Localization method of subsynchronous oscillation source based on high-resolution time-frequency distribution image and CNN

The penetration of new energy sources such as wind power is increasing,which consequently increases the occurrence rate of subsynchronous oscillation events.However,existing subsynchronous oscillation source-identification methods primarily analyze fixed-mode oscillations and rarely consider time-varying features,such as frequency drift,caused by the random volatility of wind farms when oscillations occur.This paper proposes a subsynchronous oscillation sourcelocalization method that involves an enhanced short-time Fourier transform and a convolutional neural network(CNN).First,an enhanced STFT is performed to secure high-resolution time-frequency distribution(TFD)images from the measured data of the generation unit ports.Next,these TFD images are amalgamated to form a subsynchronous oscillation feature map that serves as input to the CNN to train the localization model.Ultimately,the trained CNN model realizes the online localization of subsynchronous oscillation sources.The effectiveness and accuracy of the proposed method are validated via multimachine system models simulating forced and natural oscillation events using the Power Systems Computer Aided Design platform.Test results show that the proposed method can localize subsynchronous oscillation sources online while considering unpredictable fluctuations in wind farms,thus providing a foundation for oscillation suppression in practical engineering scenarios.

Effects of Semi-floating Ring Bearing Outer Clearance on the Subsynchronous Oscillation of Turbocharger Rotor

Semi-floating ring bearing（SFRB） is developed to control the vibration of turbocharger rotor. The outer clearance of SFRB affects the magnitude and frequency of nonlinear whirl motion, which is significant for the design of turbocharger. In order to explore the effects of outer clearance, a transient finite element analysis program for rotor and oil film bearing is built and validated by a published experimental case. The nonlinear dynamic behaviors ofrotor-SFRB system are simulated. According to the simulation results, two representative subsynchronous oscillations excited by the two hearings respectively are discovered. As the outer clearance of SFRB increases from 24 ~tm to 60 pro, the low-frequency subsynchronous oscillation experiences three steps, including a strong start, a gradual recession and a combination with the other one. At the same time, the high-frequency subsynchronous oscillation starts to appear gradually, then strengthens, and finally combines. If gravity and unbalance are neglected, the combination will start starts from high rotor speed and extents to low rotor speed, just like a ＂zipper＂. It is found from the quantitative analysis that when the outer clearance increases, the vibration amplitude experiences large value firstly, then reduction, and suddenly increasing after combination. A useful design principle of SFRB outer clearance for minimum vibration amplitude is proposed： the outer clearance value should be chosen to keep the frequency of two subsynchronous oscillations clearly separated and their amplitudes close.

Subsynchronous oscillation monitoring and alarm method based on phasor measurements

Owing to the large-scale grid connection of new energy sources, several installed power electronic devices introduce sub-/supersynchronous inter-harmonics into power signals, resulting in the frequent occurrence of subsynchronous oscillations(SSOs). The SSOs may cause significant harm to generator sets and power systems;thus, online monitoring and accurate alarms for power systems are crucial for their safe and stable operation. Phasor measurement units(PMUs) can realize the dynamic real-time monitoring of power systems. Based on PMU phasor measurements, this study proposes a method for SSO online monitoring and alarm implementation for the main station of a PMU. First, fast Fourier transform frequency spectrum analysis is performed on PMU current phasor amplitude data to obtain subsynchronous frequency components. Second, the support vector machine learning algorithm is trained to obtain the amplitude threshold and subsequently filter out safe components and retain harmful ones. Finally, the adaptive duration threshold is determined according to frequency susceptibility, amplitude attenuation, and energy accumulation to decide whether to transmit an alarm signal. Experiments based on field data verify the effectiveness of the proposed method.

Study and Mitigation of Subsynchronous Oscillations with SSC Based SSSC

This paper proposes a powerful subsynchronous component based (SSC) controller to mitigate the subsynchronous resonance (SSR) with statics synchronous series compensator (SSSC). The mitigation of SSR is achieved by increasing the network damping at those frequencies which are close to the torsional frequency of the turbine-generator shaft. The increase of network damping is done by the extraction of subsynchronous component of voltage and current from the measured signal of the system. From the knowledge of subsynchronous components, a series voltage is injected by SSSC into the transmission line to make the subsynchronous current to zero which is the main cause of turbine oscillations. To analyze the effectiveness of the proposed control scheme, IEEE first benchmark model has taken. The results show the accuracy of the proposed control scheme to mitigate the Torque amplification of SSR.

