A knowledge-based approach to voltage and power control in HV-MTDC grids

This paper proposes a new knowledge-based control philosophy for the direct voltage and power control of a multi-terminal voltage source converter based offshore HVDC grid. The limitations of the classical direct voltage droop control strategy are discussed and mainly the difficulty to reach power reference set-points is stressed. In that context, a knowledge based intelligent controller (namely Fuzzy) is proposed. It is capable of addressing these weaknesses by combining the advantages of the droop controller such as robustness and exceptional ability to compensate for imbalance during contingencies, and the constant active power controller which has the ability to easily reach power set points. In this context, the power dispatch of the HVDC grid converters is achieved without the need to solve before-hand HVDC grid load flow equations where the droop constant is included in the algorithm. The advantages of the new Fuzzy controller is the reduced computational effort, the high degree of flexibility, and the zero percentage error. The efficacy and robustness of the control strategy is demonstrated by means of time domain simulations for a three terminal voltage source converter based offshore HVDC grid system used for the grid connection of large offshore wind power plants.