Frequency adaptive repetitive control of grid-connected inverters

Abstract

Abstract-Grid-connected inverters (GCI) are widely used to feed power from renewable energy distributed generators into smarter grids. Repetitive control (RC) enables such inverters to inject high quality fundamental-frequency sinusoidal currents into the grid. However, digital RC which can get approximately zero tracking error of any periodic signal with known integer period in steady-state, cannot exactly track or reject periodic signal of frequency variations. Thus digital RC would lead to a significant power quality degradation of GCIs when grid frequency varies and causes periodic signal with non-integer periods. In this research paper a frequency adaptive repetitive control scheme (FARC) at a predefined sampling rate is proposed to deal with all types of periodic signal of variable frequency. A fractional delay filter which is based on Lagrange interpolation is used to estimate the fractional period terms in RC. This proposed FARC controller offers the fast, during process modification of fractional delay and fast revise of filter parameters, and then provides GCIs with a simple but very accurate real-time frequency adaptive control solution to the injection of high quality sinusoidal current under grid frequency variations. A case study a three-phase GCI is conducted to testify the validity of the proposed strategy.

Bulletin of the Polish Academy of Sciences: Technical Sciences

“…This value is often described as good trade off between robustness and tracking accuracy, but no analytical proof is given that this value is optimal. In [38] and [39] also performance of the system for the Q filter with higher α is described. The aforementioned tuning methods allow to achieve a stable control system but they are far from optimal as the influence of these parameters on the dynamic response of the system is by no means decoupled.…”

Analysis and Application of Repetitive Control Scheme for Three-Phase Active Power Filter with Frequency Adaptive Capability

“…Repetitive control can achieve zero steady-state error tracking of any periodic reference signals when N is a known integer [14]. However, the grid frequency is time-varying within a certain range, for instance 49.5~50.5Hz.…”

“…However, the grid frequency is time-varying within a certain range, for instance 49.5~50.5Hz. The order of repetitive control often contains a decimal at a fixed sampling rate [14][15]. Therefore, the compensation performance of APF would have a great recession when conventional repetitive control technology is employed.…”

“…In the literatures [14,20], the fractional-order filter is approximated by a Lagrange Interpolation method with an integer number. Their coefficients can be easily updated online.…”