Reliability Modelling of a Multi-terminal High Voltage Direct Current (HVDC) System based on Half-Bridge Modular Multilevel Converter (MMC)

The increase of new power generation in Europe using renewable energy sourcesleads to the application of HVDC for high efficiency transmission. The growth of energy market and the development of the HVDC technology cause the multi-terminal HVDC system based on half-bridge MMC is one of the best option of transmission system, especially for offshore power grids. The aim of designing transmission systems is to obtain a network with high reliability. In this master thesis the reliability modelling of multi-terminal HVDC system based on half-bridge MMC is analysed as an important step to designing transmission networks. Firstly, the reliability of all subsystems related to the HVDC connection is modelled. The Modular Multi-Level Converter - Voltage Source Converter(MMC-VSC) is discussed from the lowest stage. After that, the converter unit and other components such as transformer, converter reactor, control system and DC switchyard in the connection are described by their reliability and is combined into a reliability model of a converter station. Two types of converter stations (onshore and offshore) and the cables assemble the system based on the case study. Two systems are modelled: Point-to-point and three-terminal configuration. In the three-terminal configuration, two scenarios are performed: with and without possibilities. The reliability modelled is performed using two approaches: analytical approach and Monte Carlo simulation. The reliability model of the subsystems and systems involve the availability, unavailability, outage duration, energy not transmitted, failure frequency, average duration per interruption, and the range of time between failures. After having the model and the reliability parameter, the reliability analysis is performed.From the analysis, it is found that the highest unavailability and thus the outageduration in onshore and offshore converter station are the transformer and the converter reactor, respectively. The offshore converter station is found to have the highest unavailability. The failure frequency, the average duration per interruptions, and the range of time between failures, which is produced by Monte Carlo simulation, can be applied for further action regarding the asset management of the system. The energy not transmitted through the point-to-point and three-terminal system is useful as a further research to choose which scenario is the most profitable