Analytical solution for small signal stability of grid-connected converter
袁梦瞳 1薄耀龙 1夏杨红 1韦巍 1朱承治2
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作者信息
1. 浙江大学电气工程学院,浙江杭州 310027
2. 国网浙江省电力有限公司电力科学研究院,浙江杭州 310014
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摘要
锁相环(phase-locked loop,PLL)是变流器并网同步的核心环节,现有技术通常采用基于同步坐标系的锁相环(synchronous reference frame-PLL,SRF-PLL).由于SRF-PLL的引入,使得并网变流器模型复杂,稳定性分析困难,通常结合波特图等进行数值验证分析而难以获得解析解,更多关于稳定性的本质机理无法有效揭示.因此,提出一种基于代数运算的锁相(algebraic operation based PLL,AO-PLL)控制技术,同步速度更快,且在该锁相控制方式下,变流器模型阶次降低.基于此,给出系统稳定性的封闭解析解形式,并获得系统稳定性的充要条件,在此基础上,分析有功无功控制耦合对系统稳定性影响;揭示电流环比例控制器和积分控制器对系统稳定性的不同影响机理;解释利用短路比来刻画系统稳定裕度的内涵.此外,阐述所提AO-PLL和常规SRF-PLL之间的内在联系,以及稳定性结论在常规SRF-PLL控制下的适用性.最后通过算例验证前述理论分析的正确性.
Abstract
The phase-locked loop (PLL) is a core component for grid synchronization of power converters. Existing technologies commonly employ the PLL based on the synchronous reference frame (SRF-PLL). The introduction of SRF-PLL complicates the model of grid-connected converters and makes stability analysis challenging. Typically,numerical verification analysis is conducted using Bode plots,making it difficult to obtain analytical solutions and effectively reveal the underlying mechanisms of stability. Therefore,an algebraic operation-based PLL (AO-PLL) control technology is proposed,which offers faster synchronization and reduces the order of the converter model under this PLL control mode. Based on this,a closed-form analytical solution for system stability is presented,and necessary and sufficient conditions for system stability are obtained. On this basis,the impact of active and reactive power control coupling on system stability is analyzed;the different mechanisms of the proportional controller and integral controller of the current loop on system stability are revealed;and the connotation of using short-circuit ratio to describe the system stability margin is explained. Furthermore,the intrinsic relationship between the proposed AO-PLL and the conventional SRF-PLL is elaborated,as well as the applicability of stability conclusions under conventional SRF-PLL control. Finally,numerical examples are provided to verify the correctness of the aforementioned theoretical analysis.
关键词
锁相环/并网变流器/有功无功耦合/小信号稳定性/弱电网
Key words
phase-locked loop/grid-connected converter/coupling of active and reactive power/small signal stability/weak grid
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