Comparative study between different optimisation techniques for finding precise switching angle for SHE‐PWM of three‐phase seven‐level cascaded H‐bridge inverter

Abstract

Selective harmonic elimination pulse-width modulation (SHE-PWM) works at low-frequency switching, which reduces switching losses, device stress, and increases energy conversion efficiency. So, it can be an effective control strategy for multilevel inverter working on medium-voltage, high-power industrial energy conversion application. It provides desired output voltage by retaining the requested fundamental component as well as eliminating some low-order harmonics. The application of SHE-PWM in industries is having an influence on precise solvability of complex and non-linear equations. This study presents two recently reported optimisation techniques, namely backtracking search algorithm and differential search algorithm (DSA) for obtaining a more accurate solution of the harmonics elimination problem. The superiority of the proposed optimisation algorithms over the well known ancient algorithm such as genetic algorithm, BEE algorithm and particle swarm optimisation have been established by a comparative study with respect to the possibility of attaining global minima, the rank of convergence rate, and inverter performance analysis. Simulation and experimental results validate the efficacy of the DSA optimisation technique for calculating more precise switching angles that totally eliminate 5th-and 7th-order harmonics with fulfilling the requested fundamental component.

An improved SHM‐PWM scheme for three‐phase seven‐level CHB inverter to improve power quality by fulfilling CIGRE WG 36‐05 and EN 50160 and sharing equal power between the H‐bridge cells

“…For SHE‐PWM scheme, magnitude of each DC voltage sources of the output phase voltage (shown in Figure B) must be constant and equal (ie, V 1 = V 2 = V 3 = V DC ). The Fourier series expansion of the waveform can be formulated as follows: where “ n ” denotes harmonic order, “ ω ” signifies the fundamental switching frequency in radian, and the Fourier coefficients are A o , A n , and B n .…”

“…Moreover, the effectiveness of the proposed scheme over conventional SHE‐PWM scheme (presented in Kundu et al) and SHM‐PWM scheme (presented in Ghoreishy et al) has been established by simulation and experimentation. Furthermore, a comparison has been carried out to prove the supremacy of the proposed modulation schemes over the previously proposed modulation schemes, in terms of the switching instances requirement for the fulfillment of two grid codes CIGRE WG 36‐05 and EN 50160 for the three‐phase system.…”

“…In literature, several modulation schemes have been proposed for controlling the output voltage waveform quality of multilevel inverters. These can be listed as sinusoidal pulse width modulation (SPWM), space vector modulation, selective harmonic elimination (SHE)‐pulse width modulation (PWM), optimal minimization of THD (OMTHD), optimal PWM (OPWM), and selective harmonic mitigation‐(SHM) PWM . Out of these PWM schemes, SHE‐PWM scheme works on the low‐switching frequency, and it is used to completely eliminate (E‐1) number of specific low‐order harmonics of the output voltage using “E” number of switching instances in each quarter cycle of the output waveform.…”

“…Out of these PWM schemes, SHE‐PWM scheme works on the low‐switching frequency, and it is used to completely eliminate (E‐1) number of specific low‐order harmonics of the output voltage using “E” number of switching instances in each quarter cycle of the output waveform. The major drawback of this scheme is that it only eliminates a limited number of low‐order harmonics while other harmonics (which are not incorporated into the problem) are totally uncontrolled and can attain high magnitudes . Hence, for a specific number of output voltage levels, this scheme requires more number of switching instances to fulfill some power quality standards and to remove more number of low‐order harmonics.…”

“…But it requires more number of switching instances in a quarter period to fulfill some specific power quality standards. Besides that, uneven power distribution between the H‐bridge cells of CHB inverter can occur in the aforesaid SHE‐PWM and SHM‐PWM schemes . This will affect the rating and size of both semiconductor devices and input side isolation transformers.…”