Research On Complementary Dispatching Models And Solving Methods Of Cascade Hydro-Wind-Photovoltaic Power System

As the largest energy consumer in the world,China plays a pivotal role in the low-carbon transition process of global energy.Since the Paris Agreement,China has proposed a new climate action target,―peaking carbon dioxide emissions before2030 and achieving carbon neutrality before 2060‖,which has injected a strong impetus for China to develop clean energy and promote energy supply-side reform.Documents pertaining to the―14^th Five-Year Plan‖adopted across 31 provinces in China clearly state that it is necessary to strengthen the development of clean energy,use the advantages of regions rich in clean energy resources according to local conditions,and improve the level of low-carbon utilization of energy.Major power generation companies have successively proposed new installed capacity and power generation targets for clean energy in the next 5-10 years.This is self-evident to the green and low-carbon effect of using clean energy.However,due to the volatility,randomness,and anti-peak shaving characteristics of new energy power generation such as wind power and photovoltaic power,large-scale grid-connected wind power and photovoltaic power will inevitably bring many difficulties to grid dispatching and operational management,which have not only caused the frequent occurrence of the abandonment of wind power and photovoltaic power,but also severely restricted the process of clean and low-carbon energy in China.To cope with this issue,it is necessary to explore multi-energy complementary systems to utilize adjustable power sources（such as hydropower）to compensate for the output fluctuations in wind and photovoltaic power,and increase its grid-connected power consumption.The essence of complementary dispatching research is to consider the complementary modes of the system after wind and photovoltaic power are connected.Complementary dispatching faces the following challenges:uncertainty of power generation is increased;system dimensions and constraints are increased;conflicts in the coordination of scheduling objectives are intensified;difficulty in efficiently solving models is increased.It is urgent to study how to construct hydro-wind-photovoltaic complementary dispatching models that consider multiple factors,which can achieve efficiency through use of using cascade hydropower to suppress the output fluctuations of wind and photovoltaic power,promoting their consumption and meeting the load demand imposed by the gird.In this background,this paper takes the cascade hydro-wind-photovoltaic multi-energy complementary system as the research object,and systematically studies the cascade hydro-wind-photovoltaic complementary dispatching models and its solving methods considering many factors at different time-scales.It is aimed at providing technical support for the multi-factor complementary dispatching operation of large-scale hydro-wind-photovoltaic power system,and also offers a reference for strengthening the integrated management of the basin’s clean energy complementary bases and promoting the low-carbon transformation of the energy structure.The main research results are as follows:（1）Based on the criterion of system reliable output in the long-term dispatching scale,a complementary dispatching model was established based on the traditional long-term dispatching model of cascade hydropower,which aimed at maximizing the annual power generation and maximizing the reliable output of the complementary system.The solution strategy of the multi-objective high-dimensional model was improved from three aspects:feasible region,initial trajectory,and search-step size.The proposed model and method give full play to the flexible and powerful compensation and regulation ability of cascade hydropower stations,reduce the output fluctuation of wind power and photovoltaic power,and increase the total power generation and reliable output of the complementary system.Complementary operation can improve the annual water distribution from cascade hydropower,reduce the proportion of power generation during both the wet and dry seasons,and improve the stability and reliability of electricity supply.（2）Considering the uncertain factor of wind and PV output and the energy storage effect of cascade hydropower in the short-term dispatching scale,a complementary dispatching model with a random influence coefficient of wind-PV output was established with the goal of maximizing the incremental energy storage of cascade hydropower.The conditional generative adversarial network was used to generate random scenarios of wind-PV output,which can eliminate the constraint of the probability distribution model and more accurately fit the actual wind-PV output process.The PSO-DP internal and external nested optimization framework was used to solve the problem.The proposed model brings the short-term complementary dispatching results closer to the actual operating situation,realizes a more reasonable distribution of water resources and electricity among cascade hydropower stations,and reduces the compensation loss of cascade hydropower.（3）Considering the factor of grid load demand in the short-term dispatching scale,a complementary dispatching model differing from the traditional one-way information flow was constructed.The goals were minimizing the output-load difference index,maximizing clean energy generation and maximizing the cascade hydropower storage increment.The output-load matching target was coordinated by way of quantity-shape coupling.A two-stage decoupling optimization method was used to solve the model:in the first stage,the improved firefly multi-objective algorithm combined with a reverse learning strategy was adopted;in the second stage,the PSO-DP internal and external nested optimization framework was employed to ascertain the optimal load distribution.The proposed model and method can guarantee the consumption of wind power and photovoltaic power,realize coordination between electricity supply and load demand,and improve the efficient utilization of water resources,which provides a new idea for the construction of a short-term complementary dispatch model of the hydro-wind-photovoltaic power system.（4）Considering the safety factor for basin flood control in the short-term dispatching scale,a method for calculating the elastic space with safety and efficiency of the flood limit water level based on the concept of the dynamic flood limit water level and a complementary operation model of the hydro-wind-photovoltaic power system during the flood season were developed.Pre-discharge capacity constraint method and storage capacity compensation method were used to calculate the expansion in storage capacity.The G-H copula function and GAN-GMM algorithm were used to control the uncertainty around the amount of runoff and wind-PV output during the flood season.Adopting the elastic space with safety and efficiency of the flood limit water level considering the risk of flood control can increase the consumption of wind power and photovoltaic power during a flood within a safe range,reduce the abandonment power of cascade hydropower,and improve the effective utilization of water resources.