Tomas Modeer

Design and control of a GaN-based, 13-level, flying capacitor multilevel inverter

Multilevel topologies are an appealing method to achieve higher power density inverters for both mobile and stationary systems. This work discusses the design and development of a 13-level, flying capacitor multilevel (FCML) inverter. Operating from an 800 V bus, this inverter requires switches with a voltage blocking capability of less than 80 V. A 120 kHz switching frequency is enabled through the use of GaN FETs and the development of custom integrated switching cells, which reduce commutation loop inductance and allow for a modular design. Additionally, the frequency multiplication effect of FCML inverters allows the output inductor of the inverter to be made exceptionally small (4.7 μH) while maintaining a 0.7 % THD due to the 1.44 MHz effective inductor ripple frequency.

An analytical method for evaluating the power density of multilevel converters

Multilevel converter topologies have shown greal potential in high power converters with advantages including high efficiency and low distortion, and could provide the high power density necessary in new space and weight-constrained applications. A comparison of the passive component requirements, in terms of stored energy, of both flying capacitor multilevel converters (FCMCs) and modular multilevel converters (MMCs) is presented. The two topologies have different advantages, and their respective power densities. For low switching/modulation frequency ratios the MMC is favorable whereas the FCMC can yield higher power density in applications where the ratio can be large, e.g. in dc-dc, line-frequency converters and variable speed drives.

Design of a GaN-based, 9-level flying capacitor multilevel inverter with low inductance layout

Multilevel inverters such as the flying capacitor multilevel inverter (FCML) hold large potential benefit in applications where the size and weight of the inverter is constrained. This work presents the design and implementation of an inverter module which incorporates two individual 9-level FCML single-phase inverters in an interleaved design. Each inverter utilizes GaN FETs switching at 100 kHz, for an effective inductor ripple frequency of 800 kHz. The implementation features an innovative dual-sided integrated switching cell layout which decreases the effective commutation loop inductance of the inverter and enables fast switching with minimal ringing while also simplifying efficient double-sided cooling.

Hardware-in-the-loop co-design testbed for flying capacitor multilevel converters

The multilevel flying capacitor topology is a promising technology for future electric aircraft, where high specific power density power converters are required. Hardware-in-the loop co-design can improve design throughput as more complex implementations of this technology are developed. This paper presents a comparison of hardware-in-the-loop emulation and hardware prototype results for 3-, 5- and 7-level flying capacitor converters. The fidelity of the emulation is investigated for both dc-dc and inverter operation and it is shown that, within certain limits, the converter operation can be emulated closely.

Experimental evaluation of a 1 kW, single-phase, 3-level gallium nitride inverter in extreme cold environment

This work investigates the potential for high power density, high efficiency power conversion at extreme cold temperatures, for hybrid electric aircraft applications. A 1 kW GaN-based 3-level power converter was designed and successfully tested from room temperature down to −140 °C, using a custom milled cold-plate. Along with the first demonstration of a flying capacitor multi-level converter and associated components at such low temperature, this work characterized the effect on power conversion losses of various components as a function of temperature. A key finding is that careful attention must be paid to the passive component losses which can increase as the temperature is reduced.