Research On Optimal Control Strategy Of Multiple Micro-sources Low-voltage Micro-grid

With several large-scale blackouts around the world,human beings have gradually realized the shortage of a single large-grid power supply mode,and various countries have adopted distributed power generation technologies based on renewable energy.Microgrid can integrate various distributed power sources,energy storage devices,loads,control and protection devices,and is an effective form of organization for distributed generation.The microgrid voltage level is generally not high,and the traditional droop control in the low voltage microgrid does not have applicability,which will cause power coupling phenomenon.Starting from this point,this paper mainly studies the applicability of droop control to low-voltage microgrid and the problem of power splitting of parallel inverters.On this basis,coordinated optimization control of low-voltage microgrid integrating multiple micro-sources is carried out.Firstly,this paper introduces the working principle of distributed power sources such as photovoltaic power generation,energy storage battery and micro gas turbine,establishes their respective mathematical models,and analyzes the corresponding output characteristics.Then,the operation and control mode of the microgrid and the control mode of the microgrid inverter are introduced in detail.The principle,advantages and disadvantages of various control modes are analyzed,and the corresponding applicable occasions are expounded.Next,the principle of traditional droop control and the theory of micro-source transmission are analyzed,and the inapplicability of traditional droop control in low-voltage microgrid is illustrated.For this problem,virtual complex impedance is introduced in voltage and current double-loop control.Therefore,the equivalent output impedance of the inverter is inductive at the power frequency,eliminating the power coupling phenomenon.Based on the condition analysis of the traditional droop control to achieve power sharing,an improved droop control strategy for L-type inverter is proposed and compared with the traditional droop control strategy.The results show that the improved droop control strategy is improved.It can realize the accurate power distribution of each DG according to its capacity ratio,and has good applicability for parallel operation of DG of the same capacity and different capacity.Finally,a low-voltage microgrid model integrating multiple micro-sources was built.The "primary source transformation" is used to coordinate and optimize the low-voltage microgrid.The simulation model is built by MATLAB software and the simulation analysis is carried out.The results show that Under the control strategy,BESS is only a transitional main source,which can reduce the dependence of BESS on the operation of micro-grid islands,realize the complementary advantages of BESS and MT,and improve the reliability of micro-grid island operation.