Influence of different stimulation frequencies on power output and fatigue during FES-cycling in recently injured SCI people

This study investigated whether power output during 30 min sessions of functional electrical stimulation (FES)-cycling can be increased by using stimulation frequencies higher than 30 Hz. The stimulation frequencies of FES-cycling training sessions of 19 recently injured para- and tetraplegics were randomly set at 30, 50, or 60 Hz and power output (PO) was measured continually. The mean PO of the 30 min, the PO of the last minute of each session, and the minimum PO were significantly greater at 60 and 50 Hz than at 30 Hz (ANOVA without cross-product). A 19% and 25% higher mean PO was reached at 50 and 60 Hz, respectively, compared to 30 Hz. The PO of the last minute of each session was almost always higher than the mean PO of the whole session and also higher at higher frequencies, which indicates that no muscle fatigue could be detected in 30 min FES-cycling at any of the tested frequencies.     

Test bed with force-measuring crank for static and dynamicinvestigations on cycling by means of functional electrical stimulation

Cycling by means of functional electrical stimulation (FES) is an attractive training method for individuals with paraplegia. The physiological benefits of FES are combined with the psychological incentive of independent locomotion. In addition, cycling has the advantage in that the generated muscle forces are converted into drive power with relatively high efficiency compared to other means of locomotion, e.g., walking. For the design of an appropriate cycling device and the development of optimal stimulation patterns, it has to be investigated how the geometry for FES cycling, influenced by individual parameters of the FES-generated drive torques and the magnitude of variations among subjects with paraplegia, can be optimized. This study shows the design of a freely adjustable test bed with additional motor drive which allows static and dynamic measurements of force components and drive torque at the crank. Furthermore, the influence of geometry and various individual parameters on FES pedaling can be tested for each subject individually. A pedal path realized by a three-bar linkage that was optimized according to preliminary simulations further increases leg cycling efficiency. Safety precautions avoid injuries in case of excessive forces, e.g., spasms. Test results illustrate the application of the test bed and measurement routines. A test series with four paraplegic test persons showed that the presented static and dynamic measurement routines allow to provide optimal stimulation patterns for individual paraplegic subjects. While pedaling with these optimal stimulation patterns only negligible negative active drive torques, due to active muscle forces, were applied to the crank and sufficient drive power was generated to power a cycle independently     

Cycling by means of functional electrical stimulation.

The goal of this paper was the development of an optimized stimulation pattern of leg muscles that would allow paraplegic subjects to perform the movement of pedaling and thereby to drive a tricycle by means of functional electrical stimulation (FES). To obtain maximum average power output with minimum muscle force, the start, duration and amplitude of the stimulation signal applied to the individual muscles had to be optimized depending on the pedaling frequency. For the basic theoretical investigations the rider-tricycle system was modeled as a rigid body system on which the muscle forces are applied as joint moments. The muscles gluteus maximus, rectus femoris, vastii, and hamstrings were stimulated and the passive forces of some other muscles were considered. The modeling and simulation approach was then used to produce maximum power pedaling and steady-state pedaling at 35 rpm. Hamstrings (41.9%) and vastii (35.8%) were the primary contributors to the optimization cost function of maximum power with minimum muscle loading. Based on these theoretical investigations an efficient stimulation pattern could be provided, taking into account the realistic possibilities of today's practical applications.     

Cycling induced by electrical stimulation improves muscle activation and symmetry during pedaling in hemiparetic patients

A randomized controlled trial, involving 35 post-acute hemiparetic patients, demonstrated that a four-week treatment of cycling induced by functional electrical stimulation (FES-cycling) promotes motor recovery. Analyzing additional data acquired during that study, the present work investigated whether these improvements were associated to changes in muscle strength and motor coordination. Participants were randomized to receive FES-cycling or placebo FES-cycling. Clinical outcome measures were: the Motricity Index (MI), the gait speed, the electromyography activation of the rectus femoris and biceps femoris, and the mechanical work produced by each leg during voluntary pedaling. To provide a comparison with normal values, healthy adults also carried out the pedaling test. Patients were evaluated before, after training, and at follow-up visits. A significant treatment effect in favor of FES-treated patients was found in terms of MI scores and unbalance in mechanical works, while differences in gait speed were not significant (ANCOVA). Significant improvements in the activation of the paretic muscles were highlighted in the FES group, while no significant change was found in the placebo group (Friedman test). Our findings suggested that improvements in motor functions induced by FES-cycling training were associated with a more symmetrical involvement of the two legs and an improved motor coordination.     

