The Dynamic Performance Of Cryogenic Energy Storage Unit And Its Application In Wind Power Generation Absorption

The wind power is limited to access power grid on a large scale because of the fluctuation and intermittence of wind energy.And it leads to wind curtailment and energy waste.The wide application of energy storage devices has brought a new opportunity for the development of wind power.In this paper,a new kind of energy storage technology,cryogenic energy storage technology,has been studied.The dynamic characteristics of the cryogenic energy storage generating unit are analyzed,and the control strategy of wind power generation absorption using cryogenic energy storage system is established.Firstly,the charging and discharging process of cryogenic energy storage system is independent of each other.Thus,based on the dynamic and thermodynamic characteristics of energy storage unit and energy release unit,the dynamic models of air liquefaction subsystem and expansion power generation subsystem are established,respectively.Then the validity of the models was verified.In addition,the paper also sets up the two-area electrical power system frequency modulation model which includes several thermal power generating units and wind turbine generators.This model will be used to research the ability of peak regulation and frequency adjustment for cryogenic energy storage system.Secondly,the dynamic operating characteristics of the cryogenic storage generator air liquefaction subsystem and expansion power generation subsystem are researched,respectively.Based on the model of the air liquefaction subsystem and expansion power generation subsystem,the dynamic performances of both energy storage unit and energy release unit are analyzed.And the influence of input power with different time scales on energy storage unit is also analyzed.The results show that the response rate of the air liquefaction subsystem has is slow and it can only absorb the hour-level and above fluctuating power.On the other hand,the power regulation rate of expansion power generation subsystem is relatively fast and it can participate in secondary frequency modulation of power system.In order to research the ability of peak load regulation of the cryogenic storage generator,the paper established the peak load regulation strategy to make the output of the thermal power units more stable and reduce the wind curtailment phenomenon.Finally,a control strategy is developed to absorb the wind power for cryogenic storage generator.The short-term wind power forecasting curve and the top and bottom limitation of wind power fluctuation are used as the reference scheduling power output of wind farms.Thus,the difference value between this above reference power output and the actual wind power is the reference power of energy storage system.Considering the energy storage unit and energy release unit have different dynamic response rates,the empirical mode decomposition(EMD)is used to decompose the reference power of energy storage system and get several signals at different frequencies.These signals will be reconstructed based on the time scales of energy storage unit and energy release unit.Then the air liquefaction subsystem and expansion power generation subsystem will be distributed with the most suitable control signals.Research results show that this strategy can not only ensure the efficiency of cryogenic energy storage system,but also have good effect on smoothing the wind power fluctuation at middle and low frequency.