Preset Power Based Droop Control for Improving Primary Frequency Regulation of Inverters Under Large Disturbances
Lei Liu, Xianjue Luo, Liansong Xiong, Guo Jun-ming, Xiaokang Liu, Yonghui Liu, Hengyou Zhang
Abstract
Droop-controlled inverters reduce transient and steady-state frequency deviations (FDs) by providing frequency regulation (FR) power proportional to the FD during primary FR. However, with the power–frequency droop mechanism, the gap between a disturbed load and an inverter's dispatch instruction can only be eliminated by increasing the FR power at the expense of increased FDs, which are thus prone to exceeding the pertinent relay thresholds. To address this issue, a preset power based droop control scheme is developed by rapidly presetting a constant power in the active power loop to modify the dispatch instruction at the beginning of a large disturbance event. With the preset power framework, the adjusted dispatch instruction significantly suppresses most of the imbalanced power; hence the traditional droop control can eliminate the remaining imbalanced power by providing a small FR power with small FDs. To this end, first, this article demonstrates that the principle of preset power is to reduce the droop power related to FDs. Based on the above principle, analysis shows that the adaptability and rapidity of the preset power are required for better FR performance. Then, the implementation of the proposed control is elaborated, including the fast calculation of the preset power and the mode switching method. Finally, the experiment and simulation results verify the superior FR performance of the proposed control.