Abstract
Concentrating solar power (CSP) is a promising technology for exploiting solar energy. A major advantage of CSP plants lies in their capability of integrating with thermal energy storage; hence, they can have a similar operability to that of fossil-fired power plants, i.e., their power output can be adjusted as required. For this reason, the power output of such CSP plants is generally scheduled to maximize the operating revenue by participating in electric markets, which can result in frequent changes in the power reference signal and introduces challenges to real-time power tracking. To address this issue, this paper systematically studies the execution-level power tracking control strategy of an CSP plant, primarily aiming at coordinating the control of the sluggish steam generator (including the economizer, the boiler, and the superheater) and the fast steam turbine. The governing equations of the key energy conversion processes in the CSP plant are first presented and used as the simulation platform. Then, the transient behavior of the CSP plant is analyzed to gain an insight into the system dynamic characteristics and control difficulties. Then, based on the step-response data, the transfer functions of the CSP plant are identified, which form the prediction model of the model predictive controller. Finally, two control strategies are studied through simulation experiments: (1) the heuristic PI control with two operation modes, which can be conveniently implemented but cannot coordinate the control of the power tracking speed and the main steam parameters, and (2) advanced model predictive control (MPC), which overcomes the shortcoming of PI (Proportional-Integral) control and can significantly improve the control performance.
Highlights
In recent years, solar energy has become the second-largest energy source after wind energy among the renewable energy sources that are used for electricity production [1]
Step response analysis of the concentrating solar power (CSP) plant is first performed, and we find that: (1) there is a strong coupling effect between the system inputs and outputs, (2) the external disturbance has little influence on the power generation side, and (3) in the sense of execution-level control, the design of the power tracking controller is completely independent from the heat transfer fluid (HTF) temperature control at the solar collector side
(1) The heuristic PI with fast power tracking mode (FT mode) can achieve a fast power tracking rate; this causes a considerable fluctuation in the main steam parameters
Summary
Solar energy has become the second-largest energy source after wind energy among the renewable energy sources that are used for electricity production [1]. The CSP plant must be able to rapidly adjust its power output in a wide operation range and simultaneously maintain the stability of the main steam pressure and temperature for safety and economic reasons To achieve this goal, it is necessary to perform a thorough investigation of the system dynamic behavior, and on this basis find an appropriate execution-level control strategy for controlling power tracking. In CSP plants, the steam generator dynamics are much slower than the steam turbine dynamics, and it is challenging to coordinate the control of two systems with completely different response speeds Considering these issues, this paper proposes an execution-level power tracking control strategy for CSP plants that aims at achieving the dual tasks of fast power tracking and small fluctuation in the main steam parameters by coordinating the operation of the steam generator and the turbine.
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