Inverter Design for SiC-based Electric Drive Systems with Optimal Redundant States Control of Space Vector Modulation
Doctoral thesis, 2021

The need for inverters with ever increasing power density and efficiency has recently become the driving factor for research in various fields. Increasing the operating voltage of the whole drive system and utilizing newly developed SiC power switches can contribute towards this goal. Higher operating voltage allows the design of drives with lower current, which leads to lower copper losses in cables and machine, while SiC switches can drastically increase the inverter efficiency. Offshore renewable power generation, such as tidal power, is a typical application where the increase of operating voltage can be highly beneficial. The ongoing electrification of transportation calls also for high power electric powertrains with high power density,
where SiC technology has key advantages.

In the first part of the thesis, suitable control schemes for inverters in synchronous machine drive systems are derived. A properly designed Maximum Power Point Tracking algorithm for kite-based tidal power systems is presented. The speed and torque of this new tidal power generation system varies periodically and the inverter control needs to be able to handle this variable power profile. Experimental verification of the developed control is conducted on a 35 kVA laboratory emulator of the tidal power generation unit.

Electric drives using multilevel inverters are studied afterwards. Multilevel inverters use multiple low-voltage-rated switches and can operate at higher voltage than standard two-level inverters. The Neutral Point Clamped (NPC) converter is a commonly used multilevel inverter topology for medium voltage machine drives. However, the voltage balancing of its dc-side capacitors and the complexity of its control are still issues that have not been effectively solved. A new method for the optimal utilization of the redundant states in Space Vector pulse-width-Modulation (SVM) is proposed in this thesis in order to control its dc-link voltages. Experimental verification on a 4-kV-rated prototype medium-voltage PMSM drive with 5-level NPC converters is conducted in order to validate the effectiveness of the proposed control technique.

Low switching and conduction losses are typical characteristics of SiC switches that can be utilized to build inverters with high power density, due to the increased efficiency and smaller form-factor. Due to the above, SiC power modules have been particularly attractive for the automotive industry. The design approach of 2-level automotive inverters has been studied in this project. Moreover, a new design approach for the cooling system of automotive inverters has been developed in this thesis, which fine-tunes the inverter heatsink utilizing standard legislated test routines for electric vehicles. Multiple conjugate-heat-transfer (CHT) computation results showcase the iterative optimization procedure on a test-case 250 kW (450 A) automotive SiC inverter.

Finally, the experimental testing of high power machine drives in order to verify the control and the hardware design is an important step of the development process. Thus, the performance of the prototype 450 A SiC 2-level inverter has been been experimentally validated in a power hardware-in-the-loop (P-HIL) set-up that emulates an automotive drive system. Several challenges have been addressed with respect to the accurate modelling of the motor and the control of the circulating power in the system. A new control technique utilizing the redundant states of the SVM has been developed for this set-up to effectively suppress the zero-sequence current to 3.3 % of the line current at rated power.

Electric Vehicle

Common Mode Voltage

Power Hardware-in-the-Loop

Tidal power

Voltage balancing

Silicon Carbide (SiC)

Medium Voltage Converters


Neutral Point Clamped (NPC)

Maximum Power Point Tracking (MPPT)

Space Vector Modulation

Opponent: Prof. Josep Pou, School of Electrical & Electronic Engineering, Nanyang Technological University (NTU), Singapore


Georgios Mademlis

Chalmers, Electrical Engineering, Electric Power Engineering

Balancing Peak-torque and Drive-cycle Efficiency with Magnet Dimensioning of Permanent Magnet Synchronous Machines

IECON Proceedings (Industrial Electronics Conference),; Vol. 2020-October(2020)p. 883-888

Paper in proceeding

Design of Maximum Power Point Tracking for Dynamic Power Response of Tidal Undersea Kite Systems

IEEE Transactions on Industry Applications,; Vol. 56(2020)p. 2048-2060

Journal article

Circulating Current Reduction in Common DC-Link Power-HIL for Drives using SVM with Zero-Sequence Compensation

IECON Proceedings (Industrial Electronics Conference),; (2020)p. 4673-4678

Paper in proceeding

Design of a power hardware-in-the-loop test bench for a traction permanent magnet synchronous machine drive

Proceedings - 2020 International Conference on Electrical Machines, ICEM 2020,; (2020)p. 1765-1771

Paper in proceeding

Designing Thermally Uniform Heatsink with Rectangular Pins for High-Power Automotive SiC Inverters

IECON Proceedings (Industrial Electronics Conference),; Vol. 2020-October(2020)p. 1317-1322

Paper in proceeding

Performance Evaluation of Electrically Excited Synchronous Machine compared to PMSM for High-Power Traction Drives

2020 24th International Conference on Electrical Machines (ICEM),; (2020)p. 1793-1799

Paper in proceeding

Overvoltage Mitigation of Medium Voltage Electric Drives with Long Cables using Multilevel-Converters and Passive Filters

2019 21th European Conference on Power Electronics and Applications, EPE-ECCE Europe 2019,; (2019)

Paper in proceeding

Comparative Study of the Torque Ripple and Iron Losses of a Permanent Magnet Synchronous Generator Driven by Multilevel Converters

2018 23rd International Conference on Electrical Machines (ICEM),; (2018)

Paper in proceeding

Generator Speed Control and Experimental Verification of Tidal Undersea Kite Systems

2018 23rd International Conference on Electrical Machines (ICEM),; (2018)p. 1531-1537

Paper in proceeding

Feed-Forward Control for Active Voltage Balancing in Electric Drives with Five-Level NPC Converters

2018 IEEE Energy Conversion Congress and Exposition (ECCE),; (2018)

Paper in proceeding

DC Link Voltage Balancing Technique Utilizing Space Vector Control in SiC-based Five-Level Back-to-Back-Connected NPC Converters

2018 IEEE Energy Conversion Congress and Exposition (ECCE),; (2018)p. 3032-3037

Paper in proceeding

Combined Voltage Balancing Techniques of the DC Link in Five-Level Medium Voltage NPC Back-to-Back Converters for Offshore Renewable Generation

2017 19th European Conference on Power Electronics and Applications,; (2017)

Paper in proceeding

Power Take-Off System for a Subsea Tidal Kite (PowerKite)

European Commission (EC) (EC/H2020/654438), 2016-01-01 -- 2018-06-30.

iTEM - Integrated Transmission and Electric Motor

Swedish Energy Agency (45622-1), 2018-02-09 -- 2020-09-30.

Driving Forces

Sustainable development

Areas of Advance



Subject Categories

Control Engineering

Other Electrical Engineering, Electronic Engineering, Information Engineering



Doktorsavhandlingar vid Chalmers tekniska högskola. Ny serie: 4910





Opponent: Prof. Josep Pou, School of Electrical & Electronic Engineering, Nanyang Technological University (NTU), Singapore

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Latest update

3/2/2022 3