The inverter-fed induction motor drives are in these days very widely applied to the variable-speed drive systems. In these variable-speed use of induction motors, however, an instability accompanied by speed fluctuations appears often in light-load and low-speed operations. This is caused not by the introduction of the inverter but by the induction motor itself.
This phenomenon is such that an equilibrium point becomes unstable as the operating condition is varied and that a stable limit cycle appears around the equilibrium point. So, from the bifurcation-theoretical standpoint, this is to be dealt with as the Hopf bifurcation. However, only a few investigations based on such a standpoint have been reported so far.
In this work the stability of an induction motor driven by a variable-amplitude and variable-frequency sinusoidal voltage source is investigated from the bifurcation-theoretical standpoint to clarify the essential character of the instability of concern. The entire bifurcation set is determined in the control space of the system. A motor model in which the magnetic saturation is considered is adopted and the effects of the saturation on the instability are discussed.
