Research On Distributed Power Service Restoration Method For Smart Distribution Grid

Smart distribution network is a key component of smart grid and its power reliability reflects the power supply capability.Fault can reduce the power reliability and the out-of-service area should be restored as soon as possible.The centralized power service restoration method has many problems in practical application,such as complex algorithm and difficult information collection.With the increasing scale of distribution network and the increasing penetration of distributed generation(DG),the traditional power service restoration methods are increasingly difficult to meet the requirements.Therefore,it is of great significance to study a fast and adaptable power service restoration algorithm for improving the power reliability of smart distribution network.On the basis of interactive information of peer-to-peer communication between smart terminal unit(STU)at switches of smart distribution network,the distributed power service restoration method is put forward.After the fault occurs,each STU can quickly restore the power in the non-fault outage area by interacting with the adjacent terminals and controlling the terminals to cooperate with each other according to the predetermined strategy.Firstly,the system of distributed power service restoration based on STU and the method of distributed storage and management of distribution network information are introduced.Especially,the information of distribution network topology and electrical quantity stored in each STU is described in detail,and the management scope of each STU has been delineated.These work lays a foundation for solving the constraints of power service restoration and searching the whole distribution network topology.Secondly,a distributed search method of network topology based on relay search of adjacent terminals is proposed,and the main processes of restoration are introduced.First of all,the distributed method is used to search for the non-fault outage area.Then,the scope of the actual restoration is determined based on adverse searching method and constraint conditions.Finally,considering the characteristics of distributed generation and constraints,the islanding scope is determined.The corresponding search principles are formulated from three aspects:selection of starting point,relay search of intermediate nodes and determination of termination conditions.In addition,the situation of multi-power supply and multi-branch is dealt with.The problem of coordinated control in the process of power service restoration is solved.Afterwards,a distributed method for solving constraints is proposed,which is based on stepwise Thevenin equivalent and is compatible with the topology search process of distributed service restoration.Furthermore,the effect of the branch is discussed and the method is improved.By this way,each node only needs to pay attention to the network equivalent information sent by its sub-nodes and the local electrical quantity information to verify the constraints.And the global optimization problem of power service restoration is transformed into a problem that can be solved by local calculation in STU.A PG&E 69 nodes system is used to verify the proposed distributed power service restoration method.And the distributed methed is compared with the centralized method.It is proved that the distributed power service restoration method proposed in this paper has the advantages of fast calculation speed and parallel processing.Finally,considering the wide application prospects of the soft open point(SOP)in distribution network,the distributed restoration method for distribution network with SOP is proposed.The basic structure and control mode of SOP are analyzed.Based on the powerful power transmission control capability and power supply recovery capability of SOP,the power service restoration model of SOP is proposed.In addition,the proposed distributed network topology search method and power service restoration process control are revised and improved.A IEEE 33 nodes system is used to verify the proposed distributed power service restoration method.And the power service restoration schemes of distribution network with SOP and without SOP are solved and compared.The power service restoration capability of SOP and the effectiveness of the distributed power service restoration method in this paper are verified.The distributed power service restoration method proposed in this paper is suitable for the wide-ranging structure and flexible operation characteristics of distribution network.The peer-to-peer communication can reduce the communication pressure.The calculation principle is simple and the calculation amount is small.The solving speed is faster,and the result does not converge.Each STU can independently guide restoration process,so the method can restore multiple non-fault outage areas in parallel.Compared with the centralized method,the distributed method is more reliable,flexible,and fast.