Analysis of Sub-Synchronous Oscillation of Virtual Synchronous Generator and Research on Suppression Strategy in Weak Grid

At present,the direct drive permanent magnet synchronous generator(DD-PMSG)grid connected system based on virtual synchronous generator(VSG)control will experience power oscillation at sub synchronous frequencies.The mechanism and characteristics of this new type of sub-synchronous interaction(SSI)are not yet clear,and the system cannot recover to steady state solely based on the characteristics of VSG itself.Especially when connected to a weak current network,oscillations are more pronounced,affecting the stability of the system.In severe cases,the systemmay trigger shutdown protection and be disconnected from the network.Existing research has only analyzed the oscillation mechanism under this phenomenon and has not proposed corresponding control strategies.This article proposes aVSM control strategy based on the VSG control algorithm,which balances the dq axis component of voltage and current,and improves the voltage and current loop of VSG control to reduce the impact of sub-synchronous oscillation(SSO)on the power grid.In MATLAB/Simulink,a simulation model of the proposed control strategy was built to verify its correctness and effectiveness.

Improved Subsynchronous Oscillation Parameter Identification with Synchrophasor Based on Matrix Pencil Method in Power Systems

The subsynchronous oscillations(SSOs)related to renewable generation seriously affect the stability and safety of the power systems.To realize the dynamic monitoring of SSOs by utilizing the high computational efficiency and noise-resilient features of the matrix pencil method(MPM),this paper propos es an improved MPM-based parameter identification with syn chrophasors.The MPM is enhanced by the angular frequency fitting equations based on the characteristic polynomial coeffi cients of the matrix pencil to ensure the accuracy of the identi fied parameters,since the existing eigenvalue solution of the MPM ignores the angular frequency conjugation constraints of the two fundamental modes and two oscillation modes.Then,the identification and recovery of bad data are proposed by uti lizing the difference in temporal continuity of the synchropha sors before and after noise reduction.The proposed parameter identification is verified with synthetic,simulated,and actual measured phase measurement unit(PMU)data.Compared with the existing MPM,the improved MPM achieves better accuracy for parameter identification of each component in SSOs,better real-time performance,and significantly reduces the effect of bad data.

Overview of Sub-synchronous Oscillation in Wind Power System

Nowadays with the improvement in the degree of emphasis on new energy, the wind power system has developed more and more rapidly over the world. Usually the wind plants are located in the remote areas which are far from the load centers. Generally series compensated AC transmission and high voltage DC transmission are made use of to improve the transmission capacity as two main effective ways which can solve the problem of large scale wind power transmission. The paper describes the three kinds of impact varieties and impact mechanisms in the sub-synchronous oscillation phenomena of wind power system based on doubly fed induction generator (DFIG) wind generators. At last, we point out the important problem that should be stressed in the wind power system.

PROPOSALS CONCERNING THE RESEARCH WORK OF TURBOGENERATOR TORSIONAL OSCILLATIONS IN CHINA

In this paper,proposals in the following arcas of turbogenerator torsionaloscillation(TTO)researches in China are presented:* Concerning the focal points of TTO studies;* Concerning the modelling and data acquisition of TTO;* Concerning the computation and analysis of TTO transients;* Concerning the monitoring and analyzing devices of TTO;* Concerning the countermeasures against TTO.It is concluded that researches centered on torsional oscillations caused by system dis-turbances and switching events should begin the carlier the better.

Application of STATCOM for Damping Subsynchronous Resonance in a Multi-machine System

Results of an investigation on the application of STATCOM for damping subsynchronous resonance (SSR) in a multi-machine system is presented in this paper. For a multi-machine system which has a set of identical parallel turbine-generators or non-identical turbine-generators having torsional modes of the same frequency, generators may suffer from the same mode of torsional interaction corresponding to a certain series compensation degrees. Generators in such system may have different oscillation behaviors when they are unequally loaded or have different shaft and electrical parameters. Serving as the grid-side equipment, the reactive power output of a STATCOM could have an impact on all generators electrical distance nearby. Thus a single STATCOM could be used to damp torsional interactions of multi-generators when additional proper control strategy is supplemented. In this paper, control strategy of using STATCOM to damp SSR in a multi-machine system is designed and its effectiveness is validated based on a modified IEEE second benchmark model.

