This paper presents an adaptive droop-based power-sharing control strategy. The primary objective is to control the sharing of the active power transmitted by a multi-terminal voltage-source converter based high voltage direct current (MT VSC-HVDC) network among a number of onshore AC grids or offshore loads based on the desired percentage shares. The shared power is generated by remote generation plants (e.g., offshore wind farms) or is provided as surplus from AC grids. The desired percentage shares of active power are optimized by the system operator in order to fulfil the active power requirements of the connected grids with respect to meeting goals such as supporting energy adequacy, increasing renewable energy penetration, and minimizing losses. The control strategy is based on two hierarchal levels: voltage-droop control as the primary controller and an optimal-power flow (OPF) based secondary (supervisory) controller for selecting the optimal droop reference voltages. Based on the DC voltage transient and steady state dynamics, a methodology for choosing the droop gains for droop controlled converters has been developed. The proposed control strategy has been validated through simulation on the CIGRE B4 DC grid test system. The results confirmed the flexibility and effectiveness of the power-sharing control provided by the new control strategy. |
