电网不对称故障下锁相同步型并网变流器控制耦合特性与暂态同步稳定增强控制策略

doi:10.19595/j.cnki.1000-6753.tces.250572

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Abstract Under asymmetrical grid faults, there are not only violent dynamic interactions between the generation equipment and the power grid, but also between the positive sequence components and negative sequence components, which makes the transient synchronous instability of the renewable energy power generation (REPG) system very prominent. To solve this issue, with the dual-sequence phase-locked loop (PLL) control model, the coupling control characteristics between the positive and negative sequence components is revealed in this paper. Then, the influence of PLL control parameters, as well as the low voltage ride through (LVRT) reference on the transient behavior positive and negative sequence equivalent power angles is analyzed. In addition, to improve the transient synchronous stability of the REPG system under asymmetrical grid faults, a transient synchronous stability enhancement control strategy is proposed. Finally, the simulation and experimental verification are carried out.
Firstly, considering the nonlinear control characteristics of PLL, a nonlinear transient model of PLL based on the separation of positive and negative sequence is established. Based on energy function, the transient synchronous stability instability criterion of REPG system under asymmetric faults is constructed, which can realize the quantitative evaluation of transient synchronous stability of the system. The influence of critical fault removal time, LVRT current references and proportional integral coefficient of PLL on the transient synchronous stability of the system is analyzed. Finally, a transient stability control strategy of REPG system under asymmetric faults is proposed.
Simulation and experimental results show that, when the system adopts the traditional PLL control strategy in Ref.[6], the acceleration and deceleration energies of the system at stage 1 are ${{[S_{\text{acc1}}^{+}\text{ max}(S_{\text{dec1}}^{+})\text{ }S_{\text{acc1}}^{-}\text{ max}(S_{\text{dec1}}^{-})]}^{\text{T}}}=$[0.564, 0.518, 0.123, 0.421]^T. In this case, $S_{\text{acc1}}^{+}$ is greater than max ($S_{\text{dec1}}^{+}$). Consequently, the transient synchronous instability occurs in the positive and negative sequence PLL. When the system adopts the proposed control strategy, the acceleration and deceleration energies of the system at stage 1 are$[S_{\text{acc1}}^{+}\text{ max}(S_{\text{dec1}}^{+}),$$S_{\text{acc1}}^{-}\text{ max}(S_{\text{dec1}}^{-}){{]}^{\text{T}}}=$[0.564 0.602 0.123 0.483]^T. It can be seen from the calculation results that $S_{\text{acc1}}^{+}$ is smaller than max($S_{\text{dec1}}^{+}$) with the proposed control strategy is adopted. Therefore, there is no transient synchronous instability in the system. Consequently, the proposed control strategy can effectively improve the transient synchronization stability of REPG system under asymmetric faults.
The following conclusions can be drawn from the simulation analysis: (1) The unbalance of q-axis potential in the positive and negative sequence terminal voltage is the key factor that causes the transient synchronous instability of the REPG system during the asymmetric faults. Moreover, there is the control coupling relationship between the positive and negative sequence PLL due to the interconnection of the positive and negative sequence impedance networks during the asymmetric faults. (2) The improper fault detection delay and LVRT current references may lead to transient synchronous instability due to the mismatch of acceleration and deceleration energies. (3) A transient stability control strategy of REPG system under asymmetric faults is proposed, which can improve the damping coefficient of the system during asymmetrical faults, as well as the transient synchronous stability of the system.

Key words： Asymmetrical grid faults phase-locked loop-based grid-connected transient synchronous stability coupling control characteristics stability control strategy

Received: 08 April 2025

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TM712

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	Luo Yi
	Yao Jun
	Yang Dong
	Xie Hai
	Jin Rongyu
	Zhao Linsheng

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Luo Yi,Yao Jun,Yang Dong等. Coupling Control Characteristics and Transient Synchronous Stability Enhancement Control Strategy of PLL-Based Grid-Connected VSC under Asymmetrical Grid Faults[J]. Transactions of China Electrotechnical Society, 2026, 41(7): 2353-2367.

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https://dgjsxb.ces-transaction.com/EN/10.19595/j.cnki.1000-6753.tces.250572 OR https://dgjsxb.ces-transaction.com/EN/Y2026/V41/I7/2353

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