Research On The Governance Strategy Of Voltage Sag In The Medium-Voltage Distribution Based On Battery Energy Storage

With the constant improvement of the level of manufacturing industry automation,the requirement of power quality about electrical equipments are becoming more and more high.However,the problem of voltage sag is more prominent than another power quality problem,restricting the construction of high quality industrial power park directly.The existing voltage sag governance devices have many bad characteristics such as: low voltage,small capacity,decentralize and so on.Using these devices will make the voltage sag governance system in industrial park become complex,high cost or pool efficiency.Except for it,these devices are not conducive to the scale of industrial park also the implementation of custom power technology.This paper proposes two voltage sag governance strategies for medium voltage distribution network which are: “parallel modular battery & fast switch” and “series multiwinding transformer & centralized battery”.Respectively,their control algorithms are designed and their effectiveness are verified in this paper.Firstly,this paper presents the topology of “parallel modular battery & fast switch” and establishes the mathematical model of its topology structure.When the network voltage sag does not occur,this paper based on this topology proposes a three levels control strategy which are: the outer three phase current decoupling control,the middle phase SOC balancing control and the inner module SOC balancing control.Meanwhile,when the network voltage sag occurs,this paper based on this topology proposes a three levels control strategy which are: the outer voltage feedforward PI control,the middle phase SOC balancing control and the inner module SOC balancing control.The author establishes the voltage sag system simulation model about this parallel governance strategy in the side of medium voltage distribution network by Matlab/Simulink.The simulation results show that the proposed strategy can govern the harmonic,reactive power and negative sequence component of the load current and realize batteries self-charging with constant current effectively in normal.When the voltage sag occurs in the network,the proposed strategy can also support the load voltage effectively.Secondly,this paper presents the topology of “series multiwinding transformer & centralized battery” and establishes the positive sequence model and negative sequence mathematical model of its topology structure.Based on this positive sequence model and negative sequence mathematical model,this paper proposes their voltage outer loop and current inner loop control algorithm for network voltage compensation respectively.In orde to solve the circulation problem occouring in each phase winding in the secondary side of multiwinding transformer,the corresponding circulation suppression algorithm are attached to the positive and negative current inner ring.The author establishes the voltage sag system simulation model about this serices governance strategy in the side of medium voltage distribution network by Matlab/Simulink.Whether the network voltage sag is symmetric or asymmetric,the simulation results show that the proposed strategy can compensate the network voltage sag and keep the load voltage normal effectively.The inner circulation inhibition won’t impact the outer voltage compensation control algorithm.Finally,The battery capacity about“parallel modular battery & fast switch” and “series multiwinding transformer & centralized battery” are designed based on a load with 3 MVA volume.This paper summarizes the advantages and the disadvantages of these two strategies used in medium voltage distribution net work for centralized voltage sag governance and analyzes their applicable scenario respectively.