Hierarchical And Zonal Optimal Control Strategy Research For Voltage Quality Of Island Microgrid

As a link of high-permeability distributed generation(DG)connected to distribution network,micro-grid can realize flexible control of power quality supply and demand,which has attracted extensive attention of scholars at home and abroad.The uncertainties of distributed generation,the variety of operation modes and the diversification of load equipment types in micro-grid system have brought some difficulties to the power quality of micro-grid,especially voltage quality control.Therefore,according to the micro-grid load nature,voltage frequency control characteristics and different levels of user requirements,a hierarchical and zonal optimal control strategy of voltage quality of micro-grid from the dual scales of time and space is studied,and it is of great significance to improve the voltage quality of micro-grid and improve the system voltage level.This thesis focus on the following aspects of research on microgrid voltage unbalance control,voltage control area division,and diversified power quality requirements for users:1)Aiming at the three-phase voltage unbalance caused by the asymmetric load connected to the point of common coupling(PCC)of island microgrid,a networked hierarchical collaborative optimization control method is proposed,and the droop control and virtual impedance are used to realize active and reactive power distribution in local control layer.In the secondary control,the dynamic consistency algorithm is used to obtain the global average value to recover the deviation of voltage and frequency.Combined with the optimal control strategy,the coordinated compensation control of voltage imbalance between PCC and DG is realized.The results show that the proposed method can compensate the unbalanced voltage of PCC,meanwhile,take into account the output voltage quality of DG inverters.2)Aiming at the problem of voltage division control in microgrid,a voltage grid division method based on voltage increment matrix is proposed.The method uses generalized Tellegen theorem to calculate the sensitivity,constructs voltage increment matrix,and clusters with K-means clustering algorithm.In order to divided the power grid into several different sub-regions,based on the principle of optimum comprehensive modularity,the special nodes that affect the regional connectivity caused by clustering partitioning scheme and partit ioning process are selected and adjusted.The simulation results show that the proposed method can obtain the partitioning scheme with better performance in both inter-area decoupling and the robustness to the fault.3)Aiming at the diversified demand for power quality of different buses in island microgrid with multiple bus bars,the mechanism of voltage unbalance compensation for multiple bus bars is analyzed based on the partition,and a hierarchical and zonal optimal compensation strategy for voltage unbalance is proposed.In the third control layer,he improved artificial bee colony algorithm is used to obtain the optimal three-compensation gain and is sent to the secondary controller to generate compensation parameters,which are multiplied by the thr ee compensation gain and fed back to the first control layer to optimize the allocation of each DG compensation amount.The simulation results show that the method can realize the coordinated control of the unbalanced voltages of PCC,DG and buses,and mee t the diversified of power quality requirements of the system.