# Increasing the Range of Modulation Indices with the Polarities of Cells and Switching Constraint Reliefs for the Selective Harmonic Elimination Pulse Width Modulation Technique

• Najjar, Mohammad (School of Electrical and Computer Engineering, College of Engineering, University of Tehran) ;
• Iman-Eini, Hossein (School of Electrical and Computer Engineering, College of Engineering, University of Tehran) ;
• Moeini, Amirhossein (School of Electrical and Computer Engineering, University of Florida)
• Accepted : 2017.04.08
• Published : 2017.07.20

#### Abstract

In this paper an improved low frequency selective harmonic elimination-PWM (SHE-PWM) technique for Cascaded H-bridge (CHB) converters is proposed. The proposed method is able to eliminate low order harmonics from the output voltage of the converter for a wide range of modulation indices. To solve SHE-PWM equations, especially for low modulation indices, a modified method is used which employs either the positive or negative voltage polarities of H-bridge cells to increase the freedom degrees of each cell. Freedom degrees of the switching angles are also used to increase the range of available solutions for non-linear SHE equations. The proposed SHE methods can successfully eliminate up to $25^{th}$ harmonic from a 7-level output voltage by using just nine switching transitions or a 150 Hz switching frequency. To confirm the validity of the proposed method, simulation and experimental results have been presented.

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