CONSERVATIVE POWER THEORY-BASED PHASE-LOCKED LOOP-FREE CONTROL STRATEGY AND STABILITY ENHANCEMENT METHODOLOGY

Qu Keqing; Su Shijie; Mao Ling; Zhao Jinbin; Huang Yuchen; Gao Chang

doi:10.19912/j.0254-0096.tynxb.2025-0324

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Acta Energiae Solaris Sinica ›› 2026, Vol. 47 ›› Issue (7) : 675-684. DOI: 10.19912/j.0254-0096.tynxb.2025-0324

CONSERVATIVE POWER THEORY-BASED PHASE-LOCKED LOOP-FREE CONTROL STRATEGY AND STABILITY ENHANCEMENT METHODOLOGY

Qu Keqing¹, Su Shijie¹, Mao Ling¹, Zhao Jinbin², Huang Yuchen¹, Gao Chang¹

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Abstract

To address the instability issue of grid-connected inverters caused by the negative-resistance characteristic introduced by phase-locked loops （PLLs） in low-frequency range under high grid impedance conditions in weak grids, this paper proposes a single-phase PLL-free control method based on an improved second-order generalized integrator （ISOGI） and conservative power theory （CPT）.The proposed method employs the unbiased integration in CPT combined with ISOGI for phase tracking, effectively replacing conventional PLLs. Impedance modeling analysis demonstrates that this approach significantly extends the grid impedance adaptability range. Compared with PLL-based control methods, it exhibits enhanced stability and robustness under extremely weak grid conditions with high-order harmonics and DC components in grid voltage. Finally, experimental results validate the correctness of the theoretical analysis.

Key words

stability / phase-locked loop-free / weak grid / second-order generalized integrator / conservative power theory / impedance model

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Qu Keqing, Su Shijie, Mao Ling, Zhao Jinbin, Huang Yuchen, Gao Chang. CONSERVATIVE POWER THEORY-BASED PHASE-LOCKED LOOP-FREE CONTROL STRATEGY AND STABILITY ENHANCEMENT METHODOLOGY[J]. Acta Energiae Solaris Sinica. 2026, 47(7): 675-684 https://doi.org/10.19912/j.0254-0096.tynxb.2025-0324

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