Adaptive Control Algorithm For Distributed Generations In Microgrids

In order to protect the ecological environment and cope with climate change,all countries in the world are vigorously developing renewable energy.Many renewable energy sources are scattered in different areas,in the form of distributed power generation units.The direct integration of such distributed power generation units based on renewable energy into the large power grid will adversely affect the stability of the power system and seriously affect the effective use of renewable energy.By adopting the form of microgrid,it is possible to reduce the adverse impact of large-scale grid connection of distributed power sources on the power system by adjusting a variety of distributed power generation units in some areas,and to improve the utilization rate of renewable energy.However,the microgrid integrates a large number of renewable energy sources,and its voltage and frequency stability are greatly affected by the fluctuation of renewable energy generation,and most of the distributed power sources are connected to the microgrid through power electronic converters,resulting in low inertia of the microgrid.In order to cope with the threat of renewable energy volatility and intermittent power generation to the microgrid,this thesis focuses on the controllable power generation units such as small steam turbines and flywheel energy storage units in the microgrid.In view of the uncertainties of power generation and energy storage in the microgrid,the frequent changes in working conditions,and strong disturbance that have a greater impact on system stability,design and improve the adaptive control algorithm,improve the transient performance of the controller,and prevent the impact of frequency and voltage deviation from the operating point on the microgrid and users due to uncertainty and disturbanceThis thesis studies the adaptive control algorithm and its improvement method for microgrid The main contributions are as follows1.In the microgrid,for the synchronous generator connected to the small steam turbine,an adaptive valve control is designed.Based on the finite time disturbance observer,the con-troller achieves the finite time stability of the tracking error.At the same time,error trans-formation technology is used to deal with the problem of output constraints,so that the controller can realize the dynamic performance preset by the user,and realize the quantifica-tion of the convergence speed,adjustment time,overshoot and other indicators.This method does not need to know the upper bound of the disturbance,and can adaptively adjust the gain of the observer to realize the finite time stability of the observation error.2.A finite time adaptive robust control algorithm for microgrid with model uncertainty and external disturbance is studied.Considering that the energy storage system is an additional generation unit in the microgrid,when the controlled variable is the output power of the en-ergy storage system,a control algorithm is designed to improve the transient stability of the microgrid.The neural network is used to approximate the unknown part of the model,and it is unnecessary to predict the system uncertainty knowledge.The system error conversion technology and terminal sliding mode technology are used to improve the dynamic perfor-mance of the system.Furthermore,online learning is used to deal with the external bounded disturbance and neural network reconstruction error.3.In order to ensure the stability of the microgrid when charging the energy storage system,an adaptive fast charging control strategy is designed for the flywheel energy storage system.To enhance the transient performance of the flywheel energy storage system in the microgrid,the error transformation is applied to each subsystem of flywheel energy storage system,and the original constrained system is converted to a new unconstrained system.Then,the new unconstrained system is stabilized by using the backstepping method and the unknown dynamics are tackled by NN approximators.