Research On Control Strategy Of Bidirectional Interlinking Converter In AC/DC Hybrid Microgrid

Microgrid can integrate and utilize distributed electrical energy effectively.Thus it has great significance to both economy and society.The AC /DC hybrid microgrid,which combines the advantages of DC microgrid and AC microgrid,is more convenient to connect the distributed generation units.Besides,its power flow and control methods are more flexible.Inter linking converters,as the power interfaces of AC and DC subgrids,can realize mutual support between sub grids by controlling the power exchange,which promotes the reliable and stab le operation of AC/DC hybrid microgrids.In order to improve the AC/DC subgrid voltage accuracy of the traditional normalized droop control,an adaptive droop control strategy for AC/DC hybrid micro-grid interlinking interface is proposed.In this thesis,the power balance relationship and droop control principle of AC / DC hybrid microgrid are studied.As for the island mode of low voltage AC/DC hybrid micro-grid,the relationship between the droop coefficient and transmission power is deduced first.Then,the voltage variation is introduced to construct the operating criterion that characterizes the system load condition.Based on the above analysis,a control strategy whose droop coefficient is changing adaptively is designed.Moreover,the stable droop coefficient range is obtained with small signal analysis,so that the system power balance can be achieved in each operating condition.Finally,a simulation model of AC/DC hybrid micro-grid is built on the Matlab/Simulink,and the effectiveness and superiority of the proposed control strategy are verified by simulation results.Aiming at the problem of power distribution deviation caused by impedance mismatch of parallel lines in the system,a control method for improving the accuracy of power distribution is proposed.In this thesis,As interlinking converter has ability of bidirectional transmission characteristic,the droop characteristic of interlinking converter is split into two equivalent droop characteristics based on its.Then the influence of line impedance difference on power transmission and the parallel interlinking converter circulation are analyzed based on the aforementioned equivalent droop characteristics.Meanwhile,the requirements for proportional power distribution are also studied.A power distribution controller is designed based on the equivalent droop characteristic,which introduces the power adjust information into adaptive droop coefficient to realize the interlinking converter transfer power in proportion according to the capacity.To verify the effectiveness of the proposed adaptive droop control strategy and power distribution control strategy of the inter linking converters,a simulation model of AC/DC hybrid microgrid is built on the Matlab/Simulink platform.By comparing traditional normalized droop control and adaptive droop control,the simulation results verify that adaptive control strategy can not only reduce unnecessary power exchange while ensuring the bidirectional flow of power between the AC and DC sub-grids,but also improve the power transmission accuracy to realize a better compensation of the voltage deviation.The simulation results are also verified that the power distribution control can reduce the distribution deviation.