Excitation control of a synchronous generator using a lookup table

A scheme involving the use of a lookup table is developed for the excitation control of a synchronous generator. The proposed control scheme, generator speed deviation, and acceleration deviation are taken as the input signals. These input signals are sampled and converted to linguistic terms before they are fed into the controller. The controller generates the desired output (control) signal by using a set of production rules (if-then rules) that are based on previous experience to relate the input signals to the output. The output signal is converted from linguistic terms to a numerical value before it is sent to the excitation system of the synchronous machine. To demonstrate the effectiveness of the proposed control scheme, digital simulations of a synchronous generator subject to a three-phase fault under different operating conditions were performed. It was found that the controller can improve the dynamic performance of a synchronous generator over a wide range of operating conditions. Since the controller does not require model identification, it is computationally efficient and is suitable for online excitation control, using a microcomputer     

Large-eddy simulation and linear acoustic modeling of entropy mode oscillations in a model combustor with coolant injection

Lean-burn combustor is particularly susceptible to combustion instability and the unsteady heat release is usually considered as the excitation of the self-maintained thermo-acoustic oscillations. The transverse coolant injection is widely used to reduce the temperature of burnt gas, but on the other hand, it will introduce temperature fluctuation inside the combustor. Therefore, it is necessary to consider the influence of the coolant injection on combustion instability, and evaluate its dynamic feature. In this paper, Large-Eddy Simulation (LES) of the self-excited pressure oscillations in a model combustor with coolant injection is carried out. The analysis of transient flow characteristics and the identification of the pressure modes confirm that one of the low frequency pressure oscillations is related to entropy fluctuations, which is known as rumble combustion instability. The LES results show that transient coolant injection is another excitation of temperature fluctuation other than unsteady combustion. The amplitude of the entropy mode oscillation increases with increasing coolant air mass whereas the change of its frequency is insignificant. According to the major feature of entropy wave oscillation caused by coolant injection, a compact coolant injection model is proposed and applied in the One Dimensional (1D) Acoustic Network Method (ANM). Key correlations used in the model match well with LES data in low frequency range. This means that the coolant injection model is a complex one reflecting the interaction of the fluctuating coolant mass, pressure and temperature. Finally, the combustion instability frequencies and modes predicted by acoustic network method are also in good agreement with LES results.     

基于压电纤维复合材料的离心叶轮叶片高阶模态测量

为准确获取离心叶轮叶片的高阶振动特性及其模态,利用压电纤维复合材料(Marco fiber composite,MFC)对离心叶轮叶片进行模态测试。设计了MFC激励系统,提出了MFC选型、激励和测点位置的确定方法,研究了不同信号的高阶模态激励效果,并分析了MFC附加质量和刚度对叶片固有频率和模态的影响;结合有限元仿真结果,对比分析了前20阶振动模态的异同。试验结果表明:MFC具有操作简单、重复性好、信噪比高、能够稳定激励出高阶模态等优势,计算模态与测量模态吻合较好,在第6～8阶与第12～15阶之间存在模态密集区域;MFC附加质量和刚度对实验固有频率的影响低于4%。提出的MFC激励方法可用于具有较高固有频率的航空发动机部件的模态测量。     

VTOL Aircraft Control Output Tracking Sensitivity Design

A method is presented for reducing trajectory sensitivity and achieving robust asymptotic tracking for linear feedback systems when there are parameter perturbations and disturbance inputs. The controller consists of a servocompensator containing the modes of the reference signals and disturbance inputs, a stabilizing feedback loop, and a feedforward compensator. Application of the method to the design of a vertical takeoff and landing (VTOL) aircraft flight control system is discussed. The use of a precompensator allows performance maneuvers such that the aircraft tracks desired trajectories and the feedforward and feedback signals aid in reducing the trajectory sensitivity to variations of parameters due to change in airspeed and to wind gust. Simulation results are presented to show the robust tracking, disturbance rejection, and sensitivity reduction capabilities of the flight control system.     

Electromagnetic resonances in the polar ionosphere

The utilization of resonant oscillations for ionospheric modification experiments and ionospheric diagnosis, based on plasma physics and non-linear electrodynamics, is discussed. The spectra of resonant oscillations of natural and artificial origin in the polar ionosphere and the excitation of these oscillations and their development are analysed. The thermal instabilities in weakly ionized heterogeneous magnetoactive ionospheric plasma, due to plasma heating, are illustrated. The circle of resonant situations in the polar area is expanded essentially due to intense current systems in this region.     

