Methods Of Security Risk Assessment And Power Quality Evaluation For Transmission And Distribution Network Based On Dynamic Probability Power Flow

Based on deterministic power flow, dynamic probability power flow introduces probability theory into power flow, which gives full consideration of the uncertainty of network structure, load, wind power, charge and discharge power of electrical vehicles, et al. According to probabilistic statistical characteristics of uncertain factors, probability statistical distribution of output variables such as branch power, node voltage and line loss can be obtained. The results of dynamic probability power flow are applied to the assessment of line-breakage risk in transmission network, the evaluation of fundamental voltage quality in distribution network and the evaluation of harmonic voltage in distribution network.Dynamic probability power flow of fundamental frequency is applied to the assessment of line-breakage risk in transmission network. Firstly, dynamic probability models of load and wind power are established. Secondly, the overload probability of other wholesome lines and out-of-limit probability of nodal voltage are calculated using dynamic probability power flow of fundamental frequency considering line-breakage fault. Then, the line’s power betweenness and node’s power betweenness are given, as the weights of overload probability of wholesome lines and out-of-limit probability of nodal voltage respectively, and then sequence severity indices are obtained. Finally, integrating the probability of line-breakage in transmission network with sequence severity indices, the assessment method of line-breakage risk in transmission network is given. The validity and efficiency of assessment method of line-breakage risk in transmission network are confirmed by comparing with traditional method.Dynamic probability power flow of fundamental frequency is applied to the evaluation of voltage quality in distribution network. Dynamic probability models of basic load and electric vehicle’s power in distribution network are established. Probabilistic distributions of node voltage in distribution network are obtained using dynamic probability power flow of fundamental frequency based on cumulant method. And then daily voltage qualified rate of distribution network is acquired. Finally, voltage quality for distribution network is evaluated. Simulation results show that electric vehicles can result in decline of voltage quality of distribution network. But voltage quality under V2G mode is superior to that under uncoordinated charging mode. Evaluation results have important reference values for formulating charge and discharge control strategy of electric vehicles and planning distribution network in future.Dynamic probability power flow of harmonics is applied to the evaluation of harmonic voltage in distribution network. Firstly, dynamic probability model of harmonic current injected by electric vehicles is established. Secondly, dynamic probability distributions of the total voltage’s distortion are obtained. And then evaluation index of 24-hour harmonic voltage for distribution network is given. Finally, the effect of different amounts of electric vehicles on harmonic voltage in distribution network is investigated, which provides important theoretical reference for harmonic elimination of distribution network in future.The theoretical analysis and simulation results show that, it’s scientifically rational to apply dynamic probability power flow to the assessment of line-breakage risk in transmission network, the evaluation of fundamental voltage quality in distribution network and the evaluation of harmonic voltage in distribution network. The results are more suitable to actual situation, and it can provide important theoretical basis for operation planning in transmission and distribution network in future.