As more and more wind power and photovoltaic power are connected to the electrical power system, it brings great challenges to the stability of power grid. Concentrated solar power (CSP) plant with thermal energy storage (TES) can undertake the task of load regulation and frequency regulation in power grid by balancing the electricity demand and generation.
However, the maximum load variation rates of the CSP plant are not known, which restricts sufficient utilization of its advantages. In this study, a dynamic simulation model of CSP plant was built by using the APROS, and the dynamic characteristics were investigated by applying the step disturbances to molten salt flowrate, molten salt temperature, and the opening of steam regulating valve. Based on the results of dynamic characteristics, the control strategies were developed with the consideration of thermal storage in system and the feedforward signal of setting load and load variation rate. Then, the maximum load increase and reduction rates within different load ranges were studied. The results indicated that steam regulating valve, molten salt flowrate and molten salt temperature could be used to control turbine power, steam pressure and steam temperature, respectively. The designed control system could effectively follow the load variation with load deviation less than 0.3 MW and steam temperature deviation less than 1.2 °C in the condition of load variation rate at 3% Pe·min−1, which was superior to the conventional control strategy not considering the thermal storage in system. The maximum load increase and reduction rates were 11.57% Pe·min−1 and 8.94% Pe·min−1 within the load range of 75%THA-100%THA, and they were 10.42% Pe·min−1 and 7.46% Pe·min−1 within the load range of 50%THA-75%THA, respectively. The above load variation rates were first demonstrated for CSP plant, which could provide important guidance for plant operation in load regulation task and the load dispatching on grid side.
Simulation software
The software used to establish dynamic simulation model of the CSP plant is APROS, which is developed by VTT Finland. It has been widely used in the modeling of coal-fired power plant and nuclear power plant. APROS comprises thermal components (e.g. turbine, pump, and heat exchanger) and automatic control components (e.g. controller and logical operators) for dynamic simulation of thermal power plant. For each component the dynamic simulation is realized by solving non-linear differential
Dynamic characteristics of the CSP plant
In the practical operation, the molten salt flow in SGS and the opening of steam regulating valve are the potential adjusting parameters to maintain the turbine power and steam parameters at the design values. Therefore, it is necessary to understand plant dynamic characteristics under the disturbances of these parameters before designing the control strategy. In this study, on the basis of 50%THA condition, step disturbances were applied to the molten salt flowrate, molten salt temperature,
Design of control strategy
Based on the results of above acquired dynamic characteristics, the control strategy was designed by referring to the coordinated control system of coal-fired power plant. The molten salt flowrate and the opening of steam regulating valve were selected as the main adjusting parameters. The turbine output power was controlled by adjusting the opening of the regulating valve, the main steam pressure was controlled by adjusting the molten salt flowrate, and the main steam temperature was
Maximum load variation rates of the CSP plant
In this section, the maximum load variation rates in load increase and decrease processes were investigated. Since the load variation rates were related to the load level and variation amplitude, the load variation interval was set to be 50%THA-75%THA and 75%THA-100%THA with the amplitude of 25%THA. Considering the safety of power generation system, the limits for the main steam pressure and the steam temperature are: 1) the temperatures of the main steam and the reheat steam should be within
Conclusions
In this study, a dynamic simulation model of the CSP plant was built by using the APROS, and the accuracy and reliability of the model were verified. Dynamic characteristics of the plant were investigated by considering the step disturbances of the molten salt flow and the opening of steam regulating valve. Based on the results of dynamic characteristics, the control strategy were designed with the consideration of thermal storage in system and the feedforward signal of set load and load
CRediT authorship contribution statement
Gen Li: Writing – review & editing, Writing – original draft, Supervision, Conceptualization. Guanghan Du: Validation, Investigation, Data curation. Guixiu Liu: Software. Junjie Yan: Conceptualization, Resources.
Declaration of Competing Interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
