Improved Zero-crossing Method for Power System Frequency Estimation*
Fast and accurate frequency estimation is crucial for power system control, protection and monitoring. This paper proposed an improved zero-crossing method based on weighted multi-level set for frequency estimation with one and half cycle. The proposed method first uses multi-level set, i.e., different thresholds to calculate initial frequencies, then, an optimization process to calculate the weights of the initial frequencies is adopted. Finally, accurate results of power system frequency can be obtained by weighting the initial frequencies. Simulations carried out by Matlab validate the performance of the proposed method as well as the experiment executed on DSP platform.
This paper deals with the study of free transverse vibrations of rectangular plates with an internal line hinge and elastically restrained boundaries. The equations of motion and its associated boundary and transition conditions are rigorously derived using Hamilton’s principle. The governing eigenvalue equation is solved employing a combination of the Ritz method and the Lagrange multipliers method. The deflections of the plate and the Lagrange multipliers are approximated by polynomials as coordinate functions. The developed algorithm allows obtaining approximate solutions for plates with different aspect ratios, boundary conditions, including edges elastically restrained by both translational and rotational springs, and arbitrary locations of the line hinge. Therefore, a unified algorithm has been implemented. Sets of parametric studies are performed and the results are given in graphical and tabular form.