Research On The Characteristics Of Current Sharing And Oscillations In Multi-Chip High-Voltage High-Power Press-pack IGBTs

The high-voltage high-power press-pack IGBT device is the key component for manufacturing various high-voltage high-capacity power converters and controllers,which is widely used in the whole process of power collection and grid connection of renewable energy,AC/DC transmission and networking.Considering the general background of China's economic development and energy demand,the development of high-voltage high-power press-pack IGBT devices with high-reliability,inherent ruggedness and independent intellectual property rights is of great significance for China's industrial upgrading and power grid construction.The current balance regulation among a large number of IGBT chips in the device is an important technical bottleneck in the research and development of high-ruggedness and high-reliability press-pack IGBT devices,and there is a lack of relevant basic theories and key technologies in China.Therefore,combined with the reality of domestic press-pack IGBT,aiming at the electromagnetic coupling effect in large-scale parallel packaging and the transit time effect of bipolar semiconductor components,this thesis makes an in-depth study,using experimental measurements and theoretical calculations,on the common basis,characteristics,modeling methods and control applications of parallel current sharing and oscillations,which are the two core topics of current balance regulation research in high-voltage high-power press-pack IGBT devices.As the common experimental basis for current sharing and oscillation research,an experimental platform for current sharing and oscillation test among multiple parallel press-pack IGBT chips is designed and fabricated.A variety of parallel current sharing and oscillation test principles are summarized and integrated,including two parallel current sharing modes,the active switch mode and the passive injection mode,and two parallel oscillation modes,the internal self-excitation mode and the external forced mode.The open packaging design is proposed to realize the flexible configuration of the internal structure,space and material of the device,which provides new research ideas for multi-chip current measurement in dense spaces.For the first time,the parallel current sharing and oscillation test results of 9 to 16 chips in the active switching mode,the passive injection mode,the internal self-excitation and the external source forced mode were presented completely,breaking through the largest parallel chip scale in the existing literature.Taking the asymmetric external busbar as an example,this paper reveals the influence of external electromagnetic coupling effect on the current sharing performance among the internal chips of press-pack IGBT devices through experimental observation,theoretical analysis and modeling calculation.Based on the multi-chip current sharing experiment platform,the dynamic current distribution between 9 IGBT chips in the passive injection and active switching-on mode is observed,and a significant dynamic uneven current redistribution phenomenon was found and the transient current tended to flow near the busbar side.A finite element model of IGBT parallel current sharing in passive injection mode is proposed,and the electromagnetic field distribution characteristics inside the IGBT device under the influence of the busbar are calculated.The frequency-domain calculation reveals that there is high frequency magnetic field coupling between the busbar and the internal branches of the device,distorting the high frequency current gain of each branch.The time-domain calculation reproduces the transient current distribution in the experiment,confirming the effectiveness of the finite element model in passive current sharing mode.A symmetrical busbar design is proposed,which can significantly improve the parallel current sharing performance inside the device.Taking the electrode structure and spatial arrangement as an example,this paper reveals the influence of internal electromagnetic coupling effect on the current sharing performance and forced oscillations among the internal chips of press-pack IGBT devices,through theoretical analysis,modeling calculation and experimental verification.Based on the adjustment ideas of geometric symmetry and impedance compensation,two optimized schemes of electrode array circularization and electrode groove are proposed.By using the finite element method in frequency domain,the wide-band current sharing characteristics of four typical electrode designs are calculated and compared,and the distortion effect of asymmetric external electromagnetic conditions on the current sharing performance of the device is analyzed as well.The calculation results show that there is a significant divergence of high-frequency current gain between the parallel chips,which may cause severe high-frequency unbalanced current and forced oscillations by external sources.Based on the multi-chip parallel current sharing and oscillation test platform,the dynamic current distribution among FRD chips with four typical electrode designs was measured.The dynamic current sharing experimental results among 16 parallel chips were reported for the first time.It was found that there were significant dynamic current redistribution phenomena and forced oscillations between 16 FRD chips,which confirmed the calculation conclusions.Besides,comprehensive modeling calculations and experimental observations confirm that the geometric symmetry and impedance compensation control can optimize the internal dynamic current sharing characteristics of the device,but the geometric symmetry control is only applicable to symmetric external electromagnetic conditions.Aiming at the core problem of self-excited oscillation in current device development,this thesis reveals the time-domain characteristics of IGBT PETT oscillations through experimental observation,theoretical analysis and modeling calculation.Based on the PETT oscillation test platform for high-voltage press-pack IGBT chips,PETT oscillations between two IGBT chips were detected under different turn-off currents and bus voltages.A series of characteristic parameters of the PETT oscillation waveform are defined,and it is found that there is an obvious monotonous relationship between the start time,peak time,end time of the PETT oscillation and turn-off currents and bus voltages.The equivalent circuit of the PETT oscillation is proposed,and the circuit parameter conditions required for oscillation generation are calculated by the state equations.It is demonstrated that the generation and maintenance of the PETT oscillation need to limit the upper and lower bounds of the carrier concentration.A graphical analysis method is proposed,which intuitively and effectively explains the experimental law between the characteristic time of PETT oscillations and the turn-off current and the bus voltage.Furthermore,it is deduced that there is a linear relationship between the logarithmic value of the turn-off current and the start or end time of oscillations,and a linear relationship between the bus voltage and the reciprocal of the start time of oscillations,and both inferences are confirmed by the experimental results.Based on the sensitive coupling relationship between the characteristic parameters of PETT oscillations and voltage,current and temperature,a non-contact condition monitoring method for high-voltage IGBT devices based on PETT oscillation is proposed.Based on the principle of magnetic saturation,the parasitic inductance of the package can be adjusted by the excitation current,and a high-voltage IGBT device that can flexibly trigger or turn off PETT oscillation is invented,overcoming the EMI effect of PETT oscillations and paving the way for wider application of PETT oscillation in industrial practice.