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Modeling and Simulation Analysis of Bearing Current in Two-Level and Multilevel Inverter Fed Induction Motor Drive

Sharana Reddy, Dr. Basavaraja.B

Adjustable Speed Drives (ASDs) are increasingly used in many commercial and industrial applications because of many advantages in control and efficiency. But ASDs use PWM inverter with high speed switching devices such as Insulated Gate Bipolar Transistors ( IGBTs) having rise time of 0.1μSec.,that generate fast switching transients (high dv/dt) about 6000V/μSec for 400V system and common mode voltage. This common mode voltage causes unwanted shaft voltage and resulting bearing currents. Parasitic capacitive couplings create a path to discharge current in the rotor and bearings results in premature bearing failure. There are mainly two types of bearing currents such as Electric Discharge Machining (EDM) bearing current and high frequency circulating bearing current. Various mitigation techniques for bearing current have been proposed in the literature each technique has certain limitations. Advanced mitigation techniques include dual bridge inverter and multilevel inverters. This paper presents modeling, simulation and analysis of bearing current using Sinusoidal Pulse Width Modulation (SPWM) diode clamped multilevel inverter fed induction motor drive. Simulation is carried out using MATLAB / Simulink software for three phase, 3 H.P (2.2kW) induction motor and inverter switching frequency of 2 kHz.