The Research On DC Convert And It’s Low Ride Through Strategy

With the development of the national economy,traditional fossil energy cannot meet the energy demand.meanwhile,the environmental pollution caused by excessive use of fossil energy seriously threatens the survival and development of human beings.Distributed energy is integrated into the large power grid in the form of micro-grid,it can reduces the adverse impact of intermittent distributed power supply on the power grid and improves power supply reliability and power quality,so it becomes an important technical way to solve energy problems.As the core device of energy transmission in DC microgrid,DC energy router has been a research hotspot.This paper studies two typical dual-port and three-port DC energy router topologies,and proposes a mode switching control strategy based on dual-port DC energy router to solve the large current impact problem caused by grid-side fault transients.The protection of the energy router and the stable operation of the DC microgrid are of great significance.This paper first introduces a dual-port DC energy router topology,named a dualactive full-bridge DC-DC converter(DAB),and studies its operating mode,and then the DAB inductor current in one cycle.Mathematical expressions and waveforms were analyzed and summarized.Finally,the power transmission of DAB was analyzed,and the max and min values of power were discussed.Based on the understanding of the dual-active full-bridge DC-DC converter,this paper studies a three-port DC energy router(TAB),which is derived from DAB,has better properties and is more complicated.This paper continues to study the working mode,inductor current,power transfer and reflow power of TAB.Finally,this paper is based on the dual active full-bridge DC-DC converter.After introducing some basic operation modes of the DC microgrid,the inverter itself and the public power grid are harmed when the grid-side fault exceeds the low voltage ridethrough requirement.The problem is to propose a control strategy based on mode switching to suppress the instantaneous inrush current.That is,it switches to current hysteresis control at the moment of failure,and reversely switches to voltage stability control after the fault ends.The method can not only suppress the inrush current quickly,but also support the grid-connected point voltage while maintaining the converter without off-grid.The simulation results verify the correctness and effectiveness of the proposed method.