Dynamic compensation of torsional oscillation in paper machine sections

Torsional oscillations bound the velocity loop bandwidth (BW) of industrial drives and servo systems, deteriorating the transient response to commands and disturbances. This is especially harmful in multidrive systems like paper machines that need to run synchronized. This paper presents two methods to dynamically compensate the torsional oscillations produced by the compliant components between the motor and the load: either a notch filter or an acceleration feedback based on the rigid-body Luenberger observer. The evaluation includes the effect of reducer backlash, whereby both time and frequency domain responses are used to compare the benefits of each technique in a typical paper machine section. Results show that both methods, if properly tuned, are effective techniques to reduce torsional oscillations and are robust to parameter variations.     

Static VAR system auxiliary controllers for damping torsional oscillations

A new concept is presented according to which a midpoint-located static VAR system (SVS) with appropriate auxiliary control can be simultaneously employed for damping torsional oscillations and enhancing the steady state power transfer limit. Two new SVS auxiliary control signals designated as computed internal frequency (CIF) and computed rotor frequency (CRF), which can be locally synthesized, are proposed. Various locally available signals for SVS control are examined in respect of their ability to stabilize all the torsional modes. It is shown from eigenvalue analysis that with a suitable choice of signal and SVS auxiliary controller parameters, the desired objective can be achieved even when the transmission line is compensated at a level where one of the torsional modes is critically destabilized.     

Design of controllers for the damping of torsional oscillations using time-scale decomposition

A new technique is presented for the design of an excitation controller and a static VAR compensator which are used to improved the damping characteristics of torsional oscillations in a capacitor-compensated power system. To facilitate the controller design, the system matrix is reduced by means of multi-time-scale decomposition while preserving the mechanical shift modes, which are the ones to be damped by the proposed controller. The parameters of the controller are then determined on the basis of the reduced system by using modal control theory. It is found that model reduction can save the effort in controller design without any significant drift in the eigenvalues of the closed-loop system. To demonstrate the effectiveness of the proposed damping scheme under disturbance conditions, computer-simulated dynamic response tests based on a non-linear system model are also performed. It is concluded that all subsynchronous oscillation modes can be effectively damped by the proposed controller.     

Electronic line-shafting control for paper machine drives

The current synchronized motion control methods used in paper machine drives are not designed to possess the inter-shaft stiffness properties which were responsible for the coordinating force inherent in classical, mechanically coupled paper machines. Consequently, these controllers cannot easily maintain coordination for all operating conditions. This paper presents the application of an “electronic line-shafting” control technique which serves to replicate and even improve on the historical, mechanical line-shafted properties. This technique was tested on a four-shaft experimental setup to evaluate such control during periods of drive-limited torque as well as sectional drive load disturbances. The experimental results demonstrate that the “electronic line-shafting” technique significantly improves the coordination, robustness, and overall stability of paper machine drives subjected to realistic physical limitations     

Impact of synchronous machine constants and models on the analysisof torsional dynamics

The authors investigate the impact of synchronous machine parameters and second-order and third-order models on the phenomenon of torsional dynamics. The results were compared with those obtained from the conventional (2d, 1q) model. For each model, the effect of rotor-field differential leakage flux on the damping of the torsional oscillations is studied. Numerical values of the elements corresponding to each model were obtained based on a parameter fitting process to a set of stand-still frequency response (SSFR) test results. An eigen analysis method was used for the studies. The eigen analysis results were verified by digital time-domain simulation, using the electromagnetic transients program (EMTP)     

Damping torsional oscillations of nuclear generators by using firing delay angle modulation of HVDC schemes

The paper presents the results of hybrid simulation studies of HVDC firing delay angle (α) modulation as a countermeasure to subsynchronous resonance (SSR) torsional oscillations occurring in a nuclear generator interfaced to the rectifier terminals of an HVDC transmission scheme. SSR oscillations can be amplified owing to the negative damping introduced by the HVDC scheme. This report illustrates the α modulation scheme and presents hybrid simulator results to ascertain its effectiveness in damping the low frequency SSR oscillation due to HVDC system control interactions.     

