Silicon-Carbide-Based High-Voltage Submodules for HVDC Voltage-Source Converters

In order to transition to renewable energy sources and simultaneously meet the increasing demand for electrical energy, highly flexible and efficient grids are required. High-voltage direct-current (HVDC) transmission and grids are foreseen to be a vital part of the future electricity grid. Voltage source converters (VSCs), interfacing between HVDC and high-voltage alternating current (HVAC) technology, need to comply with grid code, and offer high reliability and cost efficiency. The state-of-the-art VSC topology is the modular multilevel converter (MMC), which offers tailored harmonic performance, modularity, fault handling, redundancy, and low losses. This thesis investigates improvements for VSCs enabled by novel silicon carbide (SiC) power semiconductor devices. These devices feature lower losses, higher blocking voltage, and higher maximum operation temperature. However, a co-design of the different hardware levels (i.e., converter, submodule (SM), power device, and semiconductor) is required to unleash their full potential. The thesis features contributions on several of these hardware levels, aiming at improvements regarding defined technical requirements for VSCs. It has been shown that, on converter level, future ultrahigh-voltage (UHV) SiC bipolar devices with blocking voltages of up to 50 kV have the potential for significant reduction of converter complexity, volume, and losses. The increased SM voltage is a challenge for internal fault handling, which can be met by a proposed novel SM feature, the discharge loop. On SM level, additional improvements are enabled by synergies between power semiconductor device technology and SM topology. A comparative evaluation of a large variety of SM topologies in combination with different SiC power semiconductor device technologies identifies several promising design approaches for future SMs. An alternative to the state-of-the-art half-bridge and full-bridge SM is the semi-full-bridge, which is investigated intensively. It features lower switch count and lower losses compared to the full-bridge, while offering DC fault handling capability. Another topology, the double-connected double-zero SM, features additional conduction loss reduction in combination with SiC metal-oxide-semiconductor field-effect transistors (MOSFETs), which is enabled by parallel current paths during certain switching states. A SM cluster enhancing this effect is proposed. Finally, results on the optimization of SiC PiN diodes via different charge carrier lifetime tailoring methods are presented. The target application is a high-voltage high-frequency LCC converter. In the future, such diodes will also be required as anti-parallel diodes for novel UHV bipolar SiC devices, as bootstrap diodes in gate drivers, and as a part of snubber circuits.QC 20201104</p

Silicon-Carbide-Based High-Voltage Submodules for HVDC Voltage-Source Converters

In order to transition to renewable energy sources and simultaneously meet the increasing demand for electrical energy, highly flexible and efficient grids are required. High-voltage direct-current (HVDC) transmission and grids are foreseen to be a vital part of the future electricity grid. Voltage source converters (VSCs), interfacing between HVDC and high-voltage alternating current (HVAC) technology, need to comply with grid code, and offer high reliability and cost efficiency. The state-of-the-art VSC topology is the modular multilevel converter (MMC), which offers tailored harmonic performance, modularity, fault handling, redundancy, and low losses. This thesis investigates improvements for VSCs enabled by novel silicon carbide (SiC) power semiconductor devices. These devices feature lower losses, higher blocking voltage, and higher maximum operation temperature. However, a co-design of the different hardware levels (i.e., converter, submodule (SM), power device, and semiconductor) is required to unleash their full potential. The thesis features contributions on several of these hardware levels, aiming at improvements regarding defined technical requirements for VSCs. It has been shown that, on converter level, future ultrahigh-voltage (UHV) SiC bipolar devices with blocking voltages of up to 50 kV have the potential for significant reduction of converter complexity, volume, and losses. The increased SM voltage is a challenge for internal fault handling, which can be met by a proposed novel SM feature, the discharge loop. On SM level, additional improvements are enabled by synergies between power semiconductor device technology and SM topology. A comparative evaluation of a large variety of SM topologies in combination with different SiC power semiconductor device technologies identifies several promising design approaches for future SMs. An alternative to the state-of-the-art half-bridge and full-bridge SM is the semi-full-bridge, which is investigated intensively. It features lower switch count and lower losses compared to the full-bridge, while offering DC fault handling capability. Another topology, the double-connected double-zero SM, features additional conduction loss reduction in combination with SiC metal-oxide-semiconductor field-effect transistors (MOSFETs), which is enabled by parallel current paths during certain switching states. A SM cluster enhancing this effect is proposed. Finally, results on the optimization of SiC PiN diodes via different charge carrier lifetime tailoring methods are presented. The target application is a high-voltage high-frequency LCC converter. In the future, such diodes will also be required as anti-parallel diodes for novel UHV bipolar SiC devices, as bootstrap diodes in gate drivers, and as a part of snubber circuits.QC 20201104</p

