Primary frequency control optimization of coal-fired power plants with high-low position shafts: Employing a revised strategy with power-decoupling and feedforward-compensating

Coal-fired units play a critical role in peak-shaving and frequency regulation with high penetration of renewable energy. The coal-fired unit arranged by high-low position shafts applied in power stations will participate in these regulation processes. In this study, the dynamic model of the 1100 MW supercritical coal-fired unit is built and verified, dynamic characteristics of the primary frequency regulation process are analyzed and a poor control effect of the original control strategy is illustrated. Then, the dynamic coupling relationship between high and low-level units is obtained, and there is a 14-s time delay between the two power outputs, and a revised regulation strategy that employs load distribution factor and flow-rate feedforward-compensating is proposed. Compared with the original control strategy, the revised control strategy can effectively lower fluctuations of the steam parameters by approximately 50%, and the corrective regulation time decreases from 25.1 s and 15.8 s to 6.9 s and 12.1 s under positive and negative load disturbance, respectively. Moreover, it can improve the control effect of low-level unit, whose regulation time under positive and negative load disturbance decreases from 45.7 s and 27.7 s to 9.4 and 20.6 s, respectively. This research can provide technical guidance for the operation of coal-fired units.