An active cancellation method for the common mode current of the three-phase PWM motor drives

Abstract

High carrier-frequency Pulse Width Modulation (PWM) is a popular and widely used method for driving the induction motors in Electric Vehicles (EVs) using voltage source inverters. However, it often generates high-frequency Common Mode (CM) voltages, resulting in shaft voltages. This, in turn, leads to a flow of leakage current to the earth, known as CM current, which can cause serious problems, including premature failure of the ball bearings in the motor. This paper introduces an Active Cancellation Circuit (ACC) method aimed at extensively reducing the CM current and, consequently, the CM voltage in three-phase induction motor drives. In this technique, Y-configured capacitors are employed for detecting CM voltage. After amplification, this voltage is applied to the motor frame to eliminate both the CM current and the CM voltage. Unlike conventional voltage compensating techniques, the proposed approach eliminates the need for a CM transformer between the inverter and the motor. As a result, there is no need for a high-power-rated CM transformer or any of its associated losses. To assess the effectiveness of the proposed method, experiments were conducted using an induction motor (3-phase, 1.1 kW, 415 V/60 Hz) connected to a two-level three-phase voltage source inverter.