PhD student to create a universal vector modulation algorithm for inverters | Gdańsk University of Technology

The dissertation titled “The pulse width modulation strategy for a five-phase three-level NPC voltage source inverter with DC-link voltage balancing ability” was developed under the supervision of Prof. Arkadiusz Lewicki from the Faculty of Electrical and Control Engineering.

The paper focuses on the development of a modulation method based on space vector modulation assumptions, enabling an independent formation of two output voltage vectors in a five-phase three-level NPC voltage source inverter.

– The solution will be applied for powering five-phase motors, where it should be possible to increase the electric torque by appropriate third harmonic injection. Additionally, it opens the possibility of independent control of two motors powered by a single inverter – explains the researcher.

– The proposed solution allows for the independent generation of output voltages with a minimum number of transistor s' switching, and at the same time allows controlling the voltage distribution on DC-link capacitors.

The research was conducted using a five-phase three-level neutral point clamping voltage source inverter. NPC three-level inverters (three-phase type) are widely used for industrial applications. Inverters with this topology are used in the medium voltage range, where they enable output voltages higher than the blocking voltage of the semiconductors. In low-voltage applications, they can replace commonly used two-level inverters. Three-level inverters can be built using cheaper transistors with lower blocking voltages. The main problem to be solved in multi-phase multilevel voltage inverters is to maintain (preferably) equal voltages on the DC-link capacitors and to correctly generate multiple output voltage vectors with both DC-link voltage symmetry and asymmetry. 

– The benefits of multiphase drives accrue as the number of phases increases, although to a limited extent because the control algorithms and computational requirements become remarkably more complex as the number of phases increases. In the case of seven-phase inverters, a single three-level NPC inverter with 28 transistors can replace three three-phase inverters with (a total of) 36 transistors.  As a result, such a drive system may be cheaper to produce, emphasizes Dmytro Kondratenko. – Such drives have a chance to be popularized in industrial applications. The developed vector modulation algorithm can be used in both solutions – in a multi-phase inverter powering a single multi-phase motor with increased driving torque, as well as in a single inverter powering independently controlled motors.

Three jobs, three languages

Upon graduating from engineering studies at Kyiv National University of Technology, in 2018 the researcher came to continue his studies at Gdańsk University of Technology. He defended two master's theses - at the universities in Kyiv and Gdańsk. It was a challenge because he wrote his master's thesis in two languages ​​- Polish and his native language, while the requirement for his doctoral dissertation was to write it in English.

Currently, while waiting for the defense of his doctorate, the researcher works as a research and teaching assistant at the Faculty of Electrical and Control Engineering. From the following academic year, the researcher will assume the position of an assistant professor. The researcher is also a project research team member – I have developed the concept of multi-motor drive systems, where we power e.g. two motors from one inverter, and I want to expand my research. I plan to apply for research project grants. This is a subject matter that can be pursued in many directions, and I have a lot of research plans, emphasizes the researcher. – Research is my passion, but I also enjoy teaching, which I never would have expected. After a semester of teaching, I can say that I truly like it. My method is to give students space and time to solve scientific problems on their own. I want them to come to solutions and conclusions on their own, however I am always there to help them. I can tell my approach has brought positive effects.