Dynamic performance and control scheme of variable-speed compressed air energy storage

•Doubly fed induction machine is applied to CAES system for variable-speed operation.•Variable-speed compressed air energy storage is studied and compared to fixed-speed.•Max efficiency point tracking control of speed and variable vanes is proposed.•The proposed system improves the flexibility and efficiency of CAES. To satisfy the requirements of large-scale utilization of renewable energy, the compressed air energy storage systems should exhibit a wide operating range. However, the flexibility of compressed air energy storage systems is limited by the turbomachinery character. Given that variable-speed operation can significantly broaden the flexibility of turbomachinery, a double-fed-induction-machine-based variable-speed compressed air energy storage (VS-CAES) system was proposed and studied for the first time. A numerical model integrating thermal-mechanical-electrical subsystems of VS-CAES was built. The control scheme of the VS-CAES system for max efficiency point tracking was well built and studied. The steady thermodynamic performance and dynamic performance of the VS-CAES system were analyzed and compared with those of the fixed-speed compressed air energy storage (FS-CAES) system. The results show that the variable-speed operation broadens the operation range of the charging process by 49 % under different pressure, while the influence on the operation range of discharging process is negligible. The off-design exergy efficiency increases by 0–6 % with an average of 1.8 % in the charging process and 0–1 % with an average of 0.5 % in discharging process. Under a 10 % step change of power setpoint command, the dynamic power response of VS-CAES is 0.3 s for both charging mode and discharging mode. In a contrast, the dynamic power response of FS-CAES is 26.5 s and 20.5 s. The research results of this study provide important guidance for the design and operation of compressed air energy storage system.