Research And Equipment Development Of The Low-voltage And High-current Dc/dc Converter

With the constant development of power electronics technology,high-frequency switching power supply has gradually replaced thyristor rectifier as the mainstream of electrolytic power supply with their superior performance.Since the low-voltage high-current DC/DC converter is the key link in electrolytic power supply,its performance greatly affects the production quality,power utilization rate and the cost and volume of the entire system.Therefore,high-power density and low-cost low-voltage high-current DC/DC converter is a hot topic in current research.However,single-phase DC/DC converter faces the problem of high current stress of power devices and magnetic components in high-power applications.While three-phase DC/DC converter has advantages of small input and output current ripple,low current stress of power devices and transformer,which has attracted the attention of scholars at home and abroad.In this paper,low-voltage and high-current DC/DC converters are deeply studied,especially their topological structure,control strategy and current sharing control technology for parallel power system.The research focus and achievements are as follows:A full-wave rectifier three-phase full bridge DC/DC converter is proposed,its high-frequency inverter unit adopts three-phase voltage type inverter,while the rectifier unit is consisted of three sets of full-wave rectifier circuits connected in parallel.This paper analyzed and summarized the three-phase DC/DC converter working principles in different connection modes(Y or ?)of the high-frequency transformer primary winding and different modulation methods(symmetrical pulse width modulation or asymmetrical pulse width modulation).From the analysis of device stress and loss,the full-wave rectifier three-phase-full bridge DC/DC converter with ? connection is selected,which adopts asymmetrical pulse width modulation.The soft switching process and operating characteristics of the converter under 0<D?1/3 are analyzed in detail.For the electrochemical device with variable load,a constant voltage/constant current self-switching control strategy is proposed.Compared with the conventional voltage and current double closed-loop control method,it can adjust the output voltage and current according to the load in real time to work in the constant voltage or constant current mode.For the input parallel and output parallel power system,the influence of the voltage/current sampling coefficient difference between the converters on the load current distribution in different working modes is analyzed.Aiming at the problem of current unevenness in constant voltage mode,a digital master-slave current sharing method based on CAN bus communication is proposed,which can realize the equalization of load current.At the same time,the staggered phase shifting technology is introduced,which greatly reduces the output current ripple.Finally,the simulation verifies the feasibility and effectiveness of the proposed control strategy.The engineering design of the 6.5V/3000 A DC/DC converter is carried out.The parameter design criteria of the main circuit components such as input capacitor,high frequency transformer,power semiconductor devices and output filter is elaborated.The hardware circuit and software of the control system are given,and an experimental prototype was built and the feasibility of the designed DC converter was verified.