A new design of solid state circuit breaker for HVDC applications
thesisposted on 08.06.2021, 07:39 by Shahram Negari
The global energy consumption is soaring at an unprecedented rate over the past three decades, in part due to rapid socioeconomic advancement in developing countries. This enormous demand, in turn, has pushed the energy production methods to their limits. Therefore, huge investments are predicted to be put in the energy sector to increase production at one end and enhance consumption efficiency at the other. Currently a considerable portion of electric energy is produced by power plants who consume some kind of fossil based energy carrier. However, dependency on fossil based energy carriers has brought up its own serious drawbacks including ecological problems such as global warming, increased CO2 emission, and alarming pollution levels. As a remedy, many economies have diverted from traditional means of energy production by embracing new sustainable energy production methods and simultaneously improving consumption habits. Currently, among technically available and economically viable solutions, generating energy from renewable sources, in particular wind and solar are pioneering. Finding the appropriate locations and building large scale wind farms or solar farms in urban areas, which are already suffering from congestion, has turned to be a major challenge. Consequently, many investors are now turning toward construction of off-shore farms. Transferring the electric energy from the off-shore farm to the mainland in a safe and reliable way is the next challenge. Having taken into account several technical and economic reasons, laying submarine HVDC cables at sea substrate to evacuate the power from offshore wind farms is the best available method at the present. Utilizing HVDC requires installation of AC/DC converters, which due to grid characteristics in particular in remote areas, will be mainly based on utilizing voltage source converters. Yet, as to integration of antiparallel diodes in their valves, voltage source converters are intrinsically vulnerable against massive short circuit currents and backflow of energy from transmission line to the converter. Thus developing a reliable circuit breaker topology, which is the frontline protection device for both submarine transmission line and converter seems to be essential. In this research, existing topologies and solutions for circuit breakers, including their features and drawbacks are discussed and then a new topology for HVDC circuit breaker is introduced. Many solid-state topologies have been proposed by academia and rolled out by manufacturers so far. A feature common to all existing designs is utilization of surge arrester for absorbing the energy stored in the system. However, the new topology that is put forward in this research is based on a combination of solid-state switch and a mutual inductance, which diverts the energy stored in the transmission line at the time of short circuit current to a resistor. The resistor then damps and absorbs the energy which is finally dissipated as heat. Both simple and complex Simulink models are developed to test the performance of the proposed topology. Results of both simulation scenarios corroborate and validate the functionality and reliability of the suggested design.