Research On Control Strategy Of Inverter In Microgrid

With the focus on the new energy power generation of the world， Themicrogrid technology that integrates the advantages of distributed generationbecomes a research hotspot nowadays. The inverter is an important component unitin microgrid，it needs take the appropriate control strategies according to thecontrol mode and operation mode of microgrid. In this paper，the principle andorigin of the controller’s structure of the inverter is analyzed and derived detailed,the control strategies include V/f control, PQ control and droop control. A virtualreactance is added to the voltage-current inner loop of the controller to make theoutput impedance inductive in order to decouple the active and reactive power andsimulate the active-frequency and reactive-voltage characteristic of the traditionalsynchronous generator better. Further more, a virtual inertia is also added to theouter power loop to avoid the step change of frequency when switching load, andthe dynamic characteristic of parallel operation of the droop controlled inverter andthe synchronous generator is simulated and analyzed before and after the additionof the virtual inertia.Based on the depth analysis of control strategies of the inverter, in this paper,a microgrid including multiple inverters is built on the PSCAD/EMTDC platform tosimulate the dynamic performance of the microgrid in maser-slave mode andpeer-to-peer mode. In peer-to-peer mode, a voltage and frequency recovery methodis proposed and validated on the simulation platform; and at the same time atransfer method between the two operation mode is proposed when there is nosynchronous generator;In master-slave mode, the transfer between island andgrid-connected operation mode is simulated when there is no synchronousgenerator in the microgrid, and also the master unit switching between synchronousgenerator and energy storage unit is simulated when the microgrid is in island modewith synchronous generator in it.Finally, according to the relationship of active power-phase angle and reactivepower-voltage in power system, a power flow controller is designed onPSCAD/EMTDC platform and the controller is applied to power system equivalents to get the magnitude and phase angle of the equivalent source, and two example isused to verify the effectiveness of the controller.