Decentralized controllability of multi-inverter microgrids

Network of Voltage Source Inverters (VSI) to form a microgrid has played a central role in providing reliable power supply. It is very useful to control this network of VSI using decentralized controllers rather than centralized controllers due to less dependence of decentralized controllers on communication with other systems. A difficulty frequently encountered when studying and designing decentralized controllers is the controllability of the overall network using controllers with the constraint of being decentralized, i.e. the constraint that each controller can access only local sensors and only local actuators. This paper proves that the droop controller and its class of decentralized controllers indeed allows controllability of the system for generically all system parameter values. While this has been shown for specific parameter values using numerical methods, the graph theoretic approach followed in this paper helps in proving this generically for all system parameter values. We apply a recent result on arbitrary pole-placement by a controller with structural constraints to the case of a VSI connected to the grid, and to the case of two VSIs to show that indeed pole-placement can be achieved using decentralized controllers.