Development of a new stabilized four-phase oscillator based on partial conservativity

The paper treats the development of a non-linearly stabilized oscillator model for generating four sine waves in quadrature. the treatment appears important although quadrature signals can also be generated by a well-known twophase oscillator. the latter generates only two of the signals needed in a four-phase system, but the rest of the phases signals could nevertheless be generated by simply inverting the two existing signals. For certain applications, however, the generation of all four signals in a completely cyclic and symmetrical manner is preferable. This method of generation is dealt with in the present paper. A previous paper of ours has treated a system of a similar objective. the present system, however, is much simpler. This simplicity is manifested not only through the mathematical representation but also when an electronic realization of the system is considered. the present model realization appears considerably less expensive, since the number of necessarily non-linear operations is much reduced. This reduction is due to the fact that the non-linearly stabilized model imbeds a ‘partially conservative’ linear oscillator. the concept of ‘partial conservativity’ has been introduced recently. the present work treats comprehensively the advantages that are gained by imbedding a partially conservative oscillator.     

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.     

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.     

一种用混沌振子去除局部放电信号中窄带干扰的新方法

如何有效地从现场大量的干扰中真实地提取局部放电信号,至今仍是提高在线监测系统的灵敏度和监测可靠性的难题.本文从非线性理论出发,提出用混沌振子去除局部放电信号中窄带干扰的新思路.讨论了用于判断混沌振子状态变化的Lyapunov指数的计算方法,仿真实验表明混沌振子对局部放电信号中的窄带干扰具有较强的敏感性,对局部放电信号和白噪声具有免疫力,能在保证原始局部放电信号失真较小的同时有效地去除窄带干扰.     

Duffing振子信号探测在故障电弧短路保护中的应用

Duffing振子信号检测技术利用混沌系统的分岔特性来检测外界信号,将待测信号作为Duffing方程周期策动力的摄动,利用初值敏感性可以获得很高的测量灵敏度和良好的抗噪性能。基于Duffing振子信号检测技术提出一种新型的故障电弧监测方法。在电弧没有发生燃弧之前有比较微弱的弧声信号,完全湮没在强背景噪声中,将含有噪声的弧声信号作为周期策动力加入混沌检测系统中,如果混沌检测系统处于间歇混沌状态,证明有电弧弧声产生,则故障电弧监测系统发出预警信号。实验表明,发生燃弧的瞬间,弧光、短路电流、弧声的幅值都有明显的跃变,以这3个电弧表征信息为判据,设定合适的幅值阈值,建立报警系统。实验结果表明该监测系统能实现对故障电弧的预警和报警功能。     

Effect of wind parks with doubly fed asynchronous generators on small-signal stability

This paper investigates modes of response introduced by wind parks with doubly fed asynchronous generators (DFAGs), as well as their impact on electromechanical oscillations in interconnected power systems. A DFAG model with detailed control loops is used, as it appears in the literature and commercial software. It is shown that under certain conditions and without appropriate controller tuning the voltage/VAR control loop of an interconnected DFAG tends to instability. Furthermore, the effect of increased penetration of DFAGs on the stability of inter-area oscillations in a small typical power system is examined. It is shown that the effect is generally favorable, but there are cases where the inter-area mode is less damped or can even be destabilized. Improved controller tuning to avoid instability in the latter case is proposed.     

Adaptive neural network output feedback stabilization of nonlinear non‐minimum phase systems

This paper presents an adaptive output feedback stabilization method based on neural networks (NNs) for nonlinear non‐minimum phase systems. The proposed controller comprises a linear, a neuro‐adaptive, and an adaptive robustifying parts. The NN is designed to approximate the matched uncertainties of the system. The inputs of the NN are the tapped delays of the system input–output signals. In addition, an appropriate reference signal is proposed to compensate the unmatched uncertainties inherent in the internal system dynamics. The adaptation laws for the NN weights and adaptive gains are obtained using Lyapunov's direct method. These adaptation laws employ a linear observer of system dynamics that is realizable. The ultimate boundedness of the error signals are analytically shown using Lyapunov's method. The effectiveness of the proposed scheme is shown by applying to a translation oscillator rotational actuator model. Copyright © 2009 John Wiley & Sons, Ltd.     

