Study On The Evaluation Method For Contingency Cost Used In Power System Risk Assessment

In China, with the rapid development of power system, the constructing of power system market, more and more renewable energy integration, even more uncertainties should be considered in the stages of power system planning and security assessment. Risk analysis is a powerful tool to evaluate the influence of the uncertainties, which can both consider the uncertainty and economy facts of the probability events. Power system risk assessment includes static risk assessment and transient risk assessment. And, to properly estimate the cost consequences by the contingencies is their core issue. In this paper, the cost consequences of a contingency are considered as the minimum control cost to move the system from the failure state (instability) to the normal (stability) under the contingency. In this thesis, cost consequences evaluation methods for both static and transient risk assessment are deeply investigated.Firstly, in power system static risk assessment, the cost consequences are determined through solving a linear optimal control model based on power flow sensitivities. In the model constraints, only the lines whose power exceeds the transmission limit are considered so as to reduce the dimension of the optimal model. Then the sensitivities of the power flow with respect to the output of generator and the dispatchable load are derived, which is used to linearize the power flow constraints so as to convert the problem into a typical linear optimal model. Since adjustment of the generators and load may cause the unbalance of power flow, active power of the slack bus are treated as an equal constraint in the optimal model. The effectiveness of the proposed method is validated by some systems, such as IEEE 24-bus system and New England 39-bus system.Secondly, in power system transient risk assessment, the trajectory sensitivities are employed to properly consider the transient stability constraints in the optimal power flow (OPF). The minimum objective of the OPF is the contingency cost to be determined, and the generator output and dispatchable load are considered as the optimal (control) variables. In the optimal process, adjustment to the generator output is firstly considered if generators have adequate reserve capacity. Otherwise, the load curtailment with high control cost is employed to ensure the stability. The effectiveness of the proposed method is also validated by some systems, such as IEEE 14-bus system and New England 39-bus system.Researching work of this thesis is helpful for power system planning and security assessment with properly considering the uncertainties of the contingencies.