Research On Integrated Control Strategy Of Loop-closing And Loop-opening Of Distribution Network Based On Probabilistic Load Flow

With the increasing requirements of users on the reliability and quality of electricity,building a strong and reliable distribution network has become an important responsibility of every power supply company.The loop-closing power supply operation of medium voltage distribution network can effectively reduce the power outage time of users.However,if the loop-closing operation is performed improperly,the loop-closing current may exceed the limit and cause more serious power outages.In order to reduce the risk of over-limited loop-closing current and improve the quality of power supply in the distribution network,this paper focuses on the integrated control strategy of loop-closing and loop-opening.First,the mechanism of loop-closing current generation and the basic theory of control are studied.The main influencing factors of loop-closing current are analyzed,four feeder loop-closing operation modes are classified and summarized,and based on the electrical distance on both sides of the loop-closing point,the risks of various loop-closing modes are briefly evaluated.Three calculation methods of loop-closing steady-state current are studied.Including the superposition method,the branch current method and the distribution coefficient method,the advantages and disadvantages of the three methods are compared,and finally the branch current method is selected as the calculation method of the loop-closing steady-state current in the subsequent control strategy.The formation mechanism of the loop-closing inrush current is studied,and the calculation formulas of the maximum value and the effective value of the loop-closing inrush current are deduced.The control mechanism of the transformer tap and reactive power compensation capacitor on the loop-closing current is analyzed,and the control process of the two is given.Second,aiming at the problem of unknown load data of feeder nodes during loop-closing control,a probabilistic load flow calculation method for distribution network based on the principle of similar days is proposed.On the one hand,the method selects the feeder similar days of each node based on the Pearson correlation coefficient,and on the other hand,selects the meteorological similarity days of each node based on the grey correlation degree.Finally,the two similar days are combined to filter the historical load data of the nodes,and the corresponding load samples set are established.Calculate the load semi-invariant according to the load sample set of each node,and bring it into the linearized power flow formula for calculation,obtain the semi-invariant of node voltage and branch current,and calculate the semi-invariant of each order according to Gram-Charlier the series expansion is carried out to obtain the probability distribution characteristics of node voltage and branch current.Finally,aiming the shortcomings of the existing mathematical model of loop-closing control strategy,this paper proposes a integrated control strategy based on probabilistic load flow for loop-closing and loop-opening.The strategy is based on probabilistic load flow calculation,and the optimization objectives are established with the total number of actions of the loop-closing control equipment,the probability of loop-closing current exceeding the limit,the active power loss and voltage deviation of the distribution network after the loop-opening.A mathematical model for the integrated control of loop-closing and loop-opening with the transformer taps and reactive power compensation capacitors of the busbar where the loop-closing feeder is located.The multi-objective particle swarm algorithm is used to solve the model,and the optimal control scheme solution set is obtained.The dispatcher can select a solution from the solution set as the loop-closing and loop-opening control scheme according to the actual situation.The results verify the effectiveness of the proposed control strategy.The integrated control strategy of loop-closing and loop-opening based on probabilistic load flow has been applied to the research and development of "loop-closing and loop-opening auxiliary decision-making system of distribution network".