A Novel Fuzzy Direct Torque Control System for Three-level Inverter-fed Induction Machine

Diode clamped multi-level inverter （DCMLI） has a wide application prospect in high-voltage and adjustable speed drive systems due to its low stress on switching devices, low harmonic output, and simple structure. However, the problem of complexity of selecting vectors and capacitor voltage unbalance needs to be solved when the algorithm of direct torque control （DTC） is implemented on DCMLI. In this paper, a fuzzy DTC system of an induction machine fed by a three-level neutral-point-clamped （NPC） inverter is proposed. After introducing fuzzy logic, optimal selecting switching state is realized by applying various strategies which can distinguish the grade of the errors of stator flux linkage, torque, the neutral-point potential, and the position of stator flux linkage. Consequently, the neutral-point potential unbalance, the dr/dr of output voltage and the switching loss are restrained effectively, and desirable dynamic and steady-state performances of induction machines can be obtained for the DTC scheme. A design method of the fuzzy controller is introduced in detail, and the relevant simulation and experimental results have verified the feasibility of the proposed control algorithm.

A Virtual Synchronous Machine to Support Dynamic Frequency Control in a Mini-Grid That Operates in Frequency Droop Mode

This paper addresses the problem of dynamic frequency control in a diesel-based mini-grid. It is shown that a virtual synchronous machine (VSM) can support dynamic frequency control by adding virtual inertia and damping to the system. However, it is found that the typical formulation of damping power does not work properly when the grid forming gen-set operates in droop mode because of the unknown stabilization value of the grid frequency. As a solution to this problem, an estimator for the stabilization frequency that works in conjunction with the damping function of the VSM is proposed. Theoretical and experimental results provide evidence of a satisfactory performance of the proposed VSM with estimator for different values of the gen-set droop factor. The estimated stabilization frequency converges in approximately 2 s and the maximum frequency deviation during the transient is reduced in 34%, on average.

Inverted Simulations Demonstrating Strong Ecological Fallacies in Cohort Studies

We start with a description of the statistical inferential framework and the duality between observed data and the true state of nature that underlies it. We demonstrate here that the usual testing of dueling hypotheses and the acceptance of one and the rejection of the other is a framework which can often be faulty when such inferences are applied to individual subjects. This follows from noting that the statistical inferential framework is predominantly based on conclusions drawn for aggregates and noting that what is true in the aggregate frequently does not hold for individuals, an ecological fallacy. Such a fallacy is usually seen as problematic when each data record represents aggregate statistics for counties or districts and not data for individuals. Here we demonstrate strong ecological fallacies even when using subject data. Inverted simulations, of trials rightly sized to detect meaningful differences, yielding a statistically significant p-value of 0.000001 （1 in a million） and associated with clinically meaningful differences between a hypothetical new therapy and a standard therapy, had a proportion of instances of subjects with standard therapy effect better than new therapy effects close to 30%. A ―winner take all‖ choice between two hypotheses may not be supported by statistically significant differences based on stochastic data. We also argue the incorrectness across many individuals of other summaries such as correlations, density estimates, standard deviations and predictions based on machine learning models. Despite artifacts we support the use of prospective clinical trials and careful unbiased model building as necessary first steps. In health care, high touch personalized care based on patient level data will remain relevant even as we adopt more high tech data-intensive personalized therapeutic strategies based on aggregates.

A Hybrid Diagnosis Method for Inverter Open-circuit Faults in PMSM Drives

In order to improve the evaluation process of inverter open-circuit faults diagnosis in permanent magnet synchronous motor(PMSM)drives,this paper presents a diagnosis method based on current residuals and machine learning models.The machine learning models are introduced to make a comprehensive evaluation for the current residuals obtained from a state observer,instead of evaluating the residuals by comparing with thresholds.Meanwhile,fault diagnosis and location are conducted simultaneously by the machine learning models,which simplifies the diagnosis process.Besides,a sampling strategy is designed to implement the proposed scheme online.Experiments are carried out on a DSP based PMSM drive,and the effectiveness of the proposed method is verified.

