【作者】 张鹏；

【导师】 杨奇逊； 毕天姝；

【作者基本信息】 华北电力大学 ， 电力系统及其自动化， 2014， 博士

【摘要】 随着“西电东送”发展战略的逐步实施,大容量远距离输电已经成为我国电网的重要特征。为了提高长距离输电线路的输送能力,我国电网广泛采用了串联补偿和高压直流输电技术。然而,由串联补偿和高压直流输电引起的次同步振荡风险成为电网安全稳定运行面临的重要问题。本论文对交直流互联电力系统次同步振荡的建模与机理进行了深入研究,主要工作包括：(1)提出了一种应用于次同步振荡分析的汽轮发电机组轴系扭振机械阻尼系数在线测量解耦计算的方法。揭示了并列运行的同型机组发生次同步振荡时存在的同相振荡模式和反相振荡模式现象,并阐明了反相振荡模式的力矩耦合关系。在此基础上,利用反相振荡模式下汽轮发电机组与电网解耦的特性,提出了一种通过主动激发反相振荡模式实现轴系扭振机械阻尼系数在线测量与解耦计算的方法。该方法具有严格的理论基础,且易于现场实施,并在实际系统中得到成功应用,有效的解决了轴系扭振机械阻尼系数在线测量的难题。(2)阐明了直流输电系统逆变侧故障引发汽轮发电机组次同步振荡的原因,突破了原有仅认为整流侧故障才引发机组次同步振荡的认识。论文分析了由于逆变侧交流系统扰动引起直流输电系统换相失败,进一步导致整流侧汽轮发电机组次同步振荡的物理过程,理论分析结果与实际录波数据一致,验证了理论分析的正确性。(3)完成了具有相近扭振频率的多机系统的次同步振荡机理和特性分析。揭示了在具有相近扭振频率的多机系统中,同时存在机网振荡模式和机组间振荡模式,并分析对比了两种不同振荡模式的阻尼特征。分析了决定机组间振荡模式幅值大小的因素及其对轴系扭振严重程度的影响。据此对在实际系统中发生的次同步振荡现象给出了合理、清晰的解释。(4)实现了应用于次同步振荡仿真的轴系变机械阻尼建模方法。该方法将轴系扭振机械阻尼系数作为变量代入转子运动方程,实现了轴系扭振机械阻尼系数在仿真过程中可以连续变化的功能,并在实时数字仿真器RTDS上实现。实现了一种发电机转速脉冲信号输出建模方法。该方法可以模拟与实际现场经由发电机轴系齿盘原理一样的转速脉冲输出,并具有同样的动态特性。进一步针对某大型煤电基地经交直流外送的次同步振荡问题,建立仿真模型,并开展相关次同步振荡机理与特性分析,分析结论与现场实际情况吻合。更多还原

【Abstract】 With the carrying out of West-East electricity transmission project, large capacity and long distance electricity transmission have been the characteristic of Chinese power grids. The series compensation capacitor and HVDC are widely used in Chinese power grids to increase the transmission capability of long distance lines, which might cause subsynchronous oscillation (SSO) risks to the security and stability of power systems. Simulation modeling and mechanism analysis of subsynchronous oscillations in DC/AC power systems are studied and proposed in this dissertation.(1) An on-line measurement approach of generators’torsional mechanical damping coefficients for subsynchronous oscillation analysis is developed in the dissertation. The phenomonen of in-phase mode (IPM) and anti-phase mode (APM) of parallel connected identical turbine-generators is revealed and the torque coupling relationship is analyzed. Based on the above analysis, an active stimulating method for APM is presented and a practical scheme for on-line torsional mechanical damping coefficient measurement is designed. This approach takes advantage of the features of APM and decouples the generators from grids. Moreover, the proposed approach has been implemented in field to realize the on-line measurement of the torsional mechanical damping coefficient.(2) The reason for SSO induced by AC faults at inverter station is expounded, which extends the comprehension that only the rectifier station may cause SSO. The process of AC fault at inverter station leading to commutation failure, and then SSO adjacent to rectifier side is analyzed. The SSO in field is duplicated by electromagnetic transient simulation, which verifies the correctness of the theoretical analysis.(3) In this dissertation, the mechanism and characteristic of SSO in multi-machine systems with close torsional frequencies are analyzed. The generator-grid mode and the generator-generator mode are revealed and the damping characteristics of the two modes are contrasted. Moreover, the key factor for the torsional risk caused by generator-generator mode, unit combination, is analyzed. Basing on the proposed analysis, the formation mechanism of the SSO phenomenon occurred in actual power plant is expounded clearly.(4) The modeling method for generator shaft multi-mass model with alterable mechanical damping for subsynchronous oscillation simulation is developed, by wich the torsional mechanical damping coefficients are treated as variables. The proposed modeling method is implemented at RTDS simulator. A modeling method for generator rotor speed impulse output in real time simulation is developed. By this means, the rotor impulse signals have the same dynamic response characteristics to that generated by the tooth wheel fixed on the turbine generator shafts. Furthermore, a detailed simuation model of an actual DC/AC power transmission system is developed and the mechanism and characteristic analysis of SSO is conducted, which verify the theoretical analysis.更多还原