## 1 Introduction  
Limited by light resources' features and natural conditions, photovoltaic power generation has strong volatility and randomness, and the problem of large-scale photovoltaic consumption remains to be solved. Hydropower has the advantages of rapid adjustment and storage of hydropower. Promoting hydropower and new energy jointly to improve the absorption capacity of new energy is one of the more feasible methods at present [1]. With the grid connection of large-scale centralized and distributed photovoltaic power sources, the joint dispatch of hydropower and photovoltaic power becomes particularly important. Power prediction and optimal dispatch in the process of joint operation are hot research directions of current scholars [2]. The combined operation system controls the photovoltaic active power through the regulation and storage function of the reservoir and the rapid regulation ability of the hydraulic unit, so as to achieve the smooth output curve of the combined system, increase the power quality of the photovoltaic power generation, and finally improve the absorption capacity so as to achieve the purpose of increasing the energy utilization ratio of the combined system [3]. Many well-known universities in the world, such as Colorado State University and the University of Massachusetts, have long conducted research in the field of \"wind power-photovoltaic\" complementary power generation system. [PERSON] et al. studied a multi-energy complementary system using the genetic algorithm and obtained the global optimal solution [4]. [PERSON] et al. used HOMER software to study the off-grid hybrid power supply system in a village in Ethiopia [5]. [PERSON] et al. studied the theoretical performance limit of water light complementary power plants by calculating the time complementarity index of hydropower generation and photovoltaic power generation [6]. In China, although the joint development of hydropower and photovoltaic began relatively late, it has developed rapidly in recent years under the promotion of China's energy policy. In 2011, a water-light complementary power station in Yushu City, Qinghai Province, was completed and put into operation, raising the PV capacity of China's Water Optic Complementary Power Station from the initial small capacity distributed PV to MW level centralized power station [7]. Subsequently, the Longyang Gorge Hydro PV Complementary Power Station achieved an installed capacity of 850 MW, which is actually the largest hydro photovoltaic complementary system. The operation of the Longyang Gorge Hydro PV Complementary Power Station has led Chinese scholars to study hydro PV complementation. At present, China has built several \"multi-energy complementary demonstration projects\" and achieved good results. The joint operation process of hydropower and photovoltaic is a typical multi-variable, multi-objective, and complex scheduling problem, which involves a conflict of interest between hydropower and photovoltaic, among others. Most of the traditional hydropower and photovoltaic power joint operation models aim at minimizing the photovoltaic abandon volume or maximizing the benefit of the joint operation, ignoring the uncertainty of photovoltaic power prediction, resulting in a large deviation between the operation results and the actual situation. So far, researchers have made great progress in photovoltaic power randomness, including photovoltaic power prediction [8; 9; 10], random description [11; 12], and so on. On this basis, cascade hydropower units are introduced into photovoltaic power and hydropower joint dispatch to provide standby peak shaving for photovoltaic turbines [13; 14; 15] and a stochastic optimization model considering risk constraints is established [16; 17], which can improve the influence of photovoltaic power randomness on the stable operation of the power system.