Research On Rapid Load Change Control Strategy Of Coal-Fired Power Plant

More and more new energy power like wind and solar power are generated nowadays and they will influence the stability of power grid for the huge-fluctuation and randomness. It is necessary for coal-fired power plants to improve their load change capability so as to satisfy the load dispatch demand of power system. Compared with the drum boiler-turbine units, the once-through boiler-turbine units, which are widely used, have a smaller thermal storage at boiler side. Their coordinated control system takes the mode of turbine follow and the load change is always slow. It’s valuable to make a research on rapid load change control strategy of once-through boiler-turbine units.The first strategy is a feedforward controller based on stable-inversion, which leads feed water flow and load-fuel instruction to change ahead as load instruction changes. The nonlinear model of once-through boiler-turbine units is reduced and the feedforward control variables are figured out based on the stable-inversion theory of nonlinear system. The feedforward controller enables the outputs of the coordinated system to approach to set points quickly and improves the delay of boilers. The second strategy is adding condenser throttling upon the original feedback control channel of unit load in turbine follow mode and altering the condensate flow to regulate the output of turbine fast. The principle of condensate throttling and the model between condensate flow and power output have been worked out previously. Work in this paper focuses on the modification of dual control structure so that condensate throttling, the faster channel, can be controlled effectively to increase the response rate directly. Specially, the control of deaerator level is added into the original feedback control channel, which is slower in regulating unit load but economically. The modification of dual control in deaerator level prevents the huge-fluctuation in water level and guarantees the security of unit. Besides, a decoupling controller is also given to achieve the feedback control of the other two outputs of coordinated system and the coupling of them is removed. Finally, simulation tests and analyses are carried out to prove that the coordinated control strategy combining condensate throttling proposed in this paper can effectively improve the load change capability of once-through boiler-turbine units. Meanwhile, the stability of steam pressure and deaerator level during condenser throttling are also maintained.