Robust control scheme for a microgrid with PFC capacitor connected

Capacitors are widely used for power factor correction (PFC) in power systems. When a PFC capacitor is installed with a certain load in a microgrid, it may be in parallel with the filter capacitor of the inverter interfacing the utility grid and the local DG and thus change the effective filter capacitance. Another complication is the possibility of occurrence of resonance in the microgrid. This paper conducts an in-depth investigation of the effective shunt filter capacitance variation and resonance phenomena in a microgrid due to connection of a PFC capacitor. To compensate the capacitance parameter variation, an H∞ controller is designed for the VSI 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. However with the robust H∞ controller, it will be possible to explicitly specify the degree of robustness in face of parameter variations. Furthermore, a thorough investigation is carried out to study the performance of inner current loop feedback variables under resonance conditions. It reveals that filter inductor current feedback is more effective in damping the resonance. This resonance can be further attenuated by employing the dual-inverter microgrid conditioner and controlling the series inverter as a virtual resistor affecting only harmonic components without affecting the fundamental power flow.