CONTROL STRATEGY FOR MICROGRID SYSTEM

Abstract

Capacitors are widely used for power-factor correction (PFC) in power systems. When a PFC capacitor is installed with a certain load in a micro grid, it may be in parallel with the filter capacitor of the inverter interfacing the utility grid and the local distributed-generation unit and, thus, change the effective filter capacitance. Another complication is the possibility of occurrence of resonance in the micro grid. Therefore a complete study of shunt-filter-capacitance variation and resonance phenomena in a micro grid due to a connection of a PFC capacitor will be done. To compensate the capacitance-parameter variation, an H. controller will be designed for the voltage-source inverter voltage control. By properly choosing the weighting functions, the synthesized H. controller would exhibit high gains at the vicinity of the line frequency, similar to traditional high performance P+ resonant controller and, thus, would possess nearly zero steady-state error. With the robust Floo controller, it will be possible to explicitly specify the degree of robustness in face of parameter variations. In this work the performance of inner current-loop feedback variables under resonance conditions will be evaluated and from that we will get an conclusion that filter-inductor current feedback is more effective in damping the resonance than the filter capacitor feedback.