The damping effect of the flywheel dampers installed at different shaft couplings on torsional oscillations

This paper eamines the damping effect of flywheel dampers installed at different shaft couplings on torsional oscillations on the 951 MW turbine-generator shafts due to network faults. A studied system is described and torsional fatigue on the turbine shafts following various electrical system disturbances is analyzed and evaluated. Moreover, the influence of the safety factor selected and set at the design stage to the shaft life expenditure due to fatigue damage is also presented. Useful additional insight into their modes of operation is obtained from the fast Fourier transform of the transient response results. All computer simulations thus show that the proposed dampers are effective in suppressing the torsional oscillations on the shafts. In this paper, time-domain torque evaluation is also combined with the fast Fourier transform method to derive a selection procedure for obtaining suitable flywheel dampers to depress the amplitude of these critical shaft oscillations to acceptable levels.     

A fuzzy logic‐controlled SMES for damping shaft torsional oscillations of synchronous generator

This paper presents a fuzzy logic control scheme for the superconducting magnetic energy storage (SMES) based on a PWM voltage source converter and a two‐quadrant chopper using an insulated‐gate‐bipolar‐transistor (IGBT) to dampen turbine‐generator shaft torsional oscillations. Simulation results of balanced faults in a single machine connected to an infinite bus system show that the proposed fuzzy logic‐controlled SMES is effective in damping shaft torsional oscillations of synchronous generators (GENs). © 2006 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

Optimal digital control of a laboratory-scale paper machine headbox

This paper describes the design of a multi-input multi-output (MIMO) digital-linear-quadratic-regulator (DLQR) control system for the headbox of a paper machine. The complete design procedure is described from development of a mathematical model of the nonlinear headbox system, through experimental identification of linear model, to demonstration of closed-loop system performance on a laboratory-scale mock-up of an actual headbox. The important role of computer-aided-design tools is illustrated using Matlab and associated toolboxes. The control algorithm is implemented on a personal computer running the Labtech Notebook control program. The controlled system satisfactorily controls set point changes in total pressure and water level, and rejects disturbances in feedwater pressure. The material presented in the paper is used in a senior level course in digital process control at the University of Idaho. The course is jointly offered by the chemical and electrical engineering departments     

试论造纸机多传动系统的综合控制

造纸机的多传动系统是以速度控制为基础 ,负荷配比控制、静态补偿控制、张力控制相结合的综合控制     

Startup and commissioning procedures for electronically line-shafted paper machine drives

Electronic line-shafting control has demonstrated very promising features when applied to paper machine drives. To apply this new control methodology, it is necessary to develop a starting procedure for each individual section and a method for setting the parameters of the virtual line-shaft drive and in-shafts. This paper proposes and evaluates startup and commissioning procedures for electronically line-shafted paper machine drives. The procedure for acceleration of the individual sections is implemented using virtual variable-ratio gearboxes that emulate the physical clutches and conical pulleys used in the era of line-shafts. System stiffness is implemented using virtual in-shafts with active damping. Evaluation shows that the proposed virtual clutch/conical pulley assembly and active damping allow smooth acceleration of each section and maintain well-behaved response during load disturbances for all operating conditions, even with different numbers of sections effectively connected.     

纸机生产线变频速度、张力与负荷配比控制系统设计策略

介绍了变频调速及其控制技术在纸机生产线的上浆系统、分部传动、郑取系统和辅助设施与的广泛应用，并详细阐述了具体的控制要求和实现的控制策略。     

汽轮发电机组扭振引起疲劳损伤评价

传统PSCAD/EMTDC仿真中轴系采用简单集中质量模型,难以准确描述轴系扭振特性,并且无法获取局部动态响应过程。本文在PSCAD仿真中建立了轴系的多段集中质量模型模块,更加准确仿真机网耦合振荡过程并获得局部扭应力响应;建立联轴器的有限元模型,对于不同工况下螺栓和螺孔的受力情况进行分析。结果表明,对轴系疲劳分析过程中的S-N曲线进行修正,可以使得最终疲劳损伤评估计算结果更加准确。     