基于改进自适应陷波的双馈风电场时变次同步振荡抑制策略

双馈风电场经串补电容并网时,可能引发次同步控制相互作用(subsynchronous control interaction,SSCI),严重威胁系统安全稳定运行。通过在风机控制器中引入陷波器可有效阻断SSCI,然而固定参数陷波器难以适应实际系统中次同步振荡表现出的频率大范围时变特征。为解决这一问题,该文提出一种基于改进自适应陷波(adaptive notch filter,ANF)的双馈风电场时变次同步振荡抑制策略。首先,分析ANF安装于风机转子侧变流器(rotor-side converter,RSC)不同位置时对次同步振荡分量的阻断效果,确定ANF的最佳安装位置;其次,基于紧缩技术近似投影子空间跟踪算法(projection approximation subspace tracking based on the deflation technique,PASTd)在线获取次同步振荡信息,提出总体控制架构,设计基于量测数据辨识的ANF中心频率更新策略;最终,在考虑风速、风机台数、无功出力、电网拓扑变化等多种影响因素的情况下,验证控制策略对频率时变次同步振荡的抑制效果。与现有方法相比,所提控制策略不依赖于系统的准确数学模型,且具备较强的鲁棒性和适应性。

次同步振荡在交直流电网中传播的关键影响因素

随着“双高”电力系统的发展,次同步振荡问题日益凸出,亟需研究交直流线路次同步振荡传播的关键影响因素。从系统响应量测时序数据着手,提出了一种次同步振荡传播关键影响因素定量分析方法。首先,基于自适应噪声完全集合经验模态分解(complete ensemble empirical mode decomposition, CEEMDAN)的改进小波阈值去噪方法对量测数据进行降噪处理,减少噪声对Prony分析的影响;其次,基于次同步振荡传播各影响因素的相关系数和互信息量建立相关性评价组合模型;最后,计算交直流不同参数在综合模型中的评价指标,得出次同步振荡在交直流线路中传播的关键影响因素。通过在PSCAD搭建2区域4机系统进行分析,结果表明:影响交流线路次同步振荡传播的极强相关参数为交流线路潮流,影响直流线路次同步振荡传播的极强相关参数为次同步振荡频率下交流线路阻抗特性。

应用逻辑回归法辨识风电外送系统是否产生次同步振荡的研究

风电外送系统运行环境复杂,电力电子设备、风速大小、串补度大小都可能诱发风电外送系统产生次同步振荡(Sub-synchronous oscillation,SSO)。因此提出一种利用机器学习的方法进行辨识风电外送系统是否产生次同步振荡。首先在pscad仿真系统中创建风电外送系统模型,再通过所创建的风电外送系统模型创建数据集,使用python语言编写预测系统,将所创建的数据集代入预测系统进行训练。论文创建一组新的测试数据代入已经训练好的系统得到测试结果。将结果与pscad中的结果进行对比,验证预测系统的可行性。该预测系统运行环境简单,运行速度较快,并且可以同时预测多组数据。

新能源经柔直送出系统的次同步振荡分析与抑制

2020年9—10月份,我国华北地区某新能源经柔直送出系统出现了2~6 Hz的持续振荡,导致风电机组频繁脱网和设备损坏。该文利用现场录波数据建立系统等效阻抗网络模型,解释次同步振荡的发生原因。为解决该问题,提出在风电机组变流器控制中嵌入次同步陷波环节的振荡抑制方法,依据实测数据进行参数设计,并进行现场实施与测试。多种工况下的实测结果表明,次同步陷波环节可有效抑制振荡且不影响风电机组的正常运行。该方法易于设计和实现,为解决类似问题提供一种高效实用的方案。

基于匹配控制的构网型直驱风电场次同步振荡机理与特性研究

近年来,具有低时延和惯量同步等优势的匹配控制成为主流构网型控制方案之一,但基于匹配控制的构网型直驱风电场的次同步振荡机理及特性尚不明确。因此,该文建立构网型直驱风电场并网系统的小信号模型,通过特征值法分析了系统的振荡模态及参与因子,并借鉴同步机中阻尼转矩法分析构网型直驱风电场的次同步振荡机理。结果表明,构网型直驱风电场中匹配控制主导的振荡模态在强电网下呈现负阻尼特性,系统存在次同步振荡的风险,但匹配控制振荡模态相较于跟网型控制的锁相环振荡模态具有更好的弱电网适应能力;匹配控制振荡模态存在类似于同步机转子运动方程的动态特性,使得构网型直驱风电场可能发生弱阻尼振荡;减小交流电网强度或无功控制器积分系数,增大构网型直驱风机台数或无功控制器比例系数,能够增大匹配控制振荡模态的阻尼,降低系统次同步振荡风险。

