Sinusoidal Symmetrical & Asymmetrical Pwm Based Three Phase Inverter Design

Power Inverters have a high range of applications not only in domestic appliances but also in industries for performing variety of operations regarding switching and conversion of electrical energy. The purpose of this research paper is to analyze a three phase inverter using PWM topology to obtain a smooth and pure sinusoidal wave form of good quality which ensures better operation for sensitive electronic appliances. A pulse width modulated voltage wave form is generated using an efficient inverter design to minimize the Total Harmonic Distortion (THD). A three phase inverter was evaluated first for symmetric PWM modulation and then for asymmetric modulation. In symmetric PWM modulation the reference is sampled at positive peak of carrier signal and is held constant till next positive peak of carrier signal appears. In asymmetric modulation technique reference signal is sampled at positive as well as negative peak of the carrier signal and held constant between two sampled points. An analysis has been performed to evaluate the effectiveness of the two techniques using simulation models in Matlab/Simulink. The THD analysis as well as Fourier analysis of the designed symmetric and asymmetric inverter is performed using Simulink. The results for different cut-off frequencies have been shown. With optimal modulation index value and number of levels for lower harmonics, it is shown that sinusoidal PWM based inverters not only provide good quality voltage but also reduces voltage stresses on the switches. Furthermore THD is effectively decreased by optimizing cut off frequency of filters.