Controllable Oscillation-Based Current Injection Hybrid DC Circuit Breaker
As the mainstream technical route for the selective,rapid isolation of fault lines in the VSC-based DC grid,the hybrid DC circuit breaker is the key equipment to ensure the integrity and reliable operation of the VSC-based DC grid.However,high cost is a common problem in all kinds of hybrid DC circuit breakers.The optimization topology of hybrid DC circuit breakers is critical to effectively reducing the development cost of DC circuit breakers.This paper proposes a current injection-typed hybrid DC circuit breaker based on the controllable oscillation principle is proposed.The rapid interruption of fault current is realized using a controllable oscillation negative voltage unit and reverse current injection.Firstly,the basic principles of reverse current injection for fault arc-extinguishing,negative voltage construction for the current transfer,and amplitude rapid increase of the controllable voltage are studied.Secondly,a topology of the current injection-typed hybrid DC circuit breaker is proposed,and the corresponding operation principle is described.Then,the selection method of key components of the proposed hybrid DC circuit breaker is provided.Finally,the performance of the proposed hybrid DC circuit breaker is verified with the electromagnetic transient simulation model of a±500 kV four-terminal VSC-based DC grid.The simulation results show that the proposed circuit breaker can interrupt the fault current within 3 ms.At t=2 s,a permanent positive pole-to-ground short-circuit fault is set to occur at the central position of the DC line Line34 in the constructed electromagnetic transient simulation model of the±500 kV four-terminal VSC-based DC grid.The current flowing through the main branch,equal to the current idc34p flowing through the same positive-pole DC line,is approximately 2.25 kA under normal operation.When the local fault occurs,the fault transient peak current of the DC line rapidly rises to about 5.7 kA,then gradually drops to 0 with the help of the set transient breaking voltage of the energy-dissipating branch.The simulation waveform of the fault current interruption shows that the DCCB receives the relay protection action command at t=2.003 3 s,and the fault transient current reaches its peak value at about 2.005 9 s.The total breaking time of the proposed DC circuit breaker is about 2.6 ms.Conclusions can be drawn from the simulation results.(1)A controllable oscillation negative voltage construction and rapid amplitude enhancement method is proposed,which helps to realize the rapid transfer of the fault current from the main branch to the transfer branch by establishing a conduction voltage in the transfer branch smaller than the arc voltage dropping in the fast mechanical switch of the main branch.(2)The interaction mechanism of the oscillating branch voltage and current on the rapid turning-off of the thyristor branch is revealed,which rapidly transfers the fault current from the thyristor branch to the oscillating branch.Moreover,the condition of a higher transient interruption voltage is established.(3)The transfer branch of the proposed DCCB consists of a thyristor branch and a controllable oscillating negative voltage unit module in series,which makes the DCCB economical and convenient to control.
Voltage-source converter(VSC)-based DC gridhybrid DC circuit breakercurrent injectioncontrollable oscillation
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