基于盲源分离和机器学习的光伏并网逆变器故障诊断

针对光伏并网逆变器单个开关管发生开路故障不易察觉的问题,提出了一种基于盲源分离和机器学习的诊断方法。首先,采用FastICA算法实现单个开关管开路故障的判定;其次,提取旋转电流在时域和频域下的特征值;最后,以旋转电流特征值为输入、逆变器工作状态编码为输出进行机器学习模型训练,并对模型进行交叉验证。仿真实验结果表明,该方法的开路故障诊断准确率较高。

基于数据驱动的牵引逆变器电压传感器间歇性故障诊断方法

由于间歇性故障具有随机性与不可预测性,传统的故障诊断方法难以适用于间歇性故障的诊断。为了提高牵引逆变系统的可靠性,文中提出一种针对直流侧电压传感器间歇性故障的智能诊断方法。首先,结合非线性自回归动态网络结构与极限学习机快速挖掘历史数据与异步电机定子电流之间的非线性映射关系,得到牵引电机定子电流预测器;随后,设计滑动时间窗口构建电流残差,检测间歇性故障的出现与消失时间,以此获取表征间歇性故障严重程度的评价指标。所提方法基于快速控制原型实验平台完成实验验证,结果表明,电流预测器对负载突变、速度突变等动态工况具有良好鲁棒性,提出的诊断方法可分别在0.65、0.9 ms内完成间歇性故障出现时间与消失时间的检测,且可准确辨识传感器间歇性故障的早期、中期、晚期阶段,实现了传感器间歇性故障严重程度的评价。

基于谐波注入分段供电永磁直线同步电机变流器开路推力波动抑制

该文提出一种电流谐波注入的方法,减小长定子分段并联供电永磁直线同步电机系统的驱动变流器发生单相开路故障下电机推力波动。首先,根据动子在定子段的位置,推导出分段单元电机的电压方程,得到各个单元电机的推力表达式和系统总推力。然后,依据变流器单相开路前后的全耦合状态下单元电机基波磁动势不变的原则,构造降阶坐标变换矩阵,得到电机的电压方程和推力表达式。采用注入谐波电流、优化故障后直线电机的输出推力的方式,消除变流器单相开路故障产生的4次和6次推力谐波并消除耦合因数变化对电机推力影响;通过多变流器协同控制多单元电机,有效降低变流器单相开路故障后的推力波动,提高电机的最大输出推力。仿真和实验验证该方法的有效性。

基于差模开关振荡的变频电机绕组相端绝缘状态特征提取与解耦

变频电机相端绝缘受脉冲宽度调制高频开关暂态过电压冲击易发生劣化。利用开关振荡谐振效应可望灵敏感知相端绝缘状态的微弱变化,但绝缘状态特征存在多因素高频耦合的问题。为此,该文提出一种基于差模开关振荡的相端绝缘状态特征提取与解耦方法。首先,通过分析变频电机系统开关振荡主导模态,选择高频差模开关振荡作为敏感模态,解耦逆变器功率器件分布电容的影响;然后,通过变分模态分解算法提取多模态开关振荡中的差模频率特征,解耦暂态运行工况下功率器件动态开关时间的影响。最后,利用逆变器侧和电机侧差模开关振荡电流幅值比特征,解耦电缆高频分布参数的影响。在380V/3kW永磁电机变频驱动系统中验证所提方法的有效性,结果表明,所提方法能够灵敏反映电机相端绝缘状态的微弱变化,可以有效解耦逆变器、电缆、运行工况等因素的影响。

基于中性点对地电压高频开关振荡的变频电机绕组内部绝缘在线监测

绝缘状态在线监测是提高变频电机可靠性的有效手段。在高速PWM开关暂态激励下,电机绕组漏感与内部分布电容发生谐振会产生几十至几百k Hz的电压振荡,威胁绕组内部绝缘安全可靠运行。该文利用逆变器自激高频开关振荡在线监测绕组内部绝缘状态。为避免开关振荡多模态混叠并提高状态监测灵敏度,提出一种基于中性点对地电压高频开关振荡的绝缘在线监测方法。首先,分析变频电机共模电压激励特性;然后,研究中性点对地电压高频开关振荡的形成机理与特性,从理论上推导出振荡频率与绕组内部绝缘电容状态之间的关系。设计绕组内部绝缘在线监测方案,包括开关振荡频率提取以及内部绝缘状态评估等。最后,通过热疲劳与老化模拟等实验对该方法的可行性与有效性进行验证。结果表明,该方法能有效监测变频电机内部绕组绝缘状态的微弱变化,具有信噪比高、工况鲁棒等优点。

