Analysis and Design of Spatial Six-Step Controllers for Permanent Magnet Synchronous Machines

A spatial control methodology is developed for six-step control based on deadbeat flux control. The methodology includes a spatial z-transform that allows a speed-invariant analysis of command tracking and disturbance rejection properties of six-step operation. Several design options for high-performance six-step controllers are examined, and fundamental trade-offs of six-step controllers such as speed-dependent bandwidths, limitations related to the Nyquist frequency, and critical frequencies for disturbance rejection are investigated. A key result of the analysis is that a fast deadbeat controller can result in lower dynamic stiffness than a low bandwidth or even a quasi-open-loop controller near the fundamental frequency. One way to provide excellent disturbance rejection at these frequencies is to know the disturbances in advance. This can only be achieved for a particular class of disturbances, i.e., repetitive disturbances. Therefore, a spatial repetitive controller is utilized, which can be easily included in the proposed framework.