虚拟同步发电机并网系统的低频振荡机理及抑制方法研究

Virtual synchronous generators (VSGs) are grid-friendly inverters. They can increase the inertia of power distribution systems involving distributed power sources. However, when large amount of VSGs are connected to grid, the problem of low-frequency oscillation can arise, which is similar to the problem caused by synchronous generator and brings new challenges to reliability of power system. Low-frequency oscillation caused by VSGs has attracted little attention. Its mechanism is not clarified, too. In this project, the mechanism of low-frequency oscillation and interaction between VSGs and power distribution systems are researched first time from the aspect of coupling of them. Through the establishing of dynamic coupled unified model of VSGs and power distribution systems, interaction of them is investigated. Principles of low-frequency oscillation under interaction are unveiled. Furthermore, this project will propose the methods to suppress the low-frequency oscillation and to improve the small-disturbance stability of power distribution systems involving large amount of VSGs. These methods can guide the design of VSGs. The research methods adopted in this project includes theoretical analysis, simulation analysis and experimental verification. The outputs of this project are important to assure the safety operation of power distribution systems involving large amount of VSGs and pave the way for wide application of VSGs.

虚拟同步发电机是具有友好并网特点的逆变器，能够为分布式电源接入的配电系统增加惯性。然而大量的虚拟同步机并网，可能会带来类似传统同步发电机并网的低频振荡问题，给电力系统的可靠性带来新的挑战。目前该问题尚未受到关注，且振荡机理也不明确。本项目首次从虚拟同步机与配电系统耦合的角度，提出虚拟同步机与配电系统相互作用及低频振荡机理的研究。通过建立虚拟同步机与配电系统动态耦合统一模型，考察两者之间的相互作用；揭示两者相互作用下的低频振荡机理；进而研究并提出抑制措施和提高大规模虚拟同步机接入的配电系统的小干扰稳定性的方法，以指导虚拟同步机的设计。项目采用理论分析、仿真分析和实验平台验证相结合的研究方法，对保障大量虚拟同步机接入配电系统的安全可靠运行有重要意义，为虚拟同步发电机的大规模推广作铺垫。

虚拟同步发电机技术能够改善并网逆变器的运行性能，是分布式发电领域的一项较为前沿的技术。目前国内外在这一课题上已有相当数量的研究成果，但针对虚拟同步机的小扰动稳定性问题的研究国内外鲜有报导。本项目旨在研究虚拟同步发电机并网时的小扰动稳定性特别是低频振荡问题，这一思路是受实际同步发电机运行特性的启发。经过研究，课题组成员发现，与实际电力系统同步发电机类似，虚拟同步发电机也继承了低频振荡的问题。本项目详细研究并揭示了虚拟同步发电机低频振荡的机理，指出了影响稳定性的重要参数，如虚拟阻尼，虚拟惯性和励磁调节器的综合放大系数等。并研究了采用PSS抑制低频振荡的可能性。这给虚拟同步发电机的设计提供了参考，因此具有实际意义和应用潜力。本项目用仿真和实验验证了虚拟同步机低频振荡的现象、机理和所提出的抑制措施的有效性。