Operational Risk Assessment Of Distribution Network Considering Various Uncertainties

With the sustained and rapid growth of the global economy,the large power grid is developing in the direction of long-distance,ultra-high voltage and ultra-high voltage.Due to the continuously expansion of the power system and increasingly complex of network structure,safety operation of the power grid has caused great attention.Meanwhile,more and more distributed power generation(DG)and electric vehicles(EV)connect to the distribution network and the power market faces reform.Under the background,the uncertainties in the distribution network are increasing,which have an adverse impact on the operation of the distribution network.Therefore,quantifying the risk of grid has become an important part to ensure the stable operation of the grid.The research is conducted under the framework of “risk assessment,early warning and management”.The risk model of distribution network is established with multiple uncertain factors including fluctuation of distributed wind power,photovoltaic power,load and EV charging power.A multi-dimensional risk indicator system considering voltage over-limit and line overload and load shedding is established to realize quantitative assessment of the operational risk in active distribution network with various random factors.Aiming at the forecast error,the risk warning method based on time series risk assessment is proposed in this paper.When the distribution network is in an early warning state,management strategy is set by solving the established risk management control to provide guidance for operation scheduling.The main contents are organized as follows.(1)The concept and type of grid operation risk are described and analyzed in this paper.Based on the definition of grid operation risk,the procedure of risk assessment is summarized.In addition,in two dimensions of space and time,a set of risk indicator system is designed considering node voltage,line power and load loss of distribution network,etc.The risk indicator system lays the theoretical foundation for the risk assessment,early warning and control of distribution network with multiple uncertain factors.(2)Aiming at multiple risk factors,a risk assessment method based on improved LHS is proposed.Firstly,the probability models of the risk factors in the distribution network are established including the probability distribution of the wind power,photovoltaic and load.In the basis of the improved LHS risk assessment algorithm,the models are solved to calculate the two-level risk indicators.The risk indicators are used to measure the risk level of the active distribution network with multiple risk factors and to make recommendations for the DG planning of the distribution network.(3)Aiming at the prediction error,a risk warning method based on time series risk assessment is proposed.Firstly,the reasons for the prediction error of wind power,photovoltaic and load are analyzed.Then,the prediction error probability distribution models are established correspondingly.According to the time series risk assessment,the timing risk indicators of the distribution network are calculated.Then,the risk level and risk area of each time period are determined in the terms of the proposed risk grading method.Finally,the improved IEEE-34 test system is simulated to verify that the proposed method can determine the risk level and risk area under each time period and make a visual warning.(4)In the foundation of the risk warning,a multi-time scale coordinated resource risk management model is built in the paper.Firstly,the concept and basic means of risk management are outlined.Based on the controllable means,the day-ahead and intra-day control models of active distribution networks with DG and EV are proposed with the constraints of distribution network flow regime and the constraints of distribution network operation conditions.Finally,the effectiveness of the proposed model is verified by a specific example.The optimal dispatch can ensure the economical operation of the distribution network,while can significantly reduce the risk level.