Two-dimensional linear-combination model fitting of magnetic resonance spectra to define the macromolecule baseline using FiTAID,a Fitting Tool for Arrays of Interrelated Datasets

Object  

To propose the determination of the macromolecular baseline (MMBL) in clinical 1H MR spectra based on T₁ and T₂ differentiation using 2D fitting in FