Current control of the LCL-type grid-connected inverter based on improved reduced-order extended state observer

The grid-connected inverter (GCI) with the LCL type is a crucial device for achieving energy flow between distributed generation (DG) and the power grid. To achieve error-free control of the GCI grid-side current, the abc/dq transformation is used to convert the static coordinate frame to the synchronous coordinate frame, although this transformation suffers from the coupling problem between the dq frames. An improved reduced-order extended state observer (I-RESO) for grid-side current control is proposed in this paper, which solves the complex decoupling procedure of conventional methods by treating the coupling of the dq frames as part of the total disturbance and using I-RESO for real-time observation and compensation. Meanwhile, to address the problem that the conventional reduced-order ESO method requires differentiation of the output, which introduces high-frequency noise. This paper adopts a method to achieve the reduced order of ESO without differentiating the output, which solves the problem of noise introduction and improves the dynamic performance of current control. The viability and effectiveness of the proposed strategy are verified by simulation.