Design Aspects of Three-Phase Current-Source Converter Commutation Cells with Monolithic Bidirectional GaN Transistors

The recent availability of novel monolithic bidirectional GaN switches (MBDSs) renders current-source converters (CSCs) with their inherently sinusoidal output voltages an interesting alternative to voltage-source converters (VSCs) for future motor-friendly variable-speed drives (VSDs). However, CSC commutation cells contain three MBDSs and hence obtaining low-inductance and symmetric PCB layouts is more challenging. Furthermore, CSCs employing MBDSs require special multi-step commutation sequences that rely on current-direction and/or voltage-polarity information. In this paper, we provide an overview of these challenges, and, employing Ansys Q3D simulations, comparatively evaluate CSC commutation cell PCB layouts with first-generation 600V, 140mΩ GaN MBDSs regarding commutation inductances and parasitic capacitances. Whereas clearly all available packages are optimized for VSC half-bridges, the identified CSC commutation cell layouts facilitate a compact realization of a full AC-AC VSD prototype (3D CAD model). Still, concepts such as PCB-embedding or chip-level integration of the MBDSs, gate drives, etc. could greatly benefit future high-performance CSC realizations, and ultimately lead to an intelligent power module (IPM) concept for CSCs.