/Simulink to verify the correctness of theoretical analysis,control logic and main parameters.Finally,the experimental system is built and the experiments are finished.The experimental waveforms prove that the charger can achieve the expected effects,which are consistent with the theoretical and simulation analysis.Thus it can explain the study and design of DC charging system are feasible and advanced.