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.

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.

Research on the Sub-synchronous Oscillation in Wind Power Connected to Series Compensated Power System and its Influencing Factors

When wind farms,which is based on double fed induction generator(DFIG),are connected to the series compensation power system,the phenomenon of sub-synchronous oscillation(SSO)may occur.In order to study the sub-synchronous oscillation in wind power connected to series compensated power system and its influencing factors,we used RT-LAB to establish a simulation model concerning wind power connected to series-compensation power system.This model take a wind power connected to series compensation power system in north China as prototype.All influence factors of wind power SSO are simulated and analyzed by using time domain analysis method.The simulation results show that the effects of wind speed,series compensation degree and proportional control coefficient of rotor side converter(RSC)are most obvious.

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.

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.

Characteristics of sub-synchronous oscillation in grid-connected wind farm system

With the rapid development of wind power, wind turbines are accompanied by a large quantity of power electronic converters connected to the grid, causing changes in the characteristics of the power system and leading to increasingly serious sub-synchronous oscillation (SSO) problems, which urgently require the generalized classification and characterization of the emerging oscillation problems. This paper classifies and characterizes the emerging types of SSO caused by grid-connected wind turbines to address these issues. Finally, the impact of the typical system parameters changes on the oscillation pattern is analyzed in depth to provide effective support for the subsequent suppression and prevention of SSO.

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.

HVDC输电系统次同步振荡(SSO)分析的GUI实现

为提高研究效率并普及研究结果,开发了一个用于分析HVDC输电系统次同步振荡(SSO)特性的图形用户界面(GUI)软件。这个GUI软件由人机界面及相关的回调函数组成,其中人机界面是利用MATLAB的GUI工具设计的,而编写回调函数则利用了MATLAB的数值计算和数据可视化功能。实践表明在MATLAB环境下可容易、高效地开发出令人满意的GUI软件。通过GUI软件可实现SSO参数稳定域可视化分析及特征值分析和时域仿真分析,具有直观、方便的优点,适合广大技术人员对HVDC输电系统发生SSO失稳可能性的检验。

宁夏多直流外送系统SSO特性分析及次同步阻尼控制器设计

针对宁夏电网近电气距离耦合的火电机群与多直流输电的简化等值送端系统,利用基于复频域端口等效导纳矩阵的复转矩系数法对其进行次同步振荡(SSO)特性分析。研究表明,降低宁夏电网直流输电外送功率,加强宁夏电网送端交流系统,增强直流换流站之间电气耦合强度等均有利于改善系统SSO阻尼特性。其次,针对存在SSO风险的灵武二期电厂机组,开展直流输电附加次同步阻尼控制器设计,并通过仿真证明了其有效性。该文研究成果可为宁夏电力外送系统的运行、规划及SSO抑制提供技术支撑和参考。

多HVDC输电系统SSO抑制措施的协调控制研究

近年来,HVDC输电系统引起的次同步振荡(SSO)现象引起了众多专家学者的重视,附加次同步阻尼控制器(SSDC)是目前较为普遍的抑制措施。故以贵州电网多HVDC交直流混合输电系统为背景,对SSDC的协调控制问题进行了较为深入的探索。理论分析和大量仿真验证表明,SSDC和附加次同步励磁控制器(SEDC)提供的电气阻尼是解耦的,可以分别进行整定。而对配置在不同直流线路换流站处的多台SSDC进行整定时,协调控制是十分必要的。同时,随着通信技术的不断发展,取发电机组转速作为SSDC的输入信号会达到更理想的抑制效果。

基于深度残差网络的SSO模态参数辨识

针对电力系统正常运行中的微弱次同步振荡信号趋势难以辨识,辨识算法抗噪性差、辨识结果可靠性低等问题,提出一种基于深度残差网络的次同步振荡模态参数辨识方法。建立了一种由卷积层、若干残差层和全连接层等构成的深度残差网络模型;模型训练数据集依据SSO信号特点生成,全部采用仿真数据;经参数调整和优化后的模型能够实现对现场实测的低信噪比SSO信号模态参数的盲辨识。利用理想信号、含噪仿真信号和现场实测数据3种方案对模型性能验证,结果表明该算法能有效地辨识出微弱SSO的频率和阻尼等关键参数,与卷积神经网络(CNN)和随机子空间(SSI)算法相比较,辨识精度更高,受噪声干扰小,具有盲辨识的特点,可用于电力系统次同步振荡风险的预警。

Simulation and study on mitigation measures of frequent subsynchronous oscillation with low amplitude at multi-power plants

Subsynchronous oscillation (SSO) with low amplitude that exceeds cumulative fatigue threshold of the generator shaft frequently could significantly reduce the shaft's service life, which is a new SSO problem that emerges in recent years. According to the real recording oscillograph, the basic reason for frequently over-threshold SSO with low amplitude at multi-power plants was analyzed based on Hulunbuir League system. The sensitivities of the electrical damping to the main electrical parameters in the contributing loop of subsynchronous torsional interaction were calculated. Based on the sensitivities, a simulation method was presented, which was used to excite the same oscillation as the actual case by exerting disturbance on the firing angle. The limitation of wide-band and narrow-band supplementary subsynchronous damping controller (SSDC) for mitigating this kind of SSO was analyzed based on the electromagnetic transient simulation model of Hulunbuir League system. The difference of supplementary excitation damping controller (SEDC) and parallel-form FACTS connected to the generator terminal was compared from the aspects of response time and the ability of damping torque supplying. The analysis indicates that their response time is similar but FACTS has stronger ability of damping torque supplying than SEDC. Time-domain simulation method was used to compare the mitigation effects of SEDC, static var compensator (SVC) and static synchronous compensator (STATCOM). Considering the mitigation effect, the floor space limit of the power plant and so on, STATCOM was considered as the best mitigation measure. A control strategy of cascaded STATCOM for engineering application was presented and the capacity for SSO mitigation as well as output characteristics was analyzed. The analysis indicates that STATCOM using the proposed control strategy has better mitigation effect and output characteristics with smaller capacity.

发电厂次同步振荡(SSO)问题的解决方法

当直流换流站发生单极或双极闭锁时,靠近直流换流站的发电机组就极有可能产生次同步振荡(SSO),这就迫切需要引入发电机轴系扭振保护(TSR)装置和SEDC装置来用于解决次同步振荡(SSO)引发的轴系扭振,避免造成轴系某些部件如联轴器断裂或疲劳损坏,保证机组和电网的安全运行。

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。