双馈风电机组模型简化的主要步骤和关键技术分析

针对风力发电系统的电磁暂态模型复杂、计算速度慢的问题,研究了风力发电系统的简化模型。针对双馈风电机组中可以进行简化或降阶的模块,提出了对发电机模型、轴系模型、变流器及其控制模型分别进行简化或降阶,由此获得了不同的双馈风电机组简化模型。对于发电机模型可分为:五阶暂态模型、三阶暂态模型和一阶可控电流源模型;对于轴系模型有:三质量块模型、双质量块模型和单质量块模型;针对变流器及其控制模型的简化又可以分为:将变流器用可控电压源代替,形成电磁简化模型;将发电机/变流器模型用可控电流源代替,形成机电暂态模型。在此基础上比较了各个环节的关键技术,分析各简化方法的优势与不足;进而展望相关重要研究课题与方向。     

电力系统次同步振荡轴系模型研究

针对某国产300 MW汽轮机轴系,用ANSYS建立其有限元模型并进行模态分析求解自然扭振频率;通过连续轴系的离散化,建立其多段集中质量模型;并在此基础上,通过K/M比值灵敏度法建立其简单集中质量模型。运用特征值分析法求解出两种集中质量模型的自然扭振频率。分析了该汽轮机发生次同步振荡的可能性。通过自然扭振频率,比较了这三种轴系模型的准确性。结果表明175段模型(多段集中质量模型)计算量小、在仿真中较易实现,具有较高的实用价值。     

汽轮发电机组轴系扭振模型模化及其简化

对汽轮机组轴系扭振模型模铧及当量参数的计算进行了比较深入的分析,给出了轴系模型当量惯性参数及刚性参数的计算,并对国产３００ＭＷ机组轴系进行模化,得到多质量块集中质量模型。经过分析和试算,提出一种快速、有效的模型简化方法,并应用该法对国产３００ＭＷ机组轴系多质量模型进行有效合并。最后通过对当量模型扭振特性的分析计算,证明模型当量参数的计算式是正确的,提出的模型合并方法为轴系扭振模型简化提供了一个有效     

电气扰动对汽轮发电机组轴系寿命的影响

本文通过对国产60万 kW 机组的连续质量模型进行降阶处理,建立了合理的多段、集中质量模型。利用 EMTP 程序,对东北电网中哈尔滨第三发电厂两台60万 kW 发电机组的机端短路、线路重合闸、误并列及汽门快关进行了数字仿真计算,并就上述各种非正常工况对轴系疲劳寿命消耗做了定量分析。     

短路及重合闸过程汽轮发电机轴系扭振的计算分析

鉴于大型汽轮发电机组在运行中多次发生因轴系扭振而损坏的重大事故，文中结合国产２００ＭＷ汽轮发电机组，采用多段集中质量轴系模型和雷卡迪传递矩阵法，对单机无穷大系统中，发电机组附近电网短路及重合闸过程中的机组轴系扭振进行了详细的仿真计算，并对轴系各轴段之间的扭振大小，以及扭振的机理进行了比较和分析，所得结论为大型汽输发电机组的 安全运行及研制提供了一些理论依据。     

风力发电机组动态模型研究

该文针对基于双馈感应发电机的变速风力发电机组轴系的特点，用等效集中质量法和动力学方程建立了其包含机械传动链动态的轴系模型，与发电机动态方程组成8阶微分方程组。该8阶模型同时考虑了风力发电机组的机械和电气动态特性，弥补了现有各种模型过于简化的不足。并与不考虑机械动态的简化模型进行了仿真结果的对比。采用该模型可以更加有效地进行风力发电系统控制系统的设计，以及分析机组在各种运行工况下的动态行为。     

一种多时间尺度电力系统奇异摄动模型的推导

由于电力系统是一个多时间尺度的高阶非线性系统,其稳定性分析就变得异常复杂。为了提高稳定计算的效率．研究电力系统的多时间尺度动态模型及其降阶是非常必要的,为此,以电力系统物理电路为基础．导出了一个计算快动态和慢动态的电力系统奇异摄动模型。利用系统化的降阶方法,对电力系统模型进行降阶,并通过忽略快动态和固定慢动态,得出一个简化的、符合传统电力系统储备结构的电力系统模型,这对理解系统失稳机制具有重要意义。     

光伏电磁暂态模型降阶综述

研究光伏发电系统势必要研究其动态特性,但是详细的光伏发电系统模型复杂、仿真时间长,对研究光伏电磁暂态模型有很大的阻碍,运用合适的降阶方法令其简化就显得尤为重要。对光伏电磁暂态模型的降阶展开了综述,介绍了光伏电磁暂态模型的详细模型;归纳了一些常用的降阶思路与降阶方法;对降阶的有效性进行了简单验证,并概括了光伏电磁暂态降阶领域的进一步研究内容。     

