UC Irvine

Improvement on multilevel converters is fundamental to cover the increasing demands on power, efficiency, and quality. In this thesis, 3 recently developed 5-level converters are investigated with a focus on their thermal management and cooling design. Switching device temperature limits its maximum power and switching frequency for operation. This is one of the most important constraints, particularly, in multilevel converters, where the hottest device will limit the performance of the whole system. Then, the capability of the topology to uniformly distribute the power losses plays an important role.

Flying Capacitor-Active Neutral Point Clamped (FC-ANPC) [24, 25], Dual Flying Capacitor-Active Neutral Point Clamped (DFC-ANPC) [27, 29], and Mule [35] are simulated under different modulation indices and power factors. The resulting graphs can be used as a tool for the designer to know the worst thermal condition in a particular application. The study shows the ability of DFC-ANPC and Mule to naturally reach a lower temperature with its consequent advantages. Regarding DFC-ANPC and Mule, the differences are minimal and they depend on the situation. However, because of its higher number of states, the benefits of active control power losses balancing techniques could be slightly higher in Mule. Similar comparison has been done in relation to the fluctuation of temperature, which is an important cause of the device's failure due to thermal stress.

Finally, cooling systems strategies to cool multilevel converters are explained. It is mainly focused on commercially available cold plates, which has been analyzed pointing out the optimal flow rate.