Stability‑improved repetitive control for inverters considering PLLs under weak grid conditions

Mingzhe Zhu; Jiaqing Liu; Lijuan Chen; Le Ge

Stability‑improved repetitive control for inverters considering PLLs under weak grid conditions

Vol. 25, No. 4, pp. 698-708, Apr. 2025

10.1007/s43236-024-00925-y

Abstract

This paper discusses the stability of a grid-tied inverter containing a phase-locked loop (PLL) and repetitive control (RC) under a weak grid. The application of RC significantly improves the control accuracy as well as the harmonic rejection. Frequency fluctuations of the PLL under a weak grid can seriously affect the performance of RC. This article obtains a stability analysis model that considers the PLL through a small signal model analysis. According to small gain theorem, it has been determined that the system is susceptible to instability under weak grid conditions, and attempts to employ phase compensation methods proved to be ineffective. To enhance the high-frequency stability of the inverter when grid impedance exists, a stability enhancement technique is proposed. The proposed method involves optimizing the RC control structure by incorporating a second-order low-pass filter into it. A comparative analysis of the system stability is then undertaken to demonstrate the efficacy of this approach. Furthermore, experiments are conducted under different grid impedance conditions to substantiate the effectiveness of the proposed method.

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Cite this article

[IEEE Style]

M. Zhu, J. Liu, L. Chen, L. Ge, "Stability‑improved repetitive control for inverters considering PLLs under weak grid conditions," Journal of Power Electronics, vol. 25, no. 4, pp. 698-708, 2025. DOI: 10.1007/s43236-024-00925-y.

[ACM Style]

Mingzhe Zhu, Jiaqing Liu, Lijuan Chen, and Le Ge. 2025. Stability‑improved repetitive control for inverters considering PLLs under weak grid conditions. Journal of Power Electronics, 25, 4, (2025), 698-708. DOI: 10.1007/s43236-024-00925-y.