汽轮发电机组机电联合振荡计算方法

本文采用梯形积分法,离散集中质量轴系模型的运动方程,并用数值稳定性好的雷卡迪传递矩陈方法计算轴系的扭振瞬态响应,实现了汽轮发电机组机电联合振荡过程的时域仿真。文中导出的机网接口方法,可以方便地用于发电机与电网差分方程的联解,通过对单机无穷大系统重合闸过程的计算,初步证明了本方法的有效性。     

基于暂态扭矩辨识的汽轮机组快速扭振保护研究

汽轮机组与串补系统相互作用会引发暂态扭矩放大,冲击性扭矩在极短时间内就会对轴系造成严重的破坏。然而,常规扭振保护设备无法及时将机组解列,不能够保障轴系安全。该文提出一种汽轮机组快速扭振保护方法——即时暂态扭矩保护,该方法利用轴系转速辨识暂态扭矩,根据暂态扭矩判断轴系扭振风险,当轴系存在扭振风险时及时将机组解列。另外,基于疲劳损耗优化的定值整定原则确保了保护能够将所有运行工况下轴系产生的疲劳损耗控制在允许范围内。最后,基于RTDS的硬件在环试验验证了保护样机的性能和可靠性。结果表明:所提方法能够在汽轮机组轴系存在扭振风险时及时解列机组,从而避免暂态扭矩放大导致轴系产生严重疲劳损耗乃至一次性损毁。     

机电耦合对轴系扭振动态特性的影响

应用机电耦合模型定义全模态型及扭振模态型;推导扭矩线性解,并根据扭矩解定义扭矩模态型及扭矩模态贡献因子。这些物理概念可直接分析轴系扭振动态,并获得更丰富的信息,这是以往定义的模态型无法做到的。此外,还分析自由振动模型和受迫轴系模型的理论基础和物理意义,并从机电耦合模型与自由振动模型的区别,解释固有扭振频率及模态型的计算值与测量值存在偏差的原因;应用解析解分析机电耦合模型与受迫振动模型的动态特性差别。     

一种模拟实测过程的齿槽转矩数值计算方法

为了精确计算与有效削弱齿槽转矩,采用数值仿真技术,提出通过模拟齿槽转矩的标准测量过程来计算永磁电机齿槽转矩的方法,其模型考虑了齿槽效应、铁心饱和以及运动、时变电磁场的影响.计算结果和实验结果吻合,表明该方法是正确、有效的.利用该方法对具有不同极槽数配合的9台永磁直流电动机进行了齿槽转矩的有限元计算,并验证了使极数和槽数的最小公倍数达到最大的极槽配合方案可有效削弱齿槽转矩.     

发电厂送出端采用高速重合闸影响的分析研究

本文在开发使用ＢＰＡ－ＥＭＴＰ的基础上，研究了发电厂送出线上采用高速重合闸对汽轮发电组轴系扭振和电力系统运行稳定性的影响。指出对于永久性故障的重合可能导致轴系扭力矩的放大和发电机摇摆角的增大，且与重合时刻有关。文中同时提出了对三相重合闸分组重合的方法。采用这种方法，当重合于永久故障时，可有效降低轴系扭力矩，并能改善机组与电网间的运行稳定性。     

TRANSIENTS IN SUPERCONDUCTING ALTERNATORS WITH TORQUE COMPENSATING SHELLS

ABSTRACT

In this machine the torque is not transmitted mechanically to the field winding but by an asynchronous link. The field winding is free to rotate inside the driving shaft, which acts as the squirrel cage of an induction motor. In the steady state the field winding turns at synchronous speed and the driving shaft slightly faster. During a transient the shaft acts as an electromagnetic shell protecting the low temperature parts of the cryostat from high torques and the superconducting coil from varying magnetic fields. In this paper the steady-state running, the fault torques, the critical clearing time, the steady state stability, and the losses in cold metallic parts, are compared with those of a classical superconducting alternator.     

TURBINE-GENERATOR SHAFT TORQUES AND FATIGUE LIFE EXPENDITURE PREDICTED BY FREQUENCY DOMAIN AND TIME DOMAIN METHODS FOLLOWING SEVERE DISTURBANCES ON THE SYSTEM SUPPLY

ABSTRACT

This paper examines precision of predicting time responses for torque in turbine-generator-exciter shafts together with fatigue life expenditure of shafts by frequency domain analysis not analysed in the literature heretofore following incidence and clearance of worst-case disturbances on the electrical supply system. Effect of both governor and avr action following a range of disturbances is also illustrated. The effect of steam and electrical viscous damping on maximum and minimum shaft torques predicted by frequency domain analysis for a range of disturbances as a function of the fault clearing time is also depicted

The analysis is based on Fourier analysis of generator airgap torque following incidence and clearance of a severe supply network disturbance or following mal-synchronisation to obtain torque excitation which acts on the generator rotor corresponding to each modal vibration. Amplitude and phase of each modal vibration is thereby determined. Using appropriate damping, time responses for shaft torque at each shaft cell is constructed by summing components which correspond to each modal vibration. These time responses are compared with those obtained by solution of more than 50 differential equations which simulate the shaft train, turbine, generator, governor and avr

