Feedback Path Delay Effect on Stability of Controlled PMSMs

Growing complexity of the computational algorithms in control systems invites prolonged calculation periods when executed in real-time. Feedback measurement signal path is a crucial signal path in closed-loop controlled systems, especially when requiring high bandwidth control. With high processing time, sampling of current signal tends to be delayed by multiple Pulse Width Modulation (PWM) periods depending on the interrupt priorities. This paper studies the effect of current feedback sampling delay effect on the overall stability of field oriented controlled (FOC) Permanent Magnet Synchronous Motor (PMSM) drive system. The delay effect study is done by first analyzing theoretical equation of system transfer function with the feedback sampling delay incorporated, followed by simulation results and finally by performing experiments on actual hardware. The impact of increasing sampling delay on the current feedback signal is presented with other controller design parameters.