Tuning Method of Resonant Current Controller With DC Elimination for PWM Rectifiers in Electric Multiple Units

Current control in electric multiple unit (EMU) pulsewidth-modulated (PWM) rectifiers is crucial for the system's stable operation and fast transient response. It should not only regulate the sinusoidal current under very low switching frequency but also eliminate dc current avoiding transformer core saturation. Therefore, proportional integral (PI) plus vector proportional integral with phase compensation (VPIc) controller is chosen for the current control in such single-phase rectifiers. However, the gains of PI and VPIc are coupled and determine the system performance together, invalidating the traditional gain tuning method. Therefore, a gain tuning method for PI + VPIc based on Nichols chart is proposed in this article, which decouples the two gains and simplifies the gain tuning into the tuning of gain margin and phase crossover frequency, while settling time and overshoot are considered for the optimal gain tuning. The designed system has good transient responses, stability, and robustness. The experimental results validate the theoretical analysis of the tuning method on a laboratory prototype and the effectiveness of the current control on the EMU PWM rectifiers.