The optimal stimulation pattern for skeletal muscle is dependent on muscle length

Stimulation patterns can be optimized by maximizing the force-time integral (FTI) per stimulation pulse of the elicited muscle contraction. Such patterns, providing the desired force output with the minimum number of pulses, may reduce muscle fatigue, which has been shown to correlate to the number of pulses delivered. Applications of electrical stimulation to use muscle as a controllable biological actuator may, therefore, be improved. Although muscle operates over a range of lengths, optimized patterns have been determined only at optimal muscle length. In this study, the patterns with up to four pulses that produced the highest isometric FTI were determined at 10 muscle lengths for 11 rabbit tibialis anterior muscles. The interpulse intervals (IPIs) used ranged from 4 to 54 ms. At high muscle length, the optimal stimulation pattern consisted of an initial short IPI (doublet) followed by longer IPIs, in agreement with previous studies. However, at low length, the third pulse still elicited more than linear summation (triplet); furthermore, the relative enhancement of the FTI per pulse was considerably larger at low length than at high length, suggesting that optimal stimulation patterns are length dependent.     

Boost DC-DC电路的启动性能分析

针对3个典型(单、双和三电感)升压电路的启动性能分析问题,应用PSIM仿真软件,调整3个重要影响参数(电感、电容和电流放大倍数),在获得稳定输出电压前提下,记录输出信号延迟和电路功耗的仿真数据,绘制三维图(电感/电容,电流放大倍数,延迟)和功耗延迟关系图,从中获得电路启动延迟性能和电路功耗折中考虑的最优区域。     

燃料电池稳态输出功率与效率的双目标优化

目前对燃料电池性能的研究基本上都是对燃料电池的某一个目标进行分析,这可能会导致其他重要参数产生重大偏差,从而影响燃料电池系统的性能,并且对于一个发电装置来说,其功率和效率是一对不可分割的重要参数。为此,提出了一种针对燃料电池系统稳态输出功率与效率的双目标优化算法。通过模型分析得到燃料电池稳态输出功率和效率与影响变量的关系,采用控制变量的方法实现对输出功率和效率的最优化。因系统复杂的非线性关系,仿真中采用一种带约束处理机制的自适应差分进化多目标优化算法以实现优化目标。     

有源电力滤波器输出电感的最优选取

有源电力滤波器作为消除谐波的新型电力电子装置,能有效提高用户的电能质量。其设计过程中参数的选取,直接关系到装置的补偿性能,尤其是输出电感的选取,是决定系统响应速度和补偿效果的关键。通过αβ变换,建立了有源电力滤波器的数学模型。根据数学推导分析的结果,获得输出电感的选取范围。并以总谐波畸变率最小为目标,在给出范围内通过数字仿真,获得输出电感的最优值。由分析计算得出的输出电感选取范围,能够有效避免有源滤波器在设计过程中输出电感选择的盲目性,并可以根据系统中的具体参数,选取输出电感值,提高补偿谐波性能。     

基于MVO算法与改进目标函数的电力系统负荷频率控制

针对风电并网时的随机波动功率、负荷频率控制(load frequency control, LFC)系统参数变化所引起的电力系统频率稳定问题,提出了一种基于智能优化算法与改进目标函数的互联电网LFC系统最优PID控制器设计方法。首先,分析了基于PID控制的含风电互联电力系统LFC闭环模型。其次,在时间乘误差绝对值积分(integral of time multiplied absolute error, ITAE)性能指标的目标函数中考虑了区域控制器的输出信号偏差,对优化目标函数进行改进。采用性能优良的多元宇宙优化(multi-verse optimizer, MVO)算法先计算后验证的思路,寻优获得最优PID控制器参数。最后,以两区域4机组互联电力LFC系统为例,仿真验证了基于MVO算法结合改进目标函数所获得的PID控制器,比基于MVO算法所获得的PID控制器,对阶跃负荷扰动、随机负荷扰动、风电功率偏差扰动以及系统的参数变化,具有相对较好的鲁棒性能。并且,对控制器参数也具有相对较好的非脆弱性指标。     

基于小信号法的功率放大器的设计与仿真

射频功率放大器是数传发射机中的关键部件,它是制约整个系统性能的关键因素。依据固态功率放大器的小信号设计法,设计两级L波段固态功率放大器,给出了详细的设计流程和仿真数据。首先对放大器的增益,级间耦合,输入,输出匹配进行了初步仿真,然后通过提取管子的封装后的散射参数,对其进行最大输出功率匹配仿真,最后对放大器匹配和稳定性进行总体仿真,最终结果达到设计指标。     

Optimal control of walking with functional electrical stimulation: a computer simulation study.

