Design Of Main Circuit In High Power Hybrid Dc Circuit Breaker

Quench protection breaker(QPB)is an important part of the power supply system for coils in superconducting tokamaks.It is used to release the huge magnetic energy stored in the superconducting coils in case of quench,which is significant for safe operation of the tokamak devices.The current QPBs of EAST poloidal field power supply system,which communicate the current by mechanical circuit breakers(MCB)paralleled with fuses,is requiring an upgrade to overcome the shortcoming of large amount of maintenance caused by replacing the fuses manually after quench protection.By now,the hybrid DC circuit breaker(DCCB)has already become an important solution of quench protection.The design of the main circuit in the hybrid DCCB for EAST quench protection is introduced by this dissertation.Firstly,the topology design and operation principle of the hybrid breaker is proposed.A MCB is paralleled by a full-controlled solid-state circuit breaker(SSCB),and the SSCB is based on a diode bridge rectifier to obtain the ability of bi-directional conduction and interruption.This topology not only combines the low conducting power loss of MCB and the arc-less,rapid,controllable interruption of SSCB,but also reduces the number of full-controlled semiconductor devices as much as possible,simplifying the control system and saving cost and space.Secondly,the electrical design of SSCB is described.The maximum interruptible current of the candidate devices in QPB application is calculated by simulation based on Foster thermal network.The competence of rectifier diode and feasibility of the topology is verified by tests.The conclusion of type selection is given based on the results of simulation and tests.The principle of parameter design of RC snubber and MOA is discussed.Thirdly,the structure design of the SSCB is elaborated.In order to make a trade-off among current sharing,space utilization and implementation difficulty,a stack-press structure is chosen.Detail 3D designs and layout of IGBT and diode stacks are given.Finally,the current sharing in the SSCB and the current communication of the hybrid DCCB is analyzed by simulation.Unbalanced electromagnetic coupling has limited influence on current sharing but that caused by unsynchronized turn-off is quite serious.Overvoltage and di/dt of the semiconductor devices can be limited to a safe value by integrated application of snubber,MOA and gate resistors adjustment.The methods and results of the simulation are important guides for the manufacture of the hybrid DCCB.