热声耦合振荡燃烧的实验研究与分析

热声耦合振荡是在推进系统工作中经常遇到的危害系统工作及安全的现象。它是由非稳定燃烧放热和压力脉动互相耦合产生的系统振荡过程。通过对天然气预混燃烧过程中的热声耦合振荡现象进行了实验研究,分析了不同当量比、热负荷和进出口边界条件下天然气燃烧的动态过程,分析其稳定范围及振荡模态随影响因素的变化规律。结果显示振荡频率随着当量比的减小有所增加,但是没有发生模态变化。在常压条件、接近贫燃熄火极限时,热声耦合振荡现象消失,压力脉动频率跃升至500 Hz或1000 Hz附近的高频。燃烧室出口越接近阻塞条件,燃烧过程的稳定范围越小。同时入口边界位置越接近燃烧段,压力脉动频率越高。热功率变化也会对脉动频率和声压级数值产生影响。另外还采用线性扰动分析方法对天然气燃烧动态过程进行理论分析,进一步研究了不同条件下旋流预混燃烧的热声耦合振荡模态。     

有声腔推力室的声学振型及其阻尼特性研究

为确定多声学模态压力振荡条件下带有1/4波长管声腔推力室的声学振型及其阻尼特性,揭示1/4波长管声腔对推力室压力振荡的抑制作用机理,对有声腔推力室和无声腔推力室进行近圆周壁面的定容弹激励仿真,激发了多模态的声学振型,给出了推力室压力分布的时空演化,并采用半带宽法定量评价每个激发声学振型的阻尼特性.结果表明:1/4波长管...     

模态截断与简谐载荷的响应

利用矩阵级数展开和特征值问题的谱叠加原理,将截断模态对响应的贡献用已知模态和系统矩阵来精确表达,从而可提高计算精度。数值算例表明本文方法是有效的。     

Standing Slow-Mode Waves in Hot Coronal Loops: Observations, Modeling, and Coronal Seismology

Strongly damped Doppler shift oscillations are observed frequently associated with flarelike events in hot coronal loops. In this paper, a review of the observed properties and the theoretical modeling is presented. Statistical measurements of physical parameters (period, decay time, and amplitude) have been obtained based on a large number of events observed by SOHO/SUMER and Yohkoh/BCS. Several pieces of evidence are found to support their interpretation in terms of the fundamental standing longitudinal slow mode. The high excitation rate of these oscillations in small- or micro-flares suggest that the slow mode waves are a natural response of the coronal plasma to impulsive heating in closed magnetic structure. The strong damping and the rapid excitation of the observed waves are two major aspects of the waves that are poorly understood, and are the main subject of theoretical modelling. The slow waves are found mainly damped by thermal conduction and viscosity in hot coronal loops. The mode coupling seems to play an important role in rapid excitation of the standing slow mode. Several seismology applications such as determination of the magnetic field, temperature, and density in coronal loops are demonstrated. Further, some open issues are discussed.     

Reduced-order multiple model adaptive controller for flexiblespacestructure

The robustness of a moving-bank multiple model adaptive estimator/controller to order reduction in the controller design model is examined. It is shown that the adaptive mechanism and bank-moving logic are not confounded by the effects of unmodeled higher order modes of a large flexible spacestructure. Control characteristics are achieved that are essentially equivalent to those of an artificially informed benchmark controller     

Excitation of Standing Kink Oscillations in Coronal Loops

In this work we review the efforts that have been done to study the excitation of the standing fast kink body mode in coronal loops. We mainly focus on the time-dependent problem, which is appropriate to describe flare or CME induced kink oscillations. The analytical and numerical studies in slab and cylindrical loop geometries are reviewed. We discuss the results from very simple one-dimensional models to more realistic (but still simple) loop configurations. We emphasise how the results of the initial value problem complement the eigenmode calculations. The possible damping mechanisms of the kink oscillations are also discussed.     

用于飞控系统试飞验证的识别方法

为试飞验证飞控系统的稳定性,改进,确认控制律和评价飞机的飞行品质,提出了富氏系数法（ＦＣ）,直接快速富氏变换－功率谱密度地（ＦＦＴ－ＰＳＤ）和相关函数为－功率谱密度法（ＣＦ－ＰＳＤ）确定系统频率响应,进而采用罗森布洛克无约束极值法和最小二乘－高斯牛顿迭代法进行模型参数拟合,另外,给出适合于上述方法的输入激励设计,通过用Ｔｕ－１５４Ｍ空中模拟试验机人机闭环／手动扫频试验数据和ＢＷ－１变稳机手动／自动     

Self-Tuning Excitation Control for Synchronous Machine

A novel scheme for the control of synchronous generator excitation system is described. The proposed controller, which makes use of self-tuning proportional-integral (PI) control, is very effective for improving the dynamic performance of the synchronous machine over a wide range of operating conditions when the machine is subjected to major disturbances or small random load changes. A fixed-gain PI excitation controller is also included for comparison.     