基于AB PLC的纸机负荷与速度控制

本文通过分析负荷分配产生的原因,实现罗克韦尔AB PLC通过DEVICENET网络控制施耐德变频器ATV 71,采用转矩限幅和速度相结合的方式,解决了负荷分配和速度链问题,对生产线稳定运行提供保障,也有利于生产线的节能降耗。系统运行过程中,运行稳定,断纸率大幅度降低,节能效果显著。     

MA—Ⅲ型纸机控制器的研究与设计

介绍一种智能型速度链传动控制装置—MA—Ⅲ型纸机速度链控制器。它以8031单片机为控制核心。采用数字调节、D/A、V/I转换的方法输出给定直流电流信号，并可测量数字反馈输入。同时介绍了其工作原理、硬件设计、软件编制和使用方法。     

基于PCC的纸机异步电机模糊控制系统

交流传动的纸机在高速运行时,由于系统建模带来的控制偏差对精度的影响随速度升高逐 渐增大,采用模糊控制可以摒弃建模偏差的影响。针对传统模糊控制稳态精度差的缺点,采用分段模 糊控制,并加入PI环节抑制稳态颤振,实现了高精度控制;硬件采用贝加莱公司的PCC。结果表明, 该方法接线简单,并通过软件编程实现了模糊控制,节约了硬件,克服了传统PID控制超调量大的问 题。精度高、动态响应快、开放性好、可靠性高,易于工程实现,为纸机传动控制打下了良好的理论和 实验基础。     

Frequency-response analysis of torsional dynamics

This paper introduces a frequency-domain approach for investigation of the phenomenon of torsional dynamics. The Nyquist criterion is adopted by the proposed method to identify stability regions with respect to torsional oscillations. This paper also introduces two performance indices to evaluate torsional dampings and propensity of the system to experience torsional oscillations. The proposed method is an alternative approach to the eigenvalue analysis method and the complex torque method for investigation of torsional dynamics. The salient features of the method as compared with the aforementioned two methods are: 1) its computational efficiency since it utilizes the open-loop transfer-function matrix of the system and inherently more advantages for large size systems; 2) its performance indices that readily reveal "damping of" and "propensity to" a torsional oscillatory mode; and 3) its capability to formulate a multimachine system which includes both induction and synchronous machines. The proposed method is applied to the First IEEE Benchmark Systems for SSR studies and the results are verified based on comparison with those obtained from eigenvalue studies and digital-computer time-domain simulation.     

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)     

支持向量机评定同轴度误差测量不确定度

针对目前评定同轴度误差测量不确定度过程复杂,且误差分布未知的情况下很难估计测量结果的概率分布及其不确定度的问题,以现有少量数据为基础,基于支持向量机法求取被测量数据的概率密度,并利用所得概率密度分布进行数值积分,计算其估值和标准不确定度。通过实验结果证明了在小样本数据的条件下,支持向量机法得到的样本的最佳估值和方差的准确度。最后以一个工程实例即机床芯轴的一段阶梯轴的同轴度误差为测量对象进行实测实验,评定其测量不确定度,并对比《测量不确定度表示指南》法、蒙特卡洛法的评定结果,验证了方法的可靠性及准确度。     

基于随机森林的油纸绝缘老化阶段评估

为了更准确地评估变压器油纸绝缘老化阶段,提出了一种基于EMD-SVD特征和随机森林分类器相结合的识别方法。搭建实验平台采集得到气隙缺陷样本的不同热老化阶段局部放电信号,去噪处理后对信号进行EMD-SVD特征提取得到相应局部放电信号特征量,并分别利用随机森林分类器与传统分类器BP神经网络和支持向量机对EMD-SVD特征进行分类识别。结果显示随机森林分类器识别效果优于传统分类器,对于提取的油纸绝缘局部放电信号EMD-SVD特征,随机森林分类器分类能力更强。分析表明首次将EMD-SVD特征与随机森林分类器相结合应用在油纸绝缘热老化阶段识别方面能够取得更好的效果。