Analysis and Simulation of Two Different Topologies of Three Phase Cascaded Inverter Fed Induction Motor Drive

The main objective of this paper is to control the speed of an induction motor by using five level Cascaded H-Bridge multilevel inverter to obtain high quality sinusoidal output voltage with reducedharmonics.An open loop speed control can be achieved by changing switching frequency. Two topologies of cascaded multilevel inverter have been proposed. 1st topology requires separate DC sources and the 2nd topology requires only a single DC power source, capacitors. The inverters with a large number of stepscan generate high quality voltage waveforms. The higher levels can follow a voltage reference with accuracy and with the advantage that the generated voltage can be modulated in amplitude instead of pulse-width modulation. The simulation results shows that the proposed topologies effectively controls the motor speed through reduction in total harmonic distortion(THD).The simulation of three phase five level inverter fed induction motor model is done using Matlab/Simulink. The performance of MLI is also compared with conventional inverter in terms of THD. The FFT spectrums for the outputs are analyzed to study the reduction in the harmonics.