Detection of fatigue in the isometric electrical activation of paralyzed hand muscles of persons with tetraplegia.

Paralyzed muscle fatigue is the eventual depression of force due to either prolonged or repetitive electrical stimulation of motor units. The robustness and safety of future functional electrical stimulation (FES) systems will rely on their ability to detect the onset of muscle fatigue. The relative degree of muscle activation can be estimated by monitoring the M-wave. The aim of this study was to test a proposed method of quantitative fatigue assessment that detects muscle force output and its corresponding M-wave measured concurrently. The detection of force and M-wave concurrently allows any reduction in muscle force output to be attributed to either changes in the fatigue state of the stimulated muscle or changes in the degree of stimulus activation of that muscle. The fatigue assessment scheme can thereby accommodate the corresponding changes in muscle force caused by an alteration in the stimulation intensity during fatigue. The Extensor Digitorum Communis (EDC), Extensor Pollicis Longus (EPL), and Flexor Pollicis Longus (FPL) muscles of two C5/C6 tetraplegic men were studied. Stimulation recruitment tests over the pulsewidth range from 0 to 200 micros, were performed at intervals during 20 min of maximal stimulation (200 micro/s). Muscle force correlated to the M-wave parameter, second phase area, with mean correlation coefficients of greater than 0.82, when the muscle was in either a nonfatigued or fatiguing state. After the initial force, likely to be primarily due to the fast glycolytic (FG) motor units, had declined the M-wave demonstrated only minor changes throughout the fatigue of muscle force during 20 min of constant maximal stimulation. The second phase area and root-mean-square (rms) of the M-wave [see Fig. 2(a) reflected muscle activation during modulated stimulation and also remained relatively constant during the fatigue-related force decline when the muscle was stimulated at a constant intensity. This detection of M-wave parameters satisfies the defined requirement for a myoelectric parameter that indicates electrical activation, but is relatively invariant to muscular fatigue. Index Terms-Electrical stimulation, electromyography (EMG), functional electrical stimulation (FES), muscle fatigue, spinal cord injury, tetraplegia.     

Stimulation artifact in surface EMG signal: effect of the stimulation waveform, detection system, and current amplitude using hybrid stimulation technique

The purpose of this study was to investigate the amplitude properties of the artifact generated on the recorded surface electromyography (EMG) signals during transcutaneous electrical muscle stimulation. The factors which were investigated are the shape of the stimulation waveform, the distance of the stimulating electrode from the recording system, the interelectrode distance of the detection system, the spatial filter used for signal detection, and the stimulation current amplitude. Surface EMG signals were recorded during electrical stimulation of the biceps brachii motor point with a linear adhesive array of eight electrodes. Electrical stimulation was applied with seven stimulation waveforms (mono- and biphasic triangular, sinusoidal, and rectangular), generated by a specifically designed neuromuscular stimulator with hybrid output stage. The stimulation peak current was linearly increased from 0 mA to the maximum tolerated by the subject. The detection systems investigated were single and double differential with interelectrode distances multiple of 5 mm. Two trials for each contraction were performed on three different days. The average rectified artifact values (both absolute and normalized with respect to the corresponding M-wave values) were computed to investigate the artifact amplitude properties. Results indicated that, while the artifact average rectified value, normalized with respect to the M-wave amplitude, depended on the distance of the detecting electrodes from the stimulation point, it did not depend on the stimulation waveform, on the current intensity, on the interelectrode distance, and on the spatial filter. It was concluded that, using hybrid stimulation techniques, the selection of particular stimulation waveforms, interelectrode distances, or spatial filters has a minor effect on the reduction of the artifact when recording M-waves.     

Muscle recruitment through electrical stimulation of the lumbo-sacral spinal cord.

