New structures of four‐phase oscillators obtained by strongly interweaving mono‐phase limit‐cycle oscillators

The present work is a part of our effort of developing multiphase oscillators. The particular system dealt with here is that of strongly nonlinearly coupled four oscillators that form a multiphase source. Such sources possess potential applications in power electronics, in phased‐array antennas, and in modern methods of modulation and especially in demodulating multi‐phased modulated signals. The present system can be interpreted as embracing four two‐phase oscillators. Nevertheless, as a result of the strong coupling, the second state equation of each oscillator merges with the first equation of the following oscillator. The resulted four‐phase source is, therefore, represented by merely four state equations. The applications related to communications (especially those related to receivers) may be susceptible to the noise performance of the source. We believe that the presently suggested system, which relies on strong coupling of oscillators, is advantageous in its noise performance in comparison to more straightforward recently described multiphase sources, which incorporate loosely coupled oscillators. Copyright © 2007 John Wiley & Sons, Ltd.     

Two high-performance and low-power serial communication interfaces for on-chip interconnects

This paper presents two novel methods for on-chip serial communication in which the clocks of the transmitter and the receiver are generated with two separate ring oscillators. These oscillators are identical, although they can have a small frequency difference. In the first method, a strobe line that toggles exactly once with every frame of n-bit data is used to activate the oscillators. Local counters are used to count the number of bits in the data frame and to stop the local oscillators when the frame has been processed. In the second method, a single physical line is used to transmit both data and (in-band) control information, further reducing the power dissipation. The data transmission is controlled by the output of a starter flip-flop that indicates the empty/full state of an input buffer, whereas the data reception is controlled by the decoding of a ?1? start bit and a ?0? end bit, both of which are added to the n-bit data word to form a frame. Circuit simulation results demonstrate that both communication methods have high bandwidth and low power dissipation.     

On the development of symmetrically stabilized five-phase oscillators and some implications

The paper deals with the development of a symmetrically stabilized five-phase oscillator. the development results from two origins. It employs on one hand a five-phase conservative oscillator. On the other hand the stabilization process of the oscillator is due to similar non-linear damping terms in earlier developments of stabilized three-phase oscillators. A new feature of the present system is that it possesses an interesting steady state limit-cycle behaviour. the two possible steady state oscillations are similar, since both of them consist of a five-phase balanced set of phasors which are arranged symmetrically. However, each mode of possible steady state oscillation possesses its own unique frequency, although the amplitudes are equal. Another interesting feature of the oscillator is related to the way in which the various possible solutions (oscillatory, steady state, stable and unstable dynamic behaviours) evolve from initial conditions. There seem to exist regions where the system solutions appear sensitive to minute changes in initial conditions. It appears that completely different types of dynamic behaviours can develop from initial conditions in close proximity, which may lead eventually to the development of slightly modified systems with chaotic dynamics. the paper concludes by suggesting an application of multiphase oscillators for feeding phased array antennas.     

Hyperchaotic behaviour of two bi‐directionally coupled Chua's circuits

In this paper, a non‐linear bi‐directional coupling of two Chua's circuits is presented. The coupling is obtained by using polynomial functions that are symmetric with respect to the state variables of the two Chua's circuits. Both a transverse and a tangent system are studied to ensure a global validity of the results in the state space. First, it is shown that the transverse system is an autonomous Chua's circuit, which directly allows the evaluation of the conditions on its chaotic behaviour, i.e. the absence of synchronization between the coupled circuits. Moreover, it is demonstrated that the tangent system is also a Chua's circuit, forced by the transverse system; therefore, its dynamics is ruled by a time‐dependent equation. Thus, the calculus of conditional Lyapunov exponents is necessary in order to exclude antisynchronization along the tangent manifold. The properties of the transverse and tangent systems simplify the study of the coupled Chua's circuits and the determination of the conditions on their hyperchaotic behaviour. In particular, it is shown that hyperchaotic behaviour occurs for proper values of the coupling strength between the two Chua's circuits. Finally, numerical examples are given and discussed. Copyright © 2002 John Wiley & Sons, Ltd.     

