A Failure Mode for PWM Inverter-Fed AC Motors Due to the Anti-Resonance Phenomenon

A failure mode for PWM inverter-fed AC motors due to the anti-resonance phenomenon is introduced and investigated in this paper. At high frequencies, an AC motor behaves as a series RLC circuit with a resonance point, so-called anti- resonance, typically above 1.0 MHz. If the voltage oscillation frequency, caused by the reflected wave phenomenon matches the motor anti-resonance frequency, an amplified voltage will appear internally between the turns of the stator windings. This externally unobservable state causes winding insulation failure in the AC motor. This phenomenon is experimentally verified using a rewound Permanent Magnet (PM) motor with accessible taps along the stator windings, and the results are presented in this paper.