| The global energy crisis and environmental crisis make it an inevitable trend for new energy to replace traditional fossil energy.However,the continuous improvement of new energy penetration rate has mitigated energy and pollution problems to a certain extent,and it has also had a great impact on the stability of large power grids.The development of microgrid technology can coordinate the relationship between distributed generation and large power grids,and which is the most direct and effective way to develop distributed generation technologies.Complicated and changeable way of the microgrid accessing the power grid makes it difficult to determine the value of line impedance that influences the voltage stability of the microgrid system.From the perspective of voltage stability,the influence of microgrid line impedance on system control strategy and voltage stability are studied in this paper.And,in allusion to operating characteristics of microgrid,the suitable line impedance estimation methods are analyzed and finded.Based on the parallel model of the microgrid inverter,the relationship between the reactive power flow and the voltage stability of the microgrid is analyzed,and the importance of the rational distribution of reactive power flow to the voltage stability and the system transmission loss is elaborated in this paper.Then,the The power allocation strategy of the inverter is determined,which based on the distributing principle of the nearest electrical distance.For the deficiency of droop control in voltage stability control,feeder flow control is adopted in this paper.Aiming at the case of traditional feeder flow can not guarantee the voltage steady-state accuracy when the load changes greatly,a droop control-based feeder flow control method is adopted,which changes the reference value of feeder flow according to the chang of the load and the line impedance.In view of the constraint on the system control strategy for the variability of the line impedance of the microgrid,a voltage stability control stratgy based on the extended Kalman filter for estimating the line impedance of the microgrid is proposed in this paper,which is implemented in such a way that the micro-source inverters undertake their own local load respectively,and the common load is shared according to the different line impedances of the micro-source inverters.By modeling the output side of the micro-source inverter,real-time estimation of the line impedance is completed,and the power flow distribution factor on the feeder is determined to further determine the reference value of the feeder flow,which can control real-time reactive power flows distribution on the feeders,coordinate the circulating of reactive power flow between the various feeders,and enable maintain the system voltage at a rated value to obtain a higher voltage steady-state accuracy even under severe disturbance conditions.Based on the simulation and analysis of Matlab/Simulink,a microgrid experimental platform was built,and droop control,traditional feeder flow control,feeder flow control based on line impedance estimation experiments and system stability analysis are completed.Simulation and experimental results show that the control strategy proposed in this paper significantly improves the voltage stability of the microgrid system when load and line impedance change,and reduces the line loss of the system and improves the economical efficiency of the entire microgrid system simultaneously. |
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