Research On Secondary Control And System Stability Of Nonlinear Microgrids

With the aggravation of environment pollution and energy crisis problem,we need a new way for power generation as the main grid has suffered numbers of issue.Due to the rapid development of multi-agent technology in recent years,the microgrid has attracted increasing attention.It has some features distinguished with the traditional power system,such as controllability,environmental-friendly,self-control ability and self-management ability.However,the access of numerous new energy sources(PV,solar energy)will bring severe challenge for the traditional control strategy.Hence,it is very significant to study the distributed control of microgrid.High voltage technology has been used in main grid.The lossy-line can't be neglected in microgrid because it is usually a medium and low voltage small power distribution system.This paper mainly studies the lossy-line microgrids.The primary control can keep the voltage and frequency stability.We study the phase angle stability of lossy nonlinear microgrid under primary control.In order to restore the voltage and frequency to nominal values,we also study the secondary control and stability analysis problems in lossy nonlinear microgrid.The distributed secondary voltage and frequency control schemes are proposed.The main contents are in two-folds:(1)While the nonlinear dynamics of frequency and the line impedances are considered,the frequency and phase angle synchronization and power sharing of inverter-based microgrids with distributed rotational and electronic generation are analyzed.The phase angle stability and power sharing conditions are derived by applying the secondary-order multi-agent system consensus protocol.Simulation results are provided to show the effectiveness of the proposed stability conditions.(2)While the nonlinear dynamics of power network in microgrid are considered,the observer-based secondary voltage and frequency control schemes are designed in our work.Compared with the conventional secondary control methods,our proposed control strategies have the following advantages: the proposed control schemes are totally decoupled which can meet the distributed feature.The transient stability conditions under the lossy-line network are derived and analyzed rigorously by applying large signal stability analysis method.The proposed secondary control schemes can be implemented in a fully distributed way such that the power systems enjoy the plug-and-play property.