Accurate Digital Delay Compensation of Synchronous Frame Current Regulator with Variable Switching Frequencies

High-power machines and high-speed machines often operate at low sampling-to-fundamental frequency (S2F) ratios. The inherent digital delay must be properly compensated at low S2F ratios. The technique of variable switching frequencies aims to distribute the PWM harmonics and to reduce the noise and vibration. The digital delay, if not compensated accurately, will introduce voltage error which leads to current ripple and torque ripple when the switching frequency varies. This paper proposes a method to compensate the digital delay considering the switching frequency variations and a methodology to design the current regulator with the compensation. Experimental results show that the current ripple and torque ripple are significantly reduced with the proposed compensation method. The harmonic loss is reduced and system efficiency is increased.