Frequency estimation by demodulation of two complex signals

This paper presents a method for frequency estimation in a power system by demodulation of two complex signals. In power system analysis, the αβ-transform is used to convert three phase quantities to a complex quantity where the real part is the in-phase component and the imaginary part is the quadrature component. This complex signal is demodulated with a known complex phasor rotating in opposite direction to the input. The advantage of this method is that the demodulation does not introduce a double frequency component. For signals with high signal to noise ratio, the filtering demand for the double frequency component can often limit the speed of the frequency estimator. Hence, the method can improve fast frequency estimation of signals with good noise properties. The method loses its benefits for noisy signals, where the filter design is governed by the demand to filter harmonics and white noise. The method has been previously published, but not explored to its potential. The paper presents four examples to illustrate the strengths and weaknesses of the method     

基于Duffing振子信号检测的故障电弧短路监测系统

Duffing振子信号检测技术利用混沌系统的分岔特性来检测外界信号,将待测信号作为Duffing方程周期策动力的摄动,利用初值敏感性可以获得很高的测量灵敏度和良好的抗噪性能.基于Duffing振子信号检测技术提出一种新型的电弧短路监测方法.在电弧没有发生短路之前有比较微弱弧声信号,完全湮没在强的背景噪声中,将含有噪声的信号作为周期策动力加入混沌检测中后,如果混沌检测系统处于间歇混沌状态,证明有电弧声音产生,弧声作为整个电弧短路监测系统预判和预警.弧声信号和发生电弧短路时的弧光、电流信号同时产生时,则发生电弧短路,监测系统发出报警信号.通过实验验证,证明该系统监测电弧短路具有很高的准确性和快速性.     

A series‐coupled LC quadrature oscillator using phase/amplitude calibration

In this paper, an analytic approach for the estimation of the phase and amplitude error in series coupled LC quadrature oscillator (SC‐QO) is proposed. The analysis results show that imbalances in source voltage of coupling transistor because of mismatches between LC tanks are the main source of the phase and amplitude error in this oscillator. For compensation of the phase and amplitude error, a phase and amplitude‐tunable series coupled quadrature oscillator is designed in this paper. A phase shift generation circuit, designed using an added coupling transistor, can control the coupling transistor source voltage. The phase and amplitude error can simply be controlled and removed by tuning the phase shifter, while this correction does not have undesirable impact on phase noise. In fact, the proposed SC‐QO generates a phase shift in the output current, which reduces the resonator phase shift (RPS) and improves phase noise. The phase and amplitude tunable SC‐QO is able to correct the phase error up to ±12°, while amplitude imbalances are reduced as well. To evaluate the proposed analysis, a 4.5‐GHz CMOS SC‐QO is simulated using the practical 0.18‐μm TSMC CMOS technology with a current consumption of 2 mA at 1.8‐V supply voltage. Copyright © 2016 John Wiley & Sons, Ltd.     

Damping enhancement of multimachine power system using adaptive generator control system with neural networks

The authors proposed a nonlinear adaptive generator control system with neutral networks for improving damping of power systems, and showed its effectiveness in a one-machine infinite bus test power system in a previous paper. The proposed neurocontrol system adaptively generates appropriate supplementary control signals to the conventional controllers such as the automatic voltage regulator and speed governor so as to enhance transient stability and damping of the power system. In this paper, the applicability of the proposed neurocontrol system to multimachine power systems is discussed. Digital time simulations are carried out for a 4-machine test power system, where one or several synchronous generators is equipped with the neurocontrol system. As a result, also in the multimachine power system, the proposed adaptive neurocontrol systems improve the system damping effectively and they work adaptively against the wide changes of the operating conditions and the network configuration.     

Local robust stability of mrac under persistent excitation assumption

In this paper the local robust stability of model reference adaptive control for time-varying plants with unmodelled dynamics under the persistent excitation condition is studied. It is shown that for arbitrary initial conditions of the adaptive system all signals in the adaptive loop are bounded if the command input is persistently exciting and the plant parameter variation and the magnitude of the unmodelled component are sufficiently small in the mean.     

A 5 GHz quadrature relaxation oscillator with mixing for improved testability or compact front‐end implementation

We demonstrate by measurements on a test circuit that a 5 GHz relaxation oscillator with accurate quadrature outputs and low phase‐noise can be obtained, and that these favorable properties can be preserved while the mixing function is performed by this oscillator. This is useful either to measure the quadrature error at a low frequency, or to implement a low‐intermediate frequency (IF) or zero‐IF (homodyne) radio frequency front‐end. Copyright © 2008 John Wiley & Sons, Ltd.     

