Abstract: Batteries have been widely applied in energy storage and coal-fired power plants combined frequency modulation due to the technical advantages and favorable economic performance of the modulation technology. However，the development of the combined frequency modulation system is impeded for lack of sophisticated design scheme.In order to facilitate the scaled and standardized development and the designing level of energy storage and thermal power combined frequency modulation systems in China，analysis was made on 2×350 MW units of Guodian Zhaoqing Thermal Power Company Limited based on the engineering cases of China Huadian Engineering Company Limited.Key technologies in system capacity selection，site planning，overall layout，access accounting，short circuit current calculation，relay protection configuration，control and communication，and fire-fighting system were summarized during the research on the frequency modulation auxiliary service energy storage of the two units.It provides technical basis，impetus and demonstration for the engineering design and construction of new energy storage and thermal power combined frequency modulation systems.

Key words: power storage with batteries, thermal power plant frequency modulation, ancillary service, combined frequency modulation, system design, LiFePO4 battery, new energy