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

Abstract

Summary This paper presents an improved selective harmonic minimization (SHM)‐pulse width modulation (PWM) scheme using three‐phase seven‐level cascaded H‐bridge (CHB) inverter suitable for medium‐voltage distribution systems by achieving high‐quality voltage waveform with least number of switching instances (ie, each power semiconductor devices switched once in a quarter period). Here, each isolated DC voltage sources have been taken as variable and unequal for the CHB inverter. The efficacy of the proposed SHM‐PWM scheme over selective harmonic elimination (SHE)‐PWM scheme and existing SHM‐PWM scheme has been verified through a comparative inverter performance analysis with equal number of switching instances. Both simulation and experimental results prove that the proposed SHM‐PWM scheme ensures equal percentage of power‐sharing between the H‐bridge cells, achieves desired fundamental voltage component, minimizes each individual odd nontriplen harmonics, and limits %total harmonic distortion (THD) up to 25th‐order harmonics such that, it satisfies the power quality standards CIGRE WG 36‐05 and EN 50160 for the entire modulation index range. It is also seen that the proposed scheme requires least no of switching (three) than other reported SHE‐/SHM‐PWM schemes to meet the aforesaid power quality standards. It also results lower inverter losses and improves efficiency compared with conventional schemes. Finally, the scheme is applied to a closed‐loop control of induction motor driven by back‐to‐back PWM‐controlled converter.

Meeting IEC and ER G4/5 harmonic standards in nine‐level cascaded H‐bridge inverters using an improved SHM‐PAM scheme

“…SHM‐PAM is a modified form of SHE‐PWM concept [33, 34]. In this case, the DC voltage amplitude of each level is taken as a variable within the equations, which can control a higher number of harmonics compared to constant voltage levels based SHE‐PWM scheme [13].…”

“…of switching. The work in [33, 34] presented an improved selective harmonic minimisation‐pulse amplitude modulation (SHM‐PAM) that fulfil CIGRE WG 36‐05, EN 50160 and NRS 048‐2 standards. Marzoughi et al [35] presented an optimal SHM‐PWM scheme for seven‐level CHB inverter with nine no.…”

A review on technological aspects of different PWM techniques and its comparison based on different performance parameters

“…Out of different PWM techniques, selective harmonic elimination PWM (SHE-PWM) has gained attention because of its simplicity, efficiency in eliminating lower order odd harmonics while keeping the designed fundamental intact [3][4][5] and its efficient use in low switching frequency medium voltage high power industrial application. 6 One of the main disadvantages of SHE PWM is that in order to eliminate "N" number of harmonic, it requires to solve "N + 1" no of non-linear transcendental trigonometric equation, 7 which becomes very intensive and interactive. 8 In initial days of research different numerical techniques like Newton-Raphson (NR) [9][10][11] and Gauss-Newton (GN) [12][13][14] were used, which requires a very precise guess of initial values.…”

Low switching frequency modulation for generalized three-phase multilevel inverters geared toward Grid Codes compliance

“…Low switching frequency modulations (LSFM) found their way in the field of MLI structures with the main objective of alleviating the switching losses incurred by the relative high number of power switches [6], [7]. Nowadays, there is only one well-established LSFM scheme geared toward grid-tied applications known as selective harmonic mitigation (SHM) which in turn is akin to the selective harmonic elimination (SHE) modulation technique [8]- [11]. However, SHE/SHM has some limitations that could be overcome by NLC [5], [12], especially those related to dynamic performance under real-time operation and computational effort required while using lookup tables or curve fitting polynomials or any initial guessing and iterative routines [13], [14].…”