Research On Control Strategy Of Inter-linking Converters In AC/DC Hybrid Microgrid

With the continuous development of renewable energy,more and more distributed power sources come together to form microgrids.AC / DC hybrid microgrid has become a research hotspot because it combines the advantages of AC microgrid and DC microgrid and improves the utilization efficiency of new energy.Among them,the interlinking converter is an important device for coordinating the power balance of the AC / DC hybrid microgrid.It has important research value and practical significance.In this paper,the control strategy of the interconnecting converter in AC / DC hybrid microgrid is studied in depth,and its independent control method in island mode is mainly studied.Firstly,in order to realize the direct current control of the interlinking converter,the mathematical models of the three-phase half-bridge topology in different coordinate systems are established.The parameters of the interlinking converter filter circuit are designed according to the power level and related indicators,and the rationality of the design parameters is verified through simulation.Secondly,the power distribution principles of the interlinking converter in grid-connected and island mode are analyzed.In grid-connected mode,the AC sub-microgrid is directly controlled by the large power grid.The main function of interlinking converter is to achieve stability of the DC bus grid.In the island mode,due to the lack of support from the large power grid,the power coordination between the sub-microgrids is required to maintain the stability of the system.The main function of the interlinking converter is to coordinate the power between the microgrids on both sides.Then,for the grid-connected mode of the hybrid microgrid,a DC constant voltage control strategy for the interlinking converter is designed.In island mode,by analyzing the droop characteristics of the microgrids on both sides,A control strategy of the interlinking converter is proposed,and the autonomous control of the interlinking converter in the AC / DC hybrid microgrid is realized.Then,the threshold method is used to realize the power autonomous cooperation between the interlinking converter control and the energy storage device,and to avoid unnecessary actions of the power electronic devices and reduce the harmonics caused by the operation of the power electronic devices.Finally,in view of the poor dynamic performance of the interlinking converter,the motion equations of the AC synchronous motor and the charge-discharge equations of the DC capacitor of the converter are analyzed separately.Where,a kind of adaptive droop control is designed by establishing a virtual synchronous machine and virtual capacitor derivation of the interlinking converter.Aiming at the increase of the threshold,the power distribution deviation of the microgrids on both sides is enlarged.This paper proposes a method of hysteretic droop control,which suppresses the frequent operation of the interlinking converter without expanding the power distribution deviation of the microgrids on both sides.The effectiveness of adaptive and hysteretic droop control is verified by simulation.