High Angular Rates Estimation using Numerical Phase-Locked Loop Method

In this paper, a numerical phase-locked loop (PLL) algorithm for estimation of the high angular rate of samara-inspired UAV is presented. The sinusoidal magnetometer measurements generated from the spinning UAV is proposed as the reference input to the PLL. The PLL then estimates the instantaneous frequency of the input and outputs a synchronous waveform. Significantly, the proposed approach enables estimation of the UAV's angular velocity even when it operates beyond gyro saturation condition. The proposed PLL-based method was numerically evaluated and the effects of the PLL gains parameters are demonstrated in simulation. The PLL was shown to have a fast settling time, at bout 0.02s, to a step change in the input reference with a well-selected gain. The PLL was demonstrated to accurately track a ramp input change of up to 11 Hz, which is twice the gyroscope saturation limit, with zero steady-state error. Lastly, the proposed algorithm was experimentally evaluated on a benchtop setup, for up to 6.3 Hz, with an rms error of 0.04006 Hz; and in actual UAV flight, up to 6.5 Hz, with a rms error of 0.0479 Hz.