Adaptive-Extremum Seeking Method for Impedance Identification in Distribution Grids

Abstract

This paper proposes an adaptive Extremum Seeking Control (ESC) based method for extracting the impedance of a distribution grid. An adaptive version of ESC is developed for speeding up the impedance identification process by dynamically increasing the convergence rate of ESC. An impedance change can occur at any time and may produce a disturbance in the grid voltage. Disturbance caused by a change in impedance value can cause the Extremum Seeking Controller to re-adjust its operating point. At first, this may cause the controller to take huge steps in the direction of the new impedance value. Once the value comes closer to the new impedance value, the controller then steadily converges. This steady convergence (especially observed in the distribution grid) is often too slow and may cause an unnecessary delay in estimating the correct impedance value. This work proposes a method of observing the external disturbance and dynamically adjusting the gain of demodulating signal to make the convergence process faster while keeping the ESC-based impedance identification process stable. The increased convergence rate is achieved while keeping the magnitude of applied perturbation constant throughout the process and only changing the magnitude of the demodulating signal.