Coordinated Frequency and Voltage Control of Synchronous Generators

Three different types of controllers, i.e., the conventional controller, the linear optimal controller (LOC), and the variablestructure controller (VSC) are proposed for the coordinatedfrequency and voltage control of synchronous generators. Theinteraction between the frequency and voltage control loops is takeninto account by incorporating both the speed-governing system andthe excitation system into the mathematical model of thesynchronous generator. Results obtained from computer simulationindicate that the variable structure controller can yield the bestdynamic responses following a step load change.     

Research of Compound Controller for Flight Simulator with Disturbance Observer

A compound controller is proposed to alleviate the considerable chattering in output of zero phase error tracking controller (ZPETC), when the flight simulator losses command data of simulation signal. Besides, the shortcomings, caused by conventional differential methods in retrieving velocity and acceleration signals, are avoided to a certain extent. The compound controller based on disturbance observer (DOB) is composed of a feed-forward controller and a feedback controller. It estimates velocity and acceleration of unknown tracking signal, and also velocity response with an approximate method for differential. The experiments on a single-axis flight simulator show that the proposed method has strong robustness against parameter perturbations and external disturbances, owing to the introduced DOB. Compared with the scheme with ZPETC, the proposed scheme possesses more simple design and better tracking performance. Moreover, it is less sensitive to position command distortion of flight simulator.     

非电传民机纵向气动参数辨识激励信号研究

针对非电传民机气动参数辨识时,须通过设计激励信号激发出与待辨识参数相关的飞机运动模态才能得到准确的气动参数的特点,开展了适用于非电传民机纵向气动参数辨识的激励信号设计方法研究。基于信号能量分布和幅频响应分析的信号设计方法,对激励信号进行参数设计;综合辨识效果和驾驶员的易操纵性,建议选取经参数设计后的单周期正弦信号作为非电传民机的纵向激励信号。试飞验证结果表明,所提方法能够较好地激发出飞机运动模态,使试飞数据具有较高的气动参数可辨识性。     

Flexible spacestructure control via moving-bank multiple modelalgorithms

The development and performance of moving-bank multiple model adaptive control (MMAC) algorithms for quelling vibrations induced in the SPICE 2 space structure are presented. The structure consists of a large platform and a smaller platform connected by three legs in a tripod fashion. Deviations of the line-of-sight (LOS) vector from the center of the large platform to the center of the smaller platform are used for LQG controller performance evaluation. The parameter estimator implements the maximum entropy with identity covariance (ME/I) algorithm; the moving-bank logic employs parameter position monitoring; the controller uses the modified MMAC method. Whereas parameter variations of two percent caused instabilities in the single filter/controller design, the MMAC algorithm provides an excellent method to estimate a wide range of parameter variations and to quell oscillations in the structure     

Evaluation of pressure oscillations by a laboratory motor

Aeroacoustic pressure oscillation is one of the important challenges in segmented solid rocket motors with high slenderness ratio.The reason for these oscillations can be searched in vortex shedding due to grain burning surfaces, holes and slots.In this paper, a novel sub-scaled motor was used for evaluation of aeroacoustic pressure oscillations.First, the related parameters to scale down using Buckingham’s Pi-theorem were determined and then the sub-scaled motor was designed and manufactured.Af...     

五相混合式步进电动机电流反馈型升频升压驱动方式的研究

分析了五相混合式步进电动机电流反馈型升频升压驱动系统的工作原理。从理论上和实验上,对五相混合式步进电动机电流反馈型升频升压驱动系统的绕组环形连接４－５相通电、星形连接４－５相通电和星形连接２－３相通电３种运行方式进行了详细的分析比较。     

Variable structure and adaptive control of a synchronous generator

Damping of synchronous generator oscillations has been investigated by using three types of controllers, i.e., the PI (proportional-integral) controller, the model reference adaptive controller (MRAC) and the variable-structure model-following controller (VSMFC). It was found that the PI controller fails to accommodate itself to the situation where there is a significant change in generator loading conditions. The MRAC greatly improves the dynamic responses of the generator over a wide range of operating conditions by minimizing the error in the responses obtained from the plant with a specified reference model. The damping of the generator is further improved by the VSMFC, which reduces the sensitivity of generator responses relative to plant parameter variations by providing sliding-mode operations