The Loop Closing Control Method Based On Online Self-organizing Synchronized MAS For Active Distribution Network

With the increasing demand of power users for the reliability of power supply,it has become a necessary method that through loop closing operation to achieve load transfer without blackout in distribution network.In recent years,large-scale distributed generations have been connected to the distribution network,causing several problems such as voltage fluctuations and power flow reverse,which affects the safe and stable operation of the distribution network.The traditional distribution network will be transformed into the active distribution network,actively controlling the distributed generations,weakening the negative impact of the distributed generations,and also providing a new idea for the loop closing control for the distribution network.Based on this,this dissertation proposes a loop closing control method based on online self-organizing synchronized MAS for active distribution network,aiming at improving the success rate of loop closing operation for distribution network.Firstly,this dissertation expounds the online self-organizing synchronized MAS system,designs a loop closing control technical scheme based on online self-organizing synchronized MAS,and constructs the online self-organizing synchronized MAS framework for the loop closing control,which explains the specific functions of each Agent and overall operation mode during the loop closing control in the online self-organizing synchronized MAS in detail.Then,the loop closing control method is proposed for active distribution network.The state estimation Agent will transmit comprehensive real-time running data of the pre-loop system and the network topology parameters to the main control Agent of loop closing.The main control Agent of loop closing will predict the power flow of each branch after the loop closing operation through simple loop closing calculation and judge the loop closing conditions.For the system that cannot directly performs loop closing operation,the distributed generation and flexible load Agent that can respond to the loop closing control are designed.The distributed generation Agent changes the control strategy of the distributed generation from the state that only outputs the maximum active power to the voltage/reactive power regulation control and actively adjusts the reactive power output.The flexible load Agent actively adjusts the access situation according to the load symmetry on the both sides of the loop closing.The simulation example in the PSCAD/EMTDC shows that the proposed loop closing control method for active distribution network can reduce the loop closing current,creating the favorable loop closing condition.Finally,considering that the inrush current of transformer may cause the failure of the loop closing operation,the occurrence mechanism of the inrush current and the sympathetic inrush is analyzed.For the case that ?/Y transformers are used widely in the distribution network,the relationship between the magnetic bias and closing angle of three-phase ?/Y transformer in the phase selection is studied,and a loop closing control strategy which can suppress core saturation of three-phase ?/Y transformer for distribution network is summarized,that is,the contact switch Agent determines and controls the contact switch closing time according to the voltage phasor of the loop closing bus and the system frequency obtained from the state estimation Agent,and reduces the transformer inrush current.Based on the PSCAD/EMTDC platform,it is verified that the loop closing control method can significantly reduce the inrush current and sympathetic inrush of the 10 kV ?/Y transformer in the system and lower the risk of the loop closing operation.