Dynamic performance of CAES based on switching expansion reduction

Abstract Compressed air energy storage (CAES) is considered as one of the most promising large scale energy storage technologies for the electrical grid with high penetration of renewable energy. CAES systems are required to operate under complex conditions because of the pressure change in the air storage chamber and input/output power changes considering the fluctuated renewable generation and the mismatch between energy supply and demand. A dynamic operation configuration was proposed to satisfy the adjustment of off-design conditions of CAES systems and frequency management auxiliary service market. To regulate the inlet pressure of turbines and meet the output power demand for better performance, a thermodynamic model of a CAES discharging system with thermal storage and the pressure control unit (SER) was established. The control strategy of setting adjustment width instead of single instruction curve is proposed. Then, the dynamic operation parameters including pressure, mass flow rate, and exergy change during discharging processes were investigated. The superiority of the control accuracy and efficiency was demonstrated over single throttle valve through valve characterization studies. The SER system improves control accuracy by decoupling pressure and flow rate changes in dynamic operation, solving the problem of difficult control and low accuracy of traditional throttle valves. The expansion tank in SER serves as a pressure buffer and heat exchanger with the environment, reducing energy loss during fluid flow. Furthermore, the effect of the expansion tank volume of switch expansion reduction in exergy destruction were assessed. For a 10 MW/60MWh system with dynamic load to meet the requirements of the unit to participate in the frequency modulation auxiliary service market, the optimal added expansion tank volume is about 70m 3 . The optimization method of control strategy of SER system is also explored. The proposed optimized SER system of volume and control strategy can smoothly regulate the inlet pressure of the expander. When the adjustment width is 3bar, the frequency is 50% decreased, meanwhile, the on–off action time is more evenness, which ensures the stable and efficient operation of the CAES system and improves the comprehensive performance of the system.