Adaptive method for control tuning of grid-connected inverter based on grid measurements during start-up

As the share of grid-connected converters increases, potential stability issues in the grid interface of the converters are emphasized. Impedance-based stability criterion can be used to assess the stability of the interface accurately, and the grid conditions should be considered in control design of the converter. However, the grid impedance is often an unknown parameter, and thus, adaptive control is a favorable method for addressing the uncertainties in the control design. This work presents an algorithm, in which the full-order grid impedance is measured during the start-up of the device, and control bandwidth of phase-locked loop and grid-voltage feedforward gains are adjusted to optimize sensitivity function in the grid interface, based on generalized Nyquist criterion. The method can ensure robust control in weak grid conditions, while still achieving good control performance in strong grids. The method is verified with power hardware-in-the-loop experiments with a kW-scale grid-connected three-phase inverter.