Influence of Asymmetric Sampling Delay on PMSM FOC Drives with Varying Rotor Position

This paper investigates the behavior of permanent magnet synchronous machines paired with field-oriented control under the effects of asymmetric delay in per-phase current measurement and position measurement delay effect. A mathematical model for field-oriented control with asymmetric 3-phase feedback delay was developed and used to obtain theoretical current step responses in the quadrature and direct axes, as well as obtain root locus results of the dynamic system. Step responses were also obtained in a simulated model using Simulink, and through experiments, while injecting varying levels of per-phase feedback delay. Increasing levels of asymmetric delay and increasing controller bandwidth, increased the systems’ sensitivity to instability. Delay in phase A and phase B were found to primarily affect responses in the q-axis and d-axis respectively. Unequal amounts of delay (asymmetric delay) on phase A and Phase B create substantial instability when compared with equal delay (symmetric delay). Asymmetric delay in current measurement also resulted in varying amplitudes in current response at varying rotor positions.