A weighted average mixed feedback control method based on LCL-type grid-connected inverter

The weighted average current (WAC) control method has gained recognition for its order reduction characteristics and broad control bandwidth. However, the interaction of digital control delay and grid impedance introduces an inverse resonance peak in the system loop gain, challenging the order reduction properties of conventional WAC control and system passivity across a wide frequency range. Conventional approaches, such as lead compensator-based delay compensation or weighting coefficient redesign, improve system stability to some extent but fail to retain order reduction characteristics. To address these limitations, this article proposes a new control method known as weighted average mixed feedback, incorporating distinct voltage feedforward paths. By introducing a voltage feedback path, the proposed method reconfigures the system's zero positions, enabling the pole-zero cancelation in the open-loop characteristics independent of grid impedance. Additionally, this supplementary path offers impedance reshaping capabilities, enhancing system passivity and adaptability to weak grids. The effectiveness of the proposed control method is verified through simulations and experiments. This paper presents an improved weighted average current (WAC) control method for grid-connected inverters. This method addresses the limitation of the conventional WAC control method, which fails to achieve reduced-order control of the open-loop transfer function when considering the combined impact of digital control and grid impedance. Additionally, this control method significantly enhances the system's passivity, ensuring stability.image