Research on Current Limiting Strategy Based on Large-Scale Photovoltaic DC Boost Collection System
In response to the problem of rapid rise and high amplitude of short-circuit current after bipolar faults in large-scale PV DC grid-connected pooling systems,and additional cost of adding current-limiting equipment or improved converter topology to limit the DC short-circuit current in the system,this paper proposes a modular multilevel converter(MMC)with a two-stage current-limiting control.The author proposes a two-stage current limiting control strategy of modular multilevel converter.The first stage guarantees the speed of current limiting control,and the second stage increases the degree of MMC current limiting.At the same time,the corresponding control and protection coordination schemes are proposed based on the structure of the photovoltaic DC collection system.Firstly,the influencing factors of short-circuit current are analyzed,and then a two-stage current-limiting control method is proposed to explore the influence of current-limiting control on the system and the coordinated process between current-limiting control and protection system is provided.Finally,the current-limiting control is simulated and verified in a±30 kV/30 MW PV DC grid-connected collection system.The simulation results show that the proposed two-stage current-limiting control can be quickly put into operation and significantly reduce the fault current and bridge arm current,control the design cost of DCCB,and reduce the risk of converter blocking.
HB-MMCnew energy DC grid connectionfault current suppressionactive controlphotovoltaic system
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