Performance improvement of multilevel inverter through trapezoidal triangular carrier based PWM

In this paper a new SPWM technique using a trapezoidal triangular multicarrier for a 17 level cascaded H bridge multilevel inverter is simulated and compared with other types of carrier based PWM technique for performance evaluation. Different triangular carrier modulation techniques such as constant switching frequency level shift (LS) PWM technique viz, phase disposition (PD), phase opposition disposition (POD), alternative phase disposition (APOD), phase shift carrier (PSC) PWM, and variable switching frequency (VSF PWM) are compared with proposed technique for symmetric and asymmetric structure of cascaded H bridge MLI. Simulation for 17 level CHB inverter has been carried out in MATLAB/Simulink and simulation results for voltage waveform and harmonic spectrum are presented and compared. The variation of THD with modulation index for output voltages are analyzed.