Decoupled admittance modeling of battery connected VSC for a grid-tied microgrid

Battery energy storage systems (BESS) in addition to photo-voltaic connected to voltage source converters (VSCs) offer their services to support the required reactive power for voltage regulation in distribution networks (DNs). Dynamic equivalence of microgrid and thus system identification is a powerful approach to develop model that can be conveniently applied in control design for voltage regulation problem. This paper presents an effort to develop decoupled admittance model based on dq-frame for VSC connected to battery, which in turn are integrated in low voltage network. The complete microgrid is utility grid connected. In study, real-time data is generated with regulation (multi-steps) of active/reactive powers applied at the input of VSC. With measurements of voltage at point of common coupling (PCC) and input powers, probability density function (PDF) is estimated for current variables corresponding to d-and q-axis components to quantify their dominance with respect to regulated powers. Next, single-input single-output (SISO) admittance transfer functions (TF), represented in both d-and q-axis components of admittance matrix are obtained. The identified decoupled TF models represents the combined effect of dynamics of battery and VSC at PCC. The identified admittance model is applicable for multi-operating points, as a result, being applicable over wide operating conditions. Also, in study, the discussion is given for admittance property of identified TF model of batteries using Bode plot and its stability analysis using Nyquist criteria. •Model characterization through experimental data in a grid-tied microgrid•Modeling of batteries as an admittance model in dq-frame•Perturbation of voltage source converters to generate identification data•Identification as single-input single-output transfer function models