Research On Electro-thermal Modeling And Junction Temperature Control Method Of IGBT Power Electronic System

With the rapid development of new energy technologies,a large number of power electronic devices have been put into operation,and the reliability of power electronic systems has become an increasingly prominent issue.For security purposes,the vehicle and power industries have put forward requirements for power electronic systems to maintain high reliability and low maintenance rates during their service life,thereby reducing the cost of energy utilization.The reliability of the power electronic converter is determined by its most vulnerable part,namely the semiconductor switching device.In the complicated mission profiles such as wind power generation and electric vehicles,IGBT power modules will always run in an unstable condition due to the randomness of wind speed,and the driving habits of drivers and the uncertainty of road conditions.In a complex and changeable operating environment,temperature fluctutaion inside the power modules will accelerate the fatigue aging process and reduce system reliability.Therefore,analyzing the failure mechanism of power modules,electrothermal modeling of IGBT power electronic systems,and accurately estimating the junction temperature of IGBTs are the keys to the reliability research of power electronic systems.The dissertation takes PWM inverter as the research objective.In this dissertation,the inverter electro-thermal coupling model has been established for different circuit topologies,modulation methods and inverter operation modes.In order to improve the lifetime of IGBTs,this dissertation proposes the corresponding electro-thermal design and control method.To be specifically,the details are as follows:(1)As the core of the electric control system,the widely used PWM inverter system is selected as the research object in this paper.The current status of the development and application of IGBT power modules is summarized.Then the current status of the research on the loss model and temperature model of the IGBT switching device,and the research status of the electro-thermal control and design methods of the IGBT inverter system are described.The main research content of this paper is briefly explained.(2)Study on the modeling of electrothermal coupling of traditional two-level three-phase PWM inverter.Based on the internal packaging structure of the power module and the heat transfer characteristics,a multi-time scale electrothermal simulation model has been established.According to the different current profiles for loss calculation,two current variables,output current and on-current,are used to calculate the dynamic loss.The junction temperature obtained by these loss calculation methods is compared and analyzed.The effect of the calculation step on the accuracy of the electrothermal model is also discussed.Based on the established electro-thermal coupling model,the loss distribution of the inverter at different output frequencies and switching frequencies is calculated and analyzed to prepare for the research in the subsequent chapters.(3)Research on the electrothermal modeling of new quasi-Z source inverter.Unlike the traditional two-level three-phase inverter,the quasi-Z source inverter has a unique boost function,allowing the upper and lower arms to be short-circuited.Considering the influence of this shoot-through state in the electrothermal behavior of the inverter,this paper reestablishes the electrothermal model of the quasi-Z source inverter,and proposes the power devices dynamic loss calculation method under two modulations of direct boost and segment boost.By calculating the dynamic junction temperature of the IGBT under different modulation strategies,the thermal characteristics of the inverter is compared.Taking the quasi-Z source inverter based wind power generation system as an example,the IGBT electrothermal state of the grid-connected inverter at different wind speeds is calculated and analyzed,and its lifetime assessment is performed.(4)Considering the chip area and the number of chips,the electro-thermal modeling study of the high-power drive system is carried out from chip to inverter.By this model,the relationship between the size/numbers of chips and the loss/thermal behavior of the inverter is obtained.The utilization rules of the switching device of the motor driver are analyzed and discussed.Due to the switching devices chip area,rated value,load parameters in the motor drive affect its electrothermal performance and cost,optimizing the efficiency and thermal behaviors of the inverter maks the electrothermal design more flexible.(5)An electro-thermal control method for directly controlling the junction temperature fluctuation is proposed.By dynamically adjusting the switching frequency of the inverter,the excessive junction temperature fluctuation during the transient operation of the motor is improved.The electro-thermal states of the inverter under different load conditions are simulated and analyzed,and the service life of the IGBT with and without this control methods is calculated and compared in the long-term drive cycle conditions.The analysis verifies the correctness and effectiveness of the proposed electric heating control method based on switching frequency.