Design and analysis of single phase voltage source inverter using Unipolar and Bipolar pulse width modulation techniques

摘要

This research work is organized in two sections. Performance comparison of single phase half bridge inverter and single phase full bridge inverter is done in the first section. It is observed the output current and output voltage of full bridge inverter is twice and generates less total harmonic distortion as compared to half bridge inverter. In the second section, performance comparison of Unipolar and Bipolar PWM is presented for single phase full bridge inverter with and without filter in MATLAB SIMULINK. The proper choice of Frequency Modulation Ratio (mf) is discussed in detail for bipolar and unipolar PWM scheme. Non integer value of mf results in sub-harmonics which are nearly unfilterable and cause significant losses in any power system application. It is observed that Unipolar PWM has an advantage in terms of efficiency; it offers less switching losses and generates less EMI. Also, the switching frequency becomes twice and voltage amplitude is reduced to half in case of unipolar PWM. Therefore, total harmonic distortion (THD) content of output current and output voltage is decreased, thus improving the power quality and making filter easier.