Research On Rapid Load Adjustment Control Of Large Capacity Coal-Fired Power Plant Based On The Characteristic Of Turbine Stored Energy

In order to guarantee the safe and stable operation of power grid, and reducing the effect of large-scale new energy power on the grid, it is important to improve the quick response ability of power plants. In the energy structure of China, coal-fired power plants still occupy a large proportion; therefore it is the only way to accept the large-scale new energy power by improving the load adjustment rate of coal-fired power plants. Although the traditional coal-fired power plants can execute rapid load adjustment, its load adjustment rate cannot meet the requirement of the grid. As the concept of turbine-stored energy proposed, it is provide a very efficient way to improve the dynamic response of the unit load. Therefore, to ensure the efficiency and safety usage of turbine-stored energy, the following works have been carried out in this thesis.1. On the basis of analyzing the energy storage characteristics of steam turbine regenerative system, a new method of condensate throttling used in the rapid load adjustment is proposed, i.e. it only needs to adjust the condensate water flow by the deaerator water level control valve to achieve a quick load adjustment, in this process the energy stored in the regenerative system is activated. Through the derivation of thermal equilibrium equation of turbine regenerative system, the principle and characteristic of condensate throttling system is discussed. The adjustment range of the unit load and the sustainable time of condensate throttling are analyzed in different unit load condition.2. Based on the analysis of equipment dynamic in the condensate throttling experiment, through a reasonable simplification and refining its main dynamic characteristics in the load adjustment process, a nonlinear dynamic model of condensate throttling system is proposed using compound modelling method which is combining the mechanism modelling and data analysis. In order to verify the accuracy and universality of the model, the simulation and verification on the 1000MW and 660MW power plants are conducted separately.3. Based on the characteristic analysis of the proposed nonlinear dynamic model, in order to overcome the nonlinear characteristic of condensate throttling system and achieve the global control performance, a fuzzy gain schedule control method is applied in the condensate throttling system. To ensure the efficiency and safety usage of condensate throttling system, the control system architecture is proposed. And in order to overcome interference between condensate throttling system and the original coordinate control system, the unit load control strategy based on the nonlinear model of condensate throttling system is analyzed. The simulation is conducted to verify the control performance in the initial stage of load adjustment, and the AGC unit performance evaluation index is largely improved.4. On the basis of analyzing the cold-end characteristic of direct air-cooling unit, condenser cooling refrigerant throttling control method used in the quick load adjustment is proposed, i.e. it only needs to adjust the cooling air flow by the frequency conversion fans to achieve a quick load adjustment, in this process the energy stored in the turbine exhaust steam is activated. Through the derivation of calculation model of turbine last stage, condenser and air-cooling fans in the variation condition, the adjustment range of the unit load and the unit thermal efficiency areanalyzed in the different unit load and ambient temperature, and then the control strategy of condenser cooling refrigerant throttling adjustment is proposed basing on its characteristic.