Study of fault location effect on the inter-area oscillations in stressed power systems using modal series method

Heavily loaded, stressed power systems exhibit complex dynamic behavior such as auto and hetero parametric resonances and inter-area oscillations when subjected to a disturbance. These behaviors cannot be analyzed by conventional linearization-based methods. Nonlinear tools, such as normal form and modal series methods can be utilized for studying and understanding these complex behaviors. In this paper, using modal series technique, the effect of fault location and duration on the dynamic performance of stressed power systems is investigated. Three indices are defined and used to explain the effect of different fault scenarios on the transient behaviors of the system. Also, a qualitative analysis of plant mode and inter-area mode type behaviors are presented and typical differences are highlighted. The numerical simulations on the IEEE 50-Generator test system demonstrate validity of the study carried out by modal series analysis.     

A Robust Deadbeat Control Method for UPS Inverters

The traditional deadbeat control for UPS inverters has a robustness problem. The parametric imprecision can greatly harm the stability of the system, which restricts the application. A novel robust deadbeat control method is proposed in this paper to deal with the problem. In the proposed control method, a proportional element is added to the traditional deadbeat control in order to improve the robustness to parametric imprecision. To eliminate the error between output voltage and voltage reference caused by environmental noise and parametric deviation, a model reference adaptive regulator is also added to the control method. A 1kVA prototype is built based on DSP. Theoretical analysis and experimental results show that the robustness for parametric variation of the proposed method is much better than the traditional deadbeat control. The system can remain stable even when the systemic parameters have a large deviation from calculating parameters. The system has small static error and fast dynamic response with the new control method. This method is easy to realize in DSP and is suitable for full digital realization of UPS.     

Dynamic Modes of Electromechanical Systems under Parametrical Disturbances

The results of a theoretical and experimental investigation of the influence of damping and pitch plays on the dynamics of electromechanical systems in the zones of main, harmonic, and subharmonic resonances under parametrical disturbances are presented. Design models of electromechanical systems taking into account spring linkages, pitch plays, mechanical damping, and inconstancy of a gear ratio and reduction radius are proposed. The equations and structural schematics describing the movement of electromechanical systems under consideration in the initial values and adopted system of generalized parameters and relative units are presented. The electric drive is described by a linear mechanical characteristic taking into account the electromagnetic inertia of power circuits. The problems of linearization of electromechanical systems under parametric disturbances are considered, and the zone parameters are revealed under which it is possible. The analytical relationships for determining the optimum parameters of electric drive and the estimation of resonant amplitudes of oscillations of the elastic torque are obtained. Results of analysis of the influence of pitch-play formation on the oscillations in the zones of main and subharmonic resonances are presented. Features of these oscillations related to the magnitude of average load of transmissions and the direction of change in the frequency of parametric disturbances are considered. The reliability of theoretical regulations and conclusions of the article are confirmed by the results of industrial experience in the use of various circuits of a reduction-gear electric drive of rotation of an excavator under parametric disturbances caused by a gear wheel meshing with the gear ring.     

Compensation for position‐dependent mechanical resonances in head‐positioning control of hard disk drives

We propose a compensation method for position‐dependent mechanical resonances in head‐positioning control system of hard disk drives (HDDs). To realize high‐accuracy head‐positioning control, it is important to compensate for the mechanical resonances in the head‐positioning control system. The some mechanical resonance characteristics depend on the magnetic head's location. In conventional design method, a notch filter must be designed to compensate for the mechanical resonances at any magnetic head location. The disadvantage is that phase lag caused by the notch filter worsens the stability of the head‐positioning control system. To overcome this disadvantage, we propose a magnetic head‐position‐dependent notch filter to compensate for the position‐dependent mechanical resonances in the head‐positioning control system. The simulation results in HDD benchmark model show that the proposed method can decrease the phase lag caused by the notch filter. That is, the proposed method can improve the stability compared to the conventional method. © 2015 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

