Research On Cascade Hydropower Stations Short-term Optimal Operation Under The Coordination On Power Plants And Power Grid

The short-term optimal operation of cascade hydropower stations is a nonlinear, high-dimensional, multi-constraint, complex water-machine-electrical coupling optimization problem, which is constrained by hydrological runoff process, electric load demand, the units state and water demand of downstream. The short-term optimal operation of hydropower under the coordination on power plants and power grid is one of the most important research field mixed by hydropower and complexity science. With large-scale hydropower system are completed and put into operation in China, the requirements of comprehensive utilization for hydropower have been improved. The scale and topology structure of basin hydroelectric cascade energy system has become more and more complicated. The short-term optimal operation of cascaded hydropower stations emerge a series of new problems. The optimal scheduling of basin water resources is lack of effective management of unity and coordination mechanism under the background of interconnected power grid. The contradiction between power supply and demand has become increasingly prominent. The big gap between load peak and valley appears frequently and peak-load regulating capacity is not enough. In low load period, hydropower stations are often forced to reduce output and abandon water, which will cause great loss of power grid economic benefit. Therefore, it is necessary to develop new optimization theories and methods to solve these problems. This dissertation focuses on the key scientific and technical problems of optimal operation for cascade hydropower stations under the background of joint grid all over the country. Supported by the theories of hydropower science, systems science, and swarm intelligent optimization, Three Gorges cascade hydropower stations are set as the main research object. Finally, we study the modeling and the solving method of short-term optimization operation under the coordination on power plants and power grid and get valuable achievements on theories and engineering practice. The main research contents and innovations include:(1) Aiming at the influence type and extent caused by maintenance plan, health condition and running state of the hydropower unit, the evaluation index and model of hydropower unit are proposed for comprehensive operation state. Based on the suggested operation state evaluation indexes, the comprehensive operation state of hydropower units is evaluated in the current scheduling period. And then the running and stop priorities is selected for increasing or reducing the number of units. Considering the power limits of transformer, the requirements of unit cavitation vibration area and dynamic characteristics of the units, the upper and lower limits of unit stable output are determined, which gives reliable support for security and stability of hydropower station.(2) After the comprehensive evaluation of hydropower station is presented, real-time automatic generation control strategy of cascade hydropower stations is proposed by the population-based ant colony optimization. Considering minimizing water consumption as the goal in different time scales, the model of real-time generation control of cascade hydropower stations is established in single schedule period and so is the mathematical optimization model in remaining periods. Meanwhile, a multi-population ant colony optimization is proposed in this literature. According to replace the population by optimal solutions obtained in early evolution, the convergence will be accelerated. Finally, distribute the load demand to each plant and develop the schedule scheme of optimal unit combination as well as the load distribution among each unit.(3) With analyzing the commonalities and the differences between the daily generation scheduling and internal economic operation(DAI) of the cascade hydropower stations in power grid, the seamless nested mode of the the daily generation scheduling and internal economic operation(DAI) is proposed for cascade hydropower stations. Considering the feasible region conflict problem of discharge volume engendered by the different optimization goals of DAI, the optimal results of daily generation scheduling is provided as the input of internal economic operation calculation to conduct objective reverse calculus for the daily generation scheduling. The optimal scheme of DAI is got until circulation nested calculation end with meeting the constraint conditions, and the integration operation of DAI is realized which can ensure organically coordination dispatching for the water and electricity department in the center of cascade hydropower stations as well as effective reduction of the deviation between the generation plan and actual power demand of the power grid.(4) Combined with regional distribution characteristics, relationship between district power grids, the hydraulics and electric power compensation of cascade hydropower stations, a division grade refinement scheduling method of cascade hydropower stations is proposed for the coordination model of the power plant and grid. With dividing the subregion and classification for short-term generation optimization scheduling of cascade hydropower stations, the short-term generation optimization scheduling models of cascade hydropower stations for energy maximization and benefits maximization are established according the water level fluctuating process of the long-term optimized scheduling. The optimal the optimal generation flow, active load distribution solutions and short-term optimal generation scheme are obtained by the established model to improve the short-term generation benefit of cascade hydropower stations.(5) The nonlinear coupling characteristics of the hydrologic processes, power load demand and water demands of different departments is the optimization modeling foundation for the hydrothermal power system. According to plentiful-low and peak-valley compensation characteristic of the hydrothermal electricity energy, the short-term combined optimization scheduling model of the hydrothermal power system is established. And the heuristic constraint processing strategy and optimization method of the hydrothermal power system based on the real difference quantum evolutionary algorithm, are put forward to deal with the operation constraints of the system effectively. To provide theoretical basis and number basis for the regional network safety, stability and economic operation, the operation domain boundary of the hydrothermal power system is been described accurately and short-term optimal generation scheme is formulated for the hydrothermal power system.