Study of autonomous control system for S-CO2 power cycle
Various control strategies for supercritical carbon dioxide cycle (S-CO2 cycle) have been developed. A combination of bypass and inventory controls is regarded as one of the most important and efficient strategy. When only an inventory control is actuated, the system pressure changes significantly to maintain velocity and temperature at approximately constant level. Hence, an off-design performance of turbomachinery is comparable to on-design performance so that inventory control could allow S-CO2 cycles to maintain high thermal efficiency during part load operating conditions. Nevertheless, an inventory control alone is expected to have issues of delayed response, compressor surge and unexpected system shut down. Therefore, a bypass control should compensate the slow response time of an inventory control even though the bypass control results in undesirable cycle performance at off-design operating conditions. A quantitative assessment of inventory control for an S-CO2 cycle has been rarely conducted because non-ideal thermodynamic properties of S-CO2 make the assessment of appropriate inventory for the selected operating conditions to be difficult. In this paper an S-CO2 cycle performance inventory tanks are modeled to assess various control schemes in terms of response and efficiency.
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