基于混合补偿的配电网单相接地故障消弧方法

针对配电网单相接地故障无源消弧法存在残流,有源消弧法又存在设备容量大、成本高等问题,提出了一种将线相变换器与有源补偿装置串联使用的混合补偿方法,利用线相变换器将故障相电源电动势反相接入中性点,考虑到线相变换器两侧存在电压偏差,利用有源补偿装置补偿此偏差,达到精确补偿目的,有源补偿装置采用比例谐振控制方式,对线相变换器二次侧电压进行实时跟踪控制,使线相变换器二次侧电压与有源装置输出电压之和恒等于故障相相电源电动势相反数。利用MATLAB/Simulink搭建10 kV配电网单相接地故障混合补偿仿真模型,仿真结果验证了该方法能够实现单相接地故障消弧,又能大幅度减小有源补偿装置的容量。

基于独立相电流控制的PET单级统一控制系统研究

电力电子变压器(PET)的控制系统结构通常采用dq解耦控制,当电网电压不对称时,不能自适应满足系统稳定运行,需加入复杂的辅助控制策略。提出一种独立相电流控制策略,使得不论交流系统对称与否,均能自适应保证PET系统三相间以及各子模块电容电压的稳定控制。该控制策略结合谐振变换器(CLLC型)的电压钳位特性,在保持供电可靠性的同时,简化了传统2级控制,实现单级统一控制。同时详细分析了在不对称交流电网下基于所提出控制策略的PET交流侧输入电流、电压及功率特性。基于PSCAD/EMTDC建立10 kV的PET系统仿真模型,在对称、不对称交流电网下进行功率控制和直流电压支持仿真实验,仿真结果验证了所提出的独立相电流控制策略的正确性、有效性。

Guaranteeing Wireless Communication Secrecy via a WFRFT-Based Cooperative System

In this paper, a weighted fractional Fourier transform(WFRFT) based cooperative overlay system, aiming to guarantee physical layer(PHY) security, is proposed. The paper elaborates how WFRFT and physical layer properties of the wireless medium are collaborated to guarantee the secrecy of wireless transmissions. In the proposed system, WFRFT is first preform on the secret data, such that the transmitted signal is distorted and can only be neutralized by inverse-WFRFT with the same parameter. And then two streams of the transformed sequences that bearing different messages are cooperatively and simultaneously transmitted to two legitimate receivers via a beamforming-liked method, respectively. In general, both the rapid spatial decorrelation property and the inherent security features of WFRFT are leveraged, such that only the eavesdropper's is degraded, and hence, the wireless communication secrecy is reliably guaranteed. Numerical simulations are conducted to evaluate the performance of the proposed system in terms of the average bit error rate and the secrecy capacity.

Multi-band Image Registration Method Based on Fourier Transform

This paper presented a registration method based on Fourier transform for multi-band images which is involved in translation and small rotation. Although different band images differ a lot in the intensity and features, they contain certain common information which we can exploit. A model was given that the multi-band images have linear correlations under the least-square sense. It is proved that the coefficients have no effect on the registration progress if two images have linear correlations. Finally, the steps of the registration method were proposed. The experiments show that the model is reasonable and the results are satisfying.

Fault location for parallel transmission lines using one-terminal current traveling waves

With proper phase module transformation,parallel lines can be decomposed to the same directional net and the reverse directional net. The propagation characteristics of traveling waves in the reverse directional net were analyzed,and the refraction coefficient at the fault point for a single phase fault was derived. In addition,the module selection was discussed. Simulation results show that satisfying accuracy can be achieved with the proposed method. Moreover,it is immune to fault types,fault resistances,and outside system parameters.

Thermal performances of non-equidistant helical-coil phase change accumulator for latent heat storage

Helical-coil is a common structure of heat exchanger unit in phase change heat accumulator and usually has the equal coil pitch between adjacent coils. Its thermal performances could be improved by improving the uniformity of the phase change material （PCM） temperature distribution. Thus, a novel non-equidistant helical-coil structure was proposed in this study. Its coil pitch decreased along the flow direction of heat transfer fluid, which made the heat exchange area in unit volume increase to match the decreasing temperature difference between the heat transfer fluid and PCM. The structure was optimized using numerical simulation. An experimental system was developed and the experiment results indicated that the proposed non-equidistant helical-coil heat accumulator was more effective than equidistant helical-coil for latent heat storage. The uniformity of the temperaalre distribution was also confirmed by simulation results.

Darboux Transformations and N-soliton Solutions of Two (2+1)-Dimensional Nonlinear Equations

Two Darboux transformations of the(2+1)-dimensional Caudrey–Dodd–Gibbon–Kotera–Sawaka(CDGKS)equation and(2+1)-dimensional modified Korteweg-de Vries(mKdV) equation are constructed through the Darboux matrix method, respectively. N-soliton solutions of these two equations are presented by applying the Darboux transformations N times. The right-going bright single-soliton solution and interactions of two and three-soliton overtaking collisions of the(2+1)-dimensional CDGKS equation are studied. By choosing different seed solutions, the right-going bright and left-going dark single-soliton solutions, the interactions of two and three-soliton overtaking collisions, and kink soliton solutions of the(2+1)-dimensional mKdV equation are investigated. The results can be used to illustrate the interactions of water waves in shallow water.

Spatiotemporal Rogue Waves for the Variable-Coefficient (3+1)-Dimensional Nonlinear Schrdinger Equation

With the help of the similarity transformation connected the variable-eoeicient （3＋1）-dimensionai nonlin- ear Sehroedinger equation with the standard nonlinear Schr6dinger equation, we firstly obtain first-order and second-order rogue wave solutions. Then, we investigate the controllable behaviors of these rogue waves in the hyperbolic dispersion decreasing profile. Our results indicate that the integral relation between the accumulated time T and the reai time t is the basis to realize the control and manipulation of propagation behaviors of rogue waves, such as sustainment and restraint. We can modulate the value To to achieve the sustained and restrained spatiotemporai rogue waves. Moreover, the controllability for position of sustainment and restraint for spatiotemporai rogue waves can aiso be realized by setting different values of Xo.

Exact Solutions of the Two-Dimensional Cubic-Quintic Nonlinear Schrdinger Equation with Spatially Modulated Nonlinearities

Applying the similarity transformation, we construct the exact vortex solutions for topological charge S≥1 and the approximate fundamental soliton solutions for S = 0 of the two-dimensional cubic-quintic nonlinear Schrodinger equation with spatially modulated nonlinearities and harmonic potential. The linear stability analysis and numerical simulation are used to exam the stability of these solutions. In different profiles of cubic-quintic nonlinearities, some stable solutions for S 〉 0 and the lowest radial quantum number n = 1 are found. However, the solutions for n ≥ 2 are all unstable.

Lax Pairs and Integrability Conditions of Higher-Order Nonlinear Schrdinger Equations

We derive the Lax pairs and integrability conditions of the nonlinear Schrdinger equation with higher-order terms, complex potentials, and time-dependent coefficients. Cubic and quintic nonlinearities together with derivative terms are considered. The Lax pairs and integrability conditions for some of the well-known nonlinear Schrdinger equations, including a new equation which was not considered previously in the literature, are then derived as special cases. We show most clearly with a similarity transformation that the higher-order terms restrict the integrability to linear potential in contrast with quadratic potential for the standard nonlinear Schrdinger equation.