Harmonic Suppression and Stability Enhancement of a Voltage Sensorless Current Controller for a Grid-Connected Inverter under Weak Grid

This paper presents the harmonic suppression and stability enhancement of a grid voltage Sensorless current controller for a grid-connected inverter under weak grid conditions. Given that inductive capacitive-inductive (LCL) filters represented as higher-order dynamics cause resonance problems, a considerate resonance frequency damping process is required. In particular, the resonance phenomenon of the LCL filter crucially influences the current quality when the grid-connected inverter is connected to a weak grid with uncertain grid impedance and distorted harmonics. Additionally, there is a possibility that the control system will become unstable due to changes in system parameters, even after considerate resonance frequency damping. In order to solve these problems, this paper presents an active damping (AD) method by using integral variables in an integral state feedback current controller for a grid voltage Sensorless inverter system, which significantly improves the current harmonics and stability of the grid-connected inverter under weak grid condition.

Keywords: Active damping, distorted grid, grid-connected inverter, LCL parameter uncertainty, stability enhancement, voltage Sensorless control, weak grid.