| The air is used as the cooling medium in the cold side of the direct air cooling unit.The water consumption is more than 80% more than that of the wet cold unit with the same capacity.It has been rapidly developed and widely applied in the northern area with abundant coal resources but poor water resources.In a direct air cooling system,the exhaust pressure at the outlet of a steam turbine is called back pressure,and the quality of its control directly affects the safety and economic operation of the whole unit.At present,the single-stage or cascade PID control methods are mostly used in the back pressure control of direct air cooling unit,but these two control methods have high dependence on the mathematical model of the controlled object,and can not automatically adjust the parameters of the controller online.Therefore,they can’t achieve the desired control effect.This paper takes the 2×300MW CFB unit as the research platform to study back pressure.Based on the analysis of the principle and characteristics of the direct air cooling system,the main influencing factors of the backpressure are determined.Then,three typical working conditions are selected for the step disturbance test of the axial fan speed under the condition that the ambient temperature is basically unchanged.Finally,the test run data was collected from the DCS engineer station,and the mathematical model of the direct air-cooled back pressure control system was established by the particle swarm optimization algorithm.Aiming at the characteristics of large delay,large inertia,time variation and nonlinearity of direct air-cooling unit back pressure control system,this paper proposes a control algorithm based on improved Smith compensation method combined with fuzzy PID.After the establishment of the system model,an off-line simulation control system is constructed and compared with the control effect of the conventional PID control algorithm and fuzzyPID control algorithm.The simulation results show that the fuzzy PID control algorithm based on the improved Smith compensation has better dynamic performance and steady state performance.And can adapt to the changes in operating conditions.The model’s adaptive ability and anti-jamming capability of the controlled system.Based on the actual field operation data,this project combines theoretical research with practical application,establishes the mathematical model of direct air-cooled unit back pressure control system,improves the back pressure control strategy,and controls the back pressure control system of the same type of direct air-cooled unit.Strategy optimization has a certain guiding significance. |
