Stable and highly efficient operation of open-loop controlled PM synchronous motor drive

This paper investigates stability of a drive system incorporating a high-field PM synchronous motor with the aim of identifying a real-time stability index by means of an algorithm based on the Lyapunov method. Results from computer simulation show that the first principal minor (MINR₁) of the Lyapunov function has a distinct sign change in the region of interest. Such an important finding makes it possible to use MINR₁ as a real-time stability index. A computer controller based on the computed stability index is therefore suggested to drive the system at power factors closer to unity (i.e., maximum efficiency), except if the constraints specified by MINR₁ dictate otherwise.