Research On Three-phase Self-balancing Technology Of Low-voltage Distribution Network With Distributed Generation

In order to suppress the three-phase voltage imbalance of the low-voltage distribution network when a large number of distributed power sources are connected,this paper studies a three-phase voltage unbalance control circuit topology and its control method in a low-voltage distribution network three-phase four-wire system.According to the actual situation of the low-voltage distribution network and its three-phase unbalanced characteristics,based on the principle of back-to-back DC transmission,a three-phase self-balancing device for the distribution network is designed,and the topology and circuit model of the three-phase self-balancing device for the distribution network are built,explain the working principle and control strategy of the device,and analyze the principle of achieving three-phase voltage balance.Finally,the rationality and scientificity of the new device is verified through simulation modeling.Using simulink to establish simulation modeling,comparing the simulation results with the results of traditional power grid three-phase imbalance control measures,the following results are obtained:(1)When the three-phase load of a user connected to a branch box in the distribution transformer station area is unbalanced,the resulting three-phase voltage imbalance will not only affect the power consumption of the user connected to the branch box,but also the other branch boxes in the distribution transformer station area.The power consumption of the connected users will also affect the normal operation of the distribution transformer,reduce the service life of the distribution transformer,and also affect the power quality of the superior grid.(2)When distributed power sources are connected,the three-phase voltage on the user side and the grid side will produce different degrees of harmonics,which will affect the power quality of the upper-level grid.When the distributed power supply is unbalanced,the three-phase voltage on the user side will be unbalanced,and it will affect the power consumption of users connected to other branch boxes in the distribution transformer station area and the power quality of the superior grid.(3)When the device is installed at the branch box of the distribution transformer station area,when the user’s three-phase load is unbalanced,the user’s three-phase voltage can still be balanced,and it can be connected to other branch boxes in the distribution transformer station area.The user’s electricity consumption will not be affected,and will not affect the voltage of the superior distribution network.When the three-phase load on the user side connected to a branch box is unbalanced and the distributed power supply is also unevenly distributed,the user’s three-phase voltage will fluctuate significantly in the initial stage.After 0.2s,it tends to be three-phase balanced.Ensure that the power consumption of users connected to other branch boxes connected to the distribution transformer station area will not be affected,and will not affect the voltage of the superior distribution network.Therefore,the three-phase self-balancing device can adapt to the current new situation of large-scale access of distributed power sources on the user side,and reduce the impact of voltage three-phase imbalance on users at the initial power consumption stage of users connected to a single branch box(voltage after 0.2s Tend to three-phase balance)to ensure that the power quality of other users in the distribution station area and the superior grid is not affected.