Nonlinear dynamics of semiconductor lasers with mutual optoelectronic coupling

Mutually coupled oscillators are currently of great interest because of the important insight they provide into coupled physical, chemical, and biological systems. Two semiconductor lasers with optoelectronic feedback are used as two nonlinear oscillators, and the effect of mutual coupling on these lasers is found to be significant. Depending on the operating conditions, mutual coupling can act as a negative feedback to stabilize the coupled oscillators, or it can increase the complexity of the system inducing a highly complex chaos. A quasi-periodicity and period-doubling bifurcation, or a mix of them, is found in such a system. Although the chaotic waveforms are very complex with broad spectra, a high quality of synchronization between the chaotic waveforms is observed. Such synchronization is achieved because of the effect of mutual coupling and the symmetric design between the two lasers. It is found that the time delay of coupling plays an important role on the dynamics and synchronization in the mutually coupled semiconductor lasers.     

基于事件触发的多电机系统一致性控制

针对传统环形耦合控制策略中误差传递迟滞现象随着电机数量增加变严重的问题,提出一种基于事件触发的多电机系统一致性控制策略。通过一致性算法获取多电机系统中各电机的转速补偿项,以保证各电机转速一致性的同时,提升系统的跟踪性能。当系统达到稳态后,通过事件触发机制,减少非必要的通信次数,节约通信资源。另外,环形耦合结构可保证在事件触发阈值内系统的同步性能,且触发阈值随时间增加而减小。仿真结果表明,相较于传统环形耦合控制策略,所提策略的多电机系统具有更好的同步性能及跟踪性能,且随着系统中电机数量的增加,误差传递迟滞问题得到明显的改善。同时,事件触发控制有效减少稳态过程中非必要的通信次数。     

Modelling and analysis of differential VCOs

We present a systematic non‐linear analysis of differential voltage controlled oscillators (VCOs), both bipolar and MOS. Using the standard device models, we derive the second‐order non‐linear equation describing the behaviour of these oscillators, which is formulated in a perturbation form. The solution of this equation is obtained as a particular case of the solution of the most general equation of second‐order oscillators, which is solved through a suitable perturbation method. Unlike a pure numerical analysis, simple analytical relationships are derived for predicting the steady‐state oscillation, its transient behaviour and for ascertaining the existence of a stable oscillation in differential VCOs. These relationships, leading to results which well agree with the SPICE simulations, are useful in both analysis and design. Copyright © 2004 John Wiley & Sons, Ltd.     

Coupling phenomenon of torsional modes

The coupling of the torsional modes of a steam turbine-generator (T-G) set is investigated. The impact of generator load, series capacitor compensation level, power system stabilizer, and auxiliary controllers of a static VAr compensator on the torsional coupling phenomenon is investigated. The system eigenstructure is used to develop an analytical formulation for detecting the coupling and determining its strength. The analytical results are verified by detailed digital computer simulation studies, using the BPA's Electromagnetic Transients Program. The studies indicate that, depending on the network configuration and parameters, two or more of the torsional modes of a T-G set can be coupled. The coupling level can be significantly affected by the controller parameters and feedback signals of the torsional countermeasure devices. As a result of the coupling, a torsional oscillatory mode can excite and even destabilize its corresponding coupling mode(s)     

电磁耦合谐振式传能系统的频率分裂特性研究

电磁耦合谐振式无接触电能传输系统的发射侧与接收侧同时工作于谐振状态,补偿电容的引入导致系统在不同工况下可能存在多个谐振点。控制策略选取不当,会导致负载接收功率减少、系统性能大幅下降。首先通过耦合模理论建立电磁耦合谐振系统的高阶数学模型,在此基础上深入分析模式耦合因数及品质因数对系统谐振角频率的影响,并得出不同工况下谐振角频率的变化规律。最后根据理论分析设计了盘式振荡器耦合系统进行实验。测量结果表明,实际频率分裂特性与理论推导的函数关系基本吻合,因此可为谐振式电能传输系统的设计提供参考。     

Experimental comparison of phase‐noise in cross‐coupled RC‐ and LC‐oscillators

Relaxation RC‐oscillators are notorious for their poor phase‐noise performance. However, there are reasons to expect a phase‐noise reduction in quadrature oscillators obtained by cross‐coupling two relaxation oscillators. We present measurements on 5 GHz oscillators, which show that in RC‐oscillators the coupling reduces both the phase‐noise and quadrature error, whereas in LC‐oscillators the coupling reduces the quadrature error, but increases the phase‐noise. A comparison using standard figures of merit indicates that quadrature RC‐oscillators may be a viable alternative to LC‐oscillators when area and cost are to be minimized. Copyright © 2009 John Wiley & Sons, Ltd.     

