THD Minimization Applied Directly on the Line-to-Line Voltage of Multilevel Inverters

Abstract

In this paper, total harmonic distortion (THD) minimization of the output voltage of multilevel inverters is discussed. An efficient approach in reducing the harmonic contents of the inverter's output voltage is THD minimization. In multilevel inverters with a fundamental frequency switching strategy (each switch turning on and off once per output cycle), the switching angles can be selected so that the output THD is minimized (such as the so-called optimal-minimization-of-THD strategy). To obtain the optimum switching angles, an optimization algorithm is applied to the output-voltage THD. In three-phase multilevel inverters, the optimization algorithm is commonly applied to the phase voltage of the inverter. This results in the minimum THD in phase voltage but not necessarily in the line-to-line minimum THD, whereas in three-phase applications, the line-voltage harmonics are of the main concern from the load point of view. In this paper, using the genetic algorithm, a THD minimization process is directly applied to the line-to-line voltage of the inverter. This paper is based on a seven-level inverter. To verify the simulation results, a seven-levelcascaded-H-bridge-inverter-based hardware prototype, including an ATMEGA32 AVR microcontroller, has been implemented. Both simulation and experimental results indicate superiority of this approach over the commonly used phase-voltage THD minimization approach.Index Terms-Genetic algorithm (GA), line-voltage total harmonic distortion (THD), multilevel inverter, optimal minimization of THD (OMTHD), THD minimization.

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“…several methods, such as Newton-Raphson iteration method [3], methods based on symmetric polynomials and resultants [3], and methods based genetic algorithms [6], have been proposed to solve the nonlinear transcendental equation set as show in (4). In a cascade multilevel inverter with s HBs in the context of step modulation, if more than   1 s  harmonics are considered to minimize THD, these harmonics cannot be eliminated completely since the number of variables is more than the number of equations in the equation set.…”

Optimal Allocation of TCSC and DG Unit for Congestion Management in Deregulated Power Systems

“…To qualify the output voltage waveform of multilevel inverters, different modulation strategies have been proposed. Some of popular switching strategies are space vector modulation, minimization of the total harmonic distortion, pulse width modulation (PWM), selective harmonic elimination (SHE), and sinusoidal pulse width modulation (SPWM) [18][19][20][21][22][23]. Also in [24] a technique has been proposed based on optimal minimization of THD (OMTHD).…”