An improved topology of reduced switch seven level inverter using filters for THD reduction

This paper introduces a unique seven level five switch Inverter with different type of filters to reduce total harmonic distortion (THD) and suitable for renewable energy applications. In conventional inverters output voltage and current waveforms are very far from the sinusoidal shape due to high percentage of THD. This type of distorted output voltage is not suitable for industrial drives and renewable energy based loads. Therefore the THD of output voltage from inverter is limited by replacing it with multi level inverter (MLI). As the levels of output waveform increases, it approaches the sinusoidal waveform, and its % THD is limited. However the semiconductor switches and dc sources required increases with increased complexity as the levels of MLI increase with different topologies. In this work, seven level MLI with five switches, four dc sources and using PWM technique has been implemented. Here by using phase disposition PWM (PDPWM) technique THD is reduced to a very low value and the modulated wave is nearly sine wave. Also for further reduction of THD different types of filters are used. The system model is simulated in MATLAB/SIMULINK toolbox to analyze the output waveforms.