Research On Three-Phase Unbalanced Control Of Low Voltage Distribution Network

With the rapid development of smart grid,the higher requirements about the power quality of low voltage distribution network and reducing the loss have been put forward,and three-phase load imbalance is an important factor affecting them.If there is no reasonable and efficient means to control the three-phase imbalance in distribution network,it may affect the safety and stability of the entire power system operation.Therefore,the three-phase imbalance problem in low-voltage distribution network has become a hot research topic.Usually the reactive power compensation device and intelligent switches are used to control three-phase unbalanced load of low voltage network.Although both of them can achieve the purpose of governance,but the former is not conducive to the wide application in the market because of its high cost and large volume which.While the latter is mostly based on the mechanical contact switch to phase change,which can affect the quality of power supply.Therefore,this paper designs two kinds of three-phase unbalanced control scheme.One is the reactive power compensation based on full-capacitance compensation,and the other is the solid-state intelligent commutation switch.Specific work in this paper includes as follows:1.The application of reactive power compensation and phase load adjustment are introduced,and two kinds of calculation method of three-phase unbalance are summed up.Then,the harm of distribution transformers,transmission lines,generators and so on which cause by three-phase imbalance are analyzed.At the same time,the common measures to solve the three-phase unbalanced in power system are also introduced.2.From the perspective of reactive power compensation,the principle of reactive power compensation and the power phenomenon of the three-phase unbalance are analyzed.By analyzing the compensation of the three-phase imbalance caused by the typical single-phase load,a three-phase load compensation model based on the ideal compensation network is drawn out.And the simulation analysis of the model is also given.Then aiming at the deficiency of the ideal compensation network,the compensation strategy of vector analysis is designed and the corresponding mathematical model is also inferred.3.Based on the vector analysis compensation strategy,a composite switching scheme based on full capacitance reactive power compensation is designed.In order to solve the detection problem of the active and reactive component of fundamental current in relation to the compensation capacitance value in this scheme,a current method of space vector transform is designed.Finally,the feasibility of the proposed scheme is verified by simulation analysis.4.Finally,from the perspective of load sequence adjustment,a three-phase unbalanced control scheme based on solid-state intelligent commutation is designed.The simulation results show that the voltage interruption time is greatly shortened during commutation.Then,the main function modules and the process of obtaining optimal commutation strategy of the scheme are introduced in detail.Meanwhile,the three-phase unbalance optimization model is established.And the model is solved by the accelerated particle swarm optimization algorithm.The feasibilities of the model and the solution method are verified by simulation.