Dynamic characteristics and control strategy of pumped thermal electricity storage with reversible Brayton cycle

Abstract

The pumped thermal electricity storage (PTES) based on reversible Brayton cycle can effectively absorb the instability and periodic fluctuations of renewable energy. The dynamic model of heat pump cycle in 5 MW PTES system is established and the disturbance characteristics of the electric power input are obtained. The results indicate that the thermal energy storage temperature drops by 16.52K and the specific exergy loss of molten salt is 6.67% when the electric power input ramps down by 7%. Affected by thermal inertia, the variation trend of thermal energy storage temperature is obviously lagging behind the disturbance signal of electric power input. Inventory control strategy is employed to maintain the thermal energy storage temperature of the heat pump cycle, thereby maintaining energy quality of the thermal energy storage. During the 50% ramp-down progress of electric power input, the variation range of thermal energy storage temperature is within 1.87K and the specific exergy loss of molten salt is within 0.71% by the PI controller to adjust the total amount of working fluid inventory in the cycle. As the daily output of wind power plant is used as the electric power input of system, the variation range of thermal energy storage temperature is within 1.71K and the specific exergy loss of molten salt is within 0.65%, which further verifies the feasibility of the control strategy.