Research On Distributed Cooperative Control Of Microgrid

As an effective means of distributed generation’s access to power grid, microgrids can make full use of distributed generation which is scattered all over the place, and also consider each user ’s demand. Thus microgrids are attracting more and more attention. In order to ensure reliable operation in both grid-connected and islanded operating modes, hierarchical control is usually used. Primary control of microgrids commonly adopts droop control methods, and centralized control is often used in secondary control. The disadvantages of centralized control are low reliability and high cost. Compared with centralized control, distributed control only requires sparse communication link, which is cheaper and more reliable. So the secondary distributed control in microgrids is mainly studied this thesis.Firstly, basic theories of microgrid control are introduced, including the representation of communication between distributed generations, stability theor ies of sysytem, such as Lyapunov stability theory, La Salle invariant set principle, and finite time stability theory. And the necessity of adopting distributed control is also analyzed.Secondly, the structure of distributed generation is analyzed, and a mathematical model is built, then the secondary distributed cooperative controller for microgrids is designed. An accurate model of distributed generation is established by large-signal modeling method. According to the established model, distributed generation is a nonlinear and heterogeneous system. Making use of input output feedback linearization method, the nonlinear system is transformed into linear system. Distributed voltage and frequency control cooperative algorithms for microgrids are designed based on multi-agent system consensus theory. Stability of the designed controller is analyzed, and simulation model verified the effectiveness of the controller as well.Then, considering different conditions for fixed communication topology, two different secondary distributed cooperative control strategies for microgrid are designed. For the first case, secondary distributed cooperative control strategy for microgrid is designed with saturated restrictive control input. For the other case, finite time distributed cooperative voltage and frequency control strategies for microgrid are designed. Stability for both control strategies above are analyzed, and the simulation validation is carried out.Lastly, considering the plug and play peculiarity of microgrids, switching topology can reflect the distributed generation’s communication structure more practically. And on this basis secondary distributed cooperative control strateg y and finite time secondary distributed cooperative control strategies for microgrid are designed. The voltage and frequency of microgrid will synchronize to reference values using the designed controller as long as the switching topology is jointly connected and switching time is small enough, and active power will be shared at the same time.