Research On Iteative Solution Method Of Short-term Optimal Scheduling Model Of Cascade Hydropower Stations

Many large-scale cascade hydropower stations have been built in our country.It has become the focus of hydropower development to coordinate and optimize the operation as a whole and give full play to the overall benefits of the cascade.But at present,the optimal operation of hydropower is restricted by many factors,such as close connection between hydropower and electric power,complex target demand and increasing constraints.It is difficult for the models to solve and it is difficult to meet the timeliness,practicality and refinement requirements of the current scheduling.This paper aims at solving the complex problem of short-term optimal operation of cascade hydropower stations.Taking eight hydropower stations in Wujiang Cascade as examples,and research on iterative solution method.Analyze the different factors that make the solution difficult,and propose different solutions.The main contents are as follows:(1)In view of the limitation of time coupling constraints on the solution of short-term optimal scheduling model,an iterative solution method with variable time period is proposed.The problem is transformed from simple to complex by establishing a variable time period long model.Then,according to the characteristics of constraints,appropriate methods are adopted.Finally,the successive approximation algorithm is used to solve the multi round iterative problem.Verified by examples,this method can solve the influence of time coupling constraints to a certain extent,gradually get better results.(2)The problem simplification will cause errors when solving the peak load regulation optimization model.A method of adding unit iteration to solve the problem is proposed.First of all,the feasible initial solution is obtained by using the common short-term optimization method with the power plant as the calculation unit.Then the unit is solved iteratively,determine unit combination and upper and lower limits of output.Then a series of treatment strategies are adopted to distribute the load to each unit.Verified by examples,The proposed method can reduce the scale of problem solving,ensure the efficiency of solution,and meet the requirements of refinement and practicality to ensure the accuracy of solution.(3)It is difficult to solve the model due to the large-scale multipliers in solving the unit load distribution problem.A simplified solution method is proposed in order to reduce the impact of the multiplier scale on the solution.Firstly,the period cascade power constraints are replaced with one constraint.The new con-straint is further approximated using the aggregate function and a dual optimization problem with on-ly one multiplier is established.Then,the sub-gradient method and successive approximation method are used to solve this new problem.Case study for Wujiang cascaded hydropower system shows that the method can effectively reduce problem complex it,improve solution efficiency and solution quality,and satisfy the timeliness and practicality requirements of short-term optimal scheduling.