基于功率外环附加阻尼控制的柔性直流抑制送端火电机组次同步振荡研究

利用柔性直流控制的灵活性抑制次同步振荡被广泛研究,但是对于有功、无功控制回路的抑制效果不同的机理解释很少。针对柔直近区火电机组的次同步振荡问题,提出一种基于功率外环附加阻尼控制的柔直抑制次同步振荡策略。通过对电气阻尼曲线负阻尼频段分析,结合柔直变流器控制特点,选取附加控制的最优位置,通过基于功率外环附加阻尼控制提高火电机组电气阻尼。然后,建立复转矩系数传递函数,分析有功、无功外环附加阻尼控制效果的强弱与柔直功率外环参数相关,主要是与传输有功、无功功率大小有关,揭示柔直功率外环d轴和q轴附加阻尼控制时对电气阻尼影响差异的机理。最后,通过PSCAD时域模型仿真验证分析的正确性。

一种多地DFIG联动控制的多馈入受端系统连续换相失败抑制策略

我国沿海负荷中心呈现直流多馈入的结构特征,海上风电的大规模开发使得系统在非正常工况下容易诱发次同步振荡,电压的快速波动可能会造成连续换相。针对该现象进行机理分析,通过优化双馈风电机组(doubly fed induction generator,DFIG)的控制方法,有效抑制了次同步振荡。同时,针对不同区域风电场调节能力差异,通过关联各直流落点的多馈入交互作用因子(multi-infeed interaction factor,MIIF),充分调动不同区域风电场的补偿能力抬升系统电压。该方法有效地抑制直流多馈入系统的异地连续换相失败。最后,通过PSCAD仿真对比验证所提策略的有效性。

SVC抑制SSR的机理及控制器设计

为了能同时有效地消除发电机组的多个不稳定次同步谐振模式,提出了基于SVC的多通道SSR阻尼控制器(MSSRDC)的结构、设计原则和方法。基于相位补偿原理,MSSRDC利用多个独立模式控制通道分别处理发电机组各扭振模式,使SVC能够在发电机组各危险扭振模式附近都能提供正的电气阻尼,从而达到抑制次同步谐振的目的。基于IEEESSR第一标准测试系统的频域和时域仿真表明,根据上述方法设计的MSSRDC能够提高发电机组所需要的正向电气阻尼,达到有效地抑制SSR的目的。

一种构建网络状态空间模型的新方法及其在SSR研究中的应用

在总结输电网接线特点的基础上,给出网络部分状态变量的选取方法及电容支路动态导纳矩阵的定义,并提出一种形成电力系统网络状态空间模型的新方法。该方法无需通过复杂的拓扑分析生成网络常态树即可确定网络的状态变量,无需按照严格的规则对支路和节点进行编号,即可方便地生成网络状态空间模型,且在网络结构变化时网络状态空间模型修改容易,适于进行多机系统的次同步谐振(subsynchronous resonance,SSR)特征值分析。以国内某多机串补输电系统为例,利用文中所提方法分析了系统的SSR特性及静止无功补偿器对其SSR问题的抑制作用,并通过时域仿真验证了所提方法分析结果的有效性。该方法可为火电厂的系统接入方案规划以及SSR抑制措施的设计提供指导和理论支撑。

基于有源阻尼控制的区域电网新能源基地次同步振荡抑制的研究

近年来,由于大规模新能源基地不断接入电网,导致系统转动惯量降低,产生次同步振荡问题。为此,提出了基于有源阻尼的新能源基地次同步振荡抑制策略。该控制策略将有源阻尼控制器附加于新能源并网装置的有功功率环上,通过采集电网频率,实现对振荡频段内的输出信号进行幅值和相位校正,改善系统的次同步阻尼特性,提高系统稳定性。在此基础上对有源阻尼控制器参数进行优化设计,并通过特征根分析法和Prony算法进行验证。最后,以某市区域电网为例进行仿真分析,当该电网出现次同步振荡后,在新能源基地上附加有源阻尼控制,可以快速抑制次同步振荡,提升系统阻尼,验证了有源阻尼控制的适用性和有效性。

TCSC次同步频率阻抗特性及其抑制SSR的参数设计

正确分析TCSC次同步频率阻抗特性是研究TCSC抑制次同步谐振(SSR)能力以及进行TCSC参数设计的重要基础。基于对TCSC次同步频率阻抗模型的研究,绘制了三维频率阻抗图,分析了TCSC次同步频率阻抗特性,特别提出了次同步谐振导通角的概念。基于内蒙古上都电厂串补输电线路模型,在满足工频基波阻抗调节特性的前提下,根据次同步频率阻抗特性研究了考虑TCSC自然抑制SSR时其主电路参数的设计原则。通过对上述系统各模态频率阻抗特性的综合分析,讨论了TCSC控制参数的选择方法。仿真结果证实了次同步频率阻抗特性分析结果的正确性。