Hybrid Carrier PWM Strategies for Three Phase H-bridge Multilevel Inverter

摘要

In this paper, hybrid modulation methods suitable for H-bridge MLI is discussed. The results of experimental work using dSPACE system only are presented for three phase five level cascaded type inverter. Different hybrid carrier PWM (Pulse Width Modulation) strategies using sinusoidal reference, third harmonic injection reference, 60 degree reference and stepped wave reference for the chosen inverter are initially developed using SIMULINK. Strategies developed are then implemented in real time using dSPACE/RTI. The five level output voltages of the chosen MLI (Multi Level Inverter) obtained using the dSPACE system based PWM strategies and the corresponding % THD (Total Harmonic Distortion) and V_(RMS) (fundamental) are presented and analyzed. It is seen that PS+VF (Phase shift+ Variable Frequency) and PS+PD (Phase Disposition) for sinusoidal reference. PS+VF and CO+PS for THI (Third Harmonic Injection) reference, PD+VF for 60 degree reference and APOD+PD and PD+VF for stepped wave provides output with relatively low distortion. It is found that CO+PD with sine reference, APOD+CO and CO+PS PWM with THI reference, CO+PD PWM with 60 degree reference and APOD+CO and CO+PD PWM with stepped wave reference perform better since it provides relatively higher fundamental RMS output voltage and relatively lower stress on the devices. The simulation and hardware results closely match with each other.