Thermal model for online temperature estimation of DC-link capacitor and DC-busbars considering variable switching frequency, variable modulation method and variable coolant flow rate

The use of electrical drives in automotive applications requires a high overload capability. The DC-link capacitor and the DC-busbars are components, which often determine nominal performance and are frequently operated above nominal conditions. Consequently, thermal protection for these components is mandatory. This paper therefore suggests a thermal model for online temperature estimation of the DC-link capacitor and the DC-busbars. Firstly, the complex thermal couplings between different parts of the busbars and the DC-link capacitor are analyzed using special measurements that omit certain loss sources. Based on these measurements, a thermal network is derived. Since the DC-link temperature depends on the switching frequency, the modulation method and the coolant flow rate, these quantities are incorporated into the model. This is of major importance since modern e-drives dynamically vary these quantities depending on the operating point to improve efficiency and hence increase the driving range of an electric vehicle. The parameters of the suggested thermal model are tuned using an optimization algorithm and stationary operating points as training data. Finally, the temperature estimation accuracy is validated under overload situations and dynamic vehicle drives.