Decentralized DCCB Topology Design And Research Of Flexible DC Power Grid

Flexible DC transmission technology is one of the effective means to promote the upgrading of power grid to energy Internet and enhance the trans-regional transmission of clean energy.In response to the double carbon policy,the construction of safe and reliable operation of DC network has become a hot research topic in recent years,among which,when the DC system with "low impedance and low inertia" fails,it will produce a fault current that seriously endangers the safety of the power grid within a few milliseconds,how to cut off the fault quickly and reliably is a major problem that needs to be solved in the current project.Fault isolation by DC circuit breaker(DCCB)is one of the mainstream solutions to this problem.This paper will conduct research based on the above background.This paper presents the topology and operating principle of the classic hybrid DC circuit breaker,analyzes its key technologies from the aspects of commutation mode,power electronic switch and fast mechanical switch,and builds a simulation model in the electromagnetic transient simulation software to test its fault operation characteristics in the single pole ground short circuit fault.It provides the theoretical and simulation basis for the subsequent design of DCCB.Based on the analysis of the key components of hybrid DC circuit breaker,two kinds of distributed DCCB topologies based on thyristor are proposed.Thyristor based capacitor commutation hybrid DC circuit breaker(TCC-HDCCB)topology,the topology is simple and easy to control.The thyristor,diode and pre-charged capacitor cooperate to complete the switching of different circuit states to realize the bidirectional electrical isolation between the fault side and the non-fault side.Based on the topology structure,the self-charging capacitor is completed and the adaptive reclosing scheme is designed.The main break part adopts the thyristor with large breaking capacity to avoid the harm of dynamic voltage equating caused by a large number of series IGBTs.By improving TCC-HDCCB,Thyristor based Oscillatory commutator hybrid DC Circuit breaker,Thyristor based oscillatory commutator hybrid DC circuit Breaker,TOC-HDCCB)topology,which has the function of TCC-HDCCB,adding current limiting inductance in the charging capacitor branch,the oscillating current generated reduces the fault removal time;An auxiliary branch with large resistance and isolation switch is designed to maintain capacitance voltage after leakage and discharge of charging capacitor.Both of the proposed topologies use fewer power electronic devices and have better economy.In this paper,the structural components and operating principles of TCC-HDCCB and TOC-HDCCB are introduced in detail,and the selection methods of the main device parameters in the topologies are designed and analyzed.In the electromagnetic transient simulation platform,a single-terminal DC system model and a four-terminal DC system model are built,and the two topologies are simulated and analyzed.The feasibility and engineering applicability of the two topologies are verified by comparing the performance and economy of the two topology schemes with other schemes.