A Novel Sensitivity Analysis to Moment of Inertia and Load Variations for PMSM Drives

A high-performance electrical drive with a permanent magnet synchronous motor (PMSM) should ensure superior dynamic properties, reasonable load torque compensation, and robustness against parameter variations. The performance investigation related to the dynamic properties is usually made using the step response indicators and integral performance indexes. The robustness evaluation is more complex than performance analysis since there are no simple tools for this purpose, especially if it is done experimentally to consider nonlinearities and unmodeled dynamics of the plant. In this article, sensitivity functions suitable for investigating the closed-loop control systems in the time and the frequency domain are proposed, explained, and experimentally verified. Three control schemes designed for the speed control of PMSM are analyzed: a cascade control structure, robust two-degrees-of freedom speed controller, and a cascade-free constrained state feedback controller. Studies are conducted for experimental responses of the drive in the time and the frequency domain to investigate the sensitivity of the PMSM drive against the moment of inertia and load variations. Analysis of nonlinearities influence on the developed sensitivity functions is also presented.