Research On Series Link Between Hybrid Micro-Grid And Distribution Network

With the rapid development of new energy distributed generation technology,the AC/DC hybrid micro-grid has become a research hotspot in the field of electrical engineering.Considering that in the grid-connected mode the AC/DC hybrid micro-grid is easily affected by the operation state of the distribution network,in order to improve the fault ride-through(FRT)capability and the power quality between the AC/DC hybrid micro-grid and distribution network,this paper introduces a series link between the AC/DC hybrid micro-grid and distribution network.The series link can cooperate with bi-directional AC/DC power converter between the AC and DC subnet to improve power quality of AC subnet and inhibit the fault current between the distribution network and AC/DC hybrid micro-grid at the same time.The specific research contents are as follows:Firstly,this paper introduces the basic structure and operation principle of the proposed series link.Combined with the structural characteristics of the AC/DC hybrid micro-grid,the topology of the series link is introduced in detail,and the operating principles of the series link under the two operating modes of voltage compensation and fault-current limiting are analyzed.Finally,this paper builds the mathematical models of the series link in the abc three-phase stationary coordinate system and the dq two-phase rotating coordinate system respectively.Secondly,an improved voltage compensation compound control strategy is proposed.This compares and analyzes several common voltage detection methods,and deduces the instantaneous voltage d-q detection method based on instantaneous reactive power theory at the same time.On the basis of traditional voltage compensation control strategy,this paper proposes an improved compound control strategy which includes the feed-forward of distribution network voltage and the double feedback of compensation voltage and AC subnet voltage,to ensure that in the voltage compensation mode the series link can compensate AC subnet voltage fastly and accurately.This improved compound control strategy has a fast response speed,small steady-state error and high transient stability.Thirdly,This paper designs the RL feed-forward current limiting algorithm and voltage and current double closed-loop control strategy.Based on the basic theory of RL feed-forward current limiting algorithm,the parameter selection criteria and optimization adjustment method of current limiting impedance value RL are analyzed to reduce the injected voltage and absorbed power of the series link.On the basis of introducing the basic principle of voltage and current double closed-loop control strategy in detailed,this paper obtains the virtual impedance and reactance characteristics of the series link according to the transfer function of the series injection voltage to the line current,and compares and analyzes the series injection voltage and power absorption performance as well.Lastly,in the Matlab/Simulink simulation environment and d SPACE experimental platform,the series link voltage compensation and fault-current limitation functions are realized respectively,which verifies that the proposed series link and its control strategy is feasible and effective to adjust the AC subnet voltage,limit the large fault current between the AC/DC hybrid micro-grid and distribution network.It shows that the series link is effective to block up the faults pass through in the grid-connected mode and improve the power quality of the AC/DC hybrid micro-grid.