Control mechanism of compressible volume for transcritical CO₂ cycle power system

Compressible volume control is one of the key control strategies of S-CO₂ Brayton cycle system. In this paper, the compressible volume control of buffer tank and inventory tank is proposed for transcritical CO₂ closed cycle. To clarify its control response characteristics, the dynamic simulation models are established. Its control mechanism and the influence of initial conditions on system response is investigated. The results show that the volume of buffer tank is appropriately 20 % of the system volume, which can play a buffering role and has a negligible impact on system response rate. The initial parameters and volume of the inventory tank determine its total mass of injection/extraction, which in turn determine the adjustment range of the system parameters. It is appropriate to set the initial pressure of inventory tank to the middle value of cycle maximum/minimum pressure and its volume to about 25 % of the system volume. Compared to the system response without inventory control, inventory control can control the stability of compressor inlet pressure, and it can increase the rate by 1.4 %/min when the load decreases and by 1.8 %/min when the load increases. This study provides insights into compressible volume control in transcritical CO₂ closed cycle.