Multi-step Integration Models For Risk-Limiting Dispatch Of Transmission Line Congestion And Outage Scene

The intermittent and volatility wind power and other renewable energy inserted power grid, transmission line congestion even outage fault caused by extreme weather like ice and snow, load fluctuation and other conditions increase the difficulty and risk of electric power system optimal dispatch. The existing operating mechanism based on deterministic N-1 safety standards plays an important role in the long-term dispatch practice. But the above dispatch mechanism has many shortcomings to deal with the increasingly complex power grid operation. It is significant for power system operation with random renewable energy resources to develop rational dispatching plan to deal with transmission line congestion and outage.The framework of risk limiting dispatch presented by international scholars takes into account the subsequent links random in the previous dispatch link. Day ahead dispatch predicts stochastic factors in hour ahead and real-time dispatch and expresses the conception of multi-step integration dispatch. Multi-step integration dispatch is mainly applied into the operation time when random factors fluctuate violently or the system is easily to fault. The difficulty and key is to describe the randoms such as wind power output and line outage, power system optimization object and system security constraints under the risk limiting dispatch framework.Multi-step integration models for risk-limiting dispatch of line congestion are established through the research on the framework. Estimated random information of the hour ahead and real-time dispatch is included in the day ahead dispatch model, which forms the three steps integration day ahead dispatch one, etc. Wind power is treated as main random information and as random variable in the model. The line security constraints are transformed into line congestion risk limiting constraints by means of the conditional value at risk(CVaR). The line congestion risk limiting dispatch is achieved by setting the scale line congestion CVaR value and confidence level. The example simulation shows the built model is rational compared with the traditional dispatch model. The novel multi-step integration dispatch model for line congestion risk-limiting is effective to solve the risk limiting in the smart operation of power system.The transmission line outage is treated as random information in multi-step integration model for transmission line outage scene. The scene set is comprised with scenes when the future operation time may occur. Estimated lines outage scene of the hour ahead and emergency state is included in the day ahead dispatch model, which forms the three steps integration day ahead dispatch one, etc. Graphical representation of the scenes in day ahead three-step constituted scene tree of day ahead dispatch. Scenes in day ahead scene tree use bayesian network conditional probability, offsetting the defect of independent line outage probability, i.e. a line outage mays cause other lines' outage probability changing. The results of numerical examples show that the established model has obvious economy advantage compared with the traditional dispatch model in the premise of the system safe operation. It provides theoretical basis for the dispatch staff to make more rational decision for system operation.