The goal of this study was to determine the feasibility of producing graded muscle contraction in individual muscles or muscle groups by electrically stimulating motor neurons in the lumbo-sacral spinal cord. Recruitment curves were obtained for quadriceps, tibialis anterior and triceps surae/plantaris by stimulating their activation pools in the ventral horn of the feline spinal cord. Mean twitch times-to-peak for quadriceps, tibialis anterior and triceps surae/plantaris were 33.0, 41.0, and 36.0 ms, respectively. Twitch duration as a function of stimulus strength demonstrated a mixed motor unit recruitment order, distinctively different from the inverse recruitment order exhibited by conventional methods of electrical stimulation of peripheral nerve. The recruitment curve slopes (expressed as a percentage of maximum force per nanocurrent of delivered charge) were shallow: 7.9 for quadriceps, 2.6 for tibialis anterior and 8.5 for triceps surae/plantaris. These results show that graded control of force in individual muscles or muscle groups can be obtained through spinal cord stimulation, and suggest that spinal cord stimulation could be used for functional neuromuscular stimulation applications.     

基于电压时间序列的电力系统暂态电压稳定分析

基于实时获取的广域测量信息,提出一种利用机端电压幅值偏差序列的最大Lyapunov指数指标（LLE）与机端电压幅值序列相结合的暂态电压稳定判别方法。基于无需系统模型的LLE计算方法,建立LLE与机端电压幅值偏差序列的数学关系,根据最大Lyapunov指数曲线运动的轨迹特征,以及机端电压幅值变化率-电压幅值偏差（[Vmagcr-ΔVmag]）特性曲线的运动趋势,提出一种基于LLE与机端电压幅值偏差率的暂态电压稳定判据。针对多机系统,本文提出基于临界机组对的暂态电压稳定判别方法。将本文所提方法在IEEE10机     

基于宽频传感技术的高压电机能效计量检测平台建设及关键技术研究

为满足对高压三相异步电动机能源效率的准确计量,使其满足高压高效电机的能效计量检测要求,研究分析了高压电机能效计量检测的关键技术难点和解决方案,并基于损耗分析法建设了高压电机能效计量试验平台。文章系统阐述了基于宽频功率测量系统的能效计量检测平台组成,克服了传统方式中宽频信号采集难、稳定性差、准确度不高等问题,采用了宽频测试和数字光纤传输,有效提升了各频带信号采集、分析处理、传输以及抗电磁干扰能力,极大降低损耗。平台通过变频数字电源和光纤传输、全自动化操作和人机互动界面,实现频率覆盖1Hz-1kHz,额定功率为2MW以下高压电机能效计量检测,以两表法进行了测试系统量值溯源分析并进行平台验证试验,结果表明平台的测量不确定度和技术参数满足国家能效计量检测要求,具有较好的先进性和开放性。     

Multi-objective Phasor Measurement Unit Placement in Electric Power Networks: Integer Linear Programming Formulation

A multi-objective optimal phasor measurement unit placement model using integer linear programming is presented in this article. The proposed model simultaneously optimizes two objectives, i.e., minimization of phasor measurement unit numbers and maximization of measurement redundancy. To calculate the redundancy criteria, the single-line outage and the phasor measurement unit loss are considered simultaneously. A linear formulation is presented for both objective functions. Also herein, to address conflicting attributes and identify Pareto optimal solutions of the multi-objective optimal phasor measurement unit placement problem, a new multi-objective mathematical programming method is proposed. Finally, a new index, i.e., minimum distance to utopia point, is implemented to select the most preferred solution among the available Pareto front based options on the goal to achieve judicious decision makers. Two test systems, i.e., a modified 9-bus and an IEEE 118-bus test systems, are used to illustrate the effectiveness of the proposed framework.     

A simulation study of reflex instability in spasticity: origins of clonus.

