Multi-Level Underwater Compressed Air Energy Storage Turbine-Side Power Tracking Strategy Based on Adaptive Fuzzy Control

The high intermittency of offshore renewable energy presents a major challenge to the power grid’s secondary frequency control capability. Underwater Compressed Air Energy Storage (UWCAES), which uses flexible airbags for constant-pressure energy storage and release, is a key technology for smoothing grid fluctuations. Because the storage pressure in a UWCAES system is directly proportional to the water depth, deploying airbags at different depths allows for the flexible dispatch of compressed air at multiple pressure levels. Multi-level UWCAES (M-UWCAES) deploys airbags at different depths to provide compressed air at multiple pressure levels, significantly enhancing system flexibility. This paper proposes a turbine-side power tracking strategy for M-UWCAES based on adaptive fuzzy PID. A dynamic model of the turbine side is first established to elucidate the multi-stage energy storage and release mechanism. An adaptive fuzzy PID controller is then designed to adapt to the system’s multi-mode operational characteristics. Simulation results show that compared with conventional UWCAES, M-UWCAES exhibits smaller off-design deviations under low regulation demands, with partial-load exergy efficiency improved by 4.69–13.75%. The M-UWCAES system, utilizing adaptive fuzzy PID control, exhibits a faster power tracking response speed and effectively mitigates the overshoot caused by mode switching.