Modeling and exergy analysis of an integrated cryogenic refrigeration system and superconducting magnetic energy storage

Superconducting magnetic energy storage (SMES) systems widely used in various fields of power grids over the last two decades. In this study, a thyristor-based power conditioning system (PCS) that utilizes a six-pulse converter is modeled for an SMES system. The main subject of this research is the generation of required helium for an SMES because for the coil to be at superconducting temperature, it needs to always be immersed in liquid helium. In the conducted simulation, the helium production system provided, in which primarily the gaseous helium temperature was reduced by heat transfer in LNG heat exchangers, and then after the sudden pressure drop, it turned into a liquid. The effect of the various firing angles is investigated, and it is found that at angles lower than 90 degrees, at a specific angle, the output current enhances with time. In the 90 degrees, this current remains constant, and at degrees greater than 90 degrees, the output current reduces with time. The percentage of input flows to the expanders is investigated to find the rate of the maximum liquid helium production amount to the inlet gaseous helium. The diverted ratio of mass flow via expander 1 and expander 2 was 0.46 and 0.35, respectively. The system's work utilization of network, and liquid helium production is 67.18 MW and 12.7 kg/h. Also, the exergy analysis is done and the results show 35.7 % exergy efficiency. The efficiency of helium production has a direct relation to liquid nitrogen mass flow. However, due to the required high power for producing liquid nitrogen, with mass flow rate increment, the total system's efficiency is reduced. The results are evaluated with Aspen HYSYS, Aspen Energy Analyzer, and MATLAB. Specific work obtained from the analysis is 290,097 kW.s/ kg which indicates that uses lower power in comparison with the other helium production methods which saves power and electrical costs.