An improved beatless control method of AC drives for railway traction converters

摘要

The traction converter consists of a single-phase AC-DC rectifier and a three-phase DC-AC inverter. Due to special structural characteristics of single phase rectifier, a fluctuating voltage component with the frequency twice of the grid's, exists in DC-link voltage. Fed by fluctuating DC-link voltage, a beat phenomenon occurs in traction motor, and harmonic components appear in both stator current and electromagnetic torque, especially when motor operates near the ripple frequency. In this paper, the mechanism and influence of fluctuating voltage are analyzed in detail. Based on modeling analysis of motor and switching function of inverter, a frequency compensation factor is derived in vector control of induction motor. Then an improved frequency compensation control method is proposed to suppress beat phenomenon without LC resonant circuit. Finally the modified scheme is verified by simulation and experiment.