Experimental Comparison Between a MOSFET and GaN FET Inverter for Agricultural Drone UAV’s

Battery-powered UAVs are revolutionizing today’s agriculture where they are used to spray fertilizers and more. These drones use motor drives that need to be lightweight and efficient to maximize working battery life and extend flight time between recharging. Wide-bandgap devices, and specifically Gallium Nitride (GaN) FETs, have demonstrated to improve BLDC motor drives in emobility and robotic applications. This paper will present the characteristics of GaN FETs that reduce weight and improve the motor drive system efficiency.

GaN FETs switch faster than traditional silicon MOSFET thanks to the lower RDSon and capacitances per die area. These characteristics make it possible to increase the switching frequency of the motor drive inverter and reduce harmonic distortion in the current driving the motor and thus reduce torque ripple. A high PWM switching frequency inverter can also reduce the size of the DC input filter, thus increasing the power density and reduce the inverter weight.

Experimental tests were conducted on a MOSFET inverter and compared with an equivalent GaN FET inverter driving a permanent magnet motor suitable for an unmanned Aerial Vehicle (UAV) agricultural drone. The most relevant figures of merit were characterized as a function of the motor speed and power.

The GaN FET inverter, operated at high switching frequency with sensorless sinusoidal modulation out performs both the MOSFET inverter operated with trapezoidal modulation and the MOSFET inverter op erated with low frequency sinusoidal modulation by as much as 14%.