Propeller phase synchronization for small distributed electric vehicles

Noise restrictions are imposed on aircraft flying over urban environments to reduce annoy-ance and health problems. These restrictions are predicted to be a limiting factor in unmanned aerial vehicle (UAV) deployment, particularly in the target application of urban transportation. This paper presents the design, analysis and experimental results for a propeller phase synchronization algorithm for noise reduction in UAVs with distributed electric propulsion. The propeller phase, for each propeller, is the difference between a common virtual propeller position and the real propeller position. To verify the controller performance, a testbed is designed based on the NASA GL-10 demonstration aircraft. To meet the performance requirements in steady-state, the motor dynamics are identified and the controller is designed based on this model. The designed controller is then tested in simulation with realistic time delays, sensor errors and noise models. The controller is verified on the testbed, and the performance is quantified in terms of the mean and standard deviation of the steady-state phase error. For the range of motor speeds typical of the chosen UAV, the steady-state performance is shown to be suitable for sound suppression, with phase regulation errors less than 5^◦ from a virtual phase target. These results are promising for noise reduction applications in urban transportation with distributed electric propulsion UAVs. In addition to static tests, the transient and steady-state tracking of the controller are demonstrated on the testbed to motivate future work for dynamic noise cancellation methods.