Electromagnetic interference mitigation for quasi-square wave mode PWM inverter fed AC drives

Abstract

In industry, Squirrel-cage induction motor is widely used when compared to the DC motor. Squirrel-cage induction motor has less maintenance required, and higher efficiency. Because of these advantages, induction motors are more widely used in applications requiring constant speed. By conventional methods of speed control of an induction motor wide range of speed control and also precise control of speed could not be achieved. Insulated Gate Bipolar Transistor (IGBTs) based Pulse-Width Modulated (PWM) inverter is used to get precise speed control over a wide range of speed. Electromagnetic Interference (EMI) noise is generated from IGBTs based PWM inverter switches during ON-OFF, and high rate of change of voltage (dv/dt) transient occurs. This high transient interrupts with the EMI noise current, and EMI noise is generated. Generated EMI noise is transmitted in two forms viz. 1) Radiated noise and 2) Conducted noise. Radiated noise is mitigated by metal cabinet. Conducted noise is mitigated by EMI filter. Conducted noise is classified into two types viz. 1) Differential mode (DM) noise and 2) Common mode (CM) noise. DM noise is measured between phase to phase, and hence EMI noise is circulated. CM noise is measured between phase to ground, which mitigates EMI noise. In speed control of IGBTs based PWM inverter-fed squirrel-cage induction motor, conducted EMI noise is an important problem. Due to this problem, IGBTs based inverter is affected which in turn causes loss in squirrel-cage induction motor, leading to low efficiency of the motor. In the conventional system, EMI noise generation and emission concentrated only in the load side and is compensated by using conventional filter. Time-domain and frequency-domain analysis of conducted EMI mitigation by using conventional (passive and active) filters do not give appropriate output. Active common mode noise canceller configuration techniques are used to suppress the EMI noise in a conventional system.