Minimizing DC system loss in multi-terminal HVDC systems through adaptive droop control

• Adaptive droop control is proposed for an MTDC system.
• An equivalent circuit model of the MTDC system is first formulated with droop considered.
• Droop gains are calibrated to have minimum DC system loss as well as constant dc voltage at the inverter side.
• During contingent scenarios, the droop gains will be computed again to have minimum DC system loss.
• The proposed droop control is validated by a detail-based comprehensive MTDC system in real-time digital simulation.

In this paper, droop control of inverters in a multi-terminal HVDC (MTDC) system is designed to achieve minimum DC system loss while preventing converter overvoltage. Circuit analysis along with optimization analysis is first conducted to seek the optimal droop control gains. Contingent operating conditions are then considered. The droop control gains will adapt to achieve minimum loss as well as constant inverter side dc voltage. A 6-terminal MTDC system with detailed control loops as well as PWM-based switching is built in a real-time digital simulator, RT-Lab. Time-domain simulation results validate the circuit analysis results and demonstrate the feasibility of the proposed adaptive droop control.