基于虚拟同步发电机的多机逆变系统稳定性分析

为解决新能源并网逆变系统给电网惯量和阻尼特性带来的问题,虚拟同步发电机技术(VSG)得到广泛应用,但VSG的引入也可能对系统的稳定性带来影响。对此,首先在单机逆变系统小信号模型的基础上建立多机逆变系统小信号模型;然后,分析系统关键参数特征根轨迹,从参数异步变化角度研究目标参数对多机系统整体和各VSG之间高、中、低频稳定性的影响,揭示了多机系统参数的多频段稳定性影响规律,确定了多机系统部分结构和控制参数的稳定裕度。最后,通过仿真试验验证了理论分析的结论。

构网型逆变器同步频率谐振抑制研究

对于高电力电子渗透率的未来,构网型逆变器在电力系统中的稳定运行至关重要。由于不同于传统同步机本身存在的机械转子和阻尼绕组产生的高惯性高阻尼,构网型逆变器可能由于惯性以及阻尼的不足以及耦合引入的负阻尼导致在并网后输出功率存在较为明显的同步频率谐振问题,不仅影响波形质量,严重时甚至导致暂态不稳定。针对该问题举出四种方法并结合伯德图进行分析,最后通过Matlab/Simulink进行仿真验证。

Design of a 35 kV high-temperature superconducting synchronous machine with optimized field winding

This paper proposes the application of high-voltage stator-cable windings in superconducting machines,based on the characteristics of strong magnetic fields and large air gaps.Cross-linked polyethylene cable winding can be employed to achieve a rated voltage of 35 kV in direct-current(DC)-field superconducting machines,thereby enabling a direct connection between the superconducting machine and the power grid,eliminating the need for transformers.We first,through finite element analysis,demonstrate that the proposed high-voltage high-temperature superconducting machine not only meets the requirement of a 35 kV-rated voltage,but also exhibits minimal flux leakage,torque fluctuation,and harmonic distortion.We then compare three candidate types to discuss the tradeoff between the multi-group superconducting field winding arrangement and machine performances.We propose inverted trapezoidal superconducting field winding as a promising candidate,because it has minimal superconductivity material usage,the largest safety margin for the superconducting coils(SCs),low thrust ripple,and low total harmonic distortion with the desired 35 kV-rated voltage.Finally,through large-scale design parameter sweeping,we show how we selected the optimal parameters for field winding and validated them by the finite element method.

造纸机运行状态的自动化监测方案设计

为实现对造纸机压榨部运行故障的准确识别,提升车间生产现场工作人员的管理能力,通过QZ2013-Y型压电式加速度传感器采集造纸机压榨部各部件的振动频率信号,并对所采集到的振动信号实施傅立叶逆变换和开方处理,进而得到压榨部变速箱在X、Y、Z三个方向的振动信号倒频谱,最后根据造纸机的振动信号特征来监测压榨部的运行状态。根据振动信号倒频谱输出结果可知,融合傅立叶逆变换和开方处理的二次频谱分析方法能够较为明显地展示出频率峰值,帮助车间生产管理人员了解压榨部振动状态,具有一定的应用价值。

基于DBN-ELM的构网型并网逆变器控制参数自适应调整方法

“双高”电力系统中电网阻抗呈现宽范围时变特性,构网型并网逆变器控制参数缺乏自适应调整能力,存在失稳风险。对此,提出一种基于深度置信网络-极限学习机的构网型并网逆变器控制参数自适应调整方法。建立闭环极点映射模型,利用深层架构对控制参数与关键极点之间的映射关系进行训练;通过训练好的闭环极点映射模型预测得到相应的关键极点,识别出关键极点最接近参考极点时构网型并网逆变器的控制参数;通过自适应调整控制参数,确保系统在电网阻抗变化时跟踪参考极点,实现自适应稳定控制。理论分析和仿真结果均表明,所提方法能够实现控制参数的自适应调整,有效提高构网型并网逆变器对电网阻抗变化的适应性。

