Robust Control Scheme for a Microgrid With PFC Capacitor Connected

• Published in: IEEE transactions on industry applications 2007-09, Vol.43 (5), p.1172-1182
• Main Authors: Yun Wei Li, Vilathgamuwa, D.M., Poh Chiang Loh
• Format: Article
• Language: English
• Subjects: Capacitance; Capacitors; Control systems; Control theory; Distributed generation (DG); Electric potential; Feedback; H infty control; Harmonics; Inverters; microgrids; Performance gain; Power harmonic filters; Power systems; power-factor-correction (PFC) capacitor; Resonance; resonance attenuation; Robust control; Voltage control
• ISSN: 0093-9994; 1939-9367
• DOI: 10.1109/TIA.2007.904388

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 distributed-generation unit 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 a connection of a PFC capacitor. To compensate the capacitance-parameter variation, an Hinfin controller is designed for the voltage-source- inverter voltage control. By properly choosing the weighting functions, the synthesized Hinfin 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 Hinfin 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 interference with the fundamental power flow. And finally, the study in this paper has been tested experimentally using an experimental microgrid prototype.