General Power Converter Startup

Design and build an innovative way of starting the NAVY's 250kW general converter. The final project design must provide the control and switching power for quad half-bridge inverter using both GaN and SiC MOSFET switching devices sourced from a standard US power socket.

Background
Convert one form of electric power to another efficiently and compactly for use in controlling the larger power converter project. The project will incorporate two converter designs:

Specifications
Power Converter Specifications:

* 3.3V Isolated (gate driver) * 6V, 100mA x 8 * 3.3V Isolated (gate driver) * 20V, 100mA x 8
 * Input: 120 Vac @60Hz
 * Microcontroller: 3.3 Isolated, 500mA
 * GaN System:
 * SiC System:
 * Size: ~200mm^3 (~8 in ^3)
 * Efficiency: over 90%

Power Converter Schematic
The schematic shown above describes our full test board, designed to stress our power supply’s ability to provide for a system that is close to our target system. This design is simply four parallel half bridge switching inverters with Si8274 switch drivers providing an interface with off-board controller and the half bridges. Each switch driver is accompanied by supporting capacitors and resistors with control input from a PWM signal from the controller and power from the off-board power supply. In the schematic each bridge has four switches, with two of the switches being redundant to test multiple types of devices. For now we are building one forth of this design for prototyping and testing.

Prototype(s)
This board was somewhat rushed as we did not yet have the proper tools to construct a surface mount board, even though our parts were of the surface mount variety. This was a result of some errors in oversight with our first board and ultimately didn’t work as static electricity destroyed the internals of the silicon driver chip.

Soon after the failure of the first prototype we had gained the ability to construct our own printed circuit board and prototype 2 is currently in construction. This should quicken our ability to test new ideas and future prototypes on the fly.

Steady State GaN MOSFET Thermal Testing
Observed and recorded device case temperature and Drain-Source current at constant Drain-Source and Gate-Source potential while the GaN MOSFET is operating at steady state(non-switching) while applying heat (increasing ambient temperature) to the system with a heat gun. (Vgs = 2.3 V, Vds = 6V)



Conclusion
Although GaN MOSFETs are rated for a temperature of 150 Celsius on their casing special care needs to be taken to prevent thermal runaway at much lower temperatures, around 80 degrees Celsius. If device starts thermal runaway and goes without check it will fail. This may be managed via heat sinking and control and monitoring. We will further test the thermal characteristics of these GaN devices during switching operations.

Engineering Specifications

 * SiC MOSFETS and GaN MOSFETS
 * Microcontroller
 * Gate Driver
 * DC/DC Converter
 * AC/DC Power Supply
 * Quad Half-Bridge Inverter

Agendas
Agendas

Minutes
Minutes

Project Schedule
Schedule

Design Report
Design Report

Final Presentation
Presentation