Wind-driven stand-alone DFIG with battery and pumped hydro storage system

A wind-driven doubly fed induction generator (DFIG) along with the battery and pumped hydro storage plant (PHSP) has been devised for supplying isolated loads. PHSP-based storage system is economical and viable for the MW level wind-turbine system. The proposed scheme employs a squirrel-cage induction machine (SCIM) coupled with reversible pump turbine for PHSP. The battery storage is also included in this system to cope up with the intermittent nature of wind and fast-changing load. A simple control strategy has been implemented for maintaining the set values of voltage magnitude and frequency at the stator terminals of DFIG, which serve as a virtual grid for connecting ac loads and SCIM. Based on the availability of power in the wind, PHSP and battery, various operating modes of the proposed system have been clearly identified for supplying the isolated loads. These operating modes are clearly demonstrated through the analysis developed for this purpose and validated through experimental results. The salient features of the proposed system over the existing stand-alone wind-driven generators are (i) structural simplicity, i.e., employing only one power electronic converter, (ii) wide speed operation of wind-driven DFIG, (iii) reduced battery capacity, (iv) high energy storage using PHSP and (v) availability of continuous power to the isolated loads.     

Sensored and sensorless speed control methods for brushless doubly fed reluctance motors

The study considers aspects of scalar V/f control, vector control and direct torque (and flux) control (DTC) of the brushless doubly fed reluctance machine (BDFRM) as a promising cost-effective alternative to the existing technological solutions for applications with restricted variable speed capability such as large pumps and wind turbine generators. Apart from providing a comprehensive literature review and analysis of these control methods, the development and results of experimental verification, of an angular velocity observerbased DTC scheme for sensorless speed control of the BDFRM which, unlike most of the other DTC-concept applications, can perform well down to zero supply frequency of the inverter-fed winding, have also been presented in the study     

Advances in vector control ofac motor drives — A review

This paper attempts to present a comprehensive review of the advances made in vector control or field orientation as applied to high performanceac motor drives. Brief application survey, machine models ind-q representation, implementation issues with inverters and cycloconverters, parameter effects etc for both induction and synchronous motor vector control are dealt with and sample results from studies on them are presented. The latest advance on this control like direct torque control (DTC) has been briefly discussed. A substantial updated bibliography, though by no means complete, is included for those who are interested in keeping track of the present state-of-the-art and working further in this area.     

求解无限域动力刚度矩阵的双渐近算法

采用连分式算法可以有效地求解无限域动力刚度表示的比例边界有限元方程, 它具有收敛范围广、收敛速度快等优点. 该文在高频渐近连分式算法的基础上考虑了低频渐近, 发展了一种针对矢量波动方程的双渐近算法. 随着展开阶数的增加, 双渐近算法可以在全频域范围内快速逼近准确解. 引入了系数矩阵?X(i)来增强连分式算法的数值稳定性. 通过在高频极限、低频极限时满足动力刚度表示的比例边界有限元方程, 建立了递推关系以求得动力刚度矩阵. 通过二维半无限楔形体、三维均质弹性半空间数值算例表明, 双渐近算法比单渐近算法更稳定、优越.     

Designing optimal controllers for doubly fed induction generators using a genetic algorithm

This work presents a design procedure based on evolutionary computation, more specifically on a genetic algorithm combined with the formal pole placement project, to obtain optimal controllers to the rotor-side converter of doubly fed induction generators (DFIGs), in variable-speed wind generation systems connected to the electrical grid. With this procedure it is intended to improve the global system dynamic behaviour during and after the fault period, also increasing the transient stability margin of the power system and the fault ride-through capability. The control action of the DFIG converters is accomplished by proportional and integral controllers, whose gainspsila adjustment is not a trivial task, because of the high complexity of the system. The results obtained confirm the efficiency of the proposed control design procedure.     

Three-phase doubly fed induction generators: an overview

Adjustable speed induction generators, especially the doubly fed induction generators (DFIG), are becoming increasingly popular due to their various advantages over fixed speed generator systems. A DFIG in a wind turbine has the ability to generate maximum power with varying rotational speed, ability to control active and reactive power by the integration of electronic power converters such as the back-to-back converter, low rotor power rating resulting in low cost converter components, and so on. This study presents an extensive literature survey over past 25 years on the different aspects of DFIG.     