电力系统受迫振荡检测与自适应振荡抑制研究

电力系统受迫振荡的振荡频率与系统跨区域振荡模态接近,因而能够引发强烈振荡。文中首先提出了一种受迫振荡模态检测方法,其通过小信号分析方法得出系统在受迫扰动下对应受迫振荡模态的解析形式;同时提出一种不需要安装额外的功率振荡阻尼器的功率振荡阻尼控制策略用于抑制受迫振荡以及跨区域振荡。并通过改进的14机系统验证文中方法的鲁棒性和优越性。仿真算例证明本文所提方法对于外界扰动具有较强鲁棒性,且较传统方法具有明显优越性。     

Determination of mechanical resonances in induction motors byrandom modulation and acoustic measurement

Acoustic noise emission from PWM-VSI inverter driven induction motors is a well-known problem. The generated noise depends mainly on two factors: the harmonic content of the supply voltage waveform; and the mechanical resonance frequencies of the induction motor. It is necessary to know the mechanical resonances to optimize the switching scheme of the inverter to reduce the noise emission. Measuring the resonance frequencies is normally a laborious process. This paper introduces a new method for estimating the mechanical resonances from acoustic noise measurements. Employing random modulation of the output voltage of the inverter, the voltage spectrum can be spread over a wide frequency range. Using the spectrum analysis of the measured acoustic noise, the resonances can easily be estimated as the dominant frequencies of the acoustic noise spectrum. The method was tested on a 2.2 kW induction motor at no load and full load. Some of the mechanical resonances of the motor at no load were calculated by the Holzer method. The calculations showed good agreement with the sound measurements. The influence of the fan cowl was investigated and it is concluded that this is an important factor in the acoustic noise emission. Finally, it was observed that new mechanical resonances appeared when the induction motor was loaded by a pump drive system, and they were estimated by the measurement technique     

Harmonic analysis of the output voltage of a third‐harmonic‐injected inverter for LSM drives

The superconducting magnetic leviation railway system (MAGLEV) under development in Japan uses pulse‐width‐modulation (PWM) inverter for driving a linear synchronous motor (LSM). The inverter output voltage contains nonnegligible harmonics which cause harmonic resonances in the LSM system, and therefore harmonics of the output voltage have been analyzed in order to control such harmonic resonances. This paper applies a third‐harmonic injection method to the inverter for the purpose of enhancing the output voltage without changing the circuit configuration. It performs harmonic analysis of the output voltage of the inverter based on the third‐harmonic injection. Validity of the harmonic analysis is verified by computer simulation. © 2007 Wiley Periodicals, Inc. Electr Eng Jpn, 160(1): 71–78, 2007; Published online in Wiley InterScience ( www.interscience.wiley.com ).     

A refinement procedure for PID controllers

Proportional-Integral-Derivative (PID) controllers are still extensively used in industrial systems. In the literature, many publications can be found considering PID controller design for processes with resonances, integrators and unstable transfer functions. However, due to structural limitations of PID controllers, generally, a good closed-loop performance cannot be achieved with a PID, for controlling the aforementioned processes, and usually a step response with a high overshoot and oscillation is obtained. PI-PD controllers provide very satisfactory closed-loop performances in the case of controlling processes with resonances, integrators and unstable transfer functions. This paper introduces a simple approach to get parameters of a PI-PD controller from parameters of a PID controller so that a good closed-loop system performance can be realized. Extensive simulation examples are given to illustrate the value of the approach proposed.     

Detection and clustering of light charged particles via system‐identification techniques

The problem considered in this work is the classification of the particles produced by the collision of a heavy ion beam on a target. Each particle is captured by a detector and results in a signal (which is the impulse response of a dynamic linear system), which is measured by a digital acquisition system. The assumption made herein is that the shape of the impulse‐response contains complete information on the particle, and the classification can be done by pulse‐shape, analysis. In this work, a complete procedure for the particle identification is proposed. The main idea is to use the cascade of a state‐space identification algorithm and a parametric non‐linear map using the model parameters as input regressors. The algorithm has been tested on a large set of impulse‐responses and provides a fully automatic accurate classification of the isotopes. This work focuses on isotopic identification of the most energetic light charged particles (LCP). All the experiments are made with the large detector array CHIMERA (Charge Heavy Ions Mass and Energy Resolving Array). Copyright © 2006 John Wiley & Sons, Ltd.     