Clonus is defined as an involuntary rhythmic muscle contraction that generally occurs in people who have sustained lesions involving descending motor pathways in the neuraxis, and is usually accompanied by other signs of reflex hyperexcitability such as spasticity. This paper hypothesizes that clonus arises when two conditions occur simultaneously: 1) the reflex pathway contains long delay times (implying innervation of distal limb muscles, exacerbated when these muscles display slow twitch properties) and 2) the excitability of the motoneurons is enhanced. This paper tested this dual hypothesis by developing a computer model representing the ankle reflex pathway. This model included the ankle muscles, afferent and efferent pathways, and a monosynaptic spinal link between spindle afferents and motoneurons. Simulations show that as the motoneuron current threshold was reduced (reflecting increased excitability of spinal motoneurons), normal reflex responses became unstable and oscillations developed similar to those observed in spastic patients. In parallel, when we choose reflex delay times typical for distal leg muscles in man, system stability is poor, and oscillations occur readily with increasing motoneuron excitability. As simulated pathway delays are reduced, oscillatory behavior is also reduced, and usually damps out. Conversely, as simulated reflex delays are increased, oscillations increase in amplitude and do not decay. Finally, these two phenomena interact, so that increasing motoneuron excitability will induce reflex oscillations for intermediate loop delays. These findings support the hypothesis that unstable oscillatory behavior, such as the oscillations observed in clonus, will occur when the motoneuron excitability increases in a reflex pathway containing long delays. This change in excitability is mediated by a reduction in motoneuron firing threshold, rather than by an increase in feedback gain. Furthermore, we demonstrate that sustained oscillations occur readily through self reexcitation, which reduces the need to propose that a "central oscillator" must be involved in generating clonus.     

Artificial neural nets in computer-aided macro motor unit potentialclassification

The use of macro electromyography to obtain a macro motor unit potential (MMUP) is described. At least 20 potentials are measured from a single muscle to obtain a reasonable estimate of the parameters of an average motor unit potential. The MMUP data are analyzed by means of the peak-to-peak amplitude and the integral of the central 50 ms of the signal. The possibility of using artificial neural networks (ANNs) to analyze the macro data in a way that makes no assumptions about the relationships between the parameters and without recourse to conventional modeling methods is discussed. The results of an analysis carried out on 820 MMUPs recorded from 41 subjects who were classified on the basis of a clinical opinion and the appearance of a muscle biopsy are presented and discussed.     

Switching overvoltages in motor circuits

The switching of HV motor circuits in the megawatt range can cause large overvoltages on motor terminals. The amplitude of the resulting voltage spikes depends on breaker type and circuit characteristics. If the amplitude of switching overvoltages exceeds the basic insulation level of the motor, overvoltage protection circuitry should be installed to prevent a motor insulation failure. The decision whether overvoltage protection circuitry (surge pack) must be installed requires a prediction of the overvoltage level. This paper deals with switching overvoltages in motor circuits with a unit transformer between switchgear and motor. Overvoltages of motor circuits were simulated using specially developed simulation models. The results of three case studies revealed a large impact of cabling and transformer on motor overvoltages. In most of the cases, a unit transformer connected between switchgear and motor will provide an overvoltage protection to the motor. However, the transformer can also be a main cause of large overvoltages when connected to cables of specific length and capacitance. The paper provides some simple rules to recognize such critical configurations     

Spectral compression of the electromyographic signal due to decreasing muscle fiber conduction velocity.

Spectral compression of the electromyographic (EMG) signal, due largely to decreasing muscle fiber conduction velocity, is commonly used as an indication of muscle fatigue. Current methods of estimating conduction velocity using characteristic frequencies such as the median frequency of the power spectrum, are based on an assumption of uniform spectral compression. To examine changes in the EMG frequency spectrum during fatigue, muscle fiber conduction velocity was measured during sustained, isometric contractions of the biceps brachii. Compression of the EMG power and amplitude spectra was simultaneously examined using the median frequency and an alternative method-the spectral distribution technique. The spectral distribution technique consistently gave a better estimate of the relative change in muscle fiber conduction velocity than either of the median frequencies. This was further examined using a physiologically based EMG simulation model, which confirmed these findings. The model indicated that firing statistics can significantly influence spectral compression, particularly the behavior of characteristic frequencies in the vicinity of the firing rates. The relative change in the median frequency, whether of the amplitude or frequency spectrum, was consistently greater than the relative change in conduction velocity. The most accurate indication of the relative change in conduction velocity was obtained by calculating the mean shift in the midfrequency region of the EMG amplitude spectrum using the spectral distribution technique.     

