Multi-level Inverter Topology – Enabler for New Applications
Within the aerospace industry, Liebherr is known for its expertise and knowledge in developing and manufacturing power electronics equipment for various motor drive applications. Usually, the standard inverter topology, the so-called “Two-Level Inverter” is used for these applications.
In order to support the activities and meet the requirements of our customers, we made a new approach for a motor controller family concept: Instead of suppling each motor with its dedicated inverter, it should be possible to switch the inverters to different electrical motor drives e.g. fans for cooling and galley chilling, water and hydraulic pumps as well as electrical drives for high lift applications. In concept phases we showed that the standard two-level inverter topology has several drawbacks to drive all considered load and power classes (e.g. inverter losses) in the required weight and space envelope. But, considering the usage of the multi-level inverter topology, it is possible to use the same topology for all inverters of this motor controller family.
Multi-level Inverter board designed for 10 kWA output power.
The multi- level inverter topology has proven its benefits, reliability and maturity in lots of industry applications. It is expected to reduce the overall losses (in particular at higher switching frequency) of the inverter and spread the losses to more components. This reduces power electronic component temperature stress when compared to the two-level inverter topology.
We extensively conducted testing on real hardware to compare the performance of the two topologies with identical load cases. The measured performance results have shown high coincidence to the predictions obtained by our modeling tools. By using the multi-level inverter, the losses were reduced by up to 45 % compared to the two-level inverter, leading to a considerable temperature reduction at a given output power.
Conclusion: The multi-level topology developed by Liebherr allows a simplified cooling effort on system level and hence has an overall positive effect on cost, weight and reliability as well as efficiency.
