Multi-period Optimal Scheduling Models And Methods For Hydro-thermal-wind Power System

With the purpose of promoting sustainable development of energy, economy, and environment, it has been given abroad attention to make a great effort on the development of clean energy generation like hydro and wind power. Due to large-scale development of basin cascade hydropower stations, the spatial-temporal correlation between upstream and downstream hydropower plants becomes more closely. In the hydropower optimal scheduling model, the consideration of variation of water time delay and the influence of maintenance will promote coordination of dispatch between upstream and downstream stations and the improvement of energy-saving benefit. In addition, as the wind integration increases, it would become more difficult for grid to perform peak regulation and optimal operation because of the stochastic, uncontrollable and unpredictable characters of wind power. For the better consumption of wind power, it is urgent to realize combined optimal operation among various enegies in order to make full use of the regulation potential of cascade hydropower and thermal power. Based on the above backgrounds, this dissertation focuses on the multi-period optimal scheduling. The main research work is as follows:In aspect of short-term hydropower optimal scheduling, the model considering the optimization of water time delay is proposed. This model establishes nonlinear functions of water time delay and reservoir outflow to represent the dynamic change of water time delay among cascade hydropower stations. Meanwhile, in view of the complicated non-linear function, like cascade delay time, hydraulic-electric conversion and piecewise output limit, a novel linear modeling method is proposed. The short-term optimal scheduling problem is changed into a linear mixed integer programming problem by introducing multiple sets of state variables and constraints. Simulation results show that the feasibility and economics of scheduling can be improved by this model.In aspect of mid-long term hydro-themal optimal scheduling, the multi-scenario model considering joint optimization between generation and maintenance scheduling is proposed. Firstly, the scenario tree model is established to describe the uncertainty of water inflow and load prediction. Secondly, in consideration of the continuity of equipment maintenance scheduling, nodes are divided into different scenarios based on the predicting scenario tree, and equipment maintenance model of multi-scenario scheduling is founded through the scenario-node incidence matrix. Furthermore, electric power-related nodes and energy-related nodes were set respectively to coordinate generation and maintenance scheduling, in view to their different scheduling intervals. Finally, application examples of an actual large-scale hydrothermal system are tested and analyzed. Results demonstrated that coordinate optimization between generation and maintenance scheduling can improve energy and economic efficiency, which enhances the feasibility of generation schedules in return. It also indicates that the multi-scenario optimization can improve the applicable of the system scheduling scheme.In aspect of short-term hydro-thermal-wind optimal scheduling, the stochastic unit commitment model with the peak and valley regulation constraints in next scheduling period is proposed. Firstly, in respond to the randomness of wind power, the reduced scenarios are used to simulate wind power, and the coupling operational constraints of hydro, thermal, wind power in each scenario are formulated. Secondly, for the peak regulation issue in next scheduling period, the constraints about unit start and stop status are introduced. Finally, the proposed model is sloved by mixed integer linear programming. Simulation results show that the optimized unit commitment can ensure the output feasibility of each unit type under all scenarios, and the peak demand could be satisfied while wind curtailment during low demand time could be reduced.In aspect of mid-long term hydro-themal-wind optimal scheduling, the uncertain scheduling method based on point estimate is put forward. Firstly, taking into account the complex constraints, the long-term optimal scheduling model of wind-hydro-thermal system is established. In the proposed model, all of the coupled hydraulic, wind, thermal and electricity constraints are included. In order to reduce the solution difficulty, the above large-scale, multi-constrained, nonlinear optimization problem is converted into a mixed integer linear model. Secondly, the point estimation method is used and the estimation points of stochastic variables are generated. Then the model is solved on each estimation point vector and thus the expected value of decision variables could be calculated. Finally, numerical examples show that the proposed model could accelerate the calculation speed while ensuring the precision. In addition, the combined hydro-thermal-wind optimal scheduling could enhance the system capacity to integrate clean energy and reduce the consumption of fossil fuels.The above achievements can provide theoretical support for research and development of actural generation scheduling software, and also have the application prospect in the hydro-thermal and hydro-thermal-wind power systems.