Multi-Terminal HVDC Control Strategies Applied to the Cigre B4 DC Grid Test System

Further developments in voltage source converter technology have triggered an increase in HVDC projects across Europe. To master future challenges within the energy sector, a continental DC overlay grid is discussed and seems to be feasible from a technical perspective. Therefore existing offshore wind and inter market DC links are proposed to be connected to each other in a first step. Supplemented by additional branches the resulting meshed DC system offers a higher degree of flexibility and reliability if adequate converter and grid control schemes are utilized. Especially in case of a converter outage or line fault, proposed droop and DC grid control methods with distributed back ups offer significant advantages compared to centralized techniques since power sharing between different converters distributes the burden caused by a sudden power variation. This paper presents a framework to evaluate DC grid and converter control methods. First, following the introduction of the underlying VSC model, basic converter and grid control schemes are introduced. Furthermore, advanced approaches such as deador undead-band droop and distributed grid voltage control to deal with grid contingencies are described and evaluated. Finally, results based on a MATLAB Simulink environment show adapted variations of the presented strategies which are applied to the Cigre B4 DC Grid Test System to examine suitability, performance and drawbacks of selected methods.