Reliability Assessment And Expansion Planning Of Wind-thermal-hydro Power Systems With Cascade Hydropower Using The Interval Method

With the depletion of fossil energy and the deterioration of environmental problems,countries all over the world are rapidly developing renewable energy,such as hydropower,wind power and so on.In the process of development and utilization of water resources,there often exists cascade hydropower stations comprised of several hydropower stations in the basin.Moreover,the global total rated capacity and energy production of wind power are increasing every year.The seasonal pattern and coupling of cascade hydropower and the intermittency in the fluctuation of wind power bring challenges to the reliability evaluation of wind-thermal-hydro power systems with cascade hydropower stations.Therefore,it is necessary to study the reliability of wind-thermal-hydro power systems with cascade hydropower stations.Under the support by the National Key R&D Program(2017YFB0902200)and the State Grid Corporation Science and Technology Project(5228001700CW),this thesis studies the reliability of wind-thermal-hydro power systems with cascade hydropower stations.Reliability considering the optimal operation of cascade hydropower stations and the uncertainty of primary energy sources with interval method,as well as generation expansion planning of wind-thermal-hydro power systems are studied in detail.There are hydraulic and electric connections among cascade hydropower stations.The discharge of the upper hydropower station will affect the output of the next-level hydropower station.Its output belongs to the multi-stage decision-making problem in which the decision-making of adjacent stages interacts with each other.In order to maximize the utilization of water resources and coordinate the output between power stations,a reliability assessment method for wind-thermal-hydro power systems considering the optimal operation of cascade hydropower stations is proposed based on sequential Monte Carlo method.Firstly,the sequential Monte Carlo method is used to extract the state duration of the units.Then,the output of systems is calculated according to the operation strategy and the optimization model of the wind-thermal-hydro power systems.Finally,the reliability index of the systems is obtained.Case study shows that the reliability of systems can be improved by optimizing operation of cascade hydropower stations in the process of reliability assessment.The runoff of cascade hydropower stations and wind speed are uncertain,and there are errors in the predicted value,which will affect the reliability assessment results.In order to take into account the effect of primary energy uncertainty and prediction error on the reliability of systems,the uncertainty is characterized by interval numbers.Based on interval optimization,the reliability evaluation model of wind-thermal-hydro power systems is established.Firstly,the interval optimization model of wind-thermal-hydro power systems with minimum load loss interval is established.Then,the interval optimization model is transformed into a deterministic model by using interval probability degree.Finally,based on the deterministic model,the sequential Monte Carlo method is used to evaluate the interval reliability of systems.Compared with the deterministic reliability assessment,the reliability evaluation with interval method can reflect the influence of primary energy uncertainty.Case study shows that the midpoint and radius of LOEE increase 6MWh/a and 19MWh/a,respectively.In order to deal with the growth of load demand,the generation expansion planning of systems should be carried out on the premise of ensuring the reliability of systems.Considering the optimal operation,reliability constraints and price uncertainty,the generation expansion planning model of wind-thermal-hydro power systems is established based on the interval optimization theory.Genetic algorithm is used to solve the model.In order to reduce the computation complexity of reliability index,an approximate calculation method of reliability index based on typical days is proposed.Based on the reliability evaluation with interval method,a typical day that contributes to the reliability index is selected by setting a typical day threshold.Then the output of the system is optimized in each system state within a typical day.Finally,reliability index of typical days is calculated to approximate the reliability index of systems.Case study shows that the generation expansion plan taking into account the primary energy and price uncertainty can be obtained based on the interval optimization;When typical days increases from 20 days to 30 days,the upper and lower bounds of the LOEE increase by no more than 2.7%,When typical days increases from 30 days to 89 days,the upper and lower bounds of LOEE almost remain unchanged.This shows that only typical days have an effect on the reliability index of systems,and the validity of the approximate calculation method is verified.