Research On Parallel Circulation Of Multiple Inverters In Micro-grid

With the increasing requirements of environmental protection,energy supply and power transportation supply,the large power network cannot meet the requirements of power supply technology because of its high operation and maintenance cost and poor reliability.Distributed power supply mainly uses clean energy,which is conducive to environmental protection,while investing cost saving,flexible power generation,and is able to meet the specific requirements of the power system and its users.Micro-grid technology is the foundation and core of distributed power generation technology.Most of the inverters in micro-grid operate in parallel,so it is necessary to control the operation of inverters particularly important.The inverter parallel mode can increase the data transmission capacity of the module and reduce the overall volume of the system.However,each distributed power supply in the micro-grid is often connected to the power grid through the inverter.Due to the difference in the output frequency and characteristics of each inverter power supply module,the average divided load current of each inverter is different,making a certain circulation between each inverter.The presence of circulation can affect the quality of electric energy,and can also hinder the normal operation of the system.This paper studies the distributed power parallel to control the inverter and the strategy to eliminate circulation.Firstly,a single three-phase full-bridge inverter in the micro-grid is analyzed,and the double closed-loop control of voltage feedback and current feedback is designed.The current closed loop compared by inductance and reference current current to speed up the response speed,the voltage loop adopts quasi-PR controller to achieve no-difference tracking of the voltage signal,to meet the requirements of system speed and reliability.Based on this,this paper establishes a parallel model of two inverters,derive the expression of each inverter output power,active power and reactive power,and analyzes the advantages and disadvantages and power coupling.The circulation relationship between parallel inverters simultaneously analyzes the influencing factors of circulation.The circulation will directly increase the loss of switching components,overheating,power waste and affect the normal operation of the whole system.For the circulation problem caused by the difference between inverter circuits,according to the circulation and power output characteristics between parallel inverter,a control method for indirectly changing the equivalent output impedance in the circuit,i.e.design the adaptive virtual impedance control circuit without increasing the volume of the external circuit.Finally,the MATLAB/Simulink simulation platform proves and confirm that the algorithm can effectively suppress circulation.The feasibility of this method is verified by constructing two inverter parallel prototype systems with the same capacity.The paper has 32 drawings,3 tables,and 66 references.