Enabling Short-term Over-current Capability for SiC Power Modules and its Application for Power Flow Controllers in HVDC Grids
Time: Mon 2025-04-28 10.00
Location: Kollegiesalen, Brinellvägen 8, Stockholm
Language: English
Subject area: Electrical Engineering
Doctoral student: Shubhangi Bhadoria , Elkraftteknik
Opponent: Professor Dimosthenis Peftitsis, NTNU, Department of electric energy Faculty of Information Technology and Electrical Engineering, Trondheim, Norway
Supervisor: Professor Hans-Peter Nee, Elkraftteknik; Frans Dijkhuizen, Hitachi Energy, Västerås, Sweden
QC 20250331
Abstract
With the increase in renewables integration in power systems, the demand for over current (OC) capability is increased. Until the fault clearance, converters in the power system must be able to withstand the increased currents without getting tripped by their internal protection based on thermal limits. This duration is typically 200 ms. In this thesis, various techniques have been proposed to remove the heat generated during OCs as soon as possible fromSilicon-Carbide (SiC) devices, hence increasing the OC duration. These techniques include implementing heat-absorbing materials, microchannel (MC) cooling on the top and bottom of the chip, and gate voltage augmentation during OCs. It is concluded that any cooling method (except gate voltage augmentation) gives the highest OC capability when it is implemented on top of the chip. MC cooling has the potential to increase OC capability duration until a few seconds, depending on the design of the MC block. Similarly, OC capability is significantly improved by using copper as heat-absorbing material on top and bottom (with a comparatively large block of copper) of the chip up to a few seconds, depending on the amount of OC. Even increasing the thickness of metallization on top of the chip can lead to increased OC capability. One application of the power modules with increased OC capability is in power flow controllers (PFCs). With the increase in meshing, controllability and flexibility to control the current and power in a high-voltage direct current (HVDC) system are reduced. By injecting a small amount of voltage, a PFC can change the current distribution. Existing topologies have been studied in detail by PLECS simulations and compared with respect to the number of capacitors, the control range of the PFC, the shape of voltage waveforms inserted by the PFC on the lines, number of devices, the directionality of the current, simplicity of the topology, total power semiconductor rating and losses, and protection of the topologies for external faults. A new topology, which is among the most simple topologies, has been proposed. Further, internal and external fault cases for the proposed topology have been investigated in detail. The simulations are verified by a scaled-down prototype in the lab. Simulations and experiments have been compared with respect to their per unit (pu) system and the experimental results are aligned with the simulation results.