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Power electronics for the energy transition

Wide bandgap semiconductors like gallium nitride (GaN) and silicon carbide (SiC) are gaining prevalence in demanding applications. In doing so, they are freeing up immense energy saving potential in photovoltaics inverters.

Photovoltaics (PV) are becoming increasingly important for energy supply that’s sustainable, affordable and, since the Ukraine war, secure. But before solar energy can drive electrical devices as electricity, it has to pass through an inverter. These convert the direct current from solar modules into alternating current and feed it into the low voltage network. Large 50-Hz transformers then connect it to the regional medium voltage network.

Effective with SiC

Last year, as part of the “SiC-MSBat” project, researchers from Fraunhofer ISE together with partners were able to operate a compact inverter with an efficiency of 98.4 percent for supply directly into the medium voltage network.

Power transistors made of silicon carbide (SiC) with very high blocking voltages (3.3 kV) had a key role to play here. They work with significantly lower losses in voltage than their silicon counterparts and therefore allow a frequency of the inverter stack with a switching frequency of 16 kHz. This has the advantage of enabling savings from passive components, as they can be smaller in size. At the same time, thanks to their high control dynamics, SiC inverters are able to take on the task of network stabilization, for example as a filter to compensate for the medium voltage network. And, last but not least, the much higher power densities also support a compact construction.

However, anyone who orders “energy-saving chips” now needs to be patient, as factories are fully booked well into next year. Yole Développement expects a revenue of USD 6.3 billion for SiC components by 2027.

The latecomer, gallium nitride

Gallium nitride (GaN) is not progressing quite so quickly. However, according to Yole, the GaN power market is expected to break the USD 1 billion mark for the first time by 2026. The main drivers in power generation are still in the consumer sector, such as rapid chargers for smartphones. The analysts assume that GaN transistors will also play an increasingly important role in inverters, electric vehicles and in industry in future. However, it still ranks behind SiC in terms of costs, delivery assurance and quantities. For that reason, scientists around the world are working hard to remove these hurdles.

To this end, up until April of this year, 26 partners from nine countries in the European UltimateGaN project researched processes for manufacturing high-quality GaN chips at globally competitive costs.

GaN power for solar systems

The joint research project “GaN HighPower” financed by the Federal Ministry of Economics will now use components such as these to test the next generation of cost-effective, resource-saving and efficient converters for photovoltaic applications. They will focus on string inverters with higher power in excess of 100 kVA. They convert the solar power of a string of photovoltaic modules connected in series. Gallium nitride semiconductor modules from Infineon are used together with greatly improved inductive components and current sensors.

The Infineon modules are characterized at the Hochschule Bonn-Rhein-Sieg (University of Applied Sciences, H-BRS). By knowing the exact switching behavior, the gate drivers can then be optimally matched to the semiconductor module. The H-BRS is likewise responsible for the draft and simulation of the adjusted gate drivers, as well as the associated power supply and dimensioning of the DC intermediate circuit. Here, the rapid switching transients of the semiconductor module place particular demands on the control electronics.

In this project, the Fraunhofer IEE is exploring the questions of how the newly developed components can be integrated into the complete system of a photovoltaic inverter and what demands will arise from combining high power with high switching frequencies.