Dynamic simulation and coordinated control of Carnot battery energy storage system integrated with LNG cold energy

Carnot batteries are promising for long-duration energy storage by converting electricity into thermal energy during charging and regenerating electricity during discharging. Integrating liquefied natural gas (LNG) cold energy can lower the heat sink temperature and promote low-grade thermal resource utilization. However, the dynamic behavior of LNG-assisted Carnot batteries under variable loads remains insufficiently understood. This study develops a dynamic model to investigate transient responses, heat transfer matching, storage state evolution, energy performance, and component exergy characteristics under step change ratios (SCRs) of ±2%, ±4%, ±6%, and ±8%. Coordinated regulation of working fluid and storage medium flow rates enables compressor input and expander output to track imposed load changes. For tolerance bands of 1%, 0.5%, and 0.1%, the controlled power response times are 2.80–5.57, 3.03–7.30, and 4.33–10.77 min, respectively. Thermal responses lag flow responses, while the logarithmic mean and minimum terminal temperature differences exhibit different trends, indicating that the overall heat-transfer driving force and terminal temperature approach should be jointly assessed. SCR variations alter storage inventory and subsequent operating duration, changing discharging by +3.7/−4.0 min after charging variations and charging by +6.13/−5.7 min after discharging variations. Across SCR = −8% to +8%, P2P efficiency decreases by 1.65 and 3.14 percentage points for charging and discharging variations, respectively. Exergy analysis shows that the components with the greatest cumulative exergy destruction do not necessarily exhibit the largest relative variations under SCR changes. These findings clarify the coupled effects of load variation, heat transfer, storage inventory, and component irreversibility in LNG-assisted Carnot batteries.