Research On Current Sharing Control Scheme For Parallel DC-Source

With the improvement of equipment information level,all kinds of instruments and equipment have a bigger demand for DC power supply. Due to the increasing number of electrical equipment and requirements of higher reliability, there needs a larger capacity and higher reliability of power supply. While, multiple modules in parallel is the main way to increase the DC power capacity. In order to improve the safety and reliability of the DC power supply system in parallel, the effective flow control measures must be taken to ensure system modules divide the load current approximately.In order to reduce the switching loss of the power switch tube and improve the efficiency of system, single module power supply use phase-shift full bridge converter with saturation inductance as the main circuit topology. The thesis analyses the principle of the phase-shift full bridge converter with the saturation inductance and how deputy duty ratio loss impact on the system, calculates the key parameters of converter and selects device. Cases of add and reduce load suddenly are taken into account when the thesis design the output filter capacitor.In order to reduce switch loss of system within the range of the full load, this thesis presents control method which is a combination of dual polarity control and phase shifting control.Dual polarity control is used when the load current is in shortage, while the phase shifting control is used in the opposite case to achieve soft switch.LC filter is a second-order underdamped system, which has large-gain at the resonant frequency and the existence of resonance peaks increases the difficulty of the design of the current regulator. In order to suppress the resonant peak of filter, this thesis uses active damping control method to increase the LC filter damping. This thesis established a small-signal model of the phase-shift full bridge converter with the saturation inductance and used frequency domain method to design control system voltage controller and current controller.Because the parallel system a step change in load current is likely to occur during operation, a modified voltage and current double closed-loop control strategy ,based on the double-loop voltage and current, was proposed to improve the dynamic response of the system and prevent sudden load diversification causing the output voltage dropped significantly, after the dynamic response of the system at the desired load step changes were analyzed.This thesis described the principles, advantages and disadvantages of current-sharing strategy used in the parallel system. And current sharing control strategy based on CAN bus communication was proposed.This thesis designed a parallel system with the core control chip, STM32F405RG, built two prototypes based on the theoretical analysis and simulation experiment, and conducted a single module power soft-switching experiment, sudden changing-load experiment, and parallel current sharing experiment. Experiment verified the rationality of the circuit parameters and the effectiveness of control algorithm.