Control Strategy Research Of Parallel Inverters In Microgrids

The application of the droop control in inverter parallel is studied in thispaper.There are three main issues in traditional droop control method.Firstly，onlyif the line impedance between the inverter and AC bus is pure inductive or pureresistive，decoupling control between active power and reactive power can beachieved. Secondly，the traditional droop control method will cause deviations ofbus voltage amplitude and frequency.Thirdly， when traditional droop controlmethod is adopted，if per-unit values of line impedances between inverters and ACbus are different， inverters can not allocate load power according to theircapacities.The above three issues are solved one by one in this paper. Firstly， themethod of adding virtual resistance is determined. The P-E and Q-ω droopcontrol method is used in this paper. The allocation of load according to theinverter capacity can be realized by adding virtual impedance. In addition，soft start can be realized and peak current can be weakened by adding virtualimpedance.But virtual impedance will cause a certain amount of voltagedrop. Secondly， the bus voltage deviation caused by the traditional droopcontrol is eliminated by using feedback closed loop control of bus voltageamplitude and angular frequency. But connection of communication lines isessential in the method， which reduces advantages of the droop control.Thirdly， a robust droop method is put forward in this paper based on controltheory.Active and reactive power of load can be allocated between invertersaccording to the inverter capacity in the method，free from the effect of the outputimpedance of inverter.Bus voltage deviation caused by the traditional droopcontrol can be greatly reduced in the method. Finally， the methods proposedin this paper are verified by matlab simulation. The simulation results provethat the proposed methods are correct and effective.