Reduced Switching-Frequency Active Harmonic Elimination for Multilevel Converters

Abstract

Abstract-This paper presents a reduced switching-frequency active-harmonic-elimination method (RAHEM) to eliminate any number of specific order harmonics of multilevel converters. First, resultant theory is applied to transcendental equations to eliminate low-order harmonics and to determine switching angles for a fundamental frequency-switching scheme. Next, based on the number of harmonics to be eliminated, Newton climbing method is applied to transcendental equations to eliminate high-order harmonics and to determine switching angles for the fundamental frequency-switching scheme. Third, the magnitudes and phases of the residual lower order harmonics are computed, generated, and subtracted from the original voltage waveform to eliminate these low-order harmonics. Compared to the active-harmonic-elimination method (AHEM), which generates square waves to cancel high-order harmonics, RAHEM has lower switching frequency. The simulation results show that the method can effectively eliminate all the specific harmonics, and a low total harmonic distortion (THD) near sine wave is produced. An experimental 11-level H-bridge multilevel converter with a field-programmable gate-array controller is employed to experimentally validate the method. The experimental results show that RAHEM does effectively eliminate any number of specific harmonics, and the output voltage waveform has low switching frequency and low THD.Index Terms-Field-programmable gate-array (FPGA) controller, multilevel converter, reduced switching-frequency active harmonic elimination.

Selective harmonic mitigation technique for multilevel cascaded H-bridge converters

“…The SHEPWM can also be applied to this kind of converters [14]. Again, solving the equations, the fundamental harmonic can be set to the desired value and k − 1 harmonics can be reduced to zero.…”

Implementation of a closed loop SHMPWM technique for three level converters

“…In that case, equations (1) change to (2) where q belongs to the set: (5,7,11,13,17,19 The SHMPWM technique, instead of making zero some specific harmonics as in SHEPWM, keeps them below a safe level to meet the grid codes. As a consequence, it is possible to fulfill the grid codes with a lower switching frequency.…”

“…The experimental results are compared with those obtained using the same test bench with the well known Selective Harmonic Elimination technique SHEPWM and, as it will be shown, the SHMPWM technique produces a higher performance than SHEPWM. Many papers present works where the SHEPWM technique has been used in multilevel converters [10] [11]. The SHMPWM technique was previously introduced in [8] and is able to meet several grid codes with a low switching frequency.…”

Improved SHEPWM Strategy By The Robustness Optimization Algorithm In Multilevel Inverters With Equal DC Sources

“…Thus, N trigonometric equations specifying the harmonic content must be solved to find the answers for the switching angles. There have been many approaches to this problem reported in the technical literature including: sequential homotopy-based computation [20], resultants theory [21], optimization technique [22], Walsh functions [23] and Genetic Algorithms (GA) [24,25].…”