Single-current-sensor-based active front-end-converter-fed four quadrants induction motor drive

Induction motor (IM) is a workhorse of the industry, whose dynamics can be modified close to that of a separately excited DC machine by field-oriented control technique, which is commonly known as vector control of induction machine. This paper presents a complete performance of the field-oriented control of IM drive in all four quadrants with a single-current-sensor-based active front end converter whose work is to regulate DC link voltage, draw pure sinusoidal currents at unity power factor and to facilitate bi-directional power flow between the grid and the drive. The entire system is completely modelled in MATLAB/SIMULINK and the results are discussed in detail. The vector control analogy of the back to back converters is highlighted along with the experimental results of field-oriented control of induction machine using a dsPIC30F6010A digital signal controller.     

Improved direct torque control of induction motor with dither injection

In this paper, a three-level inverter-fed induction motor drive operating under Direct Torque Control (DTC) is presented. A triangular wave is used as dither signal of minute amplitude (for torque hysteresis band and flux hysteresis band respectively) in the error block. This method minimizes flux and torque ripple in a three-level inverter fed induction motor drive while the dynamic performance is not affected. The optimal value of dither frequency and magnitude is found out under free running condition. The proposed technique reduces torque ripple by 60% (peak to peak) compared to the case without dither injection, results in low acoustic noise and increases the switching frequency of the inverter. A laboratory prototype of the drive system has been developed and the simulation and experimental results are reported.     

基于Web的数控编程动态仿真及可视化

根据硕士研究生学位公共课程“CAD/CAM基础理论与实践”网络化远程教学的需求,针对点位控制、直线控制、曲线控制等几种典型的数控类型,综合运用Java编程、数控G指令编程以及刀具切削原理等技术,开发具有动态交互及可视化功能的、能实时显示数控程序设计和执行过程的线切割、车削、铣削等基于Web的数控编程动态仿真Java软件。并将其集成在远程教学课件的Web信息架构中。     

Investigation of a new stator interior permanent magnet machine

A new stator interior permanent magnet (PM) machine which is developed from the doubly salient PM machine is proposed. The novelty of this machine lies in the split stator pole and full-pitched windings, where tooth-shoe is adopted and the PM is inserted into the stator pole. This configuration can offer higher power density and lower cogging torque ripple than the doubly salient machine. In order to achieve high power density, the smaller thickness of PM may be more favourable. In this case, an analytical method is used to examine the demagnetisation of PM under short-circuit current. A prototype machine for wind power application is designed, built and tested. The experimental results validate the theoretical analysis and the effectiveness of the proposed stator interior PM machine.     

线切割机电极丝动态稳定性的主动控制研究

分析了国产快走丝线切割机床加工精度差的运动学和动力学原因。导出了电极丝的运动方程和各种激励下的强迫响应解，指出丝架的振动和转动元件的动不平衡是影响电极丝稳定性和加工质量的主要因素。由于电极丝细而柔，结构振动和动不平衡在制造中难以完全消除，着重研究了利用主动控制方法提高电极丝动态稳定性和加工质量的理论原理和技术方法。通过理论分析，指出主动控制不应采用传统的模态控制，而应为远低于首阶模态的强迫响应控制     

Prediction of Compressive Strength of Various SCC Mixes Using Relevance Vector Machine

This paper discusses the applicability of relevance vector machine (RVM) based regression to predict the compressive strength of various self compacting concrete (SCC) mixes. Compressive strength data various SCC mixes has been consolidated by considering the effect of water cement ratio, water binder ratio and steel fibres. Relevance vector machine (RVM) is a machine learning technique that uses Bayesian inference to obtain parsimonious solutions for regression and classification. The RVM has an identical functional form to the support vector machine, but provides probabilistic classification and regression. RVM is based on a Bayesian formulation of a linear model with an appropriate prior that results in a sparse representation. Compressive strength model has been developed by using MATLAB software for training and prediction. About 75% of the data has been used for development of model and 30% of the data is used for validation. The predicted compressive strength for SCC mixes is found to be in very good agreement with those of the corresponding experimental observations available in the literature.     

矢量控制在水泵拖动系统中的应用

为了提高水泵拖动系统的可靠性和适应性,提出一种异步电动机矢量控制系统,介绍异步电动机矢量控制变频器的基本方法;实践表明,该系统具有良好的性能和节能效果.     

