Security region of compressed air energy storage systems incorporating multi-stage compressor coupling dynamics

In low-carbon power systems, Compressed Air Energy Storage (CAES) system is deployed to compensate for volatile renewable generation, thus fulfilling the desired generation schedule. This requires energy storage subsystem to operated over a wide range to meet regulation commands from the grid operator. However, the surge instability phenomenon of multi-stage compressors poses a threat on secure operation. In current practice, the compression power can only be slightly changed to maintain a stable margin, which greatly limits the operational flexibility of CAES. Accurate characterization of the stability boundary can effectively reduce this conservatism, but the variability of operating points makes it challenging to fit a point-wise boundary from time-domain simulation due to the high-dimensional characteristics. This paper proposes the concept of CAES security region, which shifts the analytical perspective from individual operating points to a system-wide domain. A multi-stage coupled compression-side dynamic model incorporating controller regulation effects is developed. The stability boundary is constructed in the control input space, which holistically assesses system stability across various regulation directions compared to the state space. Simulation results demonstrate that the proposed method comprehensively characterizes the stability boundary under variable operating conditions. After adding a damping ratio of 0.6, the system can withstand a 4% disturbance and remain stable. The introduction of the linear approximation algorithm reduced the security domain calculation time from 7 minutes to 1 s. This approach offers a novel practical and visualization tool for control design and operational assessment of CAES systems.