Silicon carbide based high-fundamental and switching frequency based inverters for high-speed drives
Upadhyay, Deepak (2026-11-02)
Väitöskirja
02.11.2026
Lappeenranta-Lahti University of Technology LUT
Acta Universitatis Lappeenrantaensis
School of Energy Systems
School of Energy Systems, Sähkötekniikka
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In reference to IEEE copyrighted material which is used with permission in this thesis, the IEEE does not endorse any of Lappeenranta-Lahti University of Technology LUT's products or services. Internal or personal use of this material is permitted. If interested in reprinting/republishing IEEE copyrighted material for advertising or promotional purposes or for creating new collective works for resale or redistribution, please go to http://www.ieee.org/publications_ standards/publications/rights/rights_link.html to learn how to obtain a License from RightsLink.
Julkaisun pysyvä osoite on
https://urn.fi/URN:ISBN:978-952-412-523-9
https://urn.fi/URN:ISBN:978-952-412-523-9
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Tiivistelmä
The demand for high-speed electrical drives has grown significantly in application areas such as aerospace, electric transportation, micro gas turbines, fuel-cell compressors, and advanced industrial systems, where compactness, high efficiency, and high-power density are critical. These applications require inverters capable of operating at high fundamental and switching frequencies while maintaining low current distortion, acceptable thermal performance, and reliable operation. However, their design is challenging because semiconductor technology, converter topology, DC-link voltage, switching frequency, modulation strategy, thermal management, and machine-side harmonic effects are strongly coupled.
This dissertation investigates silicon carbide (SiC)-based high-fundamental-frequency (HFF) and high-switching-frequency inverters (HSF) for high-speed (HS) electrical drives. The work first reviews the state of the art and identifies a clear research gap in inverter solutions capable of simultaneously achieving high power, high fundamental frequency, high switching frequency, and practical DC-link voltage levels. Based on this gap, a 30 kW, 700 V DC-link, two-level, three-phase SiC inverter is designed, modelled, and experimentally validated for operation at a 2 kHz fundamental frequency and a 40 kHz switching frequency. The prototype demonstrates stable high-frequency operation, efficiency above 98.5 %, a volumetric power density of 14.3 kW/L, and a gravimetric power density of 25 kW/kg. The dissertation also examines the interaction between the inverter and the connected high-speed machine. The transient inductance of a 27 kW, 100,000 rpm axially laminated synchronous reluctance machine is analysed and linked to current ripple, total harmonic distortion, and switching-frequency selection. These results show that high-speed-drive inverters should be designed together with the machine rather than as isolated power converters, to get best performance.
To extend the study towards higher power levels, an electrothermal feasibility framework is developed for megawatt-class SiC inverters. Two-level, T-type, and active neutralpoint- clamped topologies are evaluated at 800 V and 1500 V DC-link voltages using commercially available SiC devices. The results show that multilevel topologies and discontinuous pulse-width modulation can extend the feasible switching-frequency range while reducing losses and thermal stress. A system-level PMSM drive analysis further shows that the optimum switching frequency is determined by the combined effects of inverter losses, machine-side harmonic losses, torque ripple, thermal limits, and passivefilter volume.
The research methodology combines a literature review, analytical design, electrothermal simulation, finite-element analysis, hardware prototyping, and experimental validation. The dissertation provides design methods and scalability guidelines for compact, efficient, and application-ready SiC-based high-speed-drive inverters from tens of kilowatts towards megawatt-class applications.
This dissertation investigates silicon carbide (SiC)-based high-fundamental-frequency (HFF) and high-switching-frequency inverters (HSF) for high-speed (HS) electrical drives. The work first reviews the state of the art and identifies a clear research gap in inverter solutions capable of simultaneously achieving high power, high fundamental frequency, high switching frequency, and practical DC-link voltage levels. Based on this gap, a 30 kW, 700 V DC-link, two-level, three-phase SiC inverter is designed, modelled, and experimentally validated for operation at a 2 kHz fundamental frequency and a 40 kHz switching frequency. The prototype demonstrates stable high-frequency operation, efficiency above 98.5 %, a volumetric power density of 14.3 kW/L, and a gravimetric power density of 25 kW/kg. The dissertation also examines the interaction between the inverter and the connected high-speed machine. The transient inductance of a 27 kW, 100,000 rpm axially laminated synchronous reluctance machine is analysed and linked to current ripple, total harmonic distortion, and switching-frequency selection. These results show that high-speed-drive inverters should be designed together with the machine rather than as isolated power converters, to get best performance.
To extend the study towards higher power levels, an electrothermal feasibility framework is developed for megawatt-class SiC inverters. Two-level, T-type, and active neutralpoint- clamped topologies are evaluated at 800 V and 1500 V DC-link voltages using commercially available SiC devices. The results show that multilevel topologies and discontinuous pulse-width modulation can extend the feasible switching-frequency range while reducing losses and thermal stress. A system-level PMSM drive analysis further shows that the optimum switching frequency is determined by the combined effects of inverter losses, machine-side harmonic losses, torque ripple, thermal limits, and passivefilter volume.
The research methodology combines a literature review, analytical design, electrothermal simulation, finite-element analysis, hardware prototyping, and experimental validation. The dissertation provides design methods and scalability guidelines for compact, efficient, and application-ready SiC-based high-speed-drive inverters from tens of kilowatts towards megawatt-class applications.
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