Study on chaotic oscillator-based algorithm for weak GLONASS signal acquisition

According to the characteristics of the chaotic oscillator in detecting weak signals, an algorithm based on Duffing chaotic oscillator array was proposed for acquisition of weak GLONASS signals. By means of GLONASS intermediate frequency and Duffing chaotic oscillator models, Lyapunov exponent is adopted to judge the critical condition of phase track and decide whether GLONASS signals exist or not by the change of the critical condition, and numeric iteration procedure is used to calculate the exponent. Finally, the performance of algorithm is simulated using GLONASS intermediate frequency data. The results indicate that acquisition algorithm can satisfy the need of object positioning in low signal-to-noise ratio environment.     

A New Three-Phase Static Variable Frequency Changer

A new three-phase ac to ac static frequency changer is described. It accepts power from a conventional three-phase constant frequency (e.g., 60 Hz) source, and control signals from an auxiliary circuit, also three phase. The converter output may be represented by positive, negative, and zero sequence voltage systems, each system characterized by a particular frequency. By appropriate control, the lowest (fundamental) output frequency becomes fc -fs Hz, where fc is continuously controlled and fs is the constant supply frequency. Fundamental output frequency is associated with positive and zero sequence voltages. The process of conversion involves both free and forced commutation. It may be accomplished by four thyristors per phase, triggered by the square-wave control signals.     

Solutions for a three-dimensional non-linear stabilized oscillator

A system of coupled non-linear equations, describing a three-phase stabilized oscillator, is analysed by introducing ‘cyclotomic’ co-ordinates. We show that this system, under certain conditions, approaches asymptotically non-conservative linear systems; and yet it does have stabilized solutions (limit cycles). The non-linear system is solved analytically for an important class of stabilizing functions. We show that the frequency ω of our oscillator responds instantaneously to changes of certain parameters. This result has useful applications in building quickly responding novel electronic voltage-controlled oscillators.     

Duffing振子信号检测方法用于配电网单相故障接地保护

Duffing振子信号检测技术利用混沌系统的分岔特性来检测外界信号，将待测信号作为Duffing方程周期策动力的摄动，利用初值敏感性可以获得很高的测量灵敏度和良好的抗噪性能。基于Duffing振子信号检测技术提出一种新型的单相接地故障选线方法。故障后故障线路和非故障线路零序电流将使Duffing振子系统分别处于大周期或混沌状态，据此可以选出故障线路，从而将选线问题转化为待测故障信号从无到有的敏感检测问题，简化了选线过程，抗噪性能好，提高了接地保护的灵敏度。文中给出了该方法的具体实现步骤。采用虚拟仪器技术，开发了基于混沌选线方法的小电流接地系统单相接地故障选线仪。实验室物理模拟实验和现场录波数据分析结果证明了该方法的可行性和有效性。     

Analysis of mismatch impact on image rejection ratio for passive polyphase filters

Passive polyphase filters (PPFs) are useful symmetric RC networks for processing analog quadrature signals. Passive polyphase filters are also used to implement differential‐quadrature or quadrature‐differential converters. The quality of these quadrature signals is essential to achieve good performance in modern communication systems. However, mismatch effects can produce notable degradation in the PPF frequency response, and this results in an important reduction in quadrature signal quality, being amplitude balance and phase offset notably affected. Both these errors could be summarized and evaluated together considering image rejection ratio as a figure of merit. This work deepens in the analysis of mismatch impact on PPF, studying image rejection ratio degradation for 2 PPF types, and a systematic method is proposed to obtain the worst case of mismatch in PPFs with any number of stages. It has been validated in a 65‐nm CMOS technology.     

Synchronous generator control using neural network-based nonlinear adaptive regulator

Control equipment of synchronous generators such as automatic voltage regulators, speed governors and power system stabilizers have been developed to maintain stability and to improve damping of power systems. When an operating condition changes greatly, however, such controllers may become less effective because of nonlinearity of the power system. In this paper, a nonlinear adaptive generator control system using neural networks is proposed. The proposed neurocontrol system consists of two neural networks which work as an identifier and a controller, respectively, and generates supplementary control signals to the conventional controllers. An essential feature of the proposed system is that the internal connection weights of both neural networks are adjusted adaptively so as to generate appropriate control signals for transient stability and damping enhancement in response to changes of the operating conditions and the network configuration. To investigate the control performance of the proposed neurocontrol system, digital time simulations are carried out for a one-machine infinite bus model system. As a result, it is clarified that the proposed adaptive neurocontrol system effectively improves the system damping and shows adaptability against the wide changes of the operating conditions.