Improved rotor angular speed measurement — A key for proper power grid stabilization

This paper presents a new Extended Kalman filter-based method for the estimation of the rotor angular speed of a synchronous machine. The main utility of the estimated speed is in the power system stabilizer. The paper briefly reviews the problems associated with the existing methods for reliable and accurate rotor speed measurement or estimation. It is shown that the existing methods of rotor speed estimation have some severe drawbacks and may cause the power system stabilizer to operate suboptimal or even produce negative damping over a specific frequency range when an inaccurate rotor speed signal is used as the input to the power system stabilizer. Most importantly it demonstrates that a system equipped with it behaves as predicted in simulations, especially when examining inter-area modes. The new rotor speed estimation method was implemented on an industrial control platform and integrated in a modern digital excitation system. A series of hardware-in-the-loop simulations were run to examine the properties of the new speed estimator. The simulations confirm that the new speed offers superior performance in terms of speed estimation accuracy, which allows the proper damping of oscillations over a frequency range of interest.