Driven by the “dual carbon” goals

the proportion of renewable energy in the power grid continues to increase. However

as these energy sources are primarily distributed in remote areas with long transmission lines

the line impedance can no longer be ignored and fluctuates frequently

making the grid gradually present weak grid characteristics. As the core device for renewable energy grid integration

grid-connected inverters experience a significant decline in control performance due to the increase of grid impedance

specifically manifested by reduced crossover frequency

low fundamental frequency gain

smaller phase margin of the outer control loop of the lowest-level controller

and even instability in severe cases. In response to this issue

this paper derives an analytical expression between the control performance indicators of inverter and the parameters of the lowest-level controller

and proposes an auto-tuning strategy based on fixed-frequency small signal injection. The proposed method can ensure that the inverter operates stably under desired control performance indicators

eliminating the need for real-time measurement of grid impedance parameters or inverter parameters during rapid grid impedance variations. The proposed auto-tuning method is based on the idea of dead-beat control

which can autonomously adjust the controller parameters within one control cycle and greatly improve the adaptability of grid-connected inverters to rapid grid impedance variations. Finally

a single-phase grid-connected inverter is used for experimental verification

and the experimental results demonstrate the effectiveness of the proposed method.