Analysis and compensation of beat phenomenon for railway traction drive system fed with fluctuating DC-link voltage

The configuration of a single-phase AC-DC converter plus a three-phase DC-AC inverter traction system has been widely applied in high-speed railway electrical drive systems. The DC-link voltage contains a ripple component with a twice power line frequency because of the configuration of the single-phase converter. Fed by such a fluctuating DC-link voltage, a severe beat phenomenon of the motor current occurs, which causes torque ripple and a howling noise of the motor, especially when the electric frequency of the motor is in the neighborhood of the DC- link ripple frequency. The origin of DC-link voltage fluctuation and beat phenomena effect are analyzed in detail. For reducing the beat effect of DC-link voltage fluctuation without using an additional resonant filter at DC-link in the traction drive system, a beat-less control scheme based on the frequency modulation and vector control is discussed in detail. Simulation and hardware-in-the-loop (HIL) experimental results confirm the effectiveness and validity of the adopted scheme.