Transient-free method of indirect current control for railway traction four-quadrant converters

In the application of megawatt(MW) rated railway traction drives, as switching frequency is only several hundred hertz, the bandwidth of current loop is usually limited. Instead of instantaneous current feedback control, indirect current control (ICC) is widely used in the front-end four-quadrant converters. Suffering from the low-speed dynamic response and cross-coupling between active and reactive power, conventional indirect current control is not an ideal solution for power conversion. To realize the independent control of active and reactive power, an orthogonal phasor frame is introduced. Furthermore, in order to improve the dynamic performance of conventional ICC, a novel ac current transient-free method is proposed after detailed analyzing of the ac current responding characteristic. Simulation and experiment results proved this method to be effective.