MULTICARRIER TRAPEZOIDAL PWM STRATEGIES BASED ON CONTROL FREEDOM DEGREE FOR MSMI

This work proposes an additional clew for the carrier based PWM methods on control of multilevel inverters which is based on the combination of the Control Freedom Degree (CFD) and novel carrier/reference signals for multilevel cascaded inverter. The significance of the proposed CFD clew on multilevel PWM techniques are verified and well demonstrated by simulation for chosen five level inverter. This paper presents a novel approach for controlling the harmonics of output voltage of chosen Cascaded MultiLevel Inverter (CMLI) employing trapezoidal PWM switching strategies. Sub Harmonic PWM (SHPWM), Phase Shift PWM (PSPWM), Variable Frequency PWM (VFPWM) and Carrier Overlapping PWM (COPWM) techniques employed are evaluated for various modulation indices using spectrum of the output voltage and other performance measures such as crest factor, form factor etc and the use of inverter state redundancies to perform additional application specific control tasks. This paper focusses on MultiCarrier Trapezoidal PWM (MCTPWM) techniques with Phase Disposition (PD), Phase Shift (PS), Variable Frequency (VF) and Carrier Overlapping (CO) of carrier for the chosen CMLI. Simulations are performed using MATLAB/SIMULINK. It is observed that PD and CO methods provide output with relatively low distortion. It is also observed that CO is found to perform better since it provides relatively higher fundamental RMS output voltage and relatively lower stress on the devices.