Fault Estimation for a Class of Markov Jump Piecewise-Affine Systems: Current Feedback Based Iterative Learning Approach

In this paper, the issues of stochastic stability analysis and fault estimation are investigated for a class of continuoustime Markov jump piecewise-affine(PWA) systems against actuator and sensor faults. Firstly, a novel mode-dependent PWA iterative learning observer with current feedback is designed to estimate the system states and faults, simultaneously, which contains both the previous iteration information and the current feedback mechanism. The auxiliary feedback channel optimizes the response speed of the observer, therefore the estimation error would converge to zero rapidly. Then, sufficient conditions for stochastic stability with guaranteed performance are demonstrated for the estimation error system, and the equivalence relations between the system information and the estimated information can be established via iterative accumulating representation.Finally, two illustrative examples containing a class of tunnel diode circuit systems are presented to fully demonstrate the effectiveness and superiority of the proposed iterative learning observer with current feedback.

Thrust estimate method of an on-orbit Hall thruster using Hall drift current

In order to realize the thrust estimation of the Hall thruster during its flight mission,this study establishes an estimation method based on measurement of the Hall drift current.In this method,the Hall drift current is calculated from an inverse magnetostatic problem,which is formulated according to its induced magnetic flux density detected by sensors,and then the thrust is estimated by multiplying the Hall drift current with the characteristic magnetic flux density of the thruster itself.In addition,a three-wire torsion pendulum micro-thrust measurement system is utilized to verify the estimate values obtained from the proposed method.The errors were found to be less than 8%when the discharge voltage ranged from 250 V to 350 V and the anode flow rate ranged from 30 sccm to 50 sccm,indicating the possibility that the proposed thrust estimate method could be practically applied.Moreover,the measurement accuracy of the magnetic flux density is suggested to be lower than 0.015 mT and improvement on the inverse problem solution is required in the future.

WAVE CURRENT FORCE COEFFICIENTS ON INCLINED CYLINDER AND A NEW ESTIMATION METHOD

Based on the review of present force coefficients estimation methods, a new method in the frequency domain, revised cross-spectrum estimation method, is presented in this paper. Some experiments on the wave-current force on inclined cylinders are also described and the wave current force coefficients are estimated by the revised cross-spectrum estimation method. From the results, it is found that the wave and current directions have some regular effect on the coefficients. According to the results, some empirical formulas are obtained for converting the wave-current force coefficients on inclined cylinders into a unified coefficient. Comparisons show that the unified coefficients are in good agreement with other results.

State Estimation of Distribution Network Considering Data Compatibility

Considering that the measurement devices of the distribution network are becoming more and more abundant, on the basis of the traditional Supervisory Control And Data Acquisition (SCADA) measurement system, Phasor measurement unit (PMU) devices are also gradually applied to the distribution network. So when estimating the state of the distribution network, the above two devices need to be used. However, because the data of different measurement systems are different, it is necessary to balance this difference so that the data of different systems can be compatible to achieve the purpose of effective utilization of the estimated power distribution state. To this end, this paper starts with three aspects of data accuracy of the two measurement systems, data time section and data refresh frequency to eliminate the differences between system data, and then considers the actual situation of the three-phase asymmetry of the distribution network. The three-phase state estimation equations are constructed by the branch current method, and finally the state estimation results are solved by the weighted least square method.

经二极管整流并网的构网型风机大扰动建模与稳定性分析

二极管整流单元型高压直流(DRU-HVDC)送出系统因其经济性优势,在新能源基地直流送出领域具有良好的应用前景。然而,在当前构网型换流器的大扰动稳定性研究中,大多由大容量同步机或大电网支撑故障点的频率和相位,且查表式设定故障电流参考值,缺乏对构网型风机接入DRU-HVDC系统这类故障点频率由换流器控制主导且动态调整故障电流参考值系统的研究。为解决上述问题,首先,建立计及电流限幅和频率控制的高阶非线性微分方程模型;然后,推导故障后系统平衡点的解析表达式,并论证采用q轴优先的电流限幅策略和频率控制在保障大扰动后平衡点存在性方面的优势;最后,基于Takagi-Sugeno法构建Lyapunov函数并得到系统的估计吸引域,分析换流器关键控制参数对暂态稳定性的影响,并与PSCAD/EMTDC中仿真算例进行对比,以验证暂态稳定性分析的准确性。

