Update GaN PV inverter: losses and first efficiency results
As System Innovator, Neways is working on different innovation projects. One of these projects is the European GaNext project where we are building an Intelligent Power Module (IPM) together with our international partners to remove existing barriers for adopting the Gallium Nitride (GaN) technology for practical solutions. Gallium Nitride ”GaN” is a promising material to replace silicon in power electronics application in the 650 V market sector, such as solar (PV) inverters, power supplies, motor controllers or LED drivers. Power systems based on GaN can be lighter, more compact, significantly more efficient and potentially cheaper than those based on Silicon.
Our share is to build an extremely compact solar inverter (PV inverter) that incorporates both the GaN technology and the IPM to contribute to the miniaturization of power applications. In our previous articles on the GaN technology we have explained some of the fundamental choices with respect to the switching frequencies, and the structured way of bringing the inverter to life.
Meanwhile we extracted the first efficiency numbers from the various stages in the discrete PV inverter. One could expect large losses due to the increased switching frequencies, but the GaN components allow very low conduction and switching losses result in a very good overall efficiency in our converter. There are, however important parameters that must be optimized in order to use GaN technology to the full potential. Among these parameters which are directly related to the benefits of GaN, is the so-called dead time: the time between operation of the various switches in the inverter.
The required dead time in a GaN system is little and can be in the nanosecond range. It is nonetheless important to keep this little, because any conduction in the so-called 3rd quadrant (when during the dead-time all GaN devices are switched off in the circuit) leads to losses.
The absent intrinsic body diode in the GaN switches (in comparison with standard silicon switches), which is one of the benefits from GaN since it allows for higher switching speeds and reduced output capacitance has one major disadvantage: due to the missing intrinsic body diode, the voltage drop over the device (Vds) in 3rd quadrant operation is much higher than the voltage drop of standard silicon switches and therefore the losses can be significant during the dead-time!
The first efficiency results are measured and are promising. With the current interleaved boost implementation we can still achieve an efficiency of up to 99% in the boost stage while switching at 350KHz, which is beyond our expectation!
Next steps include optimization of the output stage in order to make sure we are getting the most out of the GaN technology!
Our enthusiastic Neways GaNext team. Top row from left to right: Roel Kampert, Marcel Boom, Rob Cremers. Bottom row from left to right: Bas Reijnen, Tim van der Loo
More information on GaNext: www.ganext-project.com