基于失效物理的多模式耦合可靠性建模方法*

电子系统由于其功能结构复杂,且工作在多载荷耦合的复杂环境条件下,导致其失效模式较多。因此,电子系统的失效更多的是多个失效模式共同作用的结果。而目前关于电子系统多模式耦合条件下的可靠性建模方法较少。针对电子系统多模式耦合条件下的可靠性建模方法进行研究。首先,通过基于失效物理的可靠性仿真分析方法获取各个单一失效模式的寿命分布信息,进而利用Copula函数对多模式耦合下的系统建立可靠性模型,给出了可靠度计算方法。最后,以某型综合电子系统进行案例研究,说明提出的方法能够获取更为准确的系统可靠度计算结果,避免了过于保守的可靠性评估。     

Hyperchaos from two coupled Wien‐bridge oscillators

This paper proposes a simple inductorless approach to generating hyperchaos by coupling two Wien‐bridge oscillators with a resistor and a diode. The whole circuit is investigated both numerically and experimentally. Also, its hyperchaotic dynamics is studied theoretically by a topological horseshoe with two‐directional expansions which provides an immediate evidence of hyperchaos. Copyright © 2007 John Wiley & Sons, Ltd.     

The Rashba effect and non-Abelian phases in quantum wire devices

We present a 2D method for studying quantum transport through arbitrary geometries under the influence of both external magnetic fields and Rashba spin-orbit coupling. We apply this method to two geometries—a straight wire and a ring structure. Our results reveal the precession of spin-polarized modes in the straight wire, and conductance resonances in the ring due to phase shifts from the magnetic field and from the Rashba effect. The conductance resonances arising from the Rashba effect are due to the non-Abelian nature of the phase shifts acquired by electrons propagating around the ring.     

基于温度场的双馈异步发电机电刷滑环系统故障诊断模拟

应用热电耦合原理,利用ANSYS有限元分析平台建立了双馈风力发电机电刷滑环系统温度场仿真模型,对正常运行状态下的电刷滑环系统温度场进行仿真,给出了系统各部件温度场及电流密度矢量分布。通过对模型中不同电刷加载大小不同的电流载荷来模拟电刷电流分布不均匀故障,对该故障进行暂态仿真分析,同时对刷环系统在正常运行状态下与故障运行状态下的热电场分布做了比较分析。最后,给出相关结论,对电刷滑环系统的温度场状态监测及其过热故障预期具有指导意义。     

采用VSC-HVDC并网的直驱风电场次/超同步振荡特性

风电、光伏经由高压直流输电系统并网外送已经成为大规模可再生能源基地的主要输送方式。对于风电引发的次/超同步振荡问题,尤其是直驱风电机组与柔性高压直流(VSC-HVDC)输电系统之间相互作用引发的次/超同步振荡问题值得深入研究。首先,分别建立直驱风电机组与VSC-HVDC的动态模型,并深入分析与推导两者之间的接口矩阵与接口动态方程,进而得到直驱风电机组经VSC-HVDC并网外送的完整动态模型。在此基础上,采用特征值分析法计算得到各振荡模式的参与因子,并根据模式参与因子判断出次/超同步振荡模式之间存在阻尼耦合。通过PSCAD/EMTDC进行时域仿真,验证了模型与特征值分析结果的正确性。进一步深入分析风电并网距离/阻抗、直驱风电机组机/网侧控制器与VSC-HVDC送/受端控制器参数对次/超同步振荡阻尼特性的影响,结果表明:同一个控制器参数可同时影响多个次/超同步模式,同一个次/超同步模式可同时受多个控制器参数影响,并且这种阻尼耦合的影响可能趋同(调节控制器参数,耦合的两种模式的阻尼比同向变化),可能趋反(调节控制器参数,耦合的两种模式的阻尼比反向变化),也可能趋同与趋反同时存在。     

数据驱动的电力系统运行方式分析

随着电网中高比例可再生能源及电力电子设备渗透率的提高,电力系统的运行形态将发生深刻变化,基于经验选择的电力系统方式分析,越来越难以应对电力系统运行、规划、保护和稳定分析的要求。为此,该文基于电力系统时序运行模拟数据,提出了数据驱动的电力系统运行方式及其形态变化分析方法。该方法首先对高维运行模拟数据进行预处理,通过聚类和紧密度指标饱和点分别辨识典型运行模式及其数量,利用t-SNE降维算法提取主要特征并可视化运行方式的时空变化规律;接着,从定量的角度,提出了描述电力系统运行方式分散性、季节一致性、时序多变性的评估指标。最后,以甘肃电网实际算例系统分析了高比例可再生能源对电力系统运行方式的影响,验证了文中数据驱动方法的有效性。实验结果表明,电力系统运行方式的分散性及典型运行方式的数量会随着可再生能源渗透率的上升而迅速增加。此外,电力系统运行方式与季节的耦合性逐渐减弱。     