基于3CPEM的主动配电网10 kV馈线合环电流评估方法

分布式能源出力的随机性对主动配电网馈线合环电流的准确计算产生了影响。为提高合环电流计算的准确性,从融入分布式能源出力与负荷变量之间相关性的角度,提出了基于Cholesky分解的三点估计法(Cholesky three-point estimate method,3CPEM)计算主动配电网馈线合环电流。该方法利用Cholesky分解处理输入变量之间的相关性,再通过三点估计法(three-poit estimate method,3PEM)计算合环电流的累积概率分布。仿真表明,3CPEM比3PEM的计算误差更小、用时更短,可为主动配电网馈线合环辅助决策提供参考。

Reference-input-based Imaginary Axis Current Estimation Method for DQ Control Strategy in Single-phase PWM Converters

For dq control strategies in single-phase pulse width modulation(PWM)converters,the-axis current must be created by imaginary axis current estimation(IACE)methods.The estimated error of the-axis current during the transient process causes d-q axis current loops to be incompletely decoupled,thereby affecting the dynamic performance of the current loop.The second-order generalized integrator(SOGI)method suffers from slow dynamic response.The fictive-axis emulation(FAE)method provides fast dynamic response but it is sensitive to circuit parameters.A reference-input(RI)-based IACE method is proposed to overcome the above shortcomings.According to the characteristic that the-axis current loop has no transient process,the-axis current is estimated by the d-q axis reference inputs.This is equivalent to introducing the-axis reference input as a feedforward term into the d-q axis current loop,so the parameter sensitivity problem is solved,and the parameter tuning is not needed.The proposed method can maintain good steadystate performance and significantly improve the dynamic performance of the current loop.Furthermore,it is straightforward and can be easily implemented in digital controllers.Comprehensive hardware-in-the-loop(HIL)experimental comparisons with the SOGI and FAE methods have been conducted to verify the correctness and effectiveness of the proposed RI-based IACE method.

MIXED FINITE ELEMENT METHODS FOR THE SHALLOW WATER EQUATIONS INCLUDING CURRENT AND SILT SEDIMENTATION (Ⅱ)——THE DISCRETE-TIME CASE ALONG CHARACTERISTICS

The mixed finite element(MFE) methods for a shallow water equation system consisting of water dynamics equations,silt transport equation,and the equation of bottom topography change were derived.A fully discrete MFE scheme for the discrete_time along characteristics is presented and error estimates are established.The existence and convergence of MFE solution of the discrete current velocity,elevation of the bottom topography,thickness of fluid column,and mass rate of sediment is demonstrated.

MIXED FINITE ELEMENT METHODS FOR THE SHALLOW WATER EQUATIONS INCLUDING CURRENT AND SILT SEDIMENTA-TION (Ⅰ)-THE CONTINUOUS-TIME CASE

An initial-boundary value problem for shallow equation system consisting of water dynamics equations,silt transport equation, the equation of bottom topography change,and of some boundary and initial conditions is studied, the existence of its generalized solution and semidiscrete mixed finite element(MFE) solution was discussed, and the error estimates of the semidiscrete MFE solution was derived.The error estimates are optimal.

Algorithms for automatic measurement of SIS-type hysteretic underdamped Josephson junction’s parameters by current-voltage characteristics

Some electrical parameters of the SIS-type hysteretic underdamped Josephson junction(JJ)can be measured by its current-voltage characteristics(IVCs).Currents and voltages at JJ are commensurate with the intrinsic noise level of measuring instruments.This leads to the need for multiple measurements with subsequent statistical processing.In this paper,the digital algorithms are proposed for the automatic measurement of the JJ parameters by IVC.These algorithms make it possible to implement multiple measurements and check these JJ parameters in an automatic mode with the required accuracy.The complete sufficient statistics are used to minimize the root-mean-square error of parameter measurement.A sequence of current pulses with slow rising and falling edges is used to drive JJ,and synchronous current and voltage readings at JJ are used to realize measurement algorithms.The algorithm performance is estimated through computer simulations.The significant advantage of the proposed algorithms is the independence from current source noise and intrinsic noise of current and voltage meters,as well as the simple implementation in automatic digital measuring systems.The proposed algorithms can be used to control JJ parameters during mass production of superconducting integrated circuits,which will improve the production efficiency and product quality.