基于波动量法的系统侧谐波阻抗幅值估计精度评价方法

系统谐波阻抗是衡量用户谐波发射水平的关键参数,准确估计其值具有重要的意义。文章基于波动量法,针对系统谐波阻抗的估计幅值构建了系统谐波阻抗幅值估计精度指标集,包括固有偏差指标和量测不确定度指标。固有偏差指标可定量评价由波动量法原理本身局限性造成的估计偏差;量测不确定度指标可综合衡量由量测、干扰等客观原因引起的量测偏差。然后提出了幅值估计精度指标的实用化计算方法。利用PSCAD仿真软件对典型系统进行了蒙特卡罗仿真分析,验证了幅值估计精度指标集可有效地筛选出较理想的工况和较精确的估计值,并在一定程度上量化估计值的精确度,可作为判定估计值是否满足工程误差要求的实用化依据。     

基于相空间重构的两相行波超声波电动机混沌运行分析

对超声波电动机驱动系统中存在的混沌现象进行了初步探求。设计超声波电动机转速闭环控制实验,获得驱动电压幅值变化的多组采样时间序列,并采用相空间重构方法对这些时间序列进行了混沌分析。计算得到的最大Lyapunov指数为正数,表明行波超声波电动机在一定工作条件下呈现出混沌特性。     

准分布式光纤传感电机测温系统设计

在介绍了光纤传感器优越特性基础上,对光纤测温传感器与电类测温传感器特点进行了比较,同时对多种光纤测温传感器特点也进行了比较,得出半导体吸收式光纤测温传感器是最合适电机测温的结论。再结合电机测温需求和光纤测温传感器特点设计了准分布式光纤传感电机测温系统,并介绍了相关系统组成、工作原理和特点。举例说明了此测温系统能满足大电机测温的应用要求。     

基于有限元分析的光纤复合低压电缆热场仿真和结构优化

光纤复合低压电缆（OPLC）是由绝缘导体和光单元组成的复合电缆,可以实现低压电力和光通信双重传输。依据OPLC的运行原理,分析其运行过程中的电热关系,对OPLC内光纤温度与光纤传输损耗关系进行研究分析,说明了光纤温度变化对其传输损耗的表征作用。针对OPLC工作时电热效应导致光纤温度升高问题,从调整OPLC结构的角度提出优化模型,依次改变光单元位置 、耐热层材料、耐热层厚度,采用具有微管结构的光单元。利用COMSOL Multiphysics多物理场耦合仿真软件进行仿真,分别计算了OPLC在额定工作状态下原始结构与优化后结构的温度分布。采用优化结构后光纤温度由86.8 ℃降低至77.25 ℃,表明本文提出的OPLC优化结构可以有效降低电热效应对光纤的影响。     

基于 场路耦合的调速永磁同步电机损耗及温度场分析

基于ANSYS/Maxwell、Simplorer和MATLAB/Simulink仿真平台搭建了调速内嵌式永磁同步电机（IPMSM）场路联合仿真模型,进行了最大转矩/电流（MTPA）和弱磁调速控制策略下电机场路耦合仿真,得到了不同控制策略及不同负载状况下电机动态特性;采用三项铁耗分离模型,计算了不同工况下考虑谐波时的定子铁耗、转子铁耗、永磁体涡流损耗;搭建样机三维温度场有限元模型,通过有限元电磁场与温度场双向耦合仿真,分析了电机在不同工况下的温度场分布;实验结果验证了损耗及温度场分析结果的正确性。     

