一种新颖的混沌时间序列分析方法

本文提出了一种新颖的混沌时间序列分析方法,即从被加性高斯白噪声污染的混沌时间序列中估计其系统参数并同时进行噪声抑制的方法。假定产生混沌时间序列的模型已知,但相应的参数未知。这种新方法把对混沌时间序列的参数估计和噪声抑制看作是一种最小化过程,并利用了最速梯度下降方法解决。数值模拟实验表明新方法要优于现有的方法,是估计混沌系统系数和噪声抑制的一种有效的方法。     

A novel method for determining the nature of time series

The delay vector variance (DVV) method, which analyzes the nature of a time series with respect to the prevalence of deterministic or stochastic components, is introduced. Due to the standardization within the DVV method, it is possible both to statistically test for the presence of nonlinearities in a time series, and to visually inspect the results in a DVV scatter diagram. This approach is convenient for interpretation as it conveys information about the linear or nonlinear nature, as well as about the prevalence of deterministic or stochastic components in the time series, thus unifying the existing approaches which deal either with only deterministic versus stochastic, or the linear versus nonlinear aspect. The results on biomedical time series, namely heart rate variability (HRV) and functional Magnetic Resonance Imaging (fMRI) time series, illustrate the applicability of the proposed DVV-method.     

Spectral mimicry: A method of synthesizing matching time series with different Fourier spectra

Given a stationary time seriesX and another stationary time seriesY (with a different power spectral density), we describe an algorithm for constructing a stationary time series Z that contains exactly the same values asX permuted in an order such that the power spectral density ofZ closely resembles that ofY. We call this methodspectral mimicry. We prove (under certain restrictions) that, if the univariate cumulative distribution function (CDF) ofX is identical to the CDF ofY, then the power spectral density ofZ equals the power spectral density ofY. We also show, for a class of examples, that when the CDFs ofX andY differ modestly, the power spectral density ofZ closely approximates the power spectral density ofY. The algorithm, developed to design an experiment in microbial population dynamics, has a variety of other applications.The work of J. E. Cohen was supported by U.S. National Science Foundation grant BSR92-07293. The research of C. M. Newman was supported in part by NSA Grant MDA 904-96-I-0033 and by NSF Grants DMS-95-00868 and DMS-98-03267. The work of O. L. Petchey and A. Gonzalez was supported by the U.K. Natural Environment Research Council.     

A novel PWM scheme for single-phase three-levelpower-factor-correction circuit

This paper presents a control scheme for a single-phase AC-to-DC power converter with three-level pulsewidth modulation. A single-phase power-factor-correction circuit is proposed to improve the power quality. The hysteresis current control technique for a diode bridge, with two power switches is adopted to achieve a high power factor and low harmonic distortion. A control scheme is presented where the line current is driven to follow the reference sinusoidal current which is derived from the DC-link voltage regulator, the capacitor voltage balance compensator and the output power estimator. The blocking voltage of each power device is clamped to half of the DC-link voltage. The high power factor and low current total harmonic distortion are verified by computer simulations and hardware tests     

A novel overmodulation technique for space-vector PWM inverters

In this paper, a novel overmodulation technique for space-vector pulsewidth modulation (PWM) inverters is proposed. The overmodulation range is divided into two modes depending on the modulation index (MI). In mode I, the reference angles are derived from the Fourier series expansion of the reference voltage which corresponds to the MI. In mode II, the holding angles are also derived in the same way. The strategy, which is easier to understand graphically, produces a linear relationship between the output voltage and the MI up to six-step operation. The relationship between those angles and the MI can be written in lookup tables or, for real-time implementation, can be piecewise linearized. In addition, harmonic components and total harmonic distortion (THD) of the output voltage are analyzed. When the method is applied to the V/f control of an induction motor, a smooth operation during transition from the linear control range to the six-step mode is demonstrated through experimental results     

Comparison of Walsh and Fourier spectroscopy of geomagneticreversals and nonsinusoidal palaeoclimatic time series

Higher resolving capabilities and theoretical appropriateness of Walsh spectral techniques as compared to Fourier spectral analyses are presented for synthetic and nonsinusoidal geotime series. Theoretical developments of Walsh transform techniques and a comparative study of Walsh and Fourier spectral estimates are presented. The Walsh spectral technique is applied specifically to two actual time series data of geomagnetic reversals in binary telegraphic wave form and nonsinusoidal palaeomagnetic and palaeoclimate time series. Walsh spectra reveal periodicities in Milankovitch frequency bands and provide exceptionally well-resolved spectral lines. The possible physical significance of these orbital periodicities is discussed. A comparative example of autocorrelation analysis in the real time domain and dyadic time domain is also presented using a telegraphic signal model of actual geomagnetic reversal time series. and the result is briefly discussed. The computational efficiency of the Walsh function could be exploited further for many other binary and nonsinusoidal geophysical/geological time series     