基于OCV模型优化的磷酸铁锂电池SOC估计

锂离子电池荷电状态(SOC)与开路电压(OCV)的关系曲线(OCV曲线)是影响其SOC估计精度的核心因素。针对小电流OCV(LO)测试耗时短但数据精度较低的问题,提出一种OCV模型及其优化方法。该方法基于LO测试的OCV数据,采用道格拉斯-普克算法和分段线性函数建立OCV模型。并将OCV曲线上的4个OCV点作为变量,建立了其他OCV点的随动模型,使曲线能够运用粒子群优化算法进行优化。基于优化后的OCV曲线,动态工况下的端电压估计绝对平均误差降低83.5%,采用自适应扩展卡尔曼滤波的SOC估计误差小于0.3%。该方法能够基于耗时短的LO测试获取准确OCV曲线,降低锂离子电池研究与应用的测试成本。

基于改进WOA-MP算法的多普勒海流计回波信号频率估计研究

受海洋环境复杂干扰影响,多普勒式海流计的超声波回波信号易受干扰影响,包含多种频率成分,这给海流流速信息的解算带来困难。为解决多普勒海流计回波信号频率估计精度较差的问题,提出一种基于信号匹配追踪(MP)的频率估计方法,并融合改进型鲸鱼优化算法(MWOA)提高估计过程的效率。该方法利用混沌映射提升初始种群多样性,并引入自适应权重和非线性收敛因子提高算法局部寻优能力、搜索速度和求解精度。而后,对改进算法与其他优化算法进行对比测试,结果显示所设计改进算法在收敛速度和寻优能力上具有有效性和优越性。此外,通过对多普勒回波信号进行特征重构,开展MWOA-MP算法在噪声环境下的频率估计精度性能测试。在回波信号信噪比为–10 dB条件下,MWOA-MP算法相对传统方法抗噪声能力提高30%。与其他智能方法融合MP后的频率估计算法相比,MWOA-MP算法的估计误差在10 Hz以内,可满足多普勒海流计频率测量精度要求。

Leakage Current Estimation of CMOS Circuit with Stack Effect

Leakage current of CMOS circuit increases dramatically with the technologyscaling down and has become a critical issue of high performance system. Subthreshold, gate andreverse biased junction band-to-band tunneling (BTBT) leakages are considered three maindeterminants of total leakage current. Up to now, how to accurately estimate leakage current oflarge-scale circuits within endurable time remains unsolved, even though accurate leakage modelshave been widely discussed. In this paper, the authors first dip into the stack effect of CMOStechnology and propose a new simple gate-level leakage current model. Then, a table-lookup basedtotal leakage current simulator is built up according to the model. To validate the simulator,accurate leakage current is simulated at circuit level using popular simulator HSPICE forcomparison. Some further studies such as maximum leakage current estimation, minimum leakage currentgeneration and a high-level average leakage current macromodel are introduced in detail.Experiments on ISCAS85 and ISCAS89 benchmarks demonstrate that the two proposed leakage currentestimation methods are very accurate and efficient.

永磁同步电机扩展卡尔曼滤波器电流观测方法

为提高前置电感电容LC滤波器永磁同步电机系统性能,提出一种基于扩展卡尔曼滤波器(extended Kalman filter,EKF)的电机电流观测控制方法。该方法采集逆变器侧电流,通过新型EKF观测器获得实际电机电流,并将估计的电机电流用于电流环反馈控制。论文给出了新型EKF电流观测器的结构和参数设计过程,并利用Lyapunov稳定性定理证明了该方法的稳定性。仿真结果表明,与传统Luenberger观测器相比,新型EKF观测方法的电流估计误差更小,电机电流跟踪性能更好,电磁转矩脉动及其谐波明显降低。

基于自适应神经模糊推理系统的避雷器有效运行寿命估计方法

估算金属氧化物避雷器的使用寿命一直是一项挑战,它决定着输电系统的安全稳定运行。基于此,文中提出了一种基于自适应神经模糊推理系统(adaptive neuro-fuzzy inference system,ANFIS)和支持向量机回归(support vector machine for regression,SVR)组成的组合时间序列预测模型,用于估算金属氧化物避雷器(metal oxide surge arrester,MOSA)的使用寿命。首先,文中进行了现场测量,考虑到该分量是避雷器监测中最常用的MOSAs劣化水平指标之一,以建立由泄漏电流三次谐波分量值组成的时间序列数据库;接着,利用ANFIS、SVR和仿真数据库,建立组合预测模型;随后,文中使用3种类型的误差:即MSE、MAE和MAPE评估预测模型的性能。最后,在对模型进行评估之后,利用所提模型对MOSA的使用寿命估算,研究结果表明,使用组合模型预测比基于ANFIS和SVR的模型提供的预测更准确,可提升估算MOSA使用寿命的精度18.9%。

