Energy And Reserve Scheduling Considering Transmission Constraints

With the expansion of power system and the increase of uncertainty,spinning reserve deliverability is more and more affected by transmission congestion,and the coupling relationship between spinning reserve and energy is very strong.Therefore,it has become an important part of security and economic operation of power system to study simultaneous scheduling of energy and spinning reserve considering network constraints.On the other hand,it is necessary to coordinate the relationship between economics and reliability to achieve the optimal allocation of spinning reserve.Since the probabilistic method pays more attention to the social benefits of spinning reserve than the deterministic method and it considers the probabilistic characteristics of the system reliability,the probabilistic method has greater potential than the deterministic method.Two different types of probabilistic models are adopted in this paper.One is an optimization model with reliability index constraints,and the other is an optimization model based on cost-benefit analysis.Although these two probabilistic models can achieve reasonable scheduling of energy and spinning reserve,but they are complex and the solution efficiency is low.So it is of great significance to find methods to achieve the optimal solution of these two models fast.Firstly,this paper summarizes several classical literatures about scheduling of energy and spinning reserve.Through the unified expression of variables and parameters,the representative models are introduced in detail.The optimizition models are further classified and summarized based on the principles of scheduling strategies,whether the network constraints are considered,the method types,the number of scenarios and so on.The essence of the evolution of the joint scheduling models in recent years is clarified by the observation and comparison of each model.It lays the foundation for the proposed simultaneous scheduling models of energy and spinning reserve and their solution methods.Secondly,this paper proposes a scheduling model of energy and spinning reserve with reliability index constraints and transmission constraints,and proposes an iterative algorithm to solve the model quickly.The iterative algorithm converts a complicated optimization problem into two optimization problems that are easy to solve,and the validity of the solution is ensured by iterative process.In each iterative process,the up spinning reserve cost is firstly minimized with respect to reserve constraints and reliability constraints by the upper level of optimization without considering the network constraints,and then the lower level of optimization considering network constraints is used to minimize the sum of expected interruption cost and down spinning reserve cost with respect to various postcontingency constraints under each contingency event to alleviate transmission congestion,and the obtained optimization results are used to measure the reliability of the users.If the reliability requirements are not meet,the upper and lower level of optimization in the next iteration is used to adjust the capacity of up and down spinning reserve respectively.Iteration stops until the reliability requirements of all users and the specified convergence criteria are met.As the previous similar method does not consider down spinning reserve which may lead to sub-optimal solutions,or even no feasible solution.Therefore,down spinning reserve is considered in the optimization model and the method is improved in this paper.The RBTS system is used in this paper to verify the feasibility of this method.This paper compares the results with the previous similar method that does not consider down spinning reserve in case studies to highlight the importance of down spinning reserve in the market-clearing models considering network constraints.Finally,this paper proposes a simultaneous scheduling model of energy and spinning reserve considering transmission constraints based on the cost-benefit analysis method and some methods are proposed to solve the model quickly.Considering that the computational efficiency is limited by the large number of constraints and variables introduced by N-1,a screening method for redundant line outage scenarios is proposed to reduce the number of variables and constraints,and the method of screening the redundant network constraints under normal conditions and the proposed method of screening redundant network constraints of each contingency is further used to reduce the number of constraints.Thereby the size of the joint optimization model is reduced,the solution efficiency is greatly improved.This paper also proposes a new redundant network constraint screening method based on the fact that the load shedding of each contingency is usually small,and an iterative algorithm along with this new screening method is proposed to solve the joint optimization model.This new redundant network constraint screening method can filter out a large number of redundant network constraints by ignoring the load shedding on the nodes,which greatly reduces the scale of the optimization model.And the optimal solution of the model can be achieved fast by iterative verification method.This iterative algorithm not only has the simple and direct features of iterative verification method,but also overcomes its shortcomings that more iterations are needed,and accelerates the convergence speed of iterative process.The single-area system of IEEE RTS and the IEEE 118-bus system with 54 units are used in this paper to verify the effectiveness of the screening of redundant network constraints and line outage scenarios,and the accuracy and rapidity of the corresponding optimization algorithms are validated.