Oscillation, instability and control of stepper motors

A novel approach to analyzing instability in permanent-magnet stepper motor s is presented. It is shown that there are two kinds of unstable phenomena in this kind of motor: mid-frequency oscillation and high-frequency instabi lity. Nonlinear bifurcation theory is used to illustrate the relationship b etween local instability and mid-frequency oscillatory motion. A novel anal ysis is presented to analyze the loss of synchronism phenomenon, which is i dentified as high-frequency instability. The concepts of separatrices and a ttractors in phase-space are used to derive a quantity to evaluate the high -frequency instability. By using this quantity one can easily estimate the stability for high supply frequencies. Furthermore, a stabilization method is presented. A generalized approach to analyze the stabilization problem b ased on feedback theory is given. It is shown that the mid-frequency stabil ity and the high-frequency stability can be improved by state feedback.