谐波分析及谐振评估软件的开发与应用

结合模态分析法和谐波潮流算法,基于C#和Matlab语言开发出一套谐波分析及谐振评估软件.除换一般的谐波分析功能外,软件还具有2个特色功能:通过频率扫描能搜索出系统中所有的谐振点,对谐振点进行模态分析,得到系统中发生谐振的严重区域,并以参与因子指标反映谐振在系统中的分布;对加入滤波器后的系统进行频率扫描,若系统谐振点次数与谐波源次数相近,则重新调整滤波器参数,经反复调整与扫描直至系统谐振点次数不与谐波源次数相近,实现滤波器参数的优化设计,解决由于其参数设计不恰当而引起的谐波谐振或谐波放大问题.算例仿真结果表明该方法对谐波谐振评估以及无源滤波器参数优化是正确、有效的.     

计及电缆和风机功率的多风机并网谐振分析

为更精确的分析多逆变器并网系统中存在的串联和并联谐振现象,提出在单台逆变器小信号模型的基础上考虑输电电缆及风机输出功率的影响。首先,风电场常通过电缆与大电网相连,而电缆存在较大的对地电容,其对系统谐振的影响不容忽略,提出基于电缆的等值模型分析电缆电容对系统谐振的影响。其次,不同的风机输出功率会在电网中产生不同的阻尼效果,提出根据风机输出功率和公共连接点(point of common coupling,PCC)处负荷水平的大小确定负荷等效阻抗,进而分析风机输出功率对谐振点阻抗幅值的影响;最后,通过仿真验证理论分析的准确性。     

储能参与风电场惯性响应的容量配置方法

在当前风电高渗透率的背景下,电力系统对风电场的惯性响应能力提出了相应的技术要求。风电机组通过转子惯性控制可以提供一定的支撑,但受转子转速限制,风电机组难以在全风况下满足惯性响应需求。针对该问题,文中提出储能参与风电场惯性响应,将风电机组的转子惯性控制和储能控制相结合,使风电场具备类似于传统电源的惯性响应能力,并分析了不同风况下的储能容量需求,提出了基于非参数核密度估计的储能容量配置方法,摆脱了传统参数估计法对风速分布特性的依赖。算例分析表明,所提方法可有效降低储能配置容量,提高储能参与风电场惯性响应的技术经济性。     

一种基于前馈神经网络的NARMAX模型辨识新方法

本文提出了一种通过分析非线性动态系统的输入输出进行系统参数辨识的新方法。     

Sensitivity Analysis on Ladder Network Equivalent Circuit Parameters of Power Transformer

In this article, novel methods and ideas are introduced, which altogether lead to an accurate model of power transformer windings. First, by the determination of non-dominant (hidden) resonances from frequency-response tests, a ladder model is proposed. Next, it is improved by assigning different values for similar elements of each section of the model. The parameters are obtained by minimizing the error function via a genetic algorithm. Sensitivity analysis is then applied to the obtained model to achieve further examinations and tests. Measurements have been driven from the windings of a 20/0.4-kV, 1600-kVA transformer. Modeling, methodologies, and sensitivity analysis in this article can be very useful for future research aiming to find internal faults of the transformer with the frequency response analysis.     