It is shown that time responses for transient turbine-generator-exciter shaft torques together with maximum shaft torques and fatigue life expenditure of the shaft can be predicted faithfully by frequency domain analysis taking due account of magnitude and phase of each modal vibration, and damping, following (i) worst-case Line-Line-Line, Line-Line, and Line-Ground disturbances from full-load to no-load with clearance, and (ii) mal-synchronisation. Simulation of damping of rotor swing, together with governor action, is important in making precise assessments of transient turbine shaft torque (and fatigue life expenditure of the shaft) at shaft locations which are close to die generator

660 MW, 1000 MW and 1300 MW two-pole Machines are analysed.     

A method for reducing transient torsional stresses ofturbine-generator shaft segments

The author presents a method for reducing transient torsional stresses of steam turbine-generators in series-capacitor-compensated power systems, which are equipped with ZnO varistor schemes. The fundamental concept is to reduce the coupling between the electrical network and the shaft system with respect to the troublesome torsional frequency. The electrical network and the rotating shaft system are coupled through the generator air-gap torque. This coupling can be attenuated by unbalancing the network with respect to the phenomenon of torsional oscillations. This is achieved by setting the protective voltage levels of the three phases of a three-phase series capacitor at unequal values. The technical feasibility of the proposed method is demonstrated on a test system, using the BPA Electromagnetic Transients Program (EMTP) as the study tool. The impact of the proposed countermeasure on the transient torques of the system, as a result of different disturbances, is demonstrated. The limitations of the proposed method are discussed     

Means of controlling induction rheostat parameters in electromagnetic working shaft system

Methods of increasing the driving torques of an electromagnetic working shaft (EMWS) by directly affecting the induction rheostat parameters by connecting the additional rheostats in parallel in the rotor circuit are examined. Original and more precise analytical expressions are obtained for the driving torques of the electromagnetic working shaft. In these expressions, the stator resistance is taken into account for the first time. It is easy to calculate the electromagnetic working shaft performances uainf these expressions and the accuracy of calculations is high.     

Berechnung der Torsions-Beanspruchung in drehelastischen Antrieben mit stromrichtergespeister Asynchronmaschine

Übersicht In Asynchronmaschinen, die über einen Phasenfolgewechselrichter mit Stromzwischenkreis gespeist werden, entstehen unvermeidliche Pendelmomente. Diese können den Wellenstrang zu Drehschwingungen anregen und dadurch unzulässige Torsionsbeanspruchungen verursachen. Ein Rechenverfahren wird beschrieben, mit dem sich solche Beanspruchungen im Entwurfsstadium erkennen und Abhilfemaßnahmen beurteilen lassen. Es berücksichtigt den Einfluß der Zwischenkreisstrom-Welligkeit auf die Pendelmomente. Ein Beispiel zeigt, daß auch höhere Torsions-Eigenfrequenzen durch ein ausreichendes mechanisches Modell einzubeziehen sind.

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Torsional stress calculation for torsionally elastic drives with induction machine fed by a current source inverter

Contents Induction machines fed by a current source inverter with autosequential interphase commutation produce inevitable pulsating torques. These may lead to inadmissible stresses due to excitation of torsional vibrations in the shaft arrangement. A method for calculation is shown, which enables us when designing the drive to discover such harmful stresses and to examine remedial steps. It considers the influence on the pulsating torques given by the harmonic content of the unsmoothed dc-link current. An example indicates that even higher characteristic torsional frequencies have to be taken into account by using an adequate mechanical shaft model.

     

风力机等效模型对双馈风机LVRT特性影响研究

风电机组单机并网容量逐步增大,为了较准确的研究风力机等效模型对双馈风力发电机组低电压穿越特性的影响,本文采用等效集中质量法,建立了同时考虑风力机叶片和传动轴柔性的风力机三质量块等效模型,以及考虑传动轴柔性的两质量块等效模型和忽略风力机柔性的单质量块等效模型。依据并网导则要求,建立了基于Crowbar电路的双馈风力发电机组低电压穿越控制策略。在电网电压不同跌落故障情况下,研究了采用不同风力机等效模型对双馈风力发电机组低电压穿越特性的影响。仿真结果表明：同时考虑风力机叶片和传动轴柔性的风力机三质量块模型更能准确地反映双馈风力发电机组低电压穿越有功功率特性。     

500kV串补系统次同步谐振问题的分析计算

本文应用EMTP程序分析了500kV串补输电系统的次同步谐振问题,计算了500MW汽轮发电机组的自振频率、振型和电网的频率阻抗特性,并有针对性地计算了系统各种运行状态下的机组轴系扭矩。计算结果表明,该系统在单机运行、补偿度为50％时将发生次同步谐振。