Analysis of voltage waveform at the stator terminal of PWM inverter fed motors

Because of the surges with short rise time in pulse-width modulated inverter fed motor, premature failure of motor insulation tends to occur. Over-voltage transients occurring at the pulse-width modulated inverter fed motor terminals are one of the major factors leading to motor insulation premature failure. The paper is focused on voltage characteristic at the terminal of pulse-width modulated inverter fed motor. Several lumped segments incorporating a lossy representation of the line are used to model the feeder cable. Its characteristic impedance represents the motor. The feeder cable-motor model is developed in a simulation tool Matlab. Simulation results obtain the voltage waveform characteristic at the terminal of motor; the influence of the length of feeder cable and the rise time of inverter output on the over-voltage is discussed. Some measures have been proposed to mitigate the over-voltage.