光学电流传感消抖卡尔曼本征信号高精度提取方法研究

本征信号是光学电流传感长期运行稳定性和高精度测量的重要性能参数。目前,传统方法如双光路法并不能消除本征信号的抖动,对光学电流传感高测量精度产生消极影响。为此,提出了光学电流传感消抖卡尔曼本征信号高精度提取方法来对本征信号进行消噪处理。首先对光学电流传感的噪声特性以及光路结构进行分析,建立了光学电流传感本征信号模型。引入消抖函数修正卡尔曼增益K,提出了消抖卡尔曼(Debouncing Kalman,DBK)算法,解决了标准卡尔曼增益K对初始状态依赖性强以及测量过程不确定性非常敏感带来的状态估计值严重抖动问题。并且引入了噪声方差递推估计,来保证在滤波过程中可以实时对噪声方差进行修正。在MATLAB进行了消抖卡尔曼滤波算法的验证并与标准卡尔曼算法进行了滤波效果的对比分析,验证了该算法的可行性,并结合李雅普诺夫稳定性分析法推导验证了该算法的稳定性。最后,搭建光学电流传感实验平台,将所提算法在LabVIEW FPGA硬件平台并行实现,验证了该算法的实时性,且能够满足实际工程需求。

Fault Current and Voltage Estimation Method in Symmetrical Monopolar MMC-based DC Grids

Symmetrical monopolar configuration is the prevailing scheme configuration for modular multilevel converter based high-voltage direct current(MMC-HVDC) links, in which severe DC overvoltage or overcurrent can be caused by the DC faults. To deal with the possible asymmetry in the DC faults and the coupling effects of the DC lines, this paper analyzes the DC fault characteristics based on the phase-mode transformation. First, the DC grid is decomposed into the common-mode and the differential-mode networks. The equivalent models of the MMCs and DC lines in the two networks are derived, respectively. Then, based on the state matrices, a unified numerical calculation method for the fault voltages and currents at the DC side is proposed. Compared with the time-domain simulations performed on PSCAD/EMTDC, the accuracy of the proposed method is validated. Last, the system parameter analysis shows that the grounding parameters play an important role in reducing the severity of the pole-to-ground faults, whereas the coupling effects of the DC lines should be considered when calculating the DC fault currents associated with the pole-to-pole faults.

Efficient estimation for additive hazards regression with bivariate current status data

This paper discusses efficient estimation for the additive hazards regression model when only bivariate current status data are available. Current status data occur in many fields including demographical studies and tumorigenicity experiments （Keiding, 1991; Sun, 2006） and several approaches have been proposed for the additive hazards model with univariate current status data （Linet M., 1998; Martinussen and Scheike, 2002）. For bivariate data, in addition to facing the same problems as those with univariate data, one needs to deal with the association or correlation between two related failure time variables of interest. For this, we employ the copula model and an efficient estimation procedure is developed for inference. Simulation studies are performed to evaluate the proposed estimates and suggest that the approach works well in practical situations. An illustrative example is provided.

基于并联双输入SOGI-FLL的磁悬浮转子系统谐波电流抑制

转子质量不平衡和位移传感器误差是磁悬浮转子系统谐波电流的主要来源,准确检测转速是谐波电流抑制的前提。为解决无转速传感器条件下磁悬浮高速电机转子系统谐波电流抑制问题,提出一种并联双输入二阶广义积分锁频环(Second-order Generalized Integrator Frequency-Locked Loop,SOGI-FLL)方法。首先建立了系统转子动力学模型并分析谐波电流产生机理。然后,为提高转速识别精度、提升动态性能,利用X,Y两方向信号正交特性,采用双输入SOGI-FLL方法自适应估计转速。在此基础上,并联双输入SOGI环节以抑制系统谐波电流。为保证系统宽转速范围内稳定运行,根据系统相频特性设计了相位补偿。实验结果表明,该方法能快速准确识别转速,转速信号跟踪误差保持在±0.8 Hz范围内;一、三和五次谐波电流分量分别减少86.20%,84.65%和81.89%,可以准确有效抑制谐波电流。

利用改进MUSIC方法进行洋流方位估计

洋流能够调节全球热量的分布,降低航运成本。以往的洋流方位估计方法未对洋流信号源之间的相关性进行完全消除,导致估计效果较差。因此,本文设计了基于改进MUSIC方法的洋流方位估计方法。首先,以采集到的洋流信号为基础,构建洋流阵列信号模型,并对洋流信号进行降噪处理,提高信号数据的质量。然后,为减少洋流信号源之间相关性对估计结果的影响,利用改进MUSIC方法及协方差矩阵,对洋流信号源相关性进行消除,通过计算信号源的相关参数,构建洋流方位估计模型。最后,通过对洋流信号源的转换,实现洋流方位的估计。在仿真试验中,以南海部分海域为试验对象,对不同谱点下估计方法的估计效果进行评价,与以往的洋流方位估计方法相比,设计的基于改进MUSIC方法的洋流方位估计方法精度高达97.2%,应用效果更好。