Voltage Control of Offshore Load Connected to a Multi-Terminal HVDC Transmission System

This paper presents a voltage control for an offshore load fed by a Multi-Terminal VSC-HVDC transmission system (MTHVDC). The studied system is composed by two GSCs (Grid Side Converters) and one OSC (Offshore Side Converter). The objective is to maintain the amplitude and frequency of the AC voltage constant at the offshore terminal with a minimum overshoot. A vector control strategy including a current control loop and a voltage control loop is proposed for the OSC and also LQG (Linear-Quadratic-Gaussian) compensator is employed to improve the voltage response of offshore load. The performance of this controller is validated using simulation in MATLAB/SIMULINK software for three operating conditions: normal operation, no-load and start-up of the offshore load. Simulation results illustrate that the AC voltage of load can be governed at its nominal value and MT-HVDC system linked to the offshore load with the proposed controller is able to provide a reliable dynamic operation and a desirable voltage quality during load variations.