Filtering of Noisy Frequency Measurements Using Coherence between Multiple Measurements

Distributed energy sources that are interfaced to the grid using power electronic converters and are connected to the medium and low voltage network, can potentially play an important role in improving the electro-mechanical stability of a grid. The bus frequency signal is the most convenient local feedback signal that can be used for this purpose. The bus voltage in a distribution system can be significantly distorted; therefore the frequency measurements are noisy and require heavy filtering. In this paper we propose the use of coherence functions of measurements taken at multiple locations to design the parameters (in non real-time) that result in very low phase delay. The filter designed using this method is found to be resilient to sudden spurious data (periodic spikes or glitches). The filtering algorithm has been tested on the real-life distribution system frequency measurements of the Indian grid.