International Research Journal of Applied and Basic Sciences © 2013 Available online at www.irjabs.com ISSN 2251-838X / Vol, 5 (10): 1329-1333 Science Explorer Publications Investigation of PWM using Inductor-Switch for each Leg of Inverter for Reduction of Total Harmonic Distortion Abdolreza Esmaeli 1 , Amir Moslemi Bidehendi 2 , Nabiollah Rezaei Charati 2 , Abdullah Ahmadi 3 1. Plasma Physics and Nuclear Fusion Research School, Nuclear Science and Technology Research Institute,Tehran, Iran. 2. Faculty of Electrical Engineering, MaziarUniversity, Nour, Iran 3. Department of Electronic, Technical and Vocational College,. Mahmoud Abad, Technical and Vocational University, Iran *Corresponding Author email: aesmaeli@aeoi.org.ir ABSTRACT: Many researchers have been done on PWM switching methods for finding better schemes to supply the loads, which have lower harmonics in outputs. In SPWM, semiconductor switches are directly connected to rectified voltage in output of rectifier. In this paper, the novel technique of using Inductor-Switch for each Leg of Inverter has been presented. In this technique an inductor is used between each semiconductor switch and rectified voltage of rectifier’s output. To validate the proposed technique, simulation studies have been carried out with SABER software. Results have been compared with conventional SPWM. The results confirm that this novel technique causes lower total harmonic distortion and lower acoustic noise. Therefore, this new technique can be used to decrease harmonics and total harmonic distortion in voltages and currents of output. Keywords: Pulse Width Modulation, SPWM, Harmonics, SABER, Total Harmonic Distortion INTRODUCTION Increasing attention has been paid to multilevel dc/ac inverters in recent years (Bowes, 1975; Carrasco et al., 2006). Various modulation methods have been developed for multilevel inverters. A very popular method in industrial applications is the classic carrier-based sinusoidal pulse width modulation (SPWM) that uses the phase shifting technique to reduce harmonics in the load voltage (Bowes,1975; Chiasson et al., 2004; Chiasson et al., 2005). In SPWM, the states of power semiconductor switches are determined by the comparison between reference signals and saw tooth signals. The determination of a switching instant can be easily carried out in real-time by an analog circuit, a microprocessor or a digital signal processor (DSP). The space vector PWM (Joachim, 1992; Lakshminarayanan et al., 2007) is also very popular in industries. The calculation to determine switching instants for the space vector PWM is more complicated than that for the SPWM, but it can still be handled by a microprocessor or a DSP. Another important modulation method for multilevel inverters is the optimal PWM, which includes step modulation (Liang and Nwankpa, 1999; Liu et al., 2005; Liu et al., 2006), multilevel selective harmonic elimination (Ozpineci et al., 2005), and optimal combination modulation (Rech and Pinheiro, 2007).With the same switching frequency, voltage quality generated by the optimal PWM is better than that by the popular SPWM or the space vector PWM. The general procedure for implementing optimal PWM is as follows: based on Fourier series analysis, equation sets whose variables are switching angles are built to meet a specific optimization aim, for example the minimization of total harmonic distortion (THD) of the voltage or the elimination of lower order harmonic components of the voltage. An equation set need to be solved with respect to a certain amplitude value of the fundamental voltage component. Generally, the equation sets are nonlinear and transcendental. Several methods, such as the Newton–Raphson iteration method with multiple variables (Liu et al., 2005), methods based on the theory of symmetric polynomials and resultants (Rech and Pinheiro, 2007), and methods based on genetic algorithms (Rodriguez, 2002; Rodriguez et al., 2004), have been proposed to solve nonlinear transcendental equation sets. Calculations based on all the methods above are very time-consuming. Therefore, they cannot be done by a microprocessor or a DSP in real time. They can only be done by a computer offline. Switching angles obtained offline have to be stored in a lookup table in a