SHE PWM technique for three phase three level voltage source inverter

With the need for clean energy, development of multilevel inverter technology plays an important role in medium voltage and high power applications. This development has gradually taken over the conventional two level inverters in various industrial applications. A variety of topologies have been developed with improved performance in terms of output voltage levels and harmonics. In this paper, a three level (Neutral point clamped) Inverter with SHE PWM technique is selected to eliminate specific lower order harmonics thereby improving the voltage THD of the output waveform. As the nature of the equation obtained from Fourier transform are nonlinear and transcendental, for any particular modulation index there may exist simple, multiple or even no solutions. A procedure has been proposed to realize the appropriate switching angles for SHE PWM technique. In this paper, Newton-Raphson method has been used to solve the transcendental equations for any number of levels of multilevel inverter with any random initial guess which produces all possible solutions. From these multiple solution sets, a generalized selective harmonics eliminated pulse width modulation technique is applied to three phase three level voltage source inverter to eliminate up to nineteenth order harmonics from the output voltage. Here 7 switching angles for 0.85 modulation index has been calculated by using Newton-Raphson algorithm & Matlab program and the calculated value is verified by P-spice software. The simulated results of three phases, three levels, VSI for phase to neutral voltage, line to line voltage, 1st Fourier transform and total harmonic distortion has been determined from output voltage of three phase three level inverter.