Study On Multi-objective Short-term Scheduling Methods For Hydropower System Responding To Load Demands Of Multiple Power Grids In Southwest China

With the construction of extra-large river basin cascade hydropower plants and the implementation of the power transmission project from west to east,China has built several hydropower bases in the southwest,which compose large scale hydropower systems and show distinctive operation characters.These hydropower systems contain a large number of giant hydropower plants in a high concentration,which result in the trans-provincial absorption of excess hydro-electricity for the resolve of the contradiction between electric power consumption and electricity production.Therefore,the mode of southwest hydro-electricity consumption has changed from local absorption to inter-regional absorption,resulting in more complex coupling constraints in cascade hydropower plants scheduling,and demanding hydropower plants for multiple power grids peak shaving while satisfying all conventional operation demands.These above factors made a big difference to the existing management and scheduling mode,serious challenged the traditional optimization methods of hydropower system generation scheduling.Taking the Hongshuihe and Jinshajiang river basins as engineering background,this dissertation focused on the multi-objective coordination optimization problem of trans-provincial absorption hydropower plants,and mainly studied on the following aspects:1.the peak shaving operation of hydropower plants serving multiple power grids with great load level difference;2.the multi-objective optimal scheduling method for hydropower plants considering complex operation constraints;3.coordination operation of large scale hydropower system in provincial power grids.The main contents of this dissertation are described as follows:(1)For the complex multi-objectives response demand for cascade hydropower plants in operation planning,a short-term optimal scheduling method based on region search strategy is proposed.Firstly,a multi-objective nonlinear programming(NLP)model is presented that aims to regulate peak loads and enhance stored energy of cascade hydropower plants.To formulate this model,the nonlinear operation constraints of hydropower plants are modeled by polynomials,and an improved constraints method based on region search strategy is presented to solve the proposed NLP model.The proposed method can generate a set of Pareto solutions and each solution represents an operation planning of the cascade.Finally,a fuzzy-based membership value assignment method is employed to extract a best compromise solution for final implementation.A case study of the hydropower plants of the Beipanjiang cascade in China is used to test the proposed approach,verifying its success in generating a practical operating schedule while providing abundant information to decision makers for decision support.(2)Focused on the coordination optimization of hydropower generation maximization objective and peak shaving objective of multiple power grids,a multi-objective optimization approach that considers the backwater influences between reservoirs is developed to solve the day-ahead scheduling of inter-regional absorption cascade hydropower plants.Taking the backwater influences into consideration,a multi-objective mixed-integer linear programming(MILP)model is presented to deal with the short-term hydropower generation scheduling that aims to regulate peak loads of multiple grids and enhance power efficiency.Non-linear constraints processing strategies is proposed to deal with the complex operation constrains of hydropower generation;and an improved objective adjacent scale method is presented to aggregate the peak-shaving objective functions of multiple grids.Then,the proposed model is solved by the improved constraints method presented in Section 2,and a set of well distributed Pareto solutions are obtained.The case study from the hydro plants of the TSQ cascade is used to test the proposed model,and the results show that it is capable to satisfies all constraints of hydro plants,and also performs a decrease in the peak load of multiple power grids while provides an enhancement in power efficiency simultaneously.(3)Focused on the short-term scheduling problem and the unit commitment problem of cascade hydropower plants that serves multiple power grids and face complicated unit grid-connected constraints,an integrated method is proposed to generate the operation schedule of cascade hydropower plants and the inner-plant economic operation result of units.Firstly,a power station reconstruction strategy is presented to handle such hydro plants that facing the unit grid-connected constraints,and units in one hydro plants and serving same power grids are reconstructed to a single power station.Secondly,a coordination algorithm is developed to calculate the optimal generation schedule of these power stations,in which the operation constraints of hydro plants,the peak shaving demands of multiple grids and the power transmission constraints have been considered.Thirdly,an economic operation method based on the goal programming is constructed to obtain the actual schedule of hydro plants and units with the aim reach the economic operation of hydropower while minimization the difference between the actual schedule and the optimal generation schedule.Finally,based on the obtained actual schedule,the corresponding power distribution plan among receiving-end grids are computed.The case study from the Xiluodu-Xiangjiaba cascade is used to test the proposed method,and the results show that it is capable to satisfy all the hydropower plants operation and power transmission constraints while regulate the peak loads of multiple grids effectively.(4)Focused on the medium and short-term peak shaving operation of large scale hydropower system serving multiple power grids,this paper presents a scheduling method for inter-basin hydropower plants scheduling that considers multiple forecasting load curves.In the first stage,a MILP model that considers three typical load curves is constructed to calculate the preliminary generation schedule of hydropower plants and the electricity trans-provincial transmission plan in large time scale.Then,in the second stage,a coordinated solving framework that takes the current load curve of power grids as correlation factors is developed.In each iteration,a fast solution strategy is proposed to calculate the ideal hydropower generation schedule in hourly time scale,and a goal programming is formulated to generate the operation scheduling result of each hydropower plant that aims to achieve the above ideal result.The case study from the Hongshuihe and Jinshajiang cascade hydropower plants in the southern China is used to test the proposed method,and obtained practical hydropower plants operation schedules and reasonable power distribution results of multiple power grids that can satisfy hydropower plants generation constraints and response the peak shaving demands of all receiving-end power grids.