变负荷条件下追踪电力系统安全最优运行轨迹的参数化方法

提出一种追踪线性约束下凸可分规划问题最优解轨迹的参数化方法。该参数优化算法可在对偶松弛凸可分规划算法的主循环之外,通过少量参数化扩展得到。参数分析表明最优解轨迹的性态是一条分段线性曲线,解轨迹上的破点和不可行现象存在密切关系。将这种方法应用到电力系统有功最优潮流问题中,得到一种统一经济调度和安全约束调度的参数化安全约束调度(security constrained economic dispatch,SCED)新算法,它可快速追踪变负荷条件下系统安全最优运行轨迹。算法在IEEE14-300节点测试系统及2个省级实际系统上通过测试,数值试验和几何分析表明了该方法的计算特性和物理内涵,同时清楚地显示了目前调度模式中存在的问题和改进方向。     

Robust adaptive iterative learning control for discrete‐time nonlinear systems with both parametric and nonparametric uncertainties

A new robust adaptive iterative learning control approach is proposed for discrete‐time nonlinear systems with both parametric and nonparametric uncertainties. By virtue of a well‐designed dead‐zone function, the learning of the parametric and nonparametric uncertainties can be performed concurrently. Rigorous Lyapunov function‐based analysis ensures that the effect of system uncertainties can be fully compensated, and the tracking error will converge to zero asymptotically in the iteration domain, even under random initial conditions and iteration‐varying reference trajectories. The efficacy of the proposed controller is demonstrated by simulating a single‐link robot manipulator with unknown frictions. Copyright © 2015 John Wiley & Sons, Ltd.     

Accurate extrapolation to zero cell size by Padé approximation

It is shown that extrapolation to zero cell size can be made accurately by means of Padé approximation. The extrapolation procedure is tested on waveguide cavity filters analysed by the finite difference‐time domain (FDTD) scheme. Extrapolation by the traditional Taylor series can yield unphysical results in the vicinity of resonances where it is outperformed by extrapolation based on the Padé approximation. Direct computation with the FDTD scheme (without extrapolation) requires extreme and infeasible resolutions to achieve a reasonable accuracy close to resonances. Copyright © 2003 John Wiley & Sons, Ltd.     

Robust damping control of power oscillation incorporating parametric resonance

In this paper we consider a damping control of low‐frequency oscillations in an electric power system. On the basis of the hypothesis that an auto‐parametric resonance model can explain a power oscillation, we propose a new model for a robust damping control, by which the system maintains stability even if some auto‐parametric resonance happens. With this model, we can express a parametric variation of a principal oscillation mode and a class of uncertainties which cover neglected dynamics. Since the model has a certain structure of uncertain parameters, we design a robust controller via µ‐synthesis. The robust controller which can be obtained from the presented design strategy has the property that the control performances are more sophisticated in comparison to controllers designed with other existing methods based on the H_∞ control. © 2002 Wiley Periodicals, Inc. Electr Eng Jpn, 142(1): 42–49, 2003; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.10069     

Computing Large-Scale System Eigenvalues Most Sensitive to Parameter Changes, With Applications to Power System Small-Signal Stability

This paper describes a new algorithm, named the sensitive pole algorithm, for the automatic computation of the eigenvalues (poles) most sensitive to parameter changes in large-scale system matrices. The effectiveness and robustness of the algorithm in tracing root-locus plots is illustrated by numerical results from the small-signal stability analysis of realistic power system models. The algorithm can be used in many other fields of engineering that also study the impact of parametric changes to linear system models.     

参数不确定Chen混沌系统鲁棒模糊控制器的设计

基于TS(Takagi-Sugeno)模糊模型，研究具有参数不确定性Chert混沌系统的鲁棒控制器设计。首先构建含有参数不确定性的TS模糊模型：然后利用并行分布补偿的方法，设计使模糊系统在平衡点附近渐近稳定的鲁棒模糊控制器。该设计通过解一组线性矩阵不等式(LMI)得到局部区域控制器，进而设计TS模糊系统的鲁棒控制器。该鲁棒模糊控制器的渐近稳定性条件更为宽松，能够降低控制器设计的保守性。最后的仿真结果表明所设计的鲁棒模糊控制器对参数不确定Chert混沌系统具有良好的控制效果。