跟网型变换器的小扰动同步稳定机理分析与致稳控制

doi:10.19595/j.cnki.1000-6753.tces.230493

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摘要

弱电网下,跟网型变换器易出现因阻尼不足导致的小扰动同步失稳问题。为此,该文借鉴复转矩分析理论,计及复杂控制耦合,建立跟网型变换器的复转矩模型。量化多环控制耦合、线路阻抗、控制参数等因素对系统阻尼转矩的影响,从阻尼的角度揭示跟网型变换器的小扰动同步失稳机理。根据理论分析,提出一种基于相位补偿的锁相环阻尼重塑控制策略,通过补偿多环控制耦合引入的负阻尼,增强变换器的小扰动同步稳定性。最后,开展相应的仿真与实验,验证理论分析的正确性与改进控制策略的有效性。

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	李红
	梁军杨
	王振民
	李国进
	陈延明

关键词 ：跟网型变换器, 小扰动同步稳定, 多环控制耦合, 复转矩分析法, 阻尼重塑

Abstract：

With the increasing integration of renewable energy and power electronic equipment, the power system is characterized by low inertia and weak damping. Consequently, grid-following converters employing a phase-locked loop (PLL) for synchronization face the risk of oscillation instability, especially in complex control coupling. This paper proposes a complex torque analysis model that examines the damping mechanism for small disturbance synchronous instability. To reveal the small disturbance synchronization instability mechanism of grid-following converters, a PLL complex torque analysis mode is built considering the current control (CC) loop and DC-link voltage control (DVC) loop. Accordingly, the accurate damping characteristics and oscillation risk of the low-frequency mode can be assessed. The effects of typical multi-loop control coupling, line impedance, and control parameters on the damping torque of the system are quantified.
Firstly, a typical grid-following topology and control strategy is introduced, including the PLL, current inner current loop, and DC-link voltage outer loop. Secondly, a synchronous dynamic analysis model is established, considering both CC and DVC, resembling in the Phillips-Heffron model used in low-frequency oscillation analysis for synchronous machines. Based on the equivalent block diagram transformation, the complex torque model of the synchronous loop is derived, enabling the examination of equivalent second-order motion driven by unbalanced voltage, as shown in Fig.A1. It indicates that by introducing equivalent voltage components by CC and DVC, control coupling has an uncertain damping effect on the PLL. Thirdly, the intrinsic damping of PLL and additional damping from CC and DVC are extracted using the developed model, facilitating an investigation into the influence of control interaction on the PLL's equivalent motion. Moreover, the study analyzes the impacts of multi-loop control coupling, line impedance, and various control parameters on the low-frequency oscillation characteristics of grid-following systems. Finally, a damping compensator, utilizing d-axis current feedback, is proposed to improve the low-frequency damping characteristics of grid-following and enhance the small perturbation synchronization stability of the converter.

Fig.A1 The complex torque analysis of PLL
The results show that incorrect controller parameters can lead to synchronization instability with oscillation frequencies below 10 Hz, particularly in weak grids. The influence of key parameters on the system's oscillation mode is summarized as follows:
(1) Increasing the proportional coefficient of PLL and the integration parameter of CC can lead to a higher oscillation frequency and exacerbate the negative damping effect.
(2) Amplifying the proportional gain in the CC loop and DVC enhances the system's oscillation frequency but weakens the negative damping effect.
(3) The increase in the grid impedance reduces the oscillation frequency and intensifies the negative damping effect of the system.
Furthermore, leveraging the enhanced PLL, the system exhibits positive damping and remains stable as the grid transitions from strong to weak. As the grid impedance increases from 0.1(pu) to 0.8(pu), the positive damping persists, signifying an improved dynamic characteristic of the grid-following system.

Key words： Grid following converter small signal synchronization stability multi-loop control coupling complex torque analysis damping reshaping

收稿日期: 2023-04-18

PACS:

TM464

基金资助:

国家自然科学基金（62141103）和广东省基础与应用基础研究基金（粤桂联合基金-重点项目）（2021B1515420006）资助项目

通讯作者: 陈延明男,1966年生,教授,博士生导师,研究方向为新能源发电技术。E-mail: yanmingchen@126.com

作者简介: 李红女,1993年生,博士研究生,研究方向为新能源并网系统的控制与稳定性分析。E-mail: lihong.me@foxmail.com

引用本文:

李红, 梁军杨, 王振民, 李国进, 陈延明. 跟网型变换器的小扰动同步稳定机理分析与致稳控制[J]. 电工技术学报, 2024, 39(12): 3802-3815. Li Hong, Liang Junyang, Wang Zhenmin, Li Guojin, Chen Yanming. Small Signal Synchronization Stability Analysis and Improved Control Strategy for Grid Following Converter. Transactions of China Electrotechnical Society, 2024, 39(12): 3802-3815.

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