大规模新能源接入弱同步支撑柔直系统的送端自适应VSG控制策略

Adaptive VSG Control Strategy of Sending End for Large-Scale Renewable Energy Connected to Weakly-Synchronized Support VSC-HVDC System

新能源汇集经柔性直流输电(voltage source converter based high voltage direct current,VSC-HVDC)技术送出是促进新能源消纳的有效方式。但新能源渗透率的持续增加导致电网强度不断下降,采用传统跟网型(grid-following,GFL)换流技术已无法满足系统稳定运行需求。为提高系统弱电网适应性,满足大规模新能源接入弱同步支撑柔直系统应用场景需求,提出在柔直系统送端换流站采用VSG控制策略。首先,建立整流侧控制小信号数学模型,利用根轨迹法深入研究虚拟阻抗对系统稳定性的影响。其次,提出利用交流电压变化率及电压差值等电气量构建虚拟电抗自适应调整项的改进VSG控制算法,在保证系统等效阻抗呈感性的同时,可提高送端交流系统的等效短路比,达到改善系统整体性能的效果。最后,通过PSCAD/EMTDC电磁暂态仿真验证所提控制策略的有效性。

Renewable energy collection and output through voltage source converter based high voltage direct current(VSC-HVDC)technology is an effective way to promote renewable energy consumption.However,the continuous increase in the penetration rate of renewable energy has led to a continuous decline in the strength of the power grid,and the traditional grid-following(GFL)converter technology can no longer meet the needs of stable system operation.In order to improve the adaptability of the weak grid of the system and meet the application scenarios of large-scale renewable energy connected to weakly-synchronized support VSCHVDC system,this paper proposes to adopt VSG control strategy in the converter station of the sending end of the VSC-HVDC system.Firstly,a small signal mathematical model of rectifier-side control is established,and the influence of virtual impedance on system stability is studied by the root locus method.Secondly,an improved virtual synchronous generator(VSG)control algorithm for constructing virtual reactance adaptive adjustment items using electrical quantities such as alternating voltage(AC)change rate and voltage difference is proposed,which can improve the equivalent short-circuit ratio of the AC system at the sending end while ensuring that the equivalent impedance of the system is inductive,so as to improve the overall performance of the system.Finally,the effectiveness of the proposed control strategy is verified by PSCAD/EMTDC electromagnetic transient simulation.