Silicon-Carbide-Based High-Voltage Submodules for HVDC Voltage-Source Converters

In order to transition to renewable energy sources and simultaneously meet the increasing demand for electrical energy, highly flexible and efficient grids are required. High-voltage direct-current (HVDC) transmission and grids are foreseen to be a vital part of the future electricity grid. Voltage source converters (VSCs), interfacing between HVDC and high-voltage alternating current (HVAC) technology, need to comply with grid code, and offer high reliability and cost efficiency. The state-of-the-art VSC topology is the modular multilevel converter (MMC), which offers tailored harmonic performance, modularity, fault handling, redundancy, and low losses. This thesis investigates improvements for VSCs enabled by novel silicon carbide (SiC) power semiconductor devices. These devices feature lower losses, higher blocking voltage, and higher maximum operation temperature. However, a co-design of the different hardware levels (i.e., converter, submodule (SM), power device, and semiconductor) is required to unleash their full potential. The thesis features contributions on several of these hardware levels, aiming at improvements regarding defined technical requirements for VSCs. It has been shown that, on converter level, future ultrahigh-voltage (UHV) SiC bipolar devices with blocking voltages of up to 50 kV have the potential for significant reduction of converter complexity, volume, and losses. The increased SM voltage is a challenge for internal fault handling, which can be met by a proposed novel SM feature, the discharge loop. On SM level, additional improvements are enabled by synergies between power semiconductor device technology and SM topology. A comparative evaluation of a large variety of SM topologies in combination with different SiC power semiconductor device technologies identifies several promising design approaches for future SMs. An alternative to the state-of-the-art half-bridge and full-bridge SM is the semi-full-bridge, which is investigated intensively. It features lower switch count and lower losses compared to the full-bridge, while offering DC fault handling capability. Another topology, the double-connected double-zero SM, features additional conduction loss reduction in combination with SiC metal-oxide-semiconductor field-effect transistors (MOSFETs), which is enabled by parallel current paths during certain switching states. A SM cluster enhancing this effect is proposed. Finally, results on the optimization of SiC PiN diodes via different charge carrier lifetime tailoring methods are presented. The target application is a high-voltage high-frequency LCC converter. In the future, such diodes will also be required as anti-parallel diodes for novel UHV bipolar SiC devices, as bootstrap diodes in gate drivers, and as a part of snubber circuits.QC 20201104</p

Dissipation Loop for Shoot-Through Faults in HVDC Converter Cells

Converter cells for HVDC applications store large amounts of energy. This energy might be dissipated in a very short time in case of a shoot-through fault. Measures to avoid shoot-through or handle the extreme currents during a fault and prevent damage from neighboring components are essential to ensure a continued operation of the converter. With future high-voltage silicon carbide semiconductors, cell voltages can be increased leading to higher stored energy per cell. In cells with thyristor-based semiconductors, e.g. IGCTs, a di/dt reactor may have to be employed. This paper presents a method to handle the dissipated energy during shoot-through which makes use of the inherently needed di/dt reactor. The majority of the stored energy in the cell can be dissipated in a dedicated discharge loop formed by the reactor and an antiparallel bypass thyristor. After diverting the fault current into the dissipation loop, there is no current through any other component of the cell.QC 20181127</p

Single-Fiber Combined Optical Power and Data Transmission for High-Voltage Applications

In this paper, power-over-fiber technology is used for combined power and data transfer applying amplitude-modulated light representing a pulse-width modulated signal that could be used for control of, for instance, power semiconductor devices in high-power converters. Even though the concept is generally applicable, an experimental verification aiming for a gate-driver of a switch in a modular multilevel converter is presented. In order to achieve a good resilience against electromagnetic noise, a concept where the modulated light is demodulated as a comparably powerful current signal is employed. A 5 MHz boost converter steps up the voltage to 15-20 V, such that silicon or silicon-carbide based power devices could be controlled. From the results, it can be concluded that it is possible to achieve transmission of a control signal with a latency of less than 500 ns for a gate drive unit of a high-power converter. The concept can easily be scaled up to powers of several watt.QC 20200828</p

MMC Converter Cells Employing Ultrahigh-Voltage SiC Bipolar Power Semiconductors

This paper investigates the benefits of using high-voltage converter cells for transmission applications. These cells employ ultrahigh-voltage SiC bipolar power semiconductors, which are optimized for low conduction losses. The Modular Multilevel Converter with half-bridge cells is used as a test case. The results indicate a reduction of converter volume and complexity, while maintaining low losses and harmonic performance.QC 20180109</p

Single-Fiber Combined Optical Power and Data Transmission for High-Voltage Applications

In this paper, power-over-fiber technology is used for combined power and data transfer applying amplitude-modulated light representing a pulse-width modulated signal that could be used for control of, for instance, power semiconductor devices in high-power converters. Even though the concept is generally applicable, an experimental verification aiming for a gate-driver of a switch in a modular multilevel converter is presented. In order to achieve a good resilience against electromagnetic noise, a concept where the modulated light is demodulated as a comparably powerful current signal is employed. A 5 MHz boost converter steps up the voltage to 15-20 V, such that silicon or silicon-carbide based power devices could be controlled. From the results, it can be concluded that it is possible to achieve transmission of a control signal with a latency of less than 500 ns for a gate drive unit of a high-power converter. The concept can easily be scaled up to powers of several watt.In proceedings ISBN 978-1-7281-5414-5QC 20200828</p