Bipedal locomotion was simulated to generate a pattern of activating muscles for walking using electrical stimulation in persons with spinal cord injury (SCI) or stroke. The simulation presented in this study starts from a model of the body determined with user-specific parameters, individualized with respect to the lengths, masses, inertia, muscle and joint properties. The trajectory used for simulation was recorded from an able-bodied subject while walking with ankle-foot orthoses. A discrete mathematical model and dynamic programming were used to determine the optimal control. A cost function was selected as the sum of the squares of the tracking errors from the desired trajectories, and the weighted sum of the squares of agonist and antagonist activations of the muscle groups acting around the hip and knee joints. The aim of the simulation was to study plausible trajectories keeping in mind the limitations imposed by the spinal cord injury or stroke (e.g., spasticity, decreased range of movements in some joints, limited strength of paralyzed, externally activated muscles). If the muscles were capable of generating the movements required and the trajectory was achieved, then the simulation provided two kinds of information: 1) timing of the onset and offset of muscle activations with respect to the various gait events and 2) patterns of activation with respect to the maximum activation. These results are important for synthesizing a rule-based controller.     

机组非停扰动下PSS调节性能评估及参数校核

研究了基于WAMS系统数据的机组非停扰动下PSS调节性能的评估和参数校核方法.首先阐释了基于相移原理的PSS调节性能评估原理.其次在额定有功功率、50％额定有功功率、发电机进相三种工况下进行了机组非停扰动下实际电网仿真计算.然后对实际电网中某次故障停机事故的WAMS数据进行了分析,进一步证实了通过有功功率与PSS输出信...     

Prediction of full load electrical power output of a base load operated combined cycle power plant using machine learning methods

Predicting full load electrical power output of a base load power plant is important in order to maximize the profit from the available megawatt hours. This paper examines and compares some machine learning regression methods to develop a predictive model, which can predict hourly full load electrical power output of a combined cycle power plant. The base load operation of a power plant is influenced by four main parameters, which are used as input variables in the dataset, such as ambient temperature, atmospheric pressure, relative humidity, and exhaust steam pressure. These parameters affect electrical power output, which is considered as the target variable. The dataset, which consists of these input and target variables, was collected over a six-year period. First, based on these variables the best subset of the dataset is explored among all feature subsets in the experiments. Then, the most successful machine learning regression method is sought for predicting full load electrical power output. Thus, the best performance of the best subset, which contains a complete set of input variables, has been observed using the most successful method, which is Bagging algorithm with REPTree, with a mean absolute error of 2.818 and a Root Mean-Squared Error of 3.787.     

Prevention of muscle disuse atrophy by low-frequency electrical stimulation in rats

When muscles lose neural drive, they atrophy rapidly. Neuromuscular electrical stimulation (NMS) has been used in attempts to prevent or reverse the atrophy, but optimal stimulation programs and parameters are not well defined. In this study, we investigated the effects of four different stimulation patterns on disuse atrophy produced in the tibialis anterior, lateral gastrocnemius, and soleus muscles of rats paralyzed with tetrodotoxin for seven days. Stimulation paradigms differed from one another by their stimulation frequency (2 or 10 pulses/s) and by their stimulation period (2 or 10 h a day). Results showed that stimulation with 2 pulses/s, paradigms were more effective at preventing disuse muscle atrophy than higher-frequency stimulation. The most marked difference was in the slow soleus muscle, which had only 10% mean atrophy when stimulated at 2 pulses/s for 10 h, compared to 26% atrophy when stimulated at 10 pulses/s for either 2 or 10 h and 32% atrophy in unstimulated, paralyzed controls. The level of atrophic change was not correlated with the levels of serum creatine kinase, used as an index of muscle damage. Results suggest that remediation of disuse atrophy may be accomplished using unphysiologically low rates of motor-unit activation despite the relatively low force produced by such unfused contractions. This may have significant implications for the design of therapies for muscle paralysis consequent to upper-motoneuron lesions.     

Sliding mode controller design for frequency regulation in an interconnected power system

In this paper, a Sliding mode controller design method for frequency regulation in an interconnected power system is presented. A sliding surface having four parameters has been selected for the load frequency control (LFC) system model. In order to achieve an optimal result, the parameter of the controller is obtained by grey wolf optimization (GWO) and particle swarm optimization (PSO) techniques. The objective function for optimization has been considered as the integral of square of error of deviation in frequency and tie-line power exchange. The method has been validated through simulation of a single area as well as a multi-area power system. The performance of the Sliding mode controller has also been analyzed for parametric variation and random loading patterns. The performance of the proposed method is better than recently reported methods. The performance of the proposed Sliding mode controller via GWO has 88.91% improvement in peak value of frequency deviation over the method of Anwar and Pan in case study 1 and similar improvement has been observed over different case studies taken from the literature.     

