Research On Integrated Models And Methods Of Cascade Hydropower Stations' Short-term Optimal Operation Under Complex Conditions

Hydroelectric energy,as a kind of clean and renewable energy with the most mature development and operation technology,plays an essential role in the energy consumption structure of our country.Under the impact of clean-energy policy,China's hydropower industry has a huge space for development.In recent years,hydropower has become the major momentum for power investment and clean energy development,and plays an increasingly vital role in the adjustment of China's energy structure.With the gradual improvement of hydropower project construction and the continual expansion of river basins' development,the operation and management of cascade hydropower stations are getting more and more important in hydropower development.Therefore,it is of great significance for the development of China's hydropower industry to carry out research on joint optimal operation of cascade hydropower stations,fully tap into the compensation regulation capacity among cascade reservoirs,and enhance the overall utilization rate of hydro resources as well as power generation benefits.Characterized by a large scale and complex operation modes,cascade hydropower stations are under the influence of such factors as aftereffect and uncertainty,which makes their short-term optimal operation complicated and therefore a research difficulty in the field of water resources management.Meanwhile,it is directly applied to actual production to guide the real-time operation of cascade reservoirs.The formulation and implementation of optimal operation schemes directly determine the actual operation process of cascade reservoirs,which is related to the power generation benefits.Thus it is of great theoretical value and practical significance to delve into this issue.From theoretical research to practical application,this thesis conducts a comprehensive and in-depth study on the construction and solution of cascade hydropower stations'short-term optimal operation models as well as the decision making and implementation of optimal operation schemes,using the theories and methods of water science,statistics,operational research and management science,etc.The main research contents and achievements are as follows.(1)Study on improvement of the traditional objective function under the 'electricity to water' mode.Under this mode,there is an unreasonable phenomenon that the traditional objective function is not accurate enough to calculate cascade hydro energy,which leads to a discrepancy between minimum energy consumption and maximum energy storage.Considering the differences in power generation efficiency and water utilization rate among hydropower stations and the influence of future operation mode,the traditional objective function is modified by introducing the energy efficiency coefficient,which unifies energy consumption and energy storage.Then,the Successive Approximation Algorithm is employed to optimize the energy efficiency coefficient of each hydropower station,based on which a new objective function of consistent energy consumption and storage is put forth.It is more suitable for the optimal operation mode,and its advantages are verified by an example.(2)Study on the general objective function of maximum cascade energy production and storage under a complex operation mode.The operation modes of cascade hydropower stations are becoming more and more complicated and the traditional single objective function cannot meet the requirement of different operation among cascade reservoirs.As a remedy,from the angle of cascade total energy in long-term operation,power generation benefits are divided into obtained benefit-energy production and future benefit-energy storage in one operation cycle.Then the general objective function of maximum cascade energy production and storage is put forward and applied to the complex hybrid operation mode.And an integrated model of cascade hydropower stations' short-term optimal operation is developed.Finally an example is given to verify the rationality and feasibility of the objective function and the integrated model.(3)Study on the formulation of precise schemes of cascade hydropower stations'short-term optimal operation.In order to meet the requirement on precise operation schemes for the actual production of cascade hydropower stations,an in-depth research is conducted from two aspects:the accurate construction and the precise solution of optimal operation models.In model construction,the influence of water hysteresis on the objective function is taken into consideration to develop the integrated model of cascade hydropower stations' short-term optimal operation with aftereffect.In model solution,the influence of both water hysteresis and tail water level variation on optimization results are taken into account.The BP neural network is used to precisely calculate the complex aftereffect variables(i.e.downstream reservoir inflow and upstream reservoir tail water level),enabling an accurate simulation of the operation process of cascade reservoirs.Plus,the influence of in-plant load distribution and startup-shutdown water consumption on optimization results is also considered.The POA-DP method is proposed to solve the model considering both intra and in-plant optimal operation.Combining the above approaches,an example is given to verify the practicability and advantages of the proposed methods for formulating precise optimal operation schemes.(4)Study on the formulation and implementation of optimal operation schemes considering the impact of uncertainties.In order to avoid the adverse effects of uncertain reservoir inflow and power load on cascade reservoirs' safe,economic operation,firstly the three implementation modes of optimal operation schemes are evaluated and ranked by post-assessment method.Having selected the optimal implementation mode,the advantages of both conventional and optimal operation are combined and the concept of warning water level in operation rules is adopted to improve the formulation and implementation of optimal operation schemes.Finally,the practicability of these approaches is proved by the risk-benefit analysis of a cascade system under different operating conditions.(5)Study on the adaptive calculation method of reservoir warning water level based on predicted information.To address the problem that when calculating Xiaoxuan's warning water level the subjective method is not scientific enough and hence cannot guarantee the safe and economic operation of the cascade system,this thesis focuses on studying the objective calculation method.Firstly,the similarities between Xiaoxuan's upper warning water level and flood-limit water level,between its lower warning water level and drought-limit water level are systematically analyzed.Based on the calculation principle of flood-limit and drought-limit water levels,Xiaoxuan's upper and lower warning water levels are hierarchically calculated with the predicted information of Pankou Reservoir's daily generated power.In addition,to further boost power generation benefits,Xiaoxuan's upper warning water level is adaptively calculated and flexibly controlled by using Pankou's predicted daily load process on the basis of the prior static calculation.Finally,the feasibility and advantages of the proposed dynamic calculation method are verified through case study.