横向巨磁阻抗效应中磁导率张量的理论研究

建立了比较完善的二维铁磁体在横向巨磁阻抗 (GMI)效应中的磁化模型 ,采用将静态磁化过程和动态磁化过程分开计算的方法 ,同时考虑畴壁移动和磁畴转动两种磁化机制的影响 ,推导出比较完善的用于二维铁磁体横向巨磁阻抗效应理论研究的磁导率张量的表达式。     

Quality estimation of resistance spot welding by using pattern recognition with neural networks

A quality estimation system of resistance spot welding has been developed using a dynamic resistance pattern. Dynamic resistance is monitored in the primary circuit of the welding machine and is mapped into a bipolarized vector for pattern recognition. The Hopfield neural network classifies the pattern vectors and utilizes them to estimate weld quality. Weld strength measurements have been made to examine the performance of the estimation system. Good agreement is obtained between the classified results and tensile-shear strengths. For a better understanding of the estimation process of the network, an example in which the dynamic resistance is classified into the stored pattern is also illustrated.     

Doubly periodic arrays of cracks and thin inhomogeneities in an infinite magnetoelectroelastic medium

A two-dimensional boundary element method for the analysis of a magnetoelectroelastic medium containing doubly periodic sets of cracks or thin inclusions is developed in this paper. The integral equations and closed-form expressions for corresponding kernels are obtained. Based on the quasi-periodicity of extended displacement and stress function, the integral representations for average stress, strain, electric displacement, magnetic induction etc. are developed. The algorithm of effective properties determination is given. The numerical examples prove the efficiency and high accuracy of the proposed approach in determination of stress, electric displacement and magnetic induction intensity factors and effective properties of the material containing doubly periodic arrays of cracks or thin inclusions.     

Dynamic model for doubly-fed induction generators with unbalanced excitation, both with and without winding faults

A detailed analytical model designed for doubly-fed induction generator (DFIG) dynamic analysis is presented. The method employs a coupled-circuit approach and uses the principles of generalised harmonic analysis and complex conductor distribution to develop a systematic method for calculating a circuit's self-inductance and mutual inductance for windings with any distribution of conductors. As such, it is capable of representing the effects that winding and excitation asymmetries have on machine performance. The accuracy of the model is verified in both the time and frequency domains against experimental results obtained from a specially constructed DFIG test rig, which can be configured to introduce a range of open-circuit and short-circuit faults. Model predictions are compared with experimental measurements for a balanced machine and for the case in which one stator phase suffers an open-circuit fault. The experimental and predicted data are shown to be in good agreement and demonstrate the effectiveness of the technique developed.     

Sequence Dependent Machine Set-Up Times and Similarity of Parts: A Mathematical Model

This paper attempts to develop a mathematical relation between machine set-up times and similarity of parts. First, the task for setting up a machine was broken down into a distinct number of elements whose state was expressed as a binary vector called set-up task elimination vector. By introducing a corresponding rime vector, it was shown that sequence dependent set-up time is the product of the two vectors. Next, a quantitative relation between set-up tasks and the design characteristics of parts was defined as a binary interaction matrix while the similarity of parts was defined as a binary vector. It turned out that the set-up tasks elimination vector is the Boolean product of the interaction matrix and the similarity vector. Using this information, a machine set-up model was developed in terms of similarity of parts. The computation of machine set-up times and a sequencing heuristic using the model were illustrated.     

双模模糊滑模控制裹包机交流转矩系统

针对接缝式裹包机交流伺服系统控制精度差的问题,采用了双模模糊滑模变结构控制器,仿真结果表明该方案有效地消除了抖动问题,具有优良的动静态性能,证明了双模模糊滑模变控制方法的合理和优越。     

Small signal stability analysis and optimal control of a wind turbine with doubly fed induction generator

A novel method using particle swarm optimisation (PSO) is proposed for optimising parameters of controllers of a wind turbine (WT) with doubly fed induction generator (DFIG). The PSO algorithm is employed in the proposed parameter tuning method to search for the optimal parameters of controllers and achieve the optimal coordinated control of multiple controllers of WT system. The implementation of the algorithm for optimising the controllers' parameters is described in detail. In the analysis, the generic dynamic model of WT with DFIG and its associated controllers is presented, and the small signal stability model is derived; based on this, an eigenvalue-based objective function is utilised in the PSO-based optimisation algorithm to optimise the controllers' parameters. With the optimised controller parameters, the system stability is improved under both small and large disturbances. Furthermore, the fault ride-through capability of the WT with DFIG can be improved using the optimised controller. Simulations are performed to illustrate the control performance.