GaN Power Devices Slash Size, Raise Efficiency Of 4-kW Solar Inverter

by Carl Blake, Transphorm, Goletta, Calif., How2Power Today, Apr 15 2013

Focus:
Gallium nitride (GaN) high-electron-mobility transistors (HEMTs) and fast-switching diodes are now being used in commercial power converter applications at voltages above 300 V. One of these applications—a commercial 4-kW grid-tied single-phase photovoltaic (PV) inverter using 600-V GaN devices from Transphorm---is described in this article. It gives data on the inverter’s benchmark small size and high efficiency and a basic description of the inverter topology. The inverter replaces silicon (Si) IGBTs with GaN HEMTs in the boost converter section—and in the bridge circuit—enabling a 50% reduction in losses, and a peak efficiency above 98%. This inverter also switches at 50 kHz versus 16 kHz for a silicon IGBT-based design. As a result, the GaN-based inverter is almost 45% smaller, yet still more efficient than the silicon-based design. This article is more of a case study than a how-to design article, but it does include some lessons learned during the design in of Transphorm’s GaN transistors into the string inverter, and there are relevant device comparisons relating to the inverter power stages: Characteristics of silicon MOSFETs and IGBTs are compared with those of GaN HEMTs, assessing the merits of these devices in hard-switched bridges. The faster switching speeds and higher efficiency achieved by GaN HEMTs versus Si IGBTs in a hard-switched bridge are documented.

What you’ll learn:

• How to understand the size and efficiency benefits of 600-V GaN HEMTs and diodes in a 4-kW PV inverter

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