Adaptive control of grid-connected inverters based on real-time measurements of grid impedance: DQ-domain approach

The increasing use of grid-connected inverters to connect renewable energy sources to a power grid will have globally important effect on grid performance. A mismatch between the grid and inverter impedance may cause harmonic resonances, which can lead to instability of the grid and disruption of inverter operation. The grid dynamics vary over time, so the inverter should adapt to the varying conditions to ensure system stability. Recent studies have presented online methods to adaptively control the grid-connected inverters in the sequence domain. This paper extends those previous studies, and presents an online method to adaptively control the inverters in the dq domain. In the method, the grid impedance is measured online using a pseudo-random-binary-sequence (PRBS) injection and Fourier techniques. The inverter control parameters are then adaptively adjusted based on the measurements. This paper presents experimental results based on a three-phase photovoltaic inverter using power hardware-in-the-loop (PHIL) setup.