Research On Stability Control Strategy Of AC Microgrid

Microgrids provide an effective solution to connect large-scale distributed new energy sources to the grid,enabling the active management of a wide range of Distributed Generations(DGs),and have become a focus of research in various countries due to their flexible mode of operation.DGs are usually connected to the grid with power electronics such as inverters as the interface.How to control these devices,achieve power balance in the grid,and ensure that the frequency and voltage are within the specified range are the key to the stable operation of microgrid systems.And droop control is an important method of controlling the inverter,both for frequency and voltage regulation,as well as for proportional power distribution and plug-and-play functionality.But the droop control has a limited ability to regulate frequency,and when the load is large or the line impedance is unequal,there is also the problem of uneven distribution of reactive power,which does not guarantee power quality and affects system stability.Therefore,it is important to study the stability control strategy of microgrids based on droop control.The main research elements of this paper are as follows.(1)In order to improve the stability of inverter-based microgrids,an accurate and complete microgrid small signal model was first constructed.And a stability domain analysis method is proposed to investigate the effect on system stability by combining the participation factors and the characteristic roots of the system.By observing the changes in the eigenvalues of the system for different parameters,the range of parameters that make the system stable is obtained,providing stability constraints for the parameter optimisation in the next section.(2)An improved droop control method is proposed to solve the problem that the frequency offset will be too large when the power changes greatly.Starting from the regulation of the local control parameters and taking into account the power fluctuations when the system state changes,an objective function weighted by frequency and power is established.Smooth power switching by varying droop coefficients and reducing frequency shifts through a hybrid particle swarm approach.The effectiveness of the proposed method is verified by comparing it with conventional methods using the MATLAB/Simulink platform.And to verify the effectiveness of the selected control variables,the effect of each variable on the dynamic performance of the microgrid is obtained by varying the value of each variable.(3)Considering that the islanded AC microgrid is in the situation of large load and large line impedance difference,the microgrid based on droop control will have the problem of inaccuracy of shared power.Therefore,this paper proposes a decomposition-based multi-objective evolutionary algorithm for optimal control of islanded AC microgrids,which is used to solve the optimal droop coefficients of DG in islanded microgrids to achieve power equalisation while maintaining voltage frequency stability.And its effectiveness is verified by MATLAB/Simulink simulation.