Energy is an indispensable material basis for the progress and development of human society.The rapid development of society leads to the increasing consumption of fossil energy and the increasing surge of energy crisis.The development of renewable energy is an important method to solve the energy problem.Microgrid is one of the main forms of renewable energy utilization,which plays an important role in reducing the influence of renewable energy on the power grid,improving energy utilization efficiency and power quality.Power router is a new type of power equipment proposed in recent years for the application of Direct Current(DC)microgrid,which is the key to the stable and reliable operation of DC microgrid.In the case of power grid failure,how to realize the fault crossing of power router and ensure its safe and stable operation has become an important topic for DC microgrid.Therefore,in this paper,the fault characteristics and corresponding protection and control strategies of power routers in the event of grid failure are studied.The main research contents are as follows:(1)Research on the topology structure and mathematical model of power routers.Basic modeling is carried out for photovoltaic power generation module,energy storage converter,grid-connected converter and Alternating Current(AC)power network ports,and their working principles and control strategies are analyzed to lay a foundation for the subsequent short-circuit characteristics analysis.(2)Analyze the transient response characteristics of series resonant converters with hybrid energy storage ports in the power router.First,based on the basic modeling analysis of the previous part,the short-circuit fault of the DC bus is divided into two types: direct grounding short-circuit fault and transit-impedance grounding short-circuit fault.Secondly,the transient response characteristics of the DC bus are analyzed when the two kinds of short-circuit faults occur.Finally,the influence of different system parameters on short-circuit current is studied,which provides theoretical support for the subsequent improvement of fault current limiting module.(3)The short-circuit fault characteristics of the power router under grid-connected operation are studied.Based on the previous analysis of transient response characteristics of energy storage converter when DC bus is faulty,the fault transient response characteristics of power router are further studied during grid-connected operation.On the other hand,when a short circuit fault occurs on the AC side of the DC microgrid system,the fault characteristics of the power router and the AC network are studied,and the electrical volume variation characteristics of the fault transient response are summarized,to lay the foundation for improving the protection and control strategy.The accuracy of the theoretical derivation is verified by MATLAB simulation platform.(4)Improve the fault protection and control strategy for the power router,so as to reduce the fault harm.Firstly,the common fault protection schemes under the current background are analyzed,focusing on the recovery protection stage.Secondly,for the fault protection of DC bus short circuit,a fault current limiting module is configured in the power router to effectively reduce the amplitude of the impulse current generated after the fault is cleared,so that the power router will not be cut out due to the impact of the fault current.The control strategy of the power router is improved to reduce the voltage and current fluctuation of the DC microgrid system when the fault is rectified.Finally,a simulation model is built in MATLAB/Simulink platform to verify the effectiveness of the improved fault protection strategy. |