Enphase's 900 V GaN work targets the number of converter stages
Enphase and Infineon have tested 900 V monolithic GaN bidirectional switches for the IQ solid-state transformer, allowing Enphase to explore a power stage with fewer series-connected converter blocks.
Each block handles part of the medium-voltage input, which exceeds the blocking capability of a single device rated below 1 kV. Giving the block more voltage headroom can reduce the number needed for a given input, provided the design retains enough margin for operating conditions and transients. Fewer blocks can then remove associated components and losses from the current path.
The switch's bidirectional behaviour helps make that arrangement possible because it combines voltage blocking and current conduction in both directions within one monolithic device. For an AC switching stage, this affects the connections needed to control current through the circuit as well as the number of semiconductor devices carrying it.
“Moving to 900 V gives us more voltage headroom while retaining the benefits of high-frequency switching,” said Enphase chief technology officer Hans van Antwerpen.
Enphase already uses 650 V GaN bidirectional switches in its IQ9 microinverters. The 900 V devices extend that work into IQ solid-state transformer development builds, with production qualification expected to follow the initial testing.
The architectural change is worth more attention than a comparison of voltage ratings alone. Raising the switching frequency can reduce the size of the transformer and other magnetics, but it also changes switching loss and the heat generated in the finished assembly. Removing a conversion block can improve the overall balance by reducing the hardware through which power must pass, rather than relying entirely on making each remaining component more efficient.
Enphase also distinguishes the bidirectional devices used in the conversion path from higher-voltage unidirectional devices on the DC side. Its references to 800 V and future 1,500 V DC systems describe complete circuit arrangements, with the voltage distributed according to the topology. The rating of an individual switch still has to suit the voltage it encounters within that arrangement.
The collaboration has reached tested devices and development builds, giving the proposed architecture a practical basis. A system efficiency curve across load and temperature would show how the reduced block count performs beyond that initial work, particularly where losses in the remaining magnetics and cooling arrangements become significant.
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Image: Internal circuitry and wiring of a KACO Powador solar inverter. Illustrative photograph; not the Enphase IQ solid-state transformer. Photo: Asurnipal / Wikimedia Commons. Image source. CC BY-SA 4.0.
