Research On Coordinated Control Strategy Of Flywheel And Compressed Air Hybrid Energy Storage System

At present,the electrification of all walks of life is deepening,and the operation and development of social economy are increasingly dependent on electric energy.With the depletion of fossil energy and a series of environmental problems such as air pollution and greenhouse effect caused by burning fossil energy in large quantities,people pay more and more attention to the development and utilization of renewable energy.However,renewable energy belongs to "depending on the weather",which is easily influenced by the natural environment.random and volatile,and difficult to control effectively.At present,a more effective solution is to stabilize the fluctuation of renewable energy and promote the consumption of renewable energy by configuring energy storage components.In this paper,a hybrid energy storage system is composed of flywheel energy storage with fast response and compressed air energy storage with large energy storage capacity,and its application and coordinated control in DC microgrid are studied.Firstly,this paper studies photovoltaic power generation and wind power generation,two common distributed power sources in microgrid.In the aspect of photovoltaic power generation,the mathematical model of photovoltaic cells is established,and the MPPT control of photovoltaic power generation is realized by variable step size disturbance observation method,the power reduction control of photovoltaic power is realized by constant voltage control,and the switching between the two control modes is realized by BOOST circuit.In the aspect of wind power generation,taking permanent magnet direct-drive wind turbine as the research object,the mathematical models of wind turbine,permanent magnet synchronous motor,generator-side converter and grid-connected inverter are established.The speed of permanent magnet synchronous motor is controlled by generator-side converter to realize the maximum wind energy tracking of wind turbine,and the grid-connected inverter is responsible for maintaining the voltage of DC bus and transmitting the remaining power to the large power grid.Secondly,the two kinds of energy storage devices are modeled and analyzed in this paper.For flywheel energy storage,a double closed-loop charging and discharging control strategy with feedforward decoupling is designed.When charging,the outer loop of speed and the inner loop of current are used to control the flywheel speed accurately.When discharging.the voltage outer loop and current inner loop are used to maintain the stability of DC side bus voltage.The effectiveness of the control strategy is verified by simulation analysis.In the aspect of compressed air energy storage,the thermodynamic models of compressor,expander,heat exchanger,gas storage and other key components are established.Based on the actual operation data,the simulation results have a small error with the actual values,which verifies the effectiveness of the model and lays the foundation for the coordinated control of hybrid energy storage in the future.Finally,the coordinated control strategy between two different energy storage devices is studied.Aiming at the shortcomings of the voltage and current double closed-loop control strategy based on first-order low-pass filtering,a hybrid energy storage double closed-loop control strategy based on improved Model Predictive Control(MPC)is proposed by establishing the predictive model of hybrid energy storage bidirectional AC/DC converter,and the improved MPC is used as the power inner loop to replace the traditional current inner loop.Through the collaborative simulation of wind,solar,storage and DC microgrid,the performance of traditional voltage and current double closed-loop control and the control strategy proposed in this paper are compared under the same disturbance.The simulation results show that the control strategy proposed in this paper has faster response speed,higher control accuracy and smaller overshoot under the same disturbance.