A supplementary power control strategy with enhanced damping is proposed for an MMC station to eliminate the active power deviation resulting from synchronous generator emulation control in the condition of steady-state grid frequency fluctuation. With the proposed method, the frequency command is corrected in real time by integrating the active power deviation to control the output power more accurately. A damping control is introduced to the supplementary power control loop. This can improve the dynamic performance and stability of the system. Also, a switching strategy is designed to achieve the selectivity needed for the converter station to participate in grid power regulation. Simulations are conducted in PSCAD/EMTDC to verify the effectiveness of the proposed scheme. The results show that the transition between grid-connection and island mode is not disturbed under the proposed method. Under steady-state grid operation, the deviation of DC voltage and output active power can be eliminated. This improves the steady-state performance of the MMC station; under the transient period, the power oscillation of the system is suppressed, and the output power of the converter station can be controlled quickly and accurately. This work is supported by National Key Research and Development Program of China (No. 2017YFB0902000) and Science and Technology Project of State Grid Corporation of China (No. SGXJ0000KXJS1700841).