基于虚拟阻尼指标的柔性直流电网小信号稳定性分析

近年来柔性直流电网得到了广泛关注和快速发展,柔性直流电网的稳定是保证交直流混联电力系统正常运行的重要前提。文中针对柔性直流电网,首先建立了不同控制方法下电压源型换流站和柔性直流电网的线性化模型,构建了以柔性直流电网中直流电压振荡模式为分析目标的柔性直流电网线性化互联模型。基于此,提出了一种物理意义更加明确的虚拟阻尼分析法,并对其概念和原理进行了介绍。然后,提出了能够评估电压源型换流站控制对柔性直流电网稳定性影响大小的虚拟阻尼指标,定量刻画了不同控制方法下电压源型换流站对柔性直流电网中直流电压振荡模式的影响。进一步,基于该虚拟阻尼指标,提出了适用于柔性直流电网中换流站控制参数的协调优化方法,提升了直流电网的小信号稳定性。最后,以一个三端柔性直流电网为例,详细展示了电压源型换流站虚拟阻尼的计算方法,并在包含下垂控制的复杂十端柔性直流电网中验证了多换流站参数优化方法的有效性及其相比于传统参数优化方法的优势。

Analysis of Small-signal Stability for Flexible DC Grid Based on Virtual Damping Index

In recent years, flexible DC grid attracts a lot of attentions and develops fast, whose stability is the important premise to make the hybrid AC/DC power system operate normally. Aiming at the flexible DC grid, the linearized model of voltage source converter (VSC) station and the flexible DC grid with different control methods is established, and the interaction model of flexible DC grid is established, which takes oscillation mode of DC voltage in the flexible DC grid as analysis target. Based on this, a virtual damping analysis method with more clear physical meaning is proposed, and its concept and principle are introduced. Then, virtual damping index which can evaluate the influence of VSC station control on the stability of flexible DC grid is proposed, and the impact of VSC on the oscillation mode of DC voltage with different control methods is quantitatively analyzed. Furthermore, based on the virtual damping index, a coordinated optimization method for the control parameters of VSC stations in flexible DC grid is proposed, which improves the small-signal stability of the DC grid. Finally, taking a three-terminal flexible DC grid as an example, the calculation method of virtual damping in VSC stations is presented in detail. And the effectiveness of parameter optimization method in multiple VSC stations and the advantages of the method compared with the traditional parameter optimization method is verified in the complex ten-terminal flexible DC grid with droop control.