Modified selective harmonic elimination employed in four-leg NPC inverters

Abstract

Three-phase four-leg neutral point clamped (NPC) inverter is more suitable in dealing with all sort of the loads especially unbalanced/nonlinear due to harmonics issues. Most control strategies applied on four-leg NPC are classified as high switching frequency lead to high power losses and low efficiency. In this paper, selective harmonic elimination pulse width amplitude modulation (SHE-PWAM) technique has been implemented on a four-leg NPC inverter to reduce the switching frequency properly. In SHE-PWAM technique, the amplitude of input voltage is considered flexible in order to eliminate one more harmonic order without increasing switching frequency. The obtained switching angles of phase legs and amplitude of input voltage are used to eliminate the non-triplen harmonics (5 th ,…,23 th ) from the output voltage. On the other hand, switching angles calculated for the fourth leg are considered to eliminate the triplen harmonics (3 th ,…,21 th ) from phase voltage. The performance of proposed technique is verified by Matlab/SPS simulations.

Newton‐Raphson algorithm–based modified SHE for CHB multilevel inverter control considering capacitor voltage balancing and power factor variation

“…Results prove that using the proposed algorithm, harmonics fifth, seventh, and 11th are completely eliminated, and capacitor voltage is balanced for various values of current‐voltage angle phase φ , introduced by the variation of the load. Output voltage harmonic quality depends strongly on the selection of the switching angles, and eliminating as much as possible of lower order harmonics is the optimum approach . On the other hand, on the basis of the proposed algorithm, we have obtained a single‐phase CHB multilevel inverter optimized in number of components and in THD by replacing real DC source and getting an output voltage waveform presenting the 13th harmonic as the first significant harmonic.…”

“…Since V AO is quarter-wave symmetry, even triplen harmonics will be automatically eliminated when SHE technique is applied in the inverter control. N-R is applied as an optimization iterative algorithm to resolve the transcendental nonlinear equation system given [17][18][19][20][21] by Equation (3).…”

“…Output voltage harmonic quality depends strongly on the selection of the switching angles, and eliminating as much as possible of lower order harmonics is the optimum approach. 18,19,24 On the other hand, on the basis of the proposed algorithm, we have obtained a single-phase CHB multilevel inverter optimized in number of components and in THD by replacing real DC source and getting an output voltage waveform presenting the 13th harmonic as the first significant harmonic. The simulation results obtained above have proved the efficiency and the robustness of the control strategy based on N-R while leading to a balanced capacitor voltage, desired modified seven-level and an optimized THD by eliminating harmonics fifth, seventh, and 11th.…”

Hybrid SHM-SHE Pulse-Amplitude Modulation for High-Power Four-Leg Inverter

“…SHE is a mathematical control strategy that is based on output voltage waveform to compute switching angles in an offline way [13][14][15]. In recent years, SHE has been introduced for four-leg inverters [16][17][18][19]. According to the proposed SHE technique, equations for three phase legs are determined to eliminate nontriplen harmonics while fourth leg equations are defined to remove the remaining triplen harmonics of three phase legs in the phase voltage.…”

“…Therefore, obtained angles in the SHM-SHE are more optimized compared to the pure SHE in [16][17][18]. However, in SHM-SHE which is based on PWM technique, only the switching angles have been considered as degrees of freedom in the equations.…”