Investigation on Total Harmonics Distortion for Transistor Clamped Cascaded H-Bridge Multilevel Inverter Using Newton-Raphson Method

The multilevel inverter is significantly important in power conversion to link the direct current (DC) renewable power supply with the general alternating current (AC) power system. Research is continuously progressing in the development and improvement of the multilevel inverter structure and output power quality. This paper centers on the design and development of the transistor clamped cascaded H-bridge multilevel inverter (TC-CHB-MLI) topology controlled by the open loop Newton-Raphson (N-R) method for single phase five and nine levels output waveforms. Evaluation on the total harmonics distortion (THD) performance of the output voltage and current based on the proposed N-R method is carried out through both simulation modelling and experimental hardware. Results show that 41.77% and 52.76% THD reduction is achieved for the output voltage and current respectively between the 5-levels and 9-levels TC-CHB-MLI. This proved the effectiveness of the N-R method in optimizing the switching angles for the selected harmonic elimination (SHE-PWM) technique used, thus easing the filter design for producing a smooth sinusoidal output waveform.