Christopher Barth with adviser R. Pilawa-Podgurski
The design of high power density motors frequently results in a significant reduction in motor reactance, which reduces the machine current filtering. A multilevel inverter strategy with high effective switching frequency is used to generate filtered, sinusoidal currents in low-reactance machine windings. This project is developing high-density, multilevel inverters using GaN devices. Work has focused on flying capacitor multilevel (FCML) inverters. An exceptional power density (50 kW/kg, excluding the mass of heatsinks) has been obtained through the development of custom integrated switching cells, which both reduces unwanted parasitics and allows for a modular design approach.

Figure 21 shows first- and second-generation 2 kW prototype inverters. Due to the scaling effect of multilevel inverters, each switch in the design must be rated for only a fraction of the total bus voltage. This enables the switches to be smaller and faster, which in turn allows for the use of smaller passive components.

barth fig21 FCML inverter

Figure 21: FCML inverter prototype

A 1 kV, 13-level FCML inverter, shown in Figure 22, has also been designed and fabricated to demonstrate the scalability of the multilevel approach. This research is funded by NASA and NSF.

barth fig22 13'level flying capacitor inverter

Figure 22: Single module for multi-phase 13-level 20 kW flying capacitor inverter