Research On Microgrid Technology Based On Improved Virtual Impedance

Microgrid is an effective means to connect users and large power grids.It is called the building blocks of smart grid,and has gradually attracted wide attention from scholars.For different voltage grades,the main parameters of the parallel operation inverter are equal,but because the inverter output circuit is different,the equivalent output line impedance of the inverter is different,the output voltage of the inverter is different,and the power and the reactive power of the inverter are coupled.The parallel running system has the circulation,the power is not balanced,and the sudden change of the system load affects the current and the active reactive power of the system when the multiple distributed generation is parallel operation.For these problems,this paper mainly studies the micro grid control strategy based on the virtual impedance of multi inverter.The main contents are as follows:(1)For the problem of uneven circulation and power distribution between parallel inverters,a ptosis control strategy based on improved virtual impedance is proposed.The active power and reactive power of the traditional droop control algorithm are analyzed,and the related voltage and current control original graph is drawn.The virtual impedance is introduced to the dual loop control strategy of voltage and current.By adjusting the degree of inductance matching,the equivalent output impedance of the inverter is approximate to the perceptual,and the influence of the inductive impedance on the power decoupling is analyzed.The influence of the sag coefficient on the power equalization precision of the inverter and the circulation of the parallel inverter system is analyzed.Then the sag coefficient of the inverter is determined according to the power formula of the inverter,and the droop control formula of the microgrid inverter is further improved.(2)A microgrid simulation model of inverter parallel operation is established in MATLAB.The model is composed of three distributed generation units connected to the common contact point,and the three distributed generation units have the same structural parameters.After the system has been running for a period of time,the load of the distributed generation unit 1 is suddenly increased.The influence of the sudden change of load on the system operation is analyzed through the simulation waveform diagram,and the simulation of the droop control simulation based on the virtual impedance and the virtual impedance based on the improved algorithm is compared,and the simulation is made.The current,active and reactive power waveforms are analyzed.