周期性任意波形总失真度的精确评价

介绍了一种周期性任意波形总失真度的定义及其评价过程和方法；借助于周期精确测量技术和傅里叶变换实现基波参数的精确测量，使用最小二乘法实现任意波形的最优估计，用时域能量方式计算失真，并对测量系统本身的影响进行了补偿。在一组仿真实验上验证了该方法的正确性及可行性。该方法可用于任意波发生器产生的任意波形失真度的精确测量和计量校准。     

螺旋针-环结构等离子体射流放电过程分析

为降低气体的击穿和维持电压,设计一种螺旋针-环电极结构的等离子体射流装置,研究不同电压下的放电电压、电流波形。研究表明,氦气等离子体射流放电可以分为电晕放电、介质阻挡放电和射流放电三个阶段,并且可以通过放电电压、电流波形的特征进行区分。分析可知,射流管管径较大时,采用螺旋针状内电极结构可以减小电极间的平均气体间隙距离,从而降低气体的击穿和维持电压,使放电更加容易进行;电压反向过程中残留电荷使得合成电场得到加强,气体将"提前"发生放电;由于电极结构的不对称,气体在正半周期更容易发生放电,放电产生的电流脉冲数目更多,电流值更大;随着外加电压增大至14k V,放电最终过渡到丝状放电状态。     

Measurement for optical arbitrary waveforms using cross-phase modulation cross-correlation frequency-resolved optical gating in a single-mode fibre

A novel scheme of cross-correlation frequency-resolved optical gating (X-FROG) measurement for optical arbitrary waveforms based on the photo-elastic effect and cross-phase modulation (XPM) effect in a single-mode fibre is proposed. In this scheme, a variable delay is generated in the former part of the single-mode fibre by a uniform lateral pressure, and the XPM effect is achieved in the latter part of the fibre. The proposed scheme is very simple and easy to be realized. The amplitude and phase of optical arbitrary waveform to be measured is retrieved from the X-FROG trace using principal component generalized projects algorithm based on matrix. The impacts of the shape of gate pulse, fibre length, relative intensity between gate pulse and optical arbitrary waveform and the complexity of the optical arbitrary waveform on the accuracy of retrieved amplitude and phase are investigated. Simulation results show that, rectangular pulse is a better gate pulse due to lower errors. The accuracy of measurement is improved with the increase in fibre length, and relative intensity between gate pulse and optical arbitrary waveform. Moreover, this scheme also can be used to measure extremely complex optical arbitrary waveforms.     

基于波形突变的电流互感器饱和辨识

电流互感器（CT）饱和是继电保护误动作的主要影响因素。在分析并仿真电流互感器典型饱和现象的基础上,运用小波变换分析电流互感器二次电流波形突变的方法,提出了基于模极大值隶属函数的有效极大值辨识方法,并利用有效模极大值准确实时地识别每个周波电流互感器二次电流过零点与进出饱和时刻,为准确辨识电流互感器的饱和区域,提供了有效的新方法。     

VWDK调制的波形优化

高带宽传输效率和高边带抑制水平对无线电通信有着重要的意义。该文利用甚小波形差健控(VWDK)已调波形的功率谱结构对其基本波形进行优化,得到带宽更窄、边带抑制更好的VWDK调制波形。     

三角波信号波形参数的测量不确定度

通过使用波形测量手段和最小二乘直线拟合方法,对三角波信号的波峰、波谷、中值、幅度、频率、沿斜率、沿线性度、对称性等指标进行了精确评价,详细讨论了方法的实现过程以及有关技术问题,并对各项参数指标进行了不确定度分析。实验验证结果表明了该方法的有效性和实用性,该方法可应用到三角波信号源的性能指标评价中。     

Effect of power parameters on micro-discharge induced by corona discharge

This research mainly describes the generation and diagnosis of plasma using a wire-plate discharge device driven by different power supplies, aimed at investigating the effect of driving source parameters on micro-discharge induced by a corona. The influence of parameters such as waveform, duty ratio and bias voltage on discharge characteristics was explored preliminarily. Experiment results show that the determination of volt-ampere characteristics under different driving source waveforms indicates that the application of square and pulse waveforms shows great advantages over that of sawtooth and sinusoidal waveforms. Similarly, the photo-thermal effects of the system were investigated by comparing the high-voltage electrode temperature and relative emission intensity of N₂ (C³П_u →B³П_g , 0–0, 337 nm), where square and pulse waveforms also achieved better performance. But the pulse waveform had a slight advantage over the square waveform in terms of energy conversion. Further, investigations of the duty ratio and bias voltage applied on the pulse waveform were conducted, and the results indicate that the duty ratio could effectively improve the discharge power and thermal effect to a certain extent; however, the application of bias voltage on the pulse signal had little influence on the discharge power and thermal effect.     

Rayleigh–Bénard convection in a Boussinesq–Stokes ferromagnetic fluid under sinusoidal and non-sinusoidal internal heat modulation

Internal heat modulation has several applications in nuclear reactor design and safety, as well as meteorology. In this paper, the influence of internal heat modulation on Rayleigh–Bénard convection in a Boussinesq–Stokes ferromagnetic fluid is explored using linear and nonlinear analyses. The impact of the square, sine, triangular, and sawtooth wave type of internal heat modulation on the onset of convection and heat transport is considered. Using a Venezian method, linear stability analysis is performed to derive the correction Rayleigh number and the critical Rayleigh number for all four waveforms. A nonautonomous Lorenz model is derived and solved for the amplitude to obtain the Nusselt number, which quantifies the heat transport. The impact of the nondimensional parameter on the convective onset and heat transfer under heat source/sink modulation is analyzed. The study shows that all four types of internal heat modulation destabilize the system. It is also found that the presence of a heat source/sink modulation affects the impact of all four types of internal heat modulation on heat transport.     

超宽带信道的频率色散特性对脉冲波形的影响

采用幂形式衰减模型和建立的抛物线型非线性相位模型分别研究了超宽带脉冲信号在频域中发生的幅度失真和相位失真,分析了超宽带信道的频率色散特性对脉冲信号波形产生的影响。仿真结果表明,传播信道中物体的边缘折射产生的频率依赖特性较强,引起的脉冲幅度失真较大;收发天线较小的非线性相位响应,也会导致较大的波形畸变。因此,在实际的超宽带信道建模时应根据实际环境考虑超宽带信道的频率色散特性。     

Power quality evaluation in smart grids considering modern distortion in electric power systems

High power quality level is required in smart grids especially for non-stationary situations due to increased use of nonlinear loads and PQ disturbances such as dips, swells, transients and interruptions. Many power quality indices (PQIs) are available. In this paper a new fuzzy-wavelet packet transform-based power quality Index (FWPTPQI) is developed to amalgamate existing power quality indices as the output of a fuzzy based module based on fuzzy inference systems, knowledge base and existing PQI as input. Fuzzy systems allow handling the uncertainties associated with the electric power quality evaluation. The proposed approach has been applied to two case studies; stationary balanced and non-stationary unbalanced three-phase systems. The results are compatible with prevalent situations. The new index gives significant sense of the quality of transmitted electrical power. A comparative study of using different wavelet basis functions is considered and results indicate that Daubechies 10 and Daubechies 15 could be considered as the overall best wavelet basis functions. Since the new index represents an amalgamation of the PQ indices with less number of wavelet coefficients, it helps reduce the size of data processed which is required in smart grid applications.