In the railway traction system, the operation of a four-quadrant pulse rectifier introduces double-frequency ripple into the DC bus voltage. These ripple voltages interact with the fundamental frequency voltage of the inverter, leading to the occurrence of beat-frequency phenomena in the motor stator voltage and current. This beat-frequency phenomenon becomes particularly pronounced when the motor operating frequency is close to the double frequency. This paper provides a detailed explanation of the causes of the beat-frequency phenomenon and analyzes the rotational direction and frequency of the harmonic components in the motor stator current. To address the beat-frequency phenomenon, a rotating beat-frequency coordinate system is proposed, which extracts the harmonic currents responsible for the beat-frequency phenomenon. These harmonic currents are transformed into DC components in the beat-frequency coordinate system, and a compensating voltage to suppress the beat-frequency phenomenon is generated using a proportional-integral controller. A motor simulation model is constructed in MATLAB/Simulink, and simulations are performed under three different motor operating conditions for verification. The simulation results show that the proposed method effectively suppresses the beat-frequency phenomenon across a wide frequency range, particularly when the motor frequency is close to the double frequency.