Research On Parallel Switching Power Supply System Based On Soft-switching And Digital Current Sharing Method

Parallel switching power supply system is a power supply system which consists of series of power modules by parallel connection. It is one of the main directions of the switching power supply technical studies owing to their simple thermal design, high reliability, lighting, standardize and modularity. However, in the design of the parallel switching power supply system high efficiency switching power supply module is difficult to design and the accuracy of the parallel current sharing is not high. In this paper, soft-switching and parallel current sharing control technology are studied to design a new type parallel switching power supply system to resolve these problems.Firstly, basic structure, features, key technologies and development status of parallel switching power system are introduced. The overall design scheme of parallel switching power system is put forward. In power module design, reasons resulting in output rectifier diodes voltage spikes and shocks during the realization of ZVS PWM soft-switching is analyzed and common methods used to eliminate the output rectifier diode voltage spikes and voltage shocks are described. Hence, power supply module main circuit topology is designed based on the ZVS PWM soft switching with clamping diodes. Then the specific working principle of the power module is introduced and power electronics simulation software of Saber is used to build model and simulation verification. In parallel current sharing control, after analying the reason of poor current sharing in parallel switching power system, automatic master-slave setting current sharing method is designed based on digital current sharing principle and CAN bus technonlogy.Then, the hardware and software system of the parallel switching power supply system are designed. In hardware design, parameters caculation and selection about each key components of the power module main circuit topology is detailed description. A suitable drive circuit is designed in accordance with the power module drive requirements. Sampling circuit, protection circuit and auxiliary power circuit is designed with the TMS320F2812 DSP at the core. Meanwhile, CAN communication interface circuit with ECAN controller, high-speed optocoupler ACSL-6210 and transceiver SN65HVD230 is designed. Software system consists of main program, CAN communication program, Bang Bang-PID algorithm program, sampling program, phase shifting program and so on. Main program is responsible for the entire system function; CAN communication program is used to implement automatic master-slave setting and current sharing control; and Bang Bang-PID algorithm is used to realize the system’s rapid response and precise control. In additional, hardware anti-jamming measures of opto-isolated, power isolation, CAN bus and PCB optimization design and software anti-jamming measures of instruction redundancy and software traps are designed to alleviate large EMI of the parallel switching power supply system.Finally, A parallel system consisted of two switching power supply module prototypes is designed. Single power supply module and parallel system were carried out experimental respectively, the results show that the parallel switching power supply system meets the design requirements. A smooth waveform and soft switching effect of power module output is achieved under constant pressure and constant current mode. Output rectifier diodes voltage spikes and shocks are also suppressed effectively. automatic master-slave setting of parallel systems and current-sharping control are achieved. Current sharing imbalance is less than 3%, indicating a good current sharing.