基于自适应虚拟阻抗的虚拟同步机功率解耦控制策略

伴随着分布式能源渗透率的提高,电力系统中同步发电机的装机比例逐渐减小,电力系统的稳定性日益受到挑战,其稳定性分析方法与提高措施均亟待研究。虚拟同步机(VSG)能够在一定程度上为系统提供惯性和阻尼,被视为提高系统稳定性的重要措施。然而,VSG通常接入中低压配电网,不仅呈阻感特性的线路阻抗会造成功率耦合,而且功角过大也会造成功率解耦控制困难。文中分析了线路阻抗及功角所造成的功率耦合机理,并通过建立VSG并网时功率与频率的响应模型,发现有功功率的大幅度增加或电网频率下降都会造成功角变大、无功功率控制出现显著偏离的情况,为此提出了基于自适应虚拟阻抗的VSG功率解耦控制策略。最后,利用PSCAD/EMTDC搭建VSG并网模型,验证了所提出解耦控制策略的正确性与有效性。

Strategy of Power Decoupling Control for Virtual Synchronous Generator Based on Adaptive Virtual Impedances

With the increase of the penetration level of distributed energy, the proportion of installed traditional generators in power system is decreasing, and the stability of the system is suffering from more and more serious threat. Virtual synchronous generator(VSG)can provide inertia and damping support for the system and thus becomes a research hotspot in recent years. However, when VSG is connected to the grid, not only the low/medium voltage line impedance, which is resistance-inductance characteristic, can cause power coupling, but also the large power angle can cause power coupling. The power coupling mechanism caused by line impedance and power angle is analyzed. By establishing the response model of the power and frequency when the VSG is connected to the grid, it is found that the large increase of the active power reference or the severe decrease of the grid frequency will cause the power angle to become larger and the reactive power control will have significant deviation. A novel power decoupling control strategy for VSG based on adaptive virtual impedances is proposed. Finally, a simulation model of VSG connected to grid is designed by using PSCAD/EMTDC, and the correctness and validity of the proposed power decoupling control strategy are verified.