Voltage and Frequency Support Scheme for Storage Systems in Distribution Grids

Power electronics converters can enable grid support functionalities under abnormal grid conditions. In this paper, a voltage-frequency support strategy based on the reactance to resistance (X/R) ratio of the grid impedance is proposed for a flywheel energy storage system. Unlike conventional support schemes where voltage and frequency support is decoupled, the proposed strategy considers the coupling between voltage and frequency due to the resistive characteristics of the grid impedance in low voltage distribution grids. In addition, the proposed strategy ensures a fair compensation between voltage and frequency support by utilizing two gains that are defined according to the event type. Simulations and experimental tests are carried out using a laboratory setup to validate the proposed strategy. The capabilities of storage systems to provide such tailor-made ancillary services for supporting the distribution grid are demonstrated.