Two-stage Frequency Control Strategy in Isolated Distribution Systems Considering Real-time Coordination of Voltage-dependent Loads

Due to low inertia and restricted frequency regulation resources, isolated system frequency may deviate from nominal operating conditions easily. The conventional solution is to install energy storage or curtail PV power, which is quite costly. This paper proposes a closed-loop feedback control strategy to provide quick frequency support based on conservation voltage reduction effect of voltage-sensitive loads. The power of different loads is regulated coordinately and continuously considering the difference in CVR effect and voltage state between each load. Thus, a two-stage adaptive control method based on the adjustable margin of each load is proposed to achieve online optimization of feedback coefficients. Voltage quality of each load can be guaranteed in the control process while system transient nadir can be minimized. The proposed scheme enables fast and continuous power support through the supply-side to respond to fast power fluctuation caused by PVs. Simulation is performed on the RTDS based on a real system in China, and results verify effectiveness of the proposed method.