Active gate drivers and wide band-gap devices: architectures, applications and limits

Abstract

Electrification is spreading constantly, even in areas usually led by other forms of energy. One of the most important markets is transportation, where a trend towards more electric aircraft, ships and vehicles can be seen. To support this evolution, Power Electronics plays a key role. Applications demand high-efficiency and high-reliability power converters, governed by high-performance control algorithms. In this work the effective use of wide band-gap devices, especially SiC MOSFETs, has been studied, paying special attention to the new requirements that these devices set for their driving. After a deep dive into the state of the art of Active Gate Drivers (AGDs), for both silicon and new-material devices, some new architectures have been developed and benchmarked. The possibility to finely control the switching waveforms suggested to take advantage of AGDs to improve reliability and power converter lifetime. The second part of the work deals with Active Thermal Control (ATC): the driver can be exploited to determine power loss and, increasing it in low load conditions, the temperature of the device can be controlled. Since thermal cycling is known to be one of the most important threats for realiability, ATC should improve device and system lifetime. To fully support and implement ATC, different loss models were devised and analyzed, taking into account not only their numerical performance, but also the effort needed to tune them. In the last part of the work, different ATC techniques were implemented, tested and compared, taking advantage of figures of merit developed on purpose. Limitations and benefits of the different techniques were found and the shoot-through ATC technique turned out to be highly promising, since it can determine almost constant power loss on the device regardless of its load condition, even in case of free-wheeling conduction. The work is far from being over: different devices should be studied, the gate driver reliability should be assessed, the effects on junction temperature shuld be studied in depth, the reliability improvement should be quantified and the reliability-efficiency trade-off determined.