大跨越输电塔动力特性

大跨越输电塔-线体系是一种复杂的空间塔线耦联体系,体系动力特性计算中由于导、地线的振型密集,输电塔的振型难以辨清。在对大跨越输电塔-线体系的动力特性研究中,采用白噪声激励体系,得到输电塔耦合了导、地线的响应;利用振动模态识别技术,可得到输电塔耦合了导、地线的低阶模态。以多条输电线路工程中不同类型、不同高度输电塔为原型,建立空间有限元模型,利用振动模态识别技术提取出大跨越输电塔-线体系中塔架结构的第1 自振周期及其振型,得到适用于大跨越酒杯塔和大跨越干字型塔的第1 周期近似计算公式。对工程实例的仿真分析表明,该公式能比较准确地反映大跨越输电塔-线体系的动力特性,值得推广应用。     

Membrain: A cellular neural network model based on a vibrating membrane

This paper introduces the Membrain model describing a neural network architecture which is similar to the architecture underlying the class of cellular neural networks (CNNs). the main difference pertains to the characteristic processing equation, which is based on a wave equation instead of a heat equation. Within the CNN framework, a cellular Membrain model may be obtained by replacing the neuron output function by a first-order state equation. Furthermore, the network-cloning templates are chosen such that the CNN behaves like a system of coupled harmonical oscillators. Since the energy of such a system is bounded, the piecewise linear neuron characteristic function may be chosen such that it always operates in the linear regime. Our starting point is the analytical and general solution for forced vibrations with damping. This solution applies to a Membrain neural network whose functional architecture is based on the specialized solution for a network of coupled harmonic oscillators. In particular, we present a Membrain CNN (MCNN) having a toroidal connection structure such that the natural modes of vibration of the net are translation-invariant. Moreover, depending on the point group of the network, some rotation invariance can also be obtained. Identifying the input of such a network with the initial state of the oscillators gives rise to an output which is in essence a transversally travelling wave made up of components which are coupled harmonic neuronal oscillators; that is, the wave is a superposition of natural modes of vibration of the network. the temporal wave pattern may be transformed into a one-dimensional temporal signal which is invariant under translation of the initial deflection pattern of the MCNN. the amplitudes of the components in the temporal signal correspond to the power spectrum of the natural vibration modes in the MCNN. Interpreting the initial deflection pattern as a grey-level image, the temporal signal can be viewed as a modulation of a translation-invariant ‘fingerprint’ of the image. the signal may be sampled such that the modulated ‘fingerprint’ can be classified using some of the traditional neural network models. In particular we show that (1) a self-organizing feature map clusters correlated images and (2) a back-propagation neural network extracts position-invariant features.     

调匝式消弧线圈自动调谐新方法

针对调匝式消弧线圈现有的调谐方法测量准确度差、不能适应在牵手变电站中并联运行的问题,提出了利用谐振法结合曲线拟合法来调谐测量系统电容电流的新方法。新方法测量准确度高,调挡数目少,能自动并联,无需相互通信,适合在各种场合并联运行。模拟电网试验和现场运行试验结果令人满意。     

风火打捆系统次同步模式相互作用特性

风电和与其打捆的火电机组的模式相互作用存在诱发次同步振荡的风险。研究了风火打捆系统的模式准强相互作用的规律：随着参数的改变,直驱风机(permanent magnetic synchronous generator, PMSG)锁相环(phase-locked loop, PLL)模式靠近火电轴系模式并发生模式准强相互作用,两个模式的运动方向发生改变,其中的弱阻尼模式穿越虚轴快速变为负阻尼模式,引发次同步振荡,模式相互远离后系统振荡消失。研究表明,火电厂汽轮发电机轴系模式和PLL模式都可能穿越虚轴导致次同步振荡,而系统主要振荡的部分由负阻尼的模式决定。增强发生耦合的模式的阻尼有利于抑制相互作用,增大并网风机数量与线路阻抗都会加剧系统次同步振荡风险和振荡程度。最后基于PSCAD/EMTDC搭建风火打捆系统模型验证了理论分析的正确性,并提出应对措施避免振荡的发生。