Design And Key Technology Research Of Solid State DC Circuit Breaker Based On Gate Controlled Thyristor

Compared with the conventional AC distribution techonology,the emerging DC distribution techonology can more efficiently accommodate distributed power sources and DC loads,which plays an important role in promoting energy conservation,pollution reduction and sustainable energy development.However,due to the small impedance and the lack of a natural current zero-crossing point,after the DC distribution network fails,the DC bus capacitor bank with large capacity will rapidly discharge to the fault point,resulting in extremely high fault current,and thus causing serious damage to a large area of the network in a short time.Therefore,the DC distribution network requires efficient,high-speed and highly reliable protection solutions to ensure the power supply quality.Solid state DC circuit breaker(SSCB)has the advantages of fast and arc-free interruption,which meets the high-speed protection requirement of the DC distribution network,thus becoming a key technology and research hopspot supporting the development of the DC distribution network.Nevertheless,the further development of SSCB is still limited by circuit topologies and internal power semiconductor devices,leading to low efficiency,insufficient reliability,small power capability and so on.Aiming at the urgent demand for high-performance SSCB in DC system protection applications,this thesis,which focuses on imporving the power efficiency and reliability of SSCB,carries out the design and key technology research of SSCB based on gate controlled thyristor.The research achievements and contents are elaborated as follows:(1)Electron injection enhancement mechanism and novel device structures.Based on the transport equation of bipolar carriers,the on-state carrier transport model of gate controlled bipolar devices is established,the quantitative relationship between electron concentration and conduction resistance is clarified,and the mechanism of electron injection enhancement is revealed,which lays a theoretical foundation for the design of low-loss devices.A novel IGBT with electron dual injection(EDI-IGBT)is proposed.By introducing accumulation injection with high electron injection efficiency,the device’s conductivity modulation effect is enhanced,leading to 31% lower conduction loss than that of the conventional IGBT.However,since the electron injection efficiency is limited by the MOS channel resistance,the conduction resistance of the EDI-IGBT is still relatively large.In order to further reduce the device’s conduction loss and improve the SSCB’s power efficiency,an electron injection enhanced MCT(EIE-MCT)is proposed.The electron injection of the EIE-MCT does not need to go through the MOS channel,so it features high injection efficiency.Moreover,by optimizing the position and contact resistance of the cathode-short region,the EIE-MCT can further enhance the electron injection efficiency,resulting in 27% lower conduction loss than that of the cathode-short MCT.The above work provides device support for the design and implementation of SSCB with high efficiency and high reliability.(2)Novel topology of high-efficiency SSCB based on EIE-MCT.Aiming at the problem of insufficient hard turn-off capability of the EIE-MCT,based on the basic current-commutation circuit,the commutation turn-off mechanism of the EIE-MCT is studied.Then,a false-trigger model is built,the false-trigger mechanism of the EIE-MCT is revealed,and the false-trigger suppression solutions are explored to achieve highcurrent interruption capability.Under the guidance of the false-trigger model,a novel topology of high efficiency SSCB(HE-SSCB)based on the EIE-MCT is proposed.In aspect of device,by adoping the EIE-MCT with extremely low conduction resistance as the main switch,the HE-SSCB obtains more than 20% lower power loss in comparison with the existing SSCBs,thus achieving high power efficiency.In aspect of circuit,by dopting current-commutation technology and desging a dedicated commutating path,the HE-SSCB successfully interrupts the fault current of 120 A,which is more than 4 times the rated current,and is also 30 times of the hard turn-off capability of the EIE-MCT,thus realizing high-current interruption capability.Moreover,the HE-SSCB also features compact size and easy control,and can guarantee the safe restart of DC systems.(3)Novel isolated current-commutation techchnology for SSCB.Aiming at the problem that the conventional current-commutation technology will produce fault surge current on the source and load sides of DC systems,a novel isolated current-commutation techchnology is proposed.The core idea of the technology is to use the electromagnetic coupling effect and isolation effect of coupled inductors.The former reversely couples the current of the commutating path to the EIE-MCT of the main path during the commutation stage,thereby forcing the device to turn off.The latter decouples the current coupling between the main path and the commutating path during the resonance stage,making the discharge current of the commutating capacitor does not flow through the source and load sides of DC systems.Consequently,the isolated current-commutation technology can completely eliminate the fault surge current.Under the guidance of the isolated commutation technology,both unidirectional and bidirectional isolated SSCBs(ISCBs)are designed.On the basis of inheriting the high efficiency advantage of the HESSCB,the designed ISCBs can improve the the reliability of the fault current interruption process by completely eliminating the fault surge current.(4)Novel power expansion techchnology for SSCB.In order to overcome the shortcomings of HE-SSCB and ISCB in high-power applications,a new SSCB power expansion technology is proposed.The technology includes both circuit and device aspects.In aspect of circuit,an SSCB without reverse recovery process is designed,which eliminates the negative transient overvoltage and the instantaneous power shock caused by the reverse recovery of the device during the conventional current interruption process.This avoids the aging or even damage of the device caused by the transient overvoltage and the instantaneous power shock,and hence improves the SSCB reliability during power expansion.Meanwhile,because the transient overvoltage is eliminated,the designed SSCB can use the low-loss EIE-MCT with filed-stop structure to improve the SSCB’s efficiency during power expansion.In aspect of device,in order to increase the operating voltage,the module design based on series EIE-MCTs is carried out,and the main factors causing the series unbalanced voltage are studied.Then,the static voltage equalization design,synchronous turn-on design and reliable turn-off design are proposed in a targeted manner,which realize the static and dynamic voltage equalization,hence further improving the SSCB’s reliability during power expansion.