A state of charge‐based linearised frequency–voltage droop for interlinking converters in an isolated hybrid microgrid

• Published in: IET renewable power generation 2021-02, Vol.15 (2), p.354-367
• Main Authors: Malik, Sarmad Majeed, Sun, Yingyun
• Format: Article
• Language: English
• Subjects: Control of electric power systems; Distributed power generation; Power convertors and power supplies to apparatus; Power system control; Secondary cells; Voltage control
• ISSN: 1752-1416; 1752-1424
• DOI: 10.1049/rpg2.12028

A battery‐dominated hybrid microgrid architecture where various battery modules are linked to the ac bus via converters is presented. A novel frequency–voltage droop scheme is proposed for the interlinking converter connecting the dc and ac grids. The ac grid frequency and dc grid voltage are linked together in outer controller loop through two factors, the ratio of which defines the frequency–voltage droop. This enables autonomous bidirectional power flow and regulation where each grid is supporting the other grid through its surplus power. A state of charge (SOC)‐based control scheme is also proposed for the battery units linked to ac bus which ensures power sharing based on the SOC of individual storage units. The system small‐signal model is developed and a stable range of operation is defined. The impact of number of battery units and SOC of an individual battery on the system performance is also analysed. In addition, the proposed strategy is compared with normalised SOC‐based control to evaluate its feasibility. Simulations in PSCAD/EMTDC show that the proposed SOC‐based scheme helps maintain charge balance while regulating the voltage and frequency and ensuring power flow among battery units and grids.