A Communication-less Cooperative dc Voltage Control Technique for a Multi-terminal HVDC Transmission System Using H∞ Control

New and upcoming regulations are requiring converters in high voltage direct current (HVDC) connections to be able provide a rapid response to support the stability of the main synchronous network to which they are connected. However, currently proposed droop-controlled HVDC networks that cover a wide geographical area require communication between converters to update the droop coefficients. The reliance on the communication becomes a limiting factor in the development of MTDC networks. In this paper, we present a novel communication-less and cooperative dc voltage control technique for a multi-terminal HVDC transmission system that employs an H
_∞
controller for the voltage regulation. One grid side converter, called the master, and an offshore wind farm are designated to guarantee the main dc voltage stability as well as to maintain a power reserve for the provision of fast grid support services. A flexible main dc voltage level is maintained by the master converter to control the power output and to indirectly signal to the wind farm to inject more or less power, hence no dedicated communication system is needed. An H°° local dc voltage controller is designed to manage efficiently the reserve of power in the form of de-loaded wind turbines. The proposed controller acts on the blade pitch angle and guarantees the internal stability of the presented multi-terminal HVDC (MTDC) transmission system locally around an equilibrium (operating) point. The studied MTDC consists of three converter terminals, a master converter, a standard active/reactive power converter and an offshore wind farm. The effectiveness of the proposed control strategy is validated through preliminary simulation results in MATLABR
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