Impact Analysis of Digital Delay on Power Factor and Compensation Strategy for Electric Traction PWM Rectifier

Due to fast dynamic response and simple implementation, the transient direct current control (TDCC) strategy is widely used for electric traction rectifiers in high-speed train drive applications. However, the inevitable digital delay may increase the steady-state error of the TDCC and consequently degrade the ac-side power factor (PF). To address this, a comprehensive effects analysis of digital delay on traction rectifier is first performed, in which the relationship between the digital delay and PF is revealed and quantified. Furthermore, a phase shift compensation scheme is proposed to improve the PF. In this scheme, the modulation signal is compensated by shifting a specified angle, where the calculation of phase shift angle only needs a few control parameters. Extensive experimental tests are carried out to verify the effectiveness of the proposed compensation method.