Research On Low-inductance Design Of Submodule In Hybrid HVDC Circuit Breaker Transfer Branch

The voltage overshoot caused by stray inductance seriously affects the reliability of the IGBT device operation in the DC circuit breaker.The operating voltage and the breaking current increase at the same time,and the impact of the voltage overshoot on the device is significantly aggravated.With the increase of the voltage level,the sub-module structure of the DC circuit breaker is more compact,and the number of series connections has increased sharply.The shutdown current is increased,and the high-power press-fit IGBT(PPI)shuts down the fault current that is several times its own rated current within a few microseconds.Reducing stray inductance is the first choice to reduce voltage overshoot.This article focuses on the internal commutation phase of the transfer branch submodule of the hybrid DC circuit breaker,and conducts research on it.This paper first establishes a high-current shutdown test platform for the diode full-bridge series sub-module,elaborates the high-current shutdown test principle and parameter coordination method,and proposes the principle of selecting the main equipment of the platform.Aiming at the IGBT boss structure,an optimized design method for IGBT chip press-fitting and a design scheme for internal connection busbars of sub-modules were proposed.The overall size of the press-fitting structure decreased by 44.4%.Finally,5 times the rated current was reliably turned off through tests,indicating that the test platform reached the design goal.Then,a coupling inductance model of the commutation circuit is established,and a method for calculating the transient voltage of the commutating IGBT inside the sub-module is proposed.The influence of the mutual inductance between bus bars)and the buffer capacitors(capacitance and internal stray inductance)in the sub-module on the voltage overshoot.The research shows that there is a strong coupling effect between the sub-modules and the busbars between the sub-modules.The strong coupling effect in the sub-modules reduces the loop stray inductance to 40.4%and the voltage overshoot to 55.5%.The mutual inductance commutation between the sub-modules The loop stray inductance increased by 36.3%;the stray inductance inside the capacitor increased the device voltage overshoot by 18.1%.At the same time,the internal stray inductance of the capacitor is increased at high frequencies,and the off time significantly affects the overvoltage and charging voltage of the internal stray inductance of the capacitor.Finally,an integrated design method for series submodules is proposed.The cross conversion method of the diode full bridge is proposed to convert the regulation of the sub-module into the stray inductance regulation of the port stacked busbar,and reveal the loop penetration characteristics of the diode topology diode.The integrated structure&reverse series solution has a voltage overshoot of 251.3 V(a 71.2%drop),a stray inductance in the converter loop of 56.33nH(a 74.9%drop),and a power density increase of 71.4%.The integrated design method of series sub-modules can significantly reduce the stray inductance of the loops in the other commutation stages.