Abstract: When the DC blocking fault occurs in the UHVDC transmission system, the instantaneous power loss in the receiving power grid relies on the power plant primary frequency regulation in the region for compensation, and the thermal power unit plays a very important role. Presently, most thermal power units are of high capacity and high parameters with very limited energy storage capacity. In the large frequency-difference primary frequency regulation triggered by the DC blocking failure of the power grid, the power contribution of the thermal power unit is affected by the energy storage of the unit, which is not conducive to the rapid recovery of the power grid accident and may cause grid frequency oscillation. In this paper, the Tianji Power Plant of Sending Power from Anhui to the East Project is taken as an example of the typical 600 MW thermal power units to conduct the testings on primary frequency regulation of large-frequency difference and the optimization of related coordination control strategies. A variety of new control strategies are adopted to improve the unit coordinated control and the primary frequency performance so as to increase the contribution of thermal power units to the power grid during faults.

Key words: thermal power generation unit, coordinated control, primary frequency regulation, UHVDC transmission system block fault, large frequency difference