A Quaternion Frequency and Phasor Estimator for Three-Phase Power   Distribution Networks
  For the first time quaternions have been used for real-time frequency estimation, where the multi-dimensional nature of quaternions allows for the full characterization of three-phase power systems. This is achieved through the use of quaternions to provide a unified framework for incorporating voltage measurements from all the phases of a three-phase system and then employing the recently introduced HR-calculus to derive a state space estimator based on the quaternion extended Kalman filter (QEKF). The components of the state space vector are designed such that they can be deployed for adaptive estimation of the system phasors. Finally, the proposed algorithm is validated through simulations using both synthetic and real-world data, which indicate that the developed quaternion frequency estimator can outperform its complex-valued counterparts. 
Sayed Pouria Talebi and Professor Danilo P. Mandic
cs.SY stat.AP