An Improved Vector Control Strategy for VSC-HVDC Connected to Weak Grid

In recent years, voltage-sourced converter (VSC) based high voltage direct current (HVDC) transmission systems have found extensive application. Traditional control loops of VSC-HVDC are mainly divided into the phase-locked loop, the outer control loop and the inner current control loop, which shows satisfactory performance under high system strength. However, when VSC-HVDC works in a weak grid condition, the traditional control method may cause voltage instability or collapse at PCC because of undesired aggravated active-reactive power coupling. To solve this problem, this paper proposes an improved vector control (IMVC) method to stabilize the voltage at the PCC. According to the voltage reference value and the active power reference value, the reactive current command compensation is calculated to improve the stability of PCC voltage and power under a low system strength. The effectiveness of this method in enhancing VSC- HVDC operational stability under low system strength is verified by simulations in MATLAB/Simulink platform.