Observer-based current control for converters with an LCL filter

This paper deals with state-feedback current control for power converters, which are equipped with an LCL filter and connected to a weak grid. The grid-side current is measured and other states needed by the current controller are estimated using a reduced-order observer. The control system is designed directly in the discrete-time domain. The gains of the control system are calculated using direct pole placement, assuming a strong grid. Recommendations for the nominal pole locations are given. The results show that the control system is robust against the unknown grid impedance, ranging from strong to very-weak grid conditions. The proposed design is validated by means of experiments.Peer reviewe