基于矢量控制的PWM整流器SIMULINK建模与仿真

在高开关频率下,应用状态空间平均法建立三相电压型PWMVSR数学模型,利用矢量合成原理,推算出各相开关函数占空比。最后,通过MATLAB的SIMULINK工具箱得到系统仿真结果,验证该模型和控制方法的可行性。     

A novel zero-voltage and zero-current-switching PWM full-bridgeconverter using two diodes in series with the lagging leg

This paper proposes a novel phase-shifted zero-voltage and zero-current-switching (ZVZCS) pulsewidth modulation full-bridge converter, which realizes ZVS for the leading leg and ZCS for the lagging leg. A blocking capacitor is added in series with the primary winding of the transformer to make the primary current decay to zero during zero state to ensure ZCS for the lagging leg. In order to prevent the primary current from reversing during zero state, two diodes in series with the lagging leg are added. The principle of operation, steady-state analysis, and design procedures are presented. The experimental results are also included to verify the theoretical analysis     

A novel and simple current controller for three-phase PWM powerinverters

A new feedback current controller for three-phase pulsewidth modulation (PWM) power inverters is presented. To achieve robustness, fast dynamical response, reduced switching frequency, and simple hardware implementation, an improved three-level hysteresis sliding-mode controller is used. All voltage vectors are accurately selected in order to minimize the current error     

A novel approach to modeling and efficient simulation offrequency-selective fading radio channels

A multipath radio channel concept based on channel orthogonalization techniques in two inner product spaces is presented and compared to the conventional approach of modeling each individual Rayleigh or Rice fading multipath ray individually. The proposed simulator can be applied to linear amplitude/phase modulation and linear fading channels including Nyquist filtering. It is shown to be a good approximation to the conventional model in the case of tight rolloff factors. Channels having quasi-or truly continuous delay profiles can now be properly represented at significantly reduced computational complexity. The proposed simulation concept leads to the lowest level of complexity being achieved for the prevailing channel and noise conditions on a particular channel     

A novel soft-switched PWM inverter for AC motor drives

A novel soft-switched inverter topology is derived from the passively clamped quasi-resonant link (PCQRL) circuit. By introducing magnetic coupling between the two resonant inductors, the number of auxiliary switches can be reduced from two to one, and only a single magnetic core is required for the resonant DC link. An analysis of this novel PCQRL topology with coupled inductors is presented to reveal the various soft-switching characteristics. In comparison with the conventional passively clamped, continuously resonant DC link inverter, this soft-switched inverter can reduce voltage stresses from more than 2 per unit (pu) to 1.1-1.3 pu. It can also provide soft-switched pulse-width modulated (PWM) operation. Simulations and experiments are performed to backup the analysis     

A dynamic regularized radial basis function network for nonlinear,nonstationary time series prediction

In this paper, constructive approximation theorems are given which show that under certain conditions, the standard Nadaraya-Watson (1964) regression estimate (NWRE) can be considered a specially regularized form of radial basis function networks (RBFNs). From this and another related result, we deduce that regularized RBFNs are m.s., consistent, like the NWRE for the one-step-ahead prediction of Markovian nonstationary, nonlinear autoregressive time series generated by an i.i.d. noise processes. Additionally, choosing the regularization parameter to be asymptotically optimal gives regularized RBFNs the advantage of asymptotically realizing minimum m.s. prediction error. Two update algorithms (one with augmented networks/infinite memory and the other with fixed-size networks/finite memory) are then proposed to deal with nonstationarity induced by time-varying regression functions. For the latter algorithm, tests on several phonetically balanced male and female speech samples show an average 2.2-dB improvement in the predicted signal/noise (error) ratio over corresponding adaptive linear predictors using the exponentially-weighted RLS algorithm. Further RLS filtering of the predictions from an ensemble of three such RBFNs combined with the usual autoregressive inputs increases the improvement to 4.2 dB, on average, over the linear predictors     

傅氏级数和多项式结合的图像灰度建模及位移测量

利用图像传感器的成像灰度实现位移测量,需要在位移过程中用相机对靶标进行成像,进而建立位移值与成像灰度值之间的映射关系,即成像灰度模型,该方法的测量精度取决于成像灰度模型与灰度噪声水平。实际测量过程中,光照不均匀、靶标制造误差、相机成像系统畸变等外部误差源以及内部不同图像传感器单元之间成像特性的差异性均会使成像灰度模型偏离理想情况,从而影响测量结果。为了进一步提高测量精度,所提方法考虑了上述的非线性因素带来的建模误差,采用Fourier级数与高阶多项式结合构造成像灰度模型类,提高模型的泛化逼近能力进而提高建模精度,校正上述误差源导致的灰度畸变。在此基础上,采用基于位移连续性原理的顺序求解法解算位移,实验结果显示,使用该改进模型在10.46 mm行程下的位移测量误差标准差由校正前的56.4 μm降低至1.5 μm。     

