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.

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An improved selective harmonic elimination-pulse width modulation (SHE-PWM) scheme has been proposed for a three-phase seven-level cascaded H-bridge (CHB) inverter that enhances the power utilisation capability of the inverter by sharing the desired amount of power among the H-bridge cells and also eliminates both 5th-and 7th-order harmonic components from the inverter output voltage maintaining the desired fundamental voltage component for a wide range of modulation index. Compared to conventional SHE-PWM, this scheme introduces two additional switching in the first cell, while the second and the third cells are switched at advanced switching angles. The differential search algorithm (DSA) technique has been applied to solve the proposed SHE-PWM scheme, and it exhibited comparatively better performance than the algorithm based on genetic algorithm, BEE algorithm and particle swarm optimisation. The effectiveness of the proposed scheme has been verified by both simulation and experimental study on a seven-level CHB inverter. Finally, the proposed scheme has been applied to the closed-loop constant V/f control of the induction motor drive application. It has been established that the proposed scheme is independent of the load power factor angle, and it improved the power conversion efficiency of the conventional SHE-PWM scheme. * reference rotor speed, rpm N r actual rotor speed, rpm T e electromagnetic torque, N-m V ab output line voltage, V i a , i b , i c output phase currents, A IET Power Electron.

In a hot strip mill, the quality of the rolled products and the productivity of the mill depend on the efficiency of roll cooling to a great extent. To study the influence of the cooling system on roll performance, a good understanding of the thermal aspects of roll cooling is essential. Mathematical models to predict temperature development in the work roll and compute thermal strain induced at the roll surface during rolling were developed and applied to the upper work roll of the 1st stand of the finishing mill of HSM at Tata Steel. The models were used to predict temperatures and thermal stresses/strains in the roll under various cooling conditions, thus examining the efficiency of the existing roll cooling system and exploring the scope of optimizing it.

This study proposes a selective harmonic minimisation-pulse amplitude modulation (SHM-PAM) technique utilising least number of switching based on optimised waveform pattern for five-level cascaded H-bridge (CHB) inverter to satisfy the NRS 048-2:2003 grid code standard. Here, particle swarm optimisation method is used to evaluate the solution of the optimised switching angles and variable DC-link voltages. A comparison between the proposed SHM-PAM and conventional selective harmonic elimination-pulse width modulation (SHE-PWM) techniques has been carried out by harmonic performance analysis (total harmonic distortion (THD), weighted current THD and harmonic loss factor) and loss analysis (conduction, switching and their cumulative losses) of the switches of five-level CHB inverter under different load power factor angles for medium-voltage application. The performances of the conventional SHE-PWM and proposed SHM-PAM techniques are examined through experimentation using a three-phase five-level CHB inverter. Finally, the proposed technique based 5-level CHB inverter is applied to shunt active power filter using tuned proportional plus parallel resonant current controller for improvement in power quality under non-ideal grid conditions.

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.

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