Research On Control Strategy Of Substation Low Voltage Bus Flexible Interconnection System

As the key link of the distribution network,the low-voltage bus in the substation often realizes the ring network operation through the bus tie switch.The traditional bus tie switch does not have the power flow control ability.At the same time,with the distributed generation(DG)and the new generation load represented by the new energy vehicle charging pile widely connected to the low-voltage bus,it will lead to low-voltage bus frequency fluctuation,unequal load rate between substations,unbalanced feeder transmission power and power loss of important loads in case of fault.As a new type of power electronic equipment,flexible interconnection device(FID)is used to replace bus tie switch to realize energy exchange between low-voltage buses and capacity sharing between substations,At the same time,the loss of power of important load caused by bus failure on one side can also provide stable voltage support.It has a certain research significance to improve the stability and reliability of low-voltage bus in substation.In this paper,the energy storage FID topology based on back to back voltage source converter(BTB-VSC)is introduced,taking one-sided VSC as an example,the dynamic differential equations in three-phase static and synchronous rotating coordinate systems are established;the common P-Q and Udc-Q control strategies of VSC are discussed respectively,and the control strategy models are built based on the power system simulation software DIgSILENT/PowerFactory.Then,the working principle of FID with energy storage is introduced,and a dual port flexible interconnection model is built.By coordinating the active power output of converters on both sides,the flexible control of charging and discharging of energy storage device is realized.In order to improve the load absorbing ability of low-voltage distribution network,active power feedback control is proposed,This control strategy takes the frequency difference of AC system caused by active power imbalance as feedback,Through controlling the active power transmission of VSC on both sides,Through the charging and discharging of the energy storage device,the load can be absorbed and compensated,So the real-time control of active power flow can be realized according to the change of active load.Then,considering the unequal load rate of substations on both sides and the unbalanced power through feeders on both sides,a power balance control strategy is proposed.This control strategy can balance the active power between two feeders in real time,and make the load rate of substation consistent.At the same time,considering the capacity limit of the transformer,when the total load exceeds the capacity of the transformer,the corresponding active power balance is compensated by controlling the discharge of the energy storage device to avoid the overload of the substation.In addition,for the problem of power loss of important loads caused by faults near the substation,the voltage support control strategy when the fault occurs is discussed.This control strategy can maintain stable voltage support by coordinating the power output of converters on both sides,controlling the energy storage discharge and providing corresponding power compensation for the fault side,so as to restore the power supply of power loss loads.The above control strategies are introduced in DIgSILENT/PowerFactory,and the algorithm implementation of each control strategy is verified,which proves that the energy storage FID has certain advantages in dealing with load mutation,realizing capacity sharing between substations and voltage support under fault conditions.Figure[59]table[5]reference[63]...