Dynamic Interaction and Small-Signal Stability Assessment of Hybrid AC/DC Grids with High Renewable Penetration (InterAcDC)

考虑到未来大规模可再生能源通过AC/DC混合电网传输带来的潜在换流器驱动的稳定风险，该项目旨在识别基于逆变器的发电(IBG)、同步电机(SM)、高压直流(HVDC)输电系统和无源电网组件之间可能存在的有害相互作用，同时考虑到HVDC的双向交-直流动态耦合。在此基础上，确定了可能产生的振荡的来源和传播范围。由于直流电压在交流系统中起着与频率相同的能量平衡指示器的作用，标准的直流电压(下垂)调节自然会在(多端)高压直流输电中引入交-直流动态耦合。此外，由于并网控制是未来高压直流输电的发展趋势，预计高压直流输电的交直流动态耦合将更加强烈，涉及更多的高压直流换流站。因此，传统的只从交流侧或直流侧进行，而简化或忽略对方动态的高压直流小干扰稳定评估，对于未来的交直流混合电网可能不会产生可靠的结果。因此，该项目将更进一步：1)建立更完整的系统模型；2)检验现有稳定性分析方法对未来交直流混合电网稳定性评估的适用性；3)对最有前景的分析方法进行必要的改进，即基于节点导纳矩阵的分析方法，如我们以前工作中所应用的方法；4)研究各种高压直流输电和IBG控制方案的稳定性影响，可分为电网跟随、电网形成等；5)开发交直流双向动态耦合指标并分析其稳定性影响。分析结果将通过时域模拟和实验室测试来验证。得益于该项目，改进的系统级建模和增强的稳定分析方法可以作为未来(多供应商)高压直流输电集成/扩建项目的去风险研究的基础。对具有代表性的高压直流输电和IBG控制方案的行为、潜在的稳定性问题所涉及的负控制相互作用的机理以及包括高压直流输电交直流动态耦合的高影响因素在内的稳定性影响的研究结果也可用于估计和分类未来的振荡不稳定，并为输电系统运营商(TSO)和制造商提供网络规划和产品开发的适当建议。

Motivated by the potential converter-driven stability risks from the future massive renewable energy transmission through hybrid AC/DC grids, the project is to identity the possibly unwanted interactions among inverter-based generations (IBGs), synchronous machines (SMs), high-voltage direct-current (HVDC) transmission systems and passive grid components taking into account the bidirectional AC-DC dynamic coupling from HVDC. On this basis, the sources and spreading ranges of the potential arising oscillations are to be determined. Since DC voltage plays the same role of energy balance indicator as the frequency in AC systems, the standard DC voltage (droop) regulation can naturally introduce AC-DC dynamic coupling in (multi-terminal) HVDC. Moreover, as grid-forming control is the future trend for HVDC, the AC-DC dynamic coupling in HVDC is expected to get stronger and to involve more HVDC converters. Therefore, the traditional small-signal stability assessment for HVDC that is conducted either from AC side or DC side while simplifying or neglecting the other side’s dynamics may not yield reliable results for the future hybrid AC/DC grids. The proposed project will thus go one step further by: 1) establishing a more complete system model; 2) examining the applicability of existing stability analysis methods for the stability assessment of future hybrid AC/DC grids; 3) developing the required enhancements to the most promising analysis method, i.e. the nodal admittance matrix based method as applied in our previous work; 4) investigating the stability impacts of various HVDC and IBG control schemes as can be classified into grid-following, grid-forming etc.; 5) developing bidirectional AC-DC dynamic coupling indicators and analyzing their stability impacts.Analytical results will be validated by time-domain stimulations and laboratory tests. Benefiting from the project, the improved system level modelling and enhanced stability analysis method can serve as a basis for the future de-risking study of (multi-vendor) HVDC integration / expansion projects. The findings on the behaviors of the representative HVDC and IBG control schemes, the mechanisms of the negative control interactions involved in the potential arising stability problems, and the stability impacts including high-impacting factors of AC-DC dynamic coupling from HVDC can also be used to estimate and classify future oscillation instabilities and to derive appropriate recommendations for transmission system operators (TSOs) and manufacturers for network planning and product development.