Design Considerations of the GaN Power Stage for a GaN/Si Internal Parallel Multilevel Converter based 1500V PV String Inverter

Increasing the power density of PV inverters have been of great interest in the PV industry. With a smaller and lighter inverter, the installation cost can be greatly reduced, making solar energy more affordable. To improve the power density of PV inverters, a new internal parallel converter has been proposed in the literature and prototyped. This paper presents the key design considerations of the Gallium Nitride (GaN) based power stage as the high switching frequency (HSF) module in the modularized prototype. Two issues have been addressed in detail, i.e. the sizing of film capacitor based flying capacitor (FC) and design of GaN power board. A current stress based sizing has been investigated for FC indicating that the volume of the FC bank is dominated by the current stress instead of the switching frequency. Furthermore, design of the GaN power board based on insulated metal substrate (IMS) board has been discussed in detail. In addition to improved thermal performance, the metal substrate can serve as a shielding layer and help reducing the power loop parasitic inductance. Experimental results have confirmed that the designed GaN HSF module can safely operate under full power.