Improved Real-Time Stability Assessment of Grid-Connected Converters Using MIMO-Identification Methods

Several stability and power quality problems have been reported recently in power systems, which experience a high penetration of power electronics converters, such as renewable energy inverters. The problems are often caused by the interaction between the converter and the grid impedance. Stability monitoring tools have been presented to gain insight into the stability margin of the power system. Online methods are most favorable since the power system has many parameters that vary with time. However, the online methods that have been presented may produce inaccurate estimate of the stability margin due to several simplifications, such as using reduced-order impedance models. This paper introduces an improved dq-domain stability analysis that takes into account the time-varying grid impedance in real time and also the multivariable inverter output impedance, including the crosscouplings.