Active Thermal Control Of Inverter Based On The New Thermal Network Model

Silicon carbide(SiC)power module have great potential in future electric vehicle inverters,which have the feature of wide band gap,high saturation rate,high thermal conductivity and high breakdown field.Studies have shown that powe r cycle fluctuations and thermal stress shocks are the main causes of power module failure.In order to quickly and accurately estimate the junction temperature of the power module and improve the reliability of the electric vehicle inverter through effect ive measures.In this thesis,an active thermal control strategy of the inverter based on the new thermal network model is proposed to realize the on-line observation and active thermal control of the junction temperature of the SiC power module.It guaran tees the safe and reliable operation of SiC power modules.Firstly,the heat transfer mechanism and switching characteristics of the SiC power module are introduced.Two common thermal network forms are introduced to describe the modeling methods and characteristics,and the defects of the two models are summarized.The loss model of the inverter power device is established using the data in the data sheet provided by the device manufacturer.Secondly,the traditional thermal network model has a complex model structure,and the thermal impedance parameters are susceptible to the reference point and the external environment.A new thermal network model based on built-in temperature sensing NTC is proposed.The temperature reference point of the new thermal network is no longer referenced to the heatsink temperature or ambient temperature but to the temperature information of the internal temperature sensor inside the module.It is not necessary to establish a heatsink to the environment,which simplifies the model structure.At the same time,the model considers the thermal coupling effect of the chip,which improves the accuracy of the model.The simulation and experimental results show that the parameters of the new thermal network model proposed in this thesis are not affected by the heat dissipation conditions and environmental temperature changes,and the model accuracy is verified.The calculation accuracy of the model is equivalent to the finite element method under sine and square wave conditions.But the calculation is faster.The proposed model provide a good foundation for active thermal control of the inverter.Finally,an active thermal control strategy is proposed.The junction temperature of the power device is observed by the electro-thermal model of the inverter.Then the thermal states and the available heat capacity of the devices are going to the current limiting controller,in which the maximum operation current of the inverter can be carried out.Finally it realizes the maximum junction control of the EV inverter.The test results show that the proposed control strategy can control the instantaneous junction temperature shock of the inverter under low frequency and high power output conditions and stalling conditions,so that the inverter work s below the safe junction temperature.In addition,compared with the reserved margin,the control strategy of setting the fixed maximum operating current can make full use of the maximum instantaneous available heat capacity of the inverter.The instantan eous load capacity of the inverter maximizes the operating limits of the system.