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Harmonics worsen the quality of electrical signals, hence, there is a need to eliminate them. The test objects under discussion are single-phase versions of cascaded H-bridge (CHB) multilevel inverters (MLIs) whose switching angles are optimized to eliminate specific harmonics. The Dragonfly Algorithm (DA) is used to eradicate low-order harmonics, and its statistical performance is compared to that of many other optimization techniques, including Particle Swarm Optimization (PSO), Accelerated Particle Swarm Optimization (APSO), Differential Evolution (DE), and Grey Wolf Optimization (GWO). Various scenarios of the algorithms' search agent population for inverters with seven, nine, and eleven levels of output voltages are comprehensively addressed in this research. No algorithm shows total dominance in every scenario. The DA is least impacted by the change in dimensions of the narrated problem. [ABSTRACT FROM AUTHOR]

This paper addresses shaft end-to-end and shaft-to-frame voltages that appear in the 400-V, 15-kW induction motor driven by a voltage-source pulsewidth modulation (PWM) inverter. A shaft-to-frame voltage can be observed at either shaft end with respect to the grounded motor frame. A shaft end-to-end voltage can be observed as a voltage difference between the shaft-to-frame voltage at the drive end (DE) and that at the nondrive end (NDE). Experimental waveforms lead to the following interesting observations: motor internal coupling and parasitic capacitance, along with the high-frequency common-mode voltage generated by the PWM inverter, cause a shaft-to-frame voltage with a peak of 8 V at both DE and NDE. When the shaft-to-frame voltage at either DE or NDE exceeds a dielectric breakdown voltage of thin bearing lubricating grease films, a shaft end-to-end voltage with a peak of 2 V and a width of 30 ns occurs along the motor shaft. This paper makes experimental discussions on the shaft end-to-end voltage generation. Installing a differential-mode filter and/or a common-mode filter on the motor drive system gives a hint on the mechanisms of the occurrence of the shaft end-to-end voltage. Index Terms--Bearing current, electromagnetic interference (EMI), ground leakage current, motor drives, pulsewidth modulation (PWM) inverters, shaft voltage.