Thermal Stress Model of Transversal Forced Air-Cooled Capacitor Banks for MW Power Converters

Capacitor banks are key components in high power applications, the reliability of which affects the overall system lifetime. It is known that the thermal stress in each capacitor can affect the lifetime performance of the entire capacitor bank. In this paper, an analytical thermal model is presented to estimate the average capacitor thermal stress in a transversal forced air-cooled three-phase AC-filter capacitor bank for MW-level power converters. The proposed model calculates the thermal resistance of a capacitor bank considering power losses, geometry, cooling conditions and physical arrangement. With a conventional Foster thermal network, the hot-spot temperature and case temperature for each capacitor can be obtained. The experimental results on a full-scale three-phase filter capacitor bank consisting of 27 film sub-capacitors have demonstrated the effectiveness of this model.