Steady-state stability criterion for induction motors

Abstract

The instability of induction motors has been widely observed when operating on variable-frequency supplies, particularly on light loads at low speeds. This phenomenon is analysed for steady-state conditions using the single-phase equivalent circuit of the motor and considering a stable system to have constant-power balance. The analysis confirms the low frequency, low-slip instability and predicts a high-slip limit of stable operation. These limits are both confirmed by measurements on a motor/inverter drive. The amplitude and frequency of oscillations are not investigated.