Research On Device-Level Highly Efficient Parallel Simulation Method And EMI Characteristics Of Large-scale Power Electronic System

Power semiconductor devices,such as IGBT and MOSFET,are widely used in power transmission and transformation in today's power system.The power electronic converters assembled by these semiconductor devices will inevitably introduce high-frequency conducted and radiated electromagnetic interference during their operation.To analyze and predict the EMC characteristics of power electronic equipment,it is imperative to model its components on the device level.Converter in modern power system usually contains a large number of devices,therefore,the simulation time consumed based on traditional power electronic analysis software will reach an unacceptable length or even nonconvergence will be encountered.In this dissertation,with the support of NSFC project "Research on broadband modeling and electromagnetic disturbance characteristics of flexible DC converter system"(Project No.:51207054),the research on fine-grained highly-efficient simulation method of device-level high-frequency modeling for large-scale power electronic system is conducted.The main contents are elaborated as follows:The system-level parallel simulation method of the two-port modular multilevel converter high voltage direct current system is proposed.The ideal model,which represents the IGBT modules with switching resistance,is applied to model the sub modules in the modular multilevel converter.Meanwhile,the Backward Euler formula is used to discrete the capacitance of the sub modules,and then the discrete circuit model of each sub module is obtained.By introducing one time-step delay,the circuit decoupling between the sub module and the connected bridge arm is realized,whose interaction is achieved through the output voltage of the sub modules and the bridge arm currents,so that the iterative algorithm program for the sub modules can be executed in parallel.Taking the actual MMC-HVDC transmission project as an example,the NVIDIA Tesla V100 GPU is used to program the parallel simulation model based on CUDA C,and the influence of different capacitor voltage balancing strategies on the system level harmonics of the two terminal transmission project is analyzed.Based on this approach,an accurate and fast method of the EMI characteristics for the MMC-HVDC system during the design stage is proposed.The wideband model for the 3.3 kV high-voltage IGBT module is established based on the "advanced physics-based model" in Simplorer,which takes the non-linear and transient switching characteristics of the device into consideration.3D modeling of the package structure is carried out through Q3D,which is used to extract the stray capacitance,resistance and inductance caused by PCB,bonding wire and connectors.Then An 8-node circuit model of the IGBT module is eobtained.In the same manner,the 3D model of the busbar connected sub module and the copper connected modular multilevel converter is built,and the stray capacitance of the whole converter tower is obtained.Through the transformation of stray capacitance matrix,the capacitance distribution in valve tower is analyzed and simplified.By the linearization and discretization in time-domain,the two-port wideband,with the ground as the common terminal,for each sub module is obtained,which contains internal independent sources,the switching characteristics of IGBT and freewheeling diode in conjunction with the stray parameters in the corresponding structure are all taken into consideration.Through programing and GPU-based parallel simulation,the prediction and analysis forthe EMI characteristics of an 201-level MMC-HVDC system are realized,and the influence of control strategy and circuit parameters on conducted EMI is elaborated.The commutation of the modular multilevel converter occurs in the half-bridge or full-bridge structure of the sub modules,while the commutation of the two-level or neutral point clamped three-level converter occurs between two bridge arms in the same phase of the converter.Therefore,the method of V-I decoupling can not be extended and copied to the solution for this kind of converter.Based on the railway DC traction system,has been proved to have a bright future,the wide-band circuit model of SiC MOSFET is established,and a hierarchical parallel simulation method from system-level to device-level for the multi-terminal DC system with three level converter as motor driving unit is studied.On the basis of conducted EMI analysis,the impact of the control strategy and circuit parameters on the radiated EMI of the power electronic converters is analyzed.Taking the valve tower of modular multilevel converter,which is recognized as one of the converters with the most complex structure,as an example,the valve tower is regarded as a complex topological space antenna,and the radiation unit of the antenna is decomposed.Then the voltage of each sub module with the most significant radiation effect is applied as the excitation.Based on the voltage waveform obtained by time-domain simulation of the high-requency circuit,the influence of capacitor voltage balancing strategy and main circuit parameter on the radiated electromagnetic interference is analyzed,which provides theoretical reference for the suppression of electromagnetic radiation in converter station.