荒漠戈壁光伏发电站施工技术

针对我国西北地区在荒漠、戈壁地带建设太阳能光伏发电站的现状,对施工技术进行了研究,分析了光伏发电站的施工步骤和施工过程的重点难点,提出了关键工序的质量控制点,并给出了相应技术参数。

滇中引水工程现浇仰拱全工序施工装备设计与应用

为实现敞开式TBM掘进与现浇仰拱同步施工,提升现浇仰拱衬砌质量,缩短工程工期,结合长大敞开式TBM水工隧洞现浇仰拱施工边界条件,研制大跨径现浇仰拱全工序施工装备。从功能要求、主桥、支腿、前后爬坡轨、行走系统、仰拱衬砌等方面对现浇仰拱全工序施工装备开展详细设计,提出将主桥行车路面抬高,在主桥下部设置11个长度12 m功能作业区的创新思路,并在现场进行充分验证。工程实践表明:1)全工序现浇仰拱装备主桥支撑系统、行走驱动系统、模板浇筑系统使用效果初步达到设计预期;2)全工序现浇仰拱装备组装效率高、整体移动便捷、与现场施工工序契合度高、人员作业空间大,劳动强度低,施工进度最高可达到240 m/月,有效提升了TBM施工现浇仰拱技术的发展水平;3)全工序施工装备作为水工隧洞全新的工装,开创了新的施工工艺。但是该装备使本来狭窄的隧道显得更为拥挤,掘进施工交通流量受限,导致浇筑混凝土、钢筋、轨排的运输与TBM掘进物料运输之间的矛盾逐步显现,保障施工通道和TBM掘进有效进度匹配性的问题有待进一步研究。

基于PWM开关高频振荡的变频电机轴承故障诊断

为了解决传统变频电机轴承故障诊断方法易受到低频噪声和基频电流干扰的问题,提出了一种利用脉冲宽度调制(PWM)开关高频振荡进行变频电机轴承故障诊断的新方法。首先,分析了变频电机轴承故障诊断的机理以及轴承电流的产生机理和流通路径,并用仿真验证了PWM开关dv/dt轴承电流对轴承故障状态敏感;然后,利用PWM开关dv/dt轴承电流是地线电流的一个分量,将地线电流中的高频振荡信号作为故障诊断特征变量和数据源;最后,设计了一种用于电机轴承故障诊断的轻量级一维卷积神经网络模型,用于特征提取和故障分类。实验结果表明,该方法的准确率达到了96.63%,能够准确诊断变频电机轴承故障。

基于FrFT-CNN的变频电机匝绝缘状态监测

定子绕组匝绝缘劣化是导致变频电机故障的主要原因之一。通过在线监测其状态,可以及时发现潜在的安全隐患,但会面临匝绝缘劣化特性微弱的挑战。为了提高匝绝缘劣化灵敏度,提出了一种利用分数阶傅里叶变换结合卷积神经网络(FrFT-CNN)的变频电机匝绝缘状态监测方法。首先,在分数域内分析了高频开关振荡电流对匝绝缘变化的灵敏性。然后,设计了一种适用于变频电机匝绝缘状态监测的一维卷积神经网络模型。实验结果表明,与传统卷积神经网络方法相比,FrFT-CNN方法显著提高了匝绝缘状态监测的准确率,且兼具稳定性较高的优点。

基于PLC的龙门往复式洗车机系统设计

随着生活质量的提高,洗车也逐渐实现自动化。针对市场上已有的洗车设备存在机械设备复杂、成本高、浪费水资源等问题,以PLC为控制中心,结合变频器技术、传感器技术和气动技术,利用人机界面进行系统参数设置和工作状态检测,完成了龙门往复式洗车机系统的设计,具有一定的推广价值。

逆变焊割设备的研发与创新

探讨上海烽火焊机有限公司在逆变焊割设备领域的研发与创新路径,以及其在市场推广和用户培训方面所取得的成就,以此展示公司在该领域的实力和前瞻性思维。首先介绍了上海烽火焊机有限公司主导产品,包括逆变直流手工弧焊机、逆变氩弧焊机、逆变半自动气体保护焊机和逆变空气等离子切割机焊接小车。随后,阐述了公司在逆变焊割设备研发过程中的技术创新、市场需求调研、产品设计、严格测试和验证等方面的策略和方法。