Optimal AGC Control Strategy For Subcritical Coal-fired Units

Power grid frequency features prominently in the safe and stable operation of the whole electric network and the life of its facilities.The frequency range is clearly stipulated in China’s Electric power system,as its constant fluctuation will not only break down the power system,but also damage the involved electrical equipment.In this connection,stability is a prerequisite of a safe and stable power grid,while a stable grid frequency demonstrates active power and load of the power grid are balanced.Nowadays,first and secondary frequency modulations are adopted to keep the power system stable.While first frequency modulation is able to reduce the small and medium load variation in the power grid.In this sense,it offers a buffer area for abrupt load changes.Compared with the secondary modulation,the first is only a deviation adjustment approach rather than a guarantee for stabilizing the grid frequency.So the secondary is engaged.The secondary frequency modulation,or AGC,automatically modifies the output of the unit using the frequency of the grid and the first modulation to adjust the deviation of the system frequency.This paper deals with the structure of the AGC control system and the formation of regional deviation as well as the energy management control center(EMS).It gives the picture of the effects of its main components and function and presents us with the concept of power system frequency modulation.Great effort is devoted to the powerside and the load-side frequency modulation,and the stability of the power system frequency modulation.Regarding the stable operation of the power system,this essay briefs us about the three main modes of its basic frequency modulation(first,secondary and third frequency modulation).According to the principle governing unit-load control,this essay recommends three basic operation modes of the unit system: boiler governs turbine,turbine governs boiler and turbine-boiler combined operation.The combined operation mode of the furnace is described in three categories: TF,BF,and the comprehensive coordination operation mode.Built on the property of the unit control system and the AGC control problems in unit No.2 of Huaneng Taicang power plant,theoretical analysis in this paper leads to an optimal scheme that can improve the performance of the AGC control.The scheme optimizes the scheme via 4 logics,namely precoaling differential,amplitude limiting,coal correction and rate limiting,first-wind pressure correction.To this end,a fluctuating load test was conducted on unit No.2 with a respective load of 210 MW,240 MW and 270 MW.The experimental data analysis with the optimized AGC control logic demonstrates that the unit takes less time to respond to the load change rate and optimizes the static and dynamic deviation in load fluctuation.The result meets the technical requirements.To sum up,the logic optimization in this paper greatly enhances the performance of AGC strategy in load control and can be applied to the daily production.Finally,the paper summarizes the performance of AGC load control and puts forward some suggestions for future research on AGC control.