Fotovoltaico

Journal of Electrical Engineering & Technology Vol. 5, No. 4, pp. 545~551, 2010 545
DOI: 10.5370/JEET.2010.5.4.545

Harmonic Elimination and Optimization of Stepped Voltage of
Multilevel Inverter by Bacterial Foraging Algorithm
Reza-Salehi*, Behrooz-Vahidi†, Naeem-Farokhnia* and Mehrdad-Abedi*
Abstract – A new family of DC to AC converters, referred to as multilevel inverter, has receivedmuch attention from industries and researchers for its high power and voltage applications. One of the
conventional techniques for implementing the switching algorithm in these inverters is optimized harmonic stepped waveform (OHSW). However, the major problem in using this technique is eliminating
low order harmonics by solving the nonlinear and complex equations. In this paper, a new approachcalled the "bacterial foraging algorithm" (BFA) is employed. This algorithm eliminates and optimizes
the harmonics in a multilevel inverter. This method has higher speed, precision, and convergence
power compared with the genetic algorithm (GA), a famous evolutionary algorithm. The proposed
technique can be expanded in any number of levels. The purpose of optimization is to remove some
loworder harmonics, as well as to ensure the fundamental harmonic retained at the desired value. As a
case study, a 13-level inverter is chosen. The comparison results by MATLAB software between the
two optimization methods (BFA and GA) have shown the effectiveness and superiority of BFA over
GA where convergence is desired to achieve global optimum.
Keywords: Multilevel Inverter, HarmonicElimination, Bacterial Foraging Algorithm, Genetic Algorithm

1. Introduction
Increasing growth in consumption and variety of loads
has been observed over time and with the expansion in the
electrical industry. In recent years, applications of high
voltage and high power equipment have grown, such that
the power levels of equipment have reached the megawatt
range. Today, creating a directconnection of single semiconductor switch to a system with medium voltage grids
(2.3, 3.2, 4.16, and 6.9 kV) is difficult to achieve [1]. This
gap has to be resolved because of the significance of some
loads and their sensitivity to voltage sag and swell, harmonic disturbances, and failing and de-rating of other loads
resulting from existing disturbances, such as voltage and
current. Inverters, suchas DC to AC converters, are notable sources of disturbance.
Inverters are widely used in many applications, such as
flexible AC transmission system (FACTS) equipment [2],
high voltage direct current (HVDC) lines [3], and electrical
drives [4]. Different methods have been suggested for improving the quality and performance of inverters. The first
approach is by using various switchingstrategies, such as
sinusoidal or “subharmonic” natural pulse width modulation (SPWM), selective harmonic-eliminated pulse width
modulation (SHE PWM), space-vector modulation (SVM),
optimized harmonic-stepped waveform (OHSW) [5-6], and
optimal minimization of THD (OMTHD) [7]. The second
†

Corresponding Author: Dept. of Electrical Engineering, Amikabir
University of Technology, Tehran, Iran(vahidi@aut.ac.ir)
* Dept. of Electrical Engineering, Amikabir University of Technology,
Tehran, Iran (hreza_salehi@aut.ac.ir, farokhnia@aut.ac.ir,
abedi@aut.ac.ir )
Received: April 14, 2010; Accepted: July 23, 2010

approach is by using low pass filters in the output of inverters to remove high order harmonics. Finally, the third
approach is by applying multilevel structures in order to
reduceharmonics and THD, as well as to omit filters in
high power applications. Conventional structures of multilevel inverters deal with diode-clamped [8], flying capacitor [9], and cascaded multilevel inverters with separate DC
sources (SDCS) [10]. The OHSW technique has been used
in multilevel inverters, as evidenced in literature. In this
method, the goal is to conduct potential elimination of...