A Subspace Identification Technique for Real Time Stability Assessment of Droop Based Microgrids

Abstract

Real time detection of the microgrid stability is crucial for determining and adjusting the power-sharing droop controllers' gains to maintain a sufficient stability margin. Maintaining minimum relative stability should be ensured at different operating conditions to accommodate any sudden system changes. This paper develops a novel subspace-based identification technique to assess microgrid stability real time without relying on offline analytical small or large-signal models. Unlike conventional system identification techniques that require the introduction of external excitation signals, the proposed method employs a simple routine through small and short-duration perturbations in the active power droop gain of inverter-based distributed generation (IBDG). The use of subspace identification does not require pre-defining the system’s order and avoids the exhaustive computations associated with iterative identification methods. The proposed stability assessment method has been tested on an IBDG microgrid considering different operating conditions in MATLAB/Simulink. The accuracy of the proposed real time stability assessment tool is determined by comparing the results to the analytically-derived small-signal model.