Smolensk Branch of Moscow Power Engineering Institute, Smolensk, Russia:

V. V. Rozhkov, Associate Professor, Head of the Department of Electromechanical Systems, Candidate of Technical Sciences, e-mail: umo@sbmpei.ru
K. K. Krutikov, Associate Professor at the Department of the Fundamentals of Electrical Engineering, Candidate of Technical Sciences, e-mail: krutikov-kk@yandex.ru
V. V. Fedotov, Undergraduate Student at the Department of Electromechanical Systems, e-mail: fedotov.smol67@gmail.com
Ya. A. Fedulov, Associate Professor at the Department of Computer Engineering, Candidate of Technical Sciences, e-mail: fedulov_yar@mail.ru

This paper uses multilevel inverter diagrams to describe some optional applications for such inverters in order to enhance the efficiency, electromagnetic compatibility and service life of electric motors utilized in the non-ferrous metals industry. The authors consider using active rectifiers with a five-level structure that serve as variable reactivity units and reactive power compensators. They also consider using a five-level independent voltage source inverter as a part of the variable frequency drive system. An option is described that can help optimize the control algorithm and voltage rectification in the DC link capacitor in the five-level active rectifier circuit. For the variable frequency drive with a five-level independent voltage source inverter, it is proposed to change the circuit topology to introduce a transformerless power circuit. The proposed solutions were analyzed for efficiency with the help of MatLab simulation package. The paper considers the problem of voltage accuracy as maintained by each DC link capacitor. Each DC link capacitor has its features typical of both studied circuits in both transient and steady-state conditions. In the circuit involving a multilevel active rectifier, the authors simulated conditions when the variable reactivity drastically changes from the initial steady-state equivalent capacitance mode to equivalent inductance. A soft start was simulated in the circuit involving a multilevel independent voltage source inverter. A feasibility study was conducted that proved the feasibility of the proposed solutions when adopted by concentrator plants and non-ferrous metals producers.
This research was carried out as part of a governmental assignment, Project No. FSWF-2020-0019.
This research was carried out at the facilities of the Shared Knowledge Centre High-Voltage Research & Development Complex, a part of Moscow Power Engineering Institute.

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