惯导平台历次测试数据时间序列建模分析

随着时间的推移,部分惯导平台参数的稳定性会发生比较明显的变化。为分析其变化情况,提出了惯导平台测试数据的小样本等时间间隔二次修正插值法,以此来构建惯导平台测试数据的时间序列。通过对已有的小样本测量数据进行准确插值,获得样本容量较大的等时间间隔的时间序列,在此基础上,通过时间序列建模的方法来研究惯导平台误差系数的变化情况,为惯导平台的使用提供指导。     

A novel zero-Voltage and zero-current-switching full-bridge PWM converter

A novel zero-voltage and zero-current-switching (ZVZCS) full-bridge pulse-width modulation converter is proposed. The ZCS condition of the lagging-leg is obtained by a simple secondary auxiliary circuit resetting the primary current during the freewheeling stage. The auxiliary circuit's capacitor is charged by the center tape of the secondary through a diode, and the capacitor's voltage is clamped through another diode to output capacitor, thus, the voltage stress on the rectifier is clamped. There are neither additional active switches nor resistances in the auxiliary circuit, which makes the proposed converter efficient.     

A novel view of Fourier analysis

A different view of a familiar subject often provides insight that leads to innovations and new discoveries. A novel view of the Fourier transform, Fourier series, and discrete Fourier transform is presented in this letter.     

Application of linear and nonlinear time series modeling to heartrate dynamics analysis

The linear autoregressive (AR) model is often used to investigate the pathophysiologic mechanisms controlling heart rate (HR) dynamics. This study implemented parametric models new to this field to determine if a more appropriate HR dynamics modeling structure exists. The linear AR and autoregressive-moving average (ARMA) models, and the nonlinear polynomial autoregressive (PAR) and bilinear (BL) models were fit to instantaneous HR time series obtained from nine subjects in the supine position. Model orders were determined by the Akaike Information Criteria (AIC). Model residual variance was used as the primary intermodel comparison criterion, with significance evaluated by a λ² distributed statistic. The BL model best represented the HR dynamics, as its residual variance was significantly (p<0.05) smaller than that of the corresponding AR model for nine out of nine data sets. In all cases, the BL model had a smaller residual variance than either the ARMA or PAR models. The bilinear model was ineffective at data forecasting, however, the authors show that this cannot reflect BL model validity because poor prediction is inherent to the BL model structure. The apparent superiority of the nonlinear bilinear model suggests that future heart rate dynamics studies should put greater emphasis on nonlinear analyses     

基于SPSS时间序列法对甲状腺疾病建模研究

收集不同城市的三家甲级医院在7年时间(2006—2012年)的所有甲状腺疾病的患者的病案数据进行整理和统计分析。利用SPSS时间序列方法建立合理的统计模型。从患者的性别、年龄和职业等常见的非生理性指标因素入手,研究甲状腺疾病的发病态势,获取甲状腺疾病的干扰因素。建立时间序列预测技术中最全面、最有效的统计方法之一——ARIMA模型,达到对疾病的预防和防控的目的。     

A novel ZVT PWM Cuk power-factor corrector

A novel zero-voltage-transition (ZVT) pulsewidth modulated (PWM) Cuk power-factor corrector (PFC) is proposed to achieve unity power factor under zero-voltage-switching (ZVS) operations. In the proposed ZVT PWM Cuk PFC, not only the power switch, but also the power diode, commutate under ZVS. The proposed topology has the shortest ZVT time and, thus, the shortest minimum duty cycle compared with other ZVT PWM topologies. The resonant inductor can be discharged regardless of the state of the main switch. Extremely short ZVT time and robust discharge of the resonant inductor make the proposed topology well qualified for variable-duty and high switching-frequency applications. Analytical studies, design rules, and experimental waveforms of the ZVT PWM Cuk PFC are presented in detail     

A COMPUTER-AIDED UNIFIED APPROACH TO MODELING PWM AND RESONANT CONVERTERS

This letter puts forward a method of modeling for the steady-state and small signal dynamic analysis on PWM, quasi-resonant and series/（parallel） resonant switching converters based on pulse-waveform integral approach. As an example, PWM and quasi-resonant converters are used to discuss the principle of the approach. The results are compared with those in the relative literatures. Computer aided analysis are made to confirm the correctness.