Thermal Model of a Traction Inverter for an Automotive Application including DC-link capacitor, power modules and electrical connections

In automotive applications a traction inverter is used for energy conversion between battery and electrical machine. For high performance drives lightweight design is demanded. Additionally, higher efficiency of the inverter results in lower cooling requirements but is often achieved by increasing component weight. Hence, thermal modelling of the components and their interactions is essential to determine the best compromise between weight, efficiency and cooling requirements. In traction inverters the DC-link capacitors, power modules, high voltage electrical connections and low voltage devices dissipate power. In this paper the focus is on the thermal modelling of the DC-link capacitor, power modules and high voltage electrical connections and their system, as the performance of the inverter is defined by these components. The thermal models are derived based on geometries and physical properties. First, the DC-link capacitor thermal model is presented and considers the anisotropic heat conductivity of the capacitor coil and the inhomogenous loss feeding in the busbars. Next, the thermal model of a power module and heatsink is explained taking temperature dependent material properties into account. Based on the input temperature of the coolant and heat dissipation of the power modules the temperature rise of the fluid is calculated. Moreover, the electrical connection thermal models are described consisting of a combination of cables, busbars and shunts. With the individual component models combined, an overall inverter thermal model is developed. As all models are based on geometric and material properties it is possible to observe the impact of sizing in the future. A comparison betweeen the thermal system model and measurements is carried out finally. For this several temperature sensors were integrated into an inverter. By comparison to measured temperatures the thermal system model is validated for stationary and dynamic load points.