PWM脉冲波对电机绕组时变特性影响研究

以变频电机定子绕组为研究对象,分析变频器输出的脉宽调制（PWM）脉冲波频率、峰值、上升时间对电机绕组暂态电压分布特性的影响。研究结果显示,频率的增加对电机损耗有直接影响,进而通过损耗影响电压分布,频率和损耗的增加对绕组对地电压与匝间电压幅值都有一定的抑制作用。随着尖峰系数的增大,各线圈对地电压幅值都有所增加,且最大对地电压幅值位置由靠近中性点转移至电机端。尖峰系数对匝间电压分布影响相对较小,匝间电压的变化范围在60~75 V之间,不同尖峰系数下匝间电压分布均匀。脉冲上升沿时间对电压分布影响较大,随着脉冲上升沿时间的减少,对地电压及匝间电压成线性增加。上升沿时间对匝间电压幅值及分布的均匀程度起着决定性的影响。     

Toward mapping spatiotemporal characteristics of muscle oxygenation in different motor modalities by multichannel near‐infrared spectroscopy

Commonly, the near‐infrared spectroscopy (NIRS) devices are used to measure muscle oxygenated hemoglobin (HBO) concentration and total hemoglobin (HBT) concentration with a single channel, which can obtain the temporal HBO and HBT signals. Lacking of the spatial information of muscle oxygenation will limit the exploration of the heterogeneity of muscle activities. In this study, a multichannel NIRS recording system was used to measure the muscle oxygenation with an attempt to simultaneously provide the temporal and spatial HBO and HBT concentration. In the experiment, the influences of four motor tasks, including active, passive, imaginary movement, and the control task (no movement), on muscle oxygenation were investigated in eight normal subjects. Our results showed that both amplitude and spatial heterogeneity associated with variation in muscle oxygenation during active and passive motor tasks were significantly different between the motor time and rest time (P < 0.05). Furthermore, the region where HBO concentration decreased during the active motor task was in accordance with the anatomical position of contracted muscle, which cannot be observed from the results of the passive task. Considering the imaginary and control tasks in which the muscle was in a fixed/stationary state, the amplitude and spatial heterogeneity associated with variations in muscle oxygenation only exhibited slight changes (P > 0.05). This pilot study suggested that the spatiotemporal information obtained from multichannel NIRS devices might be potential for accurate measurement of the variation in muscle oxygenation during motor tasks, which would be useful for different clinical applications.     

防爆型水冷电机内换热与温度场计算

采煤机电机安装空间严格受限,随着电机设计容量的提升,使单位体积损耗(发热率)增大.为了研究该类电机的发热与冷却问题,在对防爆型水冷电机的结构、材料以及换热机理进行分析的基础上,建立了防爆型水冷电机的传热数学物理模型.采用有限元法对电机定、转子及水套的温度场进行了计算与分析.通过计算结果与实测值对比,验证所建传热模型可以真实反映实际传热过程.分析计算结果表明电机定子最高温度点位于定子上层绕组近气隙侧;定子齿是热量传递的主要通道,热流密度最大;选用适当的冷却水流速,可以用最小的代价获取所需的冷却效果.研究结果可以为采煤机电机热控制和优化设计提供理论依据.     

PMU电压幅值与频率量测一致性的在线评估方法

相量测量单元(PMU)的广泛应用,为实现电网的动态安全监控提供了数据基础,也是建设智能电网的重要技术内容。然而各厂家在实际运行环境中PMU产品的精度和相量量测的一致性并没有经过严格的检验。文中提出一种PMU电压幅值与频率量测一致性的在线评估方法,分别给出了电压一致性、频率一致性与电压—频率一致性指标及其计算方法。此外,还重点分析了可能造成电压幅值及频率量测一致性差异的原因,即系统偏离额定频率对PMU量测的影响,指出应对偏离额定频率情况下的计算相量进行修正,以进一步改善实测相量的质量。     

异步电动机轻载节能运行新型策略及实现

针对轻载运行异步电动机能源浪费严重的实际情况,提出了异步电动机节能运行新型策略,进行了节能机理的分析。通过分析指出,异步电动机起动时应采用恒流软起动,轻载运行时按最大综合力能指标原则进行调压则有最优的节能效果。进行了节能系统的仿真和实验研究。仿真和实验结果都说明了该控制策略正确可行,可以取得异步电动机较好的节能效果。