【作者】 周长春；

【导师】 徐政；

【作者基本信息】 浙江大学 ， 电力系统及其自动化， 2004， 博士

【摘要】 高压直流输电(High-Voltage-Direct-Current----HVDC)系统与临近同步发电机组之间存在着扭振相互作用，HVDC的电气负阻尼作用有可能引起机组在次同步频率范围的扭转振荡。目前，直流输电技术已经在我国得到了广泛的应用，并且在今后的几十年中，直流输电在我国还将有更为广阔的应用前景。本文从电气阻尼的角度出发，重点研究了几种包含HVDC的系统的次同步振荡问题。主要内容包括： (1)基于开关函数法和仿真分析，研究了机组转子上次同步频率的小扰动，在HVDC交直流两侧响应的频率特性----转子上的小扰动经直流换流器调制后，将会在系统直流侧感应出与扰动同频率的电压分量；直流侧电流扰动反映到交流定子侧，也将发生频率偏移。基于此，指出了采用准稳态模型进行HVDC系统次同步振荡分析的局限性，并引入了分析HVDC或含有FACTS装置的系统次同步振荡问题的方法：复转矩系数----测试信号法。 (2)介绍了多机电力系统机组间电气耦合对轴系扭振特性的影响，以及机组自然频率与机组扭振相互作用的关系，并对复杂系统中并列运行的相同发电机和不同发电机间的扭振相互作用进行了分析，归纳了不同运行条件下机组等值简化的基本原则。该准则是进行以下分析的理论基础。 (3)对一个仅含有直流输电线路的系统，采用复转矩系数----测试信号法，对其次同步振荡特性进行了分析。在整个次同步频率范围内，计算得到了系统电气阻尼，并详尽地分析了同步发电机与HVDC的耦合程度、直流输送功率水平，换流阀触发角大小以及控制器参数等因素对系统电气阻尼的影响。研究表明，系统整流站附近的同步发电机组要承受电气负阻尼作用，因此有可能引起机组低频扭转振荡模式失稳；而HVDC的逆变站向其临近同步发电机组提供正阻尼，因而机组不存在次同步振荡危险。 (4)对交直流并列运行系统，采用复转矩系数----测试信号法，对其次同步振荡电气阻尼特性进行了仿真和计算。研究表明，交流输电线路的不同性质，将导致系统整体电气阻尼出现差异。其中，并列运行的无串补交流输电线路可以缓解HVDC与其临近机组之间的机电耦合程度，改善HVDC的电气负阻尼特性，从浙江大学博士学位论文摘要而减轻机组发生次同步振荡的危险性，此时系统的整体电气阻尼特性由HVDC的性质决定;但若交流线路中存在串联补偿电容，则系统幅值较大的电气负阻尼不仅可能使整流站机组发生次同步振荡，逆变站附近机组同样存在发生次同步振荡的可能性，此时系统的整体阻尼特性由串联补偿电容的性质决定。 (5)提出了一种衡量多换流站系统机组扭振作用的新指标一综合机组作用系数。并通过对含有多个直流换流站系统的电气阻尼特性分析，验证了该指标的有效性。该指标可以用来简单量化系统中所有直流换流站(整流站)与临近机组之间的相互扭振作用，可以作为一种研究多换流器系统次同步振荡问题的筛选工具。 (6)对直流输电系统的故障恢复特性进行了分析。在时域仿真的基础上，分别研究了交流系统强度以及不同无功补偿方式对直流系统恢复速度的影响。更多还原

【Abstract】 Torsional interaction exists between HVDC converters and turbine-generators, and negative electrical damping provided by HVDC may cause subsynchronous oscillation (SSO) that can lead to turbine-generator shaft failure and electrical instability at oscillation frequencies lower than the fundamental system frequency. From the viewpoint of electrical damping, this dissertation focus on the damping analysis of subsynchronous oscillation for different systems, such as HVDC system, hybrid AC/DC system and multiple-converter HVDC system. The main works are organized as follows:Based on the switching function method and time domain simulations, the small disturbance transfer a characteristic through the converter is analyzed. Because of the modulation effect of the converter, the small disturbance in the shaft of turbine generator will induce AC voltage component with the same frequency as the disturbance on the DC side. And the resulted AC current on the DC side will have the similar frequency shift when transfers to the stator of the generator. All these changes, which are of importance to subsynchronous oscillation analysis, cannot be described with the Quasi Steady State (QSS) model any more. Therefore, the deficiency of QSS-model-based eigenvalue method is pointed out and a novel method named complex torque coefficient-test signal method is adopted to analyze the subsynchronous oscillation caused by HVDC or FACTS devices.The torsional interaction from the electrical couplings among the generating sets is presented and the influence of the natural torsional frequency of the generating sets on the torsional oscillation characteristics is described. The torsional dynamics between identical parallel turbine-generators are deduced as well as that between non-identical parallel turbine-generators. Then the basic principle of equivalent simplification of generating units for different operational condition is summarized. This simplification principle is the foundation of the following analysis.Using the test signal method, a detailed analysis of subsynchronous oscillation for a HVDC system is performed. The electrical damping within the whole subsynchronous frequency range is calculated. The impacts of the unit interaction factor between HVDC and turbine generator, the DC power level, the firing delay angle and the parameter settings of HVDC controller on thehave the potential danger of subsynchronous oscillation. On the contrary, because of the effect of positive damping provided by the inverter, the unit near a inveter will have no subsynchronous oscillation risk.Based on the same method described above, a damping study is carried out for a hybrid AC/DC system, which include a HVDC link and an AC transmission line in parallel. The characteristics of damping shows that the uncompensated parallel AC transmission line can release the coupling between the HVDC and generator and improve the damping of the system, hence the possibility of subsynchronous oscillation decrease. In such a system scheme, the HVDC system dominates the changes of damping due to the small magnitude of the damping provided by AC line. When the AC transmission line is compensated with a fixed series capacitor, the situation will be totally different. The large negative damping induced by the series capacitor will impose subsynchronous oscillation danger not only to the generator near a rectifier, but also the generator close to an inverter. The compensated AC line will dominate the system electrical damping.A novel index named comprehensive unit interaction factor is proposed to quantify the torsional interaction in an AC system with multiple HVDC converters. In an AC system with multiple HVDC converters, turbine generators can interact adversely with all the converters through electrical connection, which makes the subsynchronous oscillation more complicated. The new index provided in this dissertation can be used as a screening tool to estimate the torsional interaction and to identify units and system contingencies requiring det更多还原