Simulation and analysis of common mode voltage, bearing voltage and bearing current in two-level and three-level PWM inverter fed induction motor drive with long cable

A Pulse Width Modulation (PWM) Voltage Source Inverter (VSI) fed induction motor drive has superior dynamic characteristics than sine wave driven induction motor. But it has a problem with induced bearing voltage and high frequency bearing current that flows through bearings due to parasitic capacitive coupling that results in premature bearing failure. In many industrial applications the PWM inverters and motors must be at separate locations thus requiring long motor cable, which contributes over voltage and higher common mode voltage at the motor terminal due to voltage reflection phenomenon. Higher common mode voltage results in higher induced shaft voltage and bearing currents. This paper presents simulation and analysis of influence of motor cable length on the magnitude of common mode voltage, bearing voltage and bearing current in two level and three level diode clamped multilevel inverter fed induction motor drive. The dv/dt of common mode voltage and bearing voltage also presented. Simulation is carried out using MATLAB/simulink.