Advanced control strategies for dynamic operation of a solar-assisted recompression supercritical CO2 Brayton power cycle

In this paper, we perform dynamic analysis and develop control strategies for a direct-heating solar-assisted supercritical CO2 (sCO(2)) recompression Brayton cycle. Two control schemes are developed for dealing with different levels of net solar power (NSP) fluctuation. The main control objective is to sustain a progressive process performance by controlling the turbine inlet temperature (TIT) at desirable set-point(s) when NSP drops below the design value. A comprehensive dynamic model for the integrated process is used to evaluate the control schemes performance. While sustaining process stability, the first scheme named inventory control (IC) was able to yield significant extra energy output (up to 37.1%) compared to a conventional scheme. However, the IC scheme shows its utility only when the NSP drops are significant/stable. As a result, a second scheme (flexible recompressor control, FRC) was proposed to deal with days when NSP drops are small/unstable (e.g. in summer, NSP often fluctuates around the design value). The FRC scheme has a simpler design, but able to exceptionally track the TIT set-point while achieving extra energy output and process stability. However, the extent of energy output enhancement is marginal (up to 9.4%) due to the fact that FRC scheme is intended for days where NSP does not deteriorate significantly. This work specifically suggests that operational switching between the two schemes will be critical to ensure process stability and performance, and has generally revealed the significance of control design and dynamic operations for this emerging power process.