Calculation Method And Application Of Transient Electric Field Inside Press-Pack IGBT Device

With the development of flexible DC transmission technology,high-voltage and high-power press-packed IGBT(Insulated Gate Bipolar Transistor)devices are widely used in various apparatus for DC transmission and transformation.The presspacked IGBT(PPI)devices have become the core components of the new power system.The development of PPI with independent intellectual property rights can help to break the technology blockade from foreign companies,which has important strategic significance and economic value for the development of the advanced transmission technology.During the independent development process of the PPI devices,the packaging insulation problem is one of the key challenges.The essence of the packaging insulation problem is the local electric field enhancement inside the packaging insulation structure under actual working conditions.To improve the insulation capability of the PPI device,it is significant to comprehensively and accurately analyze the transient electric field distribution of the PPI device under actual working conditions.This paper focuses on the packaging and insulation problems that restrict the independent development of PPI devices.Under the working condition of repeated turn-on and turn-off.the calculation methods,distribution characteristics,and control methods of the combined insulation structure for PPI devices are investigated.It breaks through the bottleneck of the inaccurate calculation of the electric field intensity on the dielectric interface and the disability of the transient electric field when considering the dielectric relaxation by the existing commercial finite element software.The research results aim to find the weak areas and guide the optimization and design of the packaging insulation structure for the PPI devices.Firstly,the necessity of transient electric field calculation under the working condition of repeated turn-on and turn-off is analyzed.The classical model of a parallel-plate capacitor with double-layer dielectrics is selected,and the analytical expressions of the electric field intensity and the interface charge density are derived under the ideal positive periodic square waveform(PPSW)voltage.Under different material combinations,the transient characteristics of electric field intensity and interface charge density are analyzed,and the expressions of maximum electric field intensity and maximum interface charge density under the positive square steady state are obtained.Based on it.the influences of period and duty cycle on the transient characteristics are studied.Moreover,the estimation methods of the maximum electric field intensity under the positive square steady state is proposed under the different ratio of the period to the relaxation time constant.The actual model is selected to verify the correctness of the analytical analysis.Next,a numerical method for the electric field and interface charge density on the dielectric interface with high numerical accuracy in the time domain(TD)is proposed.Under the electroquasistatic field,the transient constrained electric field equation on the boundary(TCEFEB)is proposed by introducing the normal component of the electric field intensity on the Dirichlet boundary.The problem of the electric field intensity and interface charge density on the dielectric interface with lower numerical accuracy due to the discontinuity of the normal component of the electric field on both sides of the dielectric interface is solved theoretically.The relative errors of the proposed TCEFEB and the traditional finite element method(FEM)in TD for calculating the electric field intensity and interface charge density on the interface are compared.The reason for the high numerical accuracy of the TCEFEB is investigated.Aiming at the dielectric relaxation phenomenon of materials.finite element equation and TCEFEB in the time domain are also proposed.Then,the FEM in the Complex frequency domain(CFD)for the transient electric field is proposed.By using the Laplace transform,the finite element equation and the TCEFEB in the CFD are derived.The problem that FEM in the frequency domain cannot calculate transition process and zero-input response of the transient electric field is solved.Based on the direct algorithm of numerical Laplace transform,the selection method of attenuation coefficient is investigated,and the direct algorithm of FEM in CFD is proposed.Based on the indirect algorithm of numerical Laplace transform,the selection method of summation term and the method of reducing numerical oscillation are investigated,and the indirect algorithm of FEM in CFD is also proposed.Numerical examples are used to verify the effectiveness of the proposed direct algorithm and the indirect algorithm of the proposed FEM in CFD.On this basis,the calculation procedures of the direct algorithm and the indirect algorithm of the FEM in FED for considering the dielectric relaxation phenomenon of insulating materials are proposed.Finally,the transient characteristics of the electric field inside the packaging insulation structure of the PPI device are analyzed,and the control method of the transient electric field is investigated.By comparing the calculation cost of TEM in TD and the FEM in CFD.the selection principle of the calculation method in different situations is proposed.For the packaging insulation structure of rigid PPI devices.FEM in the time domain is selected to calculate the transient electric field distribution under the PPSW voltage,and the transient characteristics of the electric field are obtained.The control method is proposed from the perspectives of geometric structure and material parameters.For the compliant PPI device,the FEM in CFD is used to calculate the transient electric field of the DBC structure under the PPSW voltage,and the control method of the electric field regulation by changing the DBC structure is proposed.