考虑调相机饱和参数的分阶段励磁控制优化策略

针对常规励磁控制在故障期间未能充分发挥调相机暂态无功输出能力和难以准确有效地支撑电网电压的问题,提出考虑调相机饱和状态下电机参数的分阶段励磁控制优化策略。首先,推导调相机暂态无功输出表达式,分析不同运行工况下饱和参数对调相机暂态无功特性的影响。其次,基于调相机参数与输出无功的数学关系引入考虑饱和参数的无功增量,分阶段优化励磁环节中内环电压参考值与外环PI控制。最后,建立锡盟-泰州特高压直流输电系统的无功控制模型,通过仿真验证励磁控制策略优化效果。研究成果为调相机的优化设计提供技术支撑,也对提高调相机的电网电压故障支撑能力和提升我国高压直流电网的电压稳定水平具有重要作用。     

Adaptive neural network control of cyclic movements using functional neuromuscular stimulation.

In this study, we evaluated the performance of an adaptive feedforward controller and its ability to automatically develop and customize stimulation patterns for use in functional neuromuscular stimulation (FNS) systems. Results from previous experiments using the pattern generator/pattern shaper (PG/PS) controller to generate isometric contractions demonstrated its ability to adjust stimulation patterns to account for recruitment nonlinearities and muscle dynamics. In this study, the PG/PS controller was tested under isotonic conditions. This evaluation required the PG/PS controller to account for muscle length-tension and force-velocity properties as well as limb dynamics. The performance of the adaptive controller was also compared with that of a proportional-derivative (PD) feedback controller. The PG/PS controller is composed of a neural network system that adaptively filters a periodic signal to produce a muscle stimulation pattern for generating cyclic movements. We used computer-simulated models to determine controller parameters for the PG/PS and PD controller that perform well across a variety of musculoskeletal systems. The controllers were then experimentally evaluated on both legs of two subjects with spinal cord injury. Results indicated that the PG/PS controller was able to achieve and maintain better tracking performance than the PD controller. This study indicates that the PG/PS control system may provide an effective mechanism for automatically customizing stimulation patterns for individuals using FNS systems.     

单轴并联式混合动力汽车动力总成建模与仿真

以优化整车动力性和经济性为目标,在Insight混合动力汽车底盘基础上,设计以镍氢电池组和永磁同步电动机驱动的汽车动力系统.利用电辅助控制策略,在满足整车动力性能指标的基础上,使用汽车专用仿真软件ADVISOR(advanced vehicle simulator)进行二次开发,采用前向仿真与后向仿真相结合的方法,根据实际情况构建系统模型,对发动机参数、电机参数选择以及能源匹配进行了仿真研究.仿真结果表明:该单轴并联式混合动力样车的动力系统设计方案是可行的,研究结果可为混合动力电动汽车动力总成的优化设计提供理论依据.     

(12期拿下）SSSC阻尼系统功率振荡的控制器设计

阻尼系统的功率振荡是静止同步串联补偿器(SSSC)重要的作用之一。考虑了SSSC内部动态的变化过程,即控制器的输出电压幅值与相角变化及直流侧电容动态调节过程,在此基础上建立SSSC的动态模型。推导脉冲宽度调制系数变化量与电角速度变化量之间的关系得到控制系统的传递函数,通过对控制系统中的参数控制从而对SSSC进行控制,而控制系统的参数是通过人工蜂群(ABC)的优化过程进行调整的。该优化方法以角速度差为目标,通过不断迭代更新,最后得到控制系统控制参数的最优解。在MATLAB中搭建模型,通过与传统PI控制仿真效果进行对比,通过优化方法能够有效快速的调整控制参数,从而更好地调节SSSC等效注入电压,有效地提高输电线路传输有功功率的能力,快速抑制系统功率振荡。     

基于神经网络的水轮机调节系统的自适应PID控制

基于有功功率反馈参与控制的水轮机调节系统,以几个典型工况下的最优ＰＩＤ系数作为训练样本,训练了一个三层ＢＰ神经网络,设计了一个用ＢＰ神经网络实现变参数的ＰＩＤ控制器;并构造了一个目标函数,设计了一个自适应神经元,利用神经元的自学习功能,在线优化控制器的输出,以期达到最优控制的目的。对简单电力系统的仿真结果表明,这种控制器可以达到较常规的变参数ＰＩＤ较好的控制效果,是实现水轮机调节系统自适应控制的一种可行的方法。