A computationally efficient impedance scanning of inverter-based resources

Abstract

Impedance-based stability assessment (IBSA) is an effective method to identify stability problems of inverter-based resources (IBRs) in modern power systems. The desired accuracy can be achieved by using the electromagnetic transient (EMT)-type impedance scanning method. This method also allows extracting the impedance models of manufacturer-specific models, thus, has gained popularity among transmission system operators (TSOs). In single-sinusoidal (SS) method, a small SS signal voltage perturbation is used to obtain the impedance/admittance of an IBR. The major drawback of the SS method is its high computational burden as the EMT simulations are performed at each frequency. The multi-sinusoidal (MS) method may be used to improve the computational efficiency of EMT-type impedance scanning. However, the high magnitudes of the superimposed MS signals can cause saturation in converter controls and/or activation of transient functions. These large magnitudes can be reduced by using a phase shift approach such as quadratic phase shift (QPS) and optimized phase shift (OPS). In this thesis, SS and MS methods for impedance scanning are investigated and evaluated. To benefit from the advantages of both schemes, a hybrid scanning method is proposed including perturbation signal, magnitude, and frequency segmentation settings. Additionally, a modified quadratic phase shift (MQPS) scheme is proposed for reducing the high magnitudes of MS signals. All methods are validated and compared using the average value model of doubly fed induction generator (DFIG) and full-size converter (FSC)-based wind parks (WPs). The guidelines and recommendations are provided for the proper usage of the proposed hybrid scanning in the sub-synchronous frequency range.