An Adaptive Resonant Regulator for Single-Phase Grid-Tied VSCs

The proportional-resonant (PR) controller is highly popular for controlling grid-connected voltage source converters. The resonant part of this controller provides an infinite gain at the nominal frequency and, in this way, ensures a zero steady-state tracking error when the grid frequency is at its nominal value. In the presence of frequency drifts, nevertheless, a zero tracking error may not be guaranteed. To deal with this problem, the resonance frequency of the PR controller may be updated using the frequency estimated by the synchronization unit, which is often a phase-locked loop. In recent years, however, there is a growing attention toward eliminating the need for a dedicated synchronization unit and designing integrated synchronization and control structures as they benefit from a simpler and more compact structure. In this letter, based on a structural resemblance between a resonant current regulator and second-order generalized integrator-based frequency-locked loop, a frequency-adaptive resonant controller is presented. The tuning procedure of the proposed controller is discussed, and some experimental results are presented to verify its effectiveness.