Stability analysis in induction motor driven by V/f controlled general-purpose inverter

For an induction motor driven by a sinusoidal voltage source of adjustable amplitude and frequency such as a PWM (pulsewidth-modulated) inverter, the problem of sustained oscillation has often been observed in the light loaded state. The authors contribute to the solution of this problem from the point of view of a linearized model. An analytical solution is given for two problems: Under what conditions is the oscillation excited, and how is the oscillating range determined in the stator voltage versus frequency (V/f) plane? A physical explanation is also given for the analytical results. They are theoretically solved with the no-load state assumed. The factor restricting the upper limit of the stator frequency regarding the unstable range is found to be the existence of transient inductance. The above analysis shows that the proposed linearized model is sufficiently appropriate to use as an analytical explanation of the experiment results.>