Analysis of Total Harmonic Distortion in 5-level Inverter fed Induction Motor

The squirrel cage induction motor is widely used in medium and high voltage variable frequency drive applications, it is known as a constant speed motor. The motor speed can be varied with certain conditions using digital control techniques, by maintaining voltage to frequency ratio constant. The author reports that some harmonic frequencies present at the neutral point of the load, results in a voltage that exists at the neutral point with reference to common point of supply. The inverter output is not sinusoidal but it is a stepped square wave output waveform. A basic two level inverter used to run the motor. As the number of levels increases the harmonic distortion is minimized. In order to reduce the voltage total harmonic distortion a multilevel inverter concept is used with space vector modulation. Due to the some frequencies component present in inverter output produces high temperature results in heat, which fails the insulation of windings and the mechanical output is lowered. The authors discuss the experimental measurement of harmonic components in inverter fed squirrel cage IM uses microcontroller. The test setup is fabricated, designed, tested and measures the phase voltages and currents using 500MHz Digital storage oscilloscope. The FFT analysis is carried out using MATLAB for simulation and used Origin software for test results. The test results of five level inverter compared with two level, three level inverter from published results of same authors and are tabulated.