Dynamic contribution of variable-speed wind energy conversion system in system frequency regulation

Frequency regulation in a generation mix having large wind power penetration is a critical issue, as wind units isolate from the grid during disturbances with advanced power electronics controllers and reduce equivalent system inertia. Thus, it is important that wind turbines also contribute to system frequency control. This paper examines the dynamic contribution of doubly fed induction generator (DFIG)-based wind turbine in system frequency regulation. The modified inertial support scheme is proposed which helps the DFIG to provide the short term transient active power support to the grid during transients and arrests the fall in frequency. The frequency deviation is considered by the controller to provide the inertial control. An additional reference power output is used which helps the DFIG to release kinetic energy stored in rotating masses of the turbine. The optimal speed control parameters have been used for the DFIG to increases its participation in frequency control. The simulations carried out in a two-area interconnected power system demonstrate the contribution of the DFIG in load frequency control.     

基于DSP感应加热电源控制系统的仿真研究

针对感应加热电源控制系统中频率跟踪的要求,介绍了一种基于数字信号处理器的数字锁相环控制方式。在分析数字锁相环数学模型的基础上建立了控制系统的仿真模型,仿真结果与理论分析一致,控制效果良好。     

An analysis of subsynchronous resonance in hybrid marine current and wind farms with squirrel cage induction generator

Subsynchronous resonance (SSR) is a well-known phenomenon in series-compensated systems with synchronous generators. With the rapid growth of renewable energy systems, it is likely that with its integration to series-compensated system for the transmission of bulk power may lead to the problem of SSR. This paper conducts an analysis of SSR phenomena in the squirrel cage induction generator-based hybrid wind farm and marine current farm connected to series-compensated system with power variation due to the addition or removal of small turbine units. A dynamic model has been developed to analyse the induction generator effect and torsional interaction of SSR on the IEEE first bench mark model for SSR studies. The eigenvalue analysis was performed on the developed model with MATLAB and the time domain electro magnetic transient simulation performed on DiGSILENT Power Factory confirms the predicted results by the eigenvalue analysis.     

颗粒污垢诱导期影响因素的实验研究

本研究是在管外水浴温度50℃和相同管内工质入口温度的条件下,进行了弧线管及其对应光管在浓度、流速不同时的颗粒污垢诱导期对比性实验.结果表明,这几种因素都在不同程度上影响着污垢形成的诱导期.希望对以后换热设备的设计及运行能起到一定的指导作用.     

具有复合介质的感应炉的电参数计算

对具有复合介质的感应电炉的电磁场理论进行了研究，导出工程实用的电参数计算公式，计算分析目前常用的两种典型复合介质熔炼炉的电参数，其结果更符合复合介质感应熔炉的实际。     

ITER高功率磁场抗扰度测试系统研究

目的  为了保证设备的安全稳定运行,受国际热核实验堆（ITER）组织监管的电力电子设备必须通过相关的磁场抗扰度测试。 方法  以ITER要求为基准,定义了所需测试系统的参数要求,选择方形螺线管线圈和方形三线圈作为研究对象,通过数值计算方法计算出最优性能的结构参数,并使用有限元的方法验证计算的正确性。 结果  对比两种线圈型式,选择功耗较小的螺线管作为最终的结构。然后以此参数为基准,分析了直流暂态的功率拓扑,计算了相关参数,确定了最终电源所需要的性能数据。 结论  研究为ITER高功率磁场抗扰度测试系统的感应线圈及其电源的设计提供了详细的计算过程和设计参考。     

Robust SVM-direct torque control of induction motor based on sliding mode controller and sliding mode observer

This paper proposes a design of control and estimation strategy for induction motor based on the variable structure approach. It describes a coupling of sliding mode direct torque control (DTC) with sliding mode flux and speed observer. This algorithm uses direct torque control basics and the sliding mode approach. A robust electromagnetic torque and flux controllers are designed to overcome the conventional SVM-DTC drawbacks and to ensure fast response and full reference tracking with desired dynamic behavior and low ripple level. The sliding mode controller is used to generate reference voltages in stationary frame and give them to the controlled motor after modulation by a space vector modulation (SVM) inverter. The second aim of this paper is to design a sliding mode speed/flux observer which can improve the control performances by using a sensorless algorithm to get an accurate estimation, and consequently, increase the reliability of the system and decrease the cost of using sensors. The effectiveness of the whole composed control algorithm is investigated in different robustness tests with simulation using Matlab/Simulink and verified by real time experimental implementation based on dS pace 1104 board.     

Rotor fault condition monitoring techniques for squirrel-cage induction machine—A review

Nowadays, manufacturing companies are making great efforts to implement an effective machinery maintenance program, which provides incipient fault detection. The machine problem and its irregularity can be detected at an early stage by employing a suitable condition monitoring accompanied with powerful signal processing technique. Among various defects occurred in machines, rotor faults are of significant importance as they cause secondary failures that lead to a serious motor malfunction. Diagnosis of rotor failures has long been an important but complicated task in the area of motor faults detection. This paper intends to review and summarize the recent researches and developments performed in condition monitoring of the induction machine with the purpose of rotor faults detection. The aim of this article is to provide a broad outlook on rotor fault monitoring techniques for the researchers and engineers.     

Creativity and domain specificity: The effect of task type on multiple indexes of creative problem-solving.

This study addresses the issue of domain specificity within creativity by understanding the characteristics of creative tasks and how participants react to the task. Participants (N = 187) were given 1 of 3 realistic everyday problems to solve. The problems differed in terms of complexity, involvement, and problem-based efficacy. Problem solutions were evaluated on several measures of creativity. Results indicate that creativity was influenced by the type of problem solved and the measure of creativity used to evaluate the solution. Furthermore, these results were obtained after controlling for the effect of ability. Results imply that not all real-world problems are equivalent and that researchers need to investigate how reactions to different problems and the creativity index used may influence conclusions regarding creative problem solving. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Increasing the difficulty of response selection does not increase the switch cost.

Several theories of task switching assume that basic task processes such as stimulus identification and response selection do not contribute to task-switch costs. This conclusion is mainly based on the finding that stimulus-identification manipulations have no influence on the size of the switch cost. The present study tested the influence of response-selection manipulations on the size of the switch cost. The authors manipulated the difficulty of response selection by using a semantically based response-side effect that is associated with numerical-judgement tasks, namely the Spatial Numerical Association of Response Codes (SNARC) effect. The authors observed a SNARC effect and a switch cost, but no interaction between the two: the task-switch cost did not differ between SNARC-compatible and -incompatible responses. The authors conclude that response selection does not contribute to the switch cost on the current trial, which provides further support for the idea that basic task processes and task-switch processes are separate. (PsycINFO Database Record (c) 2010 APA, all rights reserved)