Electromagnetic Performance Prediction for the Symmetrical Dual Three-phase Surface-mounted PMSM under Open-phase Faults Based on Accurate Subdomain Model

The paper presents an accurate analytical subdomain model for predicting the electromagnetic performance in the symmetrical dual three-phase surface-mounted permanent magnet synchronous machine(PMSM)under open-phase faulty conditions.The model derivations are extended from previous accurate subdomain models accounting for slotting effects.Compared with most conventional subdomain models for traditional three-phase machines with nonoverlapping winding arrangement,the subdomain model proposed in this paper applied for the 24-slot/4-pole dual three-phase machine with symmetrical overlapping winding arrangement.In order to investigate the postfault electromagnetic performance,the reconfigured phase currents and then current density distribution in stator slots under different open-circuit conditions are discussed.According to the developed model and postfault current density distribution,the steady-state electromagnetic performance,such as the electromagnetic torque and unbalanced magnetic force,under open-circuit faulty conditions are obtained.For validation purposes,finite element analysis(FEA)is employed to validate the analytical results.The result indicate that the postfault electromagnet performance can be accurately predicted by the proposed subdomain model,which is in good agreement with FEA results.

Coordinated Rotor-Side Control Strategy for Doubly-FedWind Turbine under Symmetrical and Asymmetrical Grid Faults

In order to solve the problems of rotor overvoltage,overcurrent and DC side voltage rise caused by grid voltage drops,a coordinated control strategy based on symmetrical and asymmetrical low voltage ride through of rotor side converter of the doubly-fed generator is proposed.When the power grid voltage drops symmetrically,the generator approximate equation under steady-state conditions is no longer applicable.Considering the dynamic process of stator current excitation,according to the change of stator flux and the depth of voltage drop,the system can dynamically provide reactive power support for parallel nodes and suppress the rise of DC side voltage and rotor over-current.When the grid voltage drops asymmetrically,the positive and negative sequence components are separated in the rotating coordinate system.The doubly fed generator model is established to suppress the rotor positive sequence current and negative sequence current respectively.At the same time,the output voltage limit of the converter is discussed,and the reference value is adjusted within the allowable output voltage range.In order to adapt to the occurrence of different types of power grid faults and complex operating conditions,a fast switching module of fault type detection and rotor control mode is designed to detect the type of power grid faults and voltage drop depth in real time and switch the rotor side control mode dynamically.Finally,the simulation model of the doubly fed wind turbine is constructed in Matlab/Simulink.The simulation results verify that the proposed control strategy can improve the low-voltage ride through performance of the system when dealing with the symmetrical and asymmetric voltage drop of the power grid and identify the power grid fault type and provide the correct control strategy.

Analysis on the fault characteristics of three-phase short-circuit for half-wavelength AC transmission lines

Half-wavelength AC transmission(HWACT) is an ultra-long distance AC transmission technology, whose electrical distance is close to half-wavelength at the system power frequency. It is very important for the construction and operation of HWACT to analyze its fault features and corresponding protection technology. In this paper, the steady-state voltage and current characteristics of the bus bar and fault point and the steady-state overvoltage distribution along the line will be analyzed when a three-phase symmetrical short-circuit fault occurs on an HWACT line. On this basis, the threephase fault characteristics for longer transmission lines are also studied.

Power Network Asymmetrical Faults Analysis Using Instantaneous Symmetrical Components

Although the application of Symmetrical Components to time-dependent variables was introduced by Lyon in 1954, for many years its application was essentially restricted to electric machines. Recently, thanks to its advantages, the Lyon transformation is also applied to power network calculation. In this paper, time-dependent symmetrical components are used to study the dynamic analysis of asymmetrical faults in a power system. The Lyon approach allows the calculation of the maximum values of overvoltages and overcurrents under transient conditions and to study network under non-sinusoidal conditions. Finally, some examples with longitudinal asymmetrical faults are illustrated.

SYMMETRICAL SISF IN DEFORMED Ni_3Al AND ITS FORMATION MECHANISM

The symmetrical superlattice intrinsic stacking faults(SISFs)formed on {111} planes are the predominant crystal defects in polycrystalline Ni_3AI after slight deformation at room temper- ature.The formation of this kind of SISF is resulted from the dipoles which are distributed on the neighboring {111} planes after reorientation,dissociation and annihilation under applied stress.

基于SDP和MCNN-LSTM的齿轮箱故障诊断方法

齿轮箱在长期使用过程中,不可避免地会产生齿轮故障和轴承故障,严重影响传动精度和设备运行安全。基于此,针对齿轮箱常见故障类型,研究多通道对称点图案(symmetrized dot pattern, SDP)数据处理方法,并利用最小能量误差法实现SDP关键参数的选取。结合多尺度卷积神经网络(multi-scale convolutional neural network, MCNN)的空间处理优势、长短时记忆网络(long short term memory, LSTM)的时间处理优势及其良好的抗噪性和鲁棒性,提出了一种基于SDP和MCNN-LSTM的齿轮箱故障诊断模型。同时利用东南大学齿轮箱数据集,验证了基于SDP和MCNN-LSTM的齿轮箱故障诊断方法对齿轮和轴承常见故障类型特征提取的有效性,并与现有其他故障诊断方法进行对比,结果表明了所提方法具有更高的精度。

基于EMD-SDP图像特征和改进DenseNet车用PMSM故障诊断

永磁同步电机(permanent magnet synchronous motor,PMSM)因转速范围宽、输出转矩大、调速响应快、尺寸小、质量轻等优点被广泛应用于电动汽车驱动系统。受恶劣气候、异常振动和频繁起动-制动工况因素影响,PMSM易发生匝间短路、退磁、轴承磨损等故障。本文针对PMSM相似故障单一维度信号下难区分以及工作条件发生变化时传统诊断方法鲁棒性差的问题,提出了一种基于经验模态分解-对称点模式(empirical mode decomposition-symmetric dot pattern,EMD-SDP)图像特征和改进DenseNet相结合的车用永磁同步电机故障诊断方法。首先,通过实验获取不同状态的电机在多种工况下振动信号,将预处理的振动信号进行EMD处理,求解不同层级本征模态函数(intrinsic mode function,IMF);其次,将原始振动信号转化为SDP图像,对不同层级IMF转化为RGB色彩特征在SDP图像上显示出来;然后,通过融合scSE注意力机制改进DenseNet学习图像数据集构建分类网络模型;最后,按照信号-图像-网络的流程对待测电机状态进行评估与诊断。诊断结果表明:所提出的方法在稳态和变速瞬态工况下均表现良好的性能。在恒速恒载工况下,所提的方法达到最高的故障诊断准确率(99.72%),相比基准的DenseNet的准确率(98.06%)提升了1.66个百分点。改进后的DenseNet模型和DenseNet模型的ROC曲线最接近左上角,AUC均值分别为0.9974和0.9745;在加速恒载和减速恒载工况下,改进后的DenseNet模型也达到了最高的诊断准确率,分别为96.88%和97.08%。AUC均值分别为0.9877和0.9869。本文所提出的方法的总体性能优于传统方法,能有效地用于速度变化时的故障诊断。

基于SDP和改进SAM⁃MobileNetv2的滚动轴承故障诊断方法研究

针对传统的滚动轴承故障诊断方法难以准确高效的实现故障分类,提出了一种融合对称点模式(Symmetrized Dot Pattern,SDP)和改进SAM⁃MobileNetv2的滚动轴承故障分类方法。首先,将轴承振动信号通过SDP算法转化为含有丰富特征信息的二维图像。然后,将二维图像输入到改进SAM⁃MobileNetv2网络模型中,对故障特征信息进行提取和分类。在改进SAM⁃MobileNetv2网络中,使用自适应激活函数ACON(Activate or not)对SAM⁃MobileNetv2中的ReLU6激活函数进行替换,提高模型分类性能。最后,将本模型与多种网络模型做对比。试验结果表明,本模型可以准确高效地实现对滚动轴承故障的分类,使用凯斯西储大学轴承故障数据的准确率为99.5%,使用渥太华大学轴承故障数据的准确率为97.2%。

基于对称分量法的调相机定子故障特征分析

传统同步调相机定子绕组匝间短路故障机理分析方法通常认为电机定子电流接近三相对称,并以此为基础建立同步调相机故障电流的数学表征。但是,一旦发生定子绕组匝间短路故障,同步调相机三相定子电流的对称性将遭到破坏,使得传统故障机理分析方法所建立的数学表征无法准确反映电机内部电气量的变化。文中通过引入对称分量法,建立故障后同步调相机瞬时有功/无功功率的数学模型,提出利用瞬时有功/无功功率中的2次谐波进行定子绕组匝间短路故障诊断。仿真和实验的结果表明:相较于利用定子电流3次谐波与基波幅值之比诊断故障的传统方法,文中方法在轻微故障状态下能提高至少7倍的诊断灵敏度,更易完成早期故障诊断。同时,所提方法中的故障特征量不受同步调相机工况和故障位置的影响,具有强鲁棒性。

基于负序分量的含光伏电源配电网故障区段定位方法

针对光伏电源接入配电网导致故障电流无法正确反映故障区段的问题,分析含光伏电源配电网故障时三序分量,选择负序分量作为故障特征量;对于不对称故障场景提出负序重构方案;采用曼肯德尔(Mann-Kendall,MK)趋势检测寻求故障特征最明显的负序重构序列;利用负序重构电压幅值确定可疑故障区段,结合负序重构电流相位方向确定故障区段。在PSCAD/EMTDC仿真平台搭建含光伏电源的配电网模型。结果表明:提出的方法能够实现含光伏电源配电网在不同故障类型、故障位置下的故障区段准确定位,为含光伏电源配电网快速故障定位提供了理论依据。

基于空间域图像生成和混合卷积神经网络的配电网故障选线方法

传统的配电网故障选线方法大多基于一维零序电流序列构建故障诊断模型,单一的诊断模型往往限制了故障特征的深层挖掘。为了提高故障选线的准确率,提出一种基于空间域图像和混合卷积神经网络的配电网故障选线方法。首先,利用优化的降噪光滑模型对零序电流信号进行降噪处理,减少外界环境的电磁干扰。其次,利用对称希尔伯特变换将一维时域信号转成二维空间域图像,图像的颜色、形状和纹理特征能够充分反映当前系统的运行状态。最后,将一维时域信号和二维空间域图像同步作为混合卷积神经网络的输入,充分挖掘系统的故障特征,利用Sigmoid函数实现故障选线。在辐射状配电网、IEEE-13节点模型、IEEE-34节点、StarSim仿真平台上模型上进行了实验验证。实验结果表明,该选线方法可以有效克服传统方法过度依赖主观特征选择、抗噪性能差等问题,能够在高阻接地、采样时间不同步、两点接地故障等极端情况下可靠地筛选出故障线路。

受端电网故障下真双极柔性直流输电系统电压协同控制方法

盈余功率积累可能诱发基于模块化多电平换流器的高压柔性直流输电系统(high-voltage direct current based on the modular multilevel converter,MMC-HVDC)过压闭锁,乃至引发海上风电场机组失步或受端电网低频减载。现有降压或升频等直流电压控制方法仅针对伪双极接线,缺乏讨论不同控制模式的换流器间协同原则;且控制参考值未能自适应受端电网的故障严重程度,导致海上风电场有功功率调节过量。该文基于受端电网故障下MMC-HVDC平均值模型,解析了海上正负极换流器和风电场的功率耦合特性,提出了交流母线电压控制极换流器平衡换流站间有功功率,有功和无功功率控制极换流站抑制极间不平衡的协同原理。通过解析海上风电场在交流母线电压控制极换流器降压作用下的功率外特性,提出了恰好避免直流电压越限的临界交流母线电压计算方法。通过解析使得受端换流站有功电流受限的交流母线电压作为启动门槛,提出了受端电网故障下真双极MMC-HVDC电压协同控制方法。理论分析和仿真结果表明,所提方法令海上正负极换流器分别运行于临界交流母线电压和抑制极间不平衡的有功功率,可在避免直流电压越限的前提下,最大限度提升MMC-HVDC在受端电网故障工况下的有功功率传输能力。

计及电压幅值检测延时及相位跳变的IIDG故障电流解析计算

逆变型分布式电源(inverter interfaced distributed generation,IIDG)的波动性、弱馈性及强受控性,使其在故障下具有与同步发电机不同的短路电流特性,对其进行准确解析是继电保护适应性分析与保护新原理研究的基础,具有重要意义。针对现有研究忽略电压幅值检测延时导致IIDG故障特性难以准确解析的问题,以新能源送出线路发生三相短路为例,综合考虑电压幅值检测延时以及相位跳变所引起锁相环动态响应特性的影响,对IIDG故障暂态过程进行精细化划分,分别针对故障暂态过程的2个阶段,建立了电压电流双环控制和电流环控制下的故障电流解析表达式,明确了电压检测延时与锁相环动态响应对IIDG故障电流暂态特性的影响机理。最后,基于Matlab/Simulink仿真平台,验证了所提故障电流解析计算模型的正确性。

Fault-tolerant stator flux oriented decoupling control for dual three-phase permanent magnet motor without diagnosis and reconfiguration

In this paper,the fault-tolerant capability of the existing stator-flux-oriented decoupling control(SFOC)for the DTP-PM motor is investigated,and a simple fault-tolerant SFOC is further designed to enhance fault tolerance.Firstly,the mathematical model of the DTP-PM motor in the stator-flux-oriented rotating coordinate system is analyzed.An SFOC is proposed to guarantee healthy operation performance,considering torque,flux linkage,and harmonic currents.Secondly,the coupling relationship under open-phase conditions is assessed.The assessed result shows that the coupling relationship between the harmonic and fundamental components results in conflicts and poor post-fault operation.Thirdly,the proposed SFOC includes an automatic deactivation module to detect conflicts with a variable threshold.The conflicted harmonic current controllers can be excluded automatically.Hence,fault-tolerant control can be remedied without diagnosing the specific fault scenario,and excellent faulttolerant capability can be achieved.Finally,experiments on a DTP-PM motor are carried out to verify the feasibility and effectiveness of the proposed strategy.

Open-circuit fault diagnosis and fault tolerance for shunt active power filter

The open-circuit fault of the power switches in shunt active power filter(SAPF) would exacerbate the harmonic pollution of power grid, and degrade the reliability of the devices and system. A fault diagnosis method is proposed based on reference model and an over-modulation strategy under hardware fault tolerance for SAPF. First, a mathematic model is established for SAPF. Second, the residuals are generated by comparing the outputs of reference model and those of actual model, and open-switch fault is detected and diagnosed by residual evaluation. After that, hardware fault tolerance is performed with the three-phase four-switch(TPFS) topology to isolate the faulty phase. Finally, the over-modulation strategy is proposed to increase the voltage transfer ratio of the TPFS topology. Simulation and experimental results verified the feasibility and effectiveness of the proposed method.

Characteristics of piecewise linear symmetric tri-stable stochastic resonance system and its application under different noises

Weak signal detection has become an important means of mechanical fault detections. In order to solve the problem of poor signal detection performance in classical tristable stochastic resonance system(CTSR), a novel unsaturated piecewise linear symmetric tristable stochastic resonance system(PLSTSR) is proposed. Firstly, by making the analysis and comparison of the output and input relationship between CTSR and PLSTSR, it is verified that the PLSTSR has good unsaturation characteristics. Then, on the basis of adiabatic approximation theory, the Kramers escape rate, the mean first-passage time(MFPT), and output signal-to-noise ratio(SNR) of PLSTSR are deduced, and the influences of different system parameters on them are studied. Combined with the adaptive genetic algorithm to synergistically optimize the system parameters, the PLSTSR and CTSR are used for numerically simulating the verification and detection of low-frequency, high-frequency,and multi-frequency signals. And the results show that the SNR and output amplitude of the PLSTSR are greatly improved compared with those of the CTSR, and the detection effect is better. Finally, the PLSTSR and CTSR are applied to the bearing fault detection under Gaussian white noise and Levy noise. The experimental results also show that the PLSTSR can obtain larger output amplitude and SNR, and can detect fault signals more easily, which proves that the system has better performance than other systems in bearing fault detection, and has good theoretical significance and practical value.

考虑故障限流的VSG暂态功角稳定控制方法

当电网发生严重故障时,虚拟同步发电机(VSG)易发生功角失稳并导致故障电流越限,现有方法大多忽略功角失稳与故障过流之间的内在关联性而将二者单独处理,导致二者难以同时解决.为此,分析了VSG的暂态功角特性和故障电流特性,阐释了产生上述问题的原因及相互关系;基于相图理论分析了多影响因素下VSG的暂态功角稳定性,提出了一种考虑故障限流的VSG暂态功角稳定控制方法,该方法在自适应调节有功功率指令以保持功角稳定的基础上联合调节无功调压系数,并引入准静态近似虚拟阻抗,同时实现了故障期间VSG的暂态功角稳定和全故障限流.仿真和实验结果验证了理论分析的正确性及所提控制方法的有效性.

基于反步自适应准谐振控制的双馈风机次同步振荡抑制策略

随着电力系统容量和规模的不断扩大,常采取串补电容的方式提升输电线路的输电能力,但这加剧了电力系统中出现次同步振荡(SSO)的风险。SSO的产生会影响双馈感应发电机(DFIG)转子侧变流器(RSC)的控制,进而引起定子电流的振荡发散,严重时将会导致风机解列脱网。因此,为解决SSO对RSC控制产生扰动的问题,该文提出了基于自适应准谐振控制的RSC反步次同步振荡抑制策略。首先对SSO在RSC控制系统中的传播路径及其频率变化对控制的影响等内容展开研究;然后通过反步控制器与自适应准谐振控制器的协同控制,对DFIG定子中宽频带SSO电流进行抑制,避免发电系统输出受到SSO的影响;最后通过搭建仿真模型与实验平台,验证所提理论与控制策略的有效性。该文分别对在10 Hz、20 Hz、30 Hz及频率变化时SSO影响下的DFIG定子振荡电流抑制效果进行验证。实验结果表明,所提策略对DFIG系统中宽频带SSO具有良好的抑制效果。

基于参数优化SDP分析的转子故障诊断方法

针对存在多种故障类型不同故障严重程度的转子故障诊断问题,提出了一种基于参数优化对称点模式(symmetrized dot pattern,SDP)分析的智能诊断方法。首先,利用SDP分析提取多个传感器信号的故障特征并将其融合为SDP图像;然后,以基于欧氏距离定义的图像区分度函数为适应度函数,基于天牛须搜索(beetle antennae search,BAS)算法获得SDP分析中角域增益因子与时间延滞系数的最佳取值;最后,利用SDP图像训练卷积神经网络(convolutional neural network,CNN)获得转子故障诊断模型。试验研究表明,该方法相较于其他故障诊断方法具有更高的诊断精度,且在强噪声环境下的诊断表现良好。基于BAS算法优化后的SDP分析放大了不同类型不同严重程度转子故障的表征差异,提高了故障诊断精度。

离心泵故障诊断的对称极坐标变换和图像形状特征方法

针对基于时频变换图像特征的机械故障诊断方法耗时长、诊断精度不高等问题,提出基于对称极坐标变换和图像形状特征的离心泵故障诊断新方法。该方法以对称极坐标变换(Symmetrized Dot Pattern,SDP)为基础,通过简单的公式将一维振动信号转换为二维极坐标下的对称花瓣图像,而后进行对称花瓣图像的形状特征提取,以此作为离心泵故障特征,实现离心泵故障诊断。SDP方法计算简单,且故障辨识度高,因此可以在耗时更短的情况下得到更高的故障诊断精度。离心泵故障诊断实例表明,所提方法诊断精度更高,耗时更短。为离心泵的故障诊断提供一种新方法。