Introduction  The DCS system of two 700 MW units adopting "constant-sliding-constant" variable pressure operation mode in Zhuhai Power Plant adopts DIASYS Netmation distributed control system， which is provided by Mitsubishi company of Japan. At present， when the units are running in the AGC mode， the load changing rate is on the low side， with the poor performance of load precision control and the frequency modulation response， while the pressure and temperature of main steam， reheater steam temperature and other main parameters fluctuate greatly with bad quality of adjustment， which does no good to the long-term safe and stable operation of the units.

  Method  Through modeling of the way of control combined with experimental data， the direction of system designing was determined. Based on the basic frame construction of "Advanced Control" real time optimized control software pack， plans for primary frequency control， unit Coordinated Control System（CCS）， main steam temperature， reheater temperature control and new AGC control on the basis of advanced control technology were designed in a targeted manner. Besides， with the tests of simulation system， the initial parameters of every circuit were determined.

  Result  After the implementation of the project， the plug-in advanced control system of frequency modulation auxiliary service and the main frame DCS system realize undisturbed switching， and the comprehensive frequency modulation performance is significantly improved.

  Conclusion  The comprehensive frequency modulation performance of AGC of the units is greatly improved and the expected target is achieved while the units adopted the plug-in advanced control system using optimized control strategy. Meanwhile， the actual load rate and the precision and response speed of frequency modulation is improved， and the comprehensive frequency modulation performance is obviously enhanced， which lays a solid foundation for the units to participate in the frequency modulation market competition.