Design And Implementation Of Vehicle Low Voltage 24V DC-DC Converter

Under the background of less and less petroleum fuels and serious environmental pollution,the development of new energy electric vehicles has gradually grown,The low-voltage power converters are an important part of the charging of low-voltage equipment for electric vehicles.With the development of scientific research,on-board low-voltage DC-DC converters tend to be smaller,high-frequency,low loss and high efficiency.In this paper,the research on 3kW vehicle low-voltage cascade DC/DC converter is carried out for large step-down ratio DC-DC converters.The main research contents are as follows:The overall system structure of the vehicle low-voltage DC-DC converter circuit is designed,the specific technical specifications of the paper are determined,the overall scheme of the main circuit structure of the two-stage cascaded double-channel interleaved Buck+ full-bridge LLC resonant converter is proposed.The system function of the converter is analyzed,the working principle of the pre-stage staggered parallel circuit and the latter stage full-bridge LLC resonant converter is analyzed.The soft start mode can reduce the starting current voltage impulse of the capacitor,the soft switching technology in the latter stage can reduce the loss of the power device when the system switching frequency is increased.The stable output can be obtained by using PID closed-loop control strategy.The state space average model of the pre-staggered parallel Buck circuit and the approximate fundamental equivalent model of the post-stage full-bridge LLC resonant converter are established,the specific parameters design and component type selection of the two-part circuit are carried out,the design is in line with the gain optimization range,and finally the loss of the two-stage circuit is analyzed.The hardware control circuit of the system is designed,including the main control DSP design,driving IGBT/MOSFET signal circuit,sampling board,etc.In order to improve the safety and reliability,relevant hardware start-up,short circuit protection,acquisition over-voltage and over-current protection,OC protection of driving signal and CAN communication fault protection functions are formulated.The program control flow of the main control,interrupt,communication and protection is carried out for the software control.The pre-stage circuit and the post-stage circuit are modeled separately by MATLAB simulation.The latter stage uses phase shift and frequency modulation to compare the simulated waveform to obtain a better solution.Then the two circuits are cascaded and simulated,and the simulation results verify the rationality of the design.Finally,a 3kW on-board system converter is built in the laboratory,and a prototype of 24V/125 A is output under 500 V input.The test data conformed to the system design requirements of this paper,which verified the feasibility of the design and the effectiveness of the system.