The Research On Self-regulating Droop Control Of Microgrid Islanding/Grid-connected

In recent years,as the environmental pollution and energy crisis are getting increasingly prominent,the development of renewable energy became the focus of global attention.As an important branch of the distributed generation technology,microgrid technology has become a hot research focus.Due to the uncertainty and randomness of the distributed power within the system,it will cause a certain impact on the operation of the large power grid when the microgrid connected with the large power grid.Accordingly,in the process of transient switching between microgrid and large power grid,it is the key point to realize smooth switching between them and ensure the normal operation of load.On the basis of above considerations,this thesis propose reasonable control strategies to shift between microgrid islanding/grid-connected mode and the transient switching process,as well as the self-adjusting-droop-control strategy for ensuring the stability of any mode operation and the smoothness of the transient switching.The following work is done in this thesis:1)The working model of the three-phase full-bridge inverter and the selection of the filter parameters are studied.Then,the basic principle and characteristics of droop control are analyzed.The droop control strategy based on three-phase full-bridge inverter including power measurement module,droop control module and voltage and current dual loop control module is studied.Moreover,the principle and structure of each module is analyzed,and the application of droop control strategy in microgrid is introduced.2)In consideration of the uneven power distribution caused by the differences of line connected impedance and the voltage instability caused by load variation,the relationship between droop coefficient and voltage is studied and an improved droop control method based on dynamic droop coefficient is proposed.At the same time,the droop control of grid connected power is analyzed.in view of the uneven distribution of power and the voltage instability caused by the load fluctuation.At the same time,the power of grid connected droop control is analyzed.Finally,the simulation results show the effectiveness of the proposed method,and the control of the active power and reactive power in the islanding/grid connected mode is achieved.3)Aiming at the difficulties to achieve smooth switching in process of transient switching between microgrid and large power grid,which cannot guarantee the normal operation of the load.On the basis of studying the transient switching characteristics of microgrid isolated and connected modes,this thesis considers the practical problem of switching hysteresis.By conducting the droop control method and improved frequency and voltage pre synchronous control of isolated and connected modes,the problem of mismatch between control strategy and running mode is solved,realizing the smooth switching operation mode of microgrid.Finally,the simulation results are shown in this thesis.