Design of a High Power Density Inverter and FOC Implementation for UAVs

Abstract:
Even nowadays, still some small huts in the alps need a helicopter to provide them with the necessities for living. This task is always connected with high costs and organisational effort. With the ongoing development in the field of unmanned aerial vehicles (UAVs) already a drone exist which can take over this task. Currently, this drone is limited to a payload of 100 kg. In this paper, the design and optimisation of a 19.5kW 2-level inverter based on half-bridge configuration modules using Silicon Carbide (SiC) technology for this type of cargo drones is presented. The 1200 V, 16mOmega SiC half-bridge modules of Wolfspeed provide the base for the power stage. With a switching frequency of 25 kHz and a power density of 8.29 kW/dm3 and 20.06 kW/kg the system achieves several advantages for this use-case, including a maximum payload of 200 kg. In addition, the layout of the Printed Circuit Boards (PCB’s) is optimised for altitudes over 3500m. In terms of control strategy, a Field Oriented Control (FOC) implementation on an ST microcontroller is performed. The system is optimised to work with a 19.5kW Permanent Magnet Synchronous Motor (PMSM) of MAD Components. For validation of the functionality, several tests are performed including double-pulse tests, tests on a passive RL load as well as tests with a Motor test bench including the selected PMSM and a torque sensor. The measured system efficiency of the inverter and PMSM combination reaches 91.37%. The inverter itself reaches a peak efficiency of 98.42%. Further tests on the real drone are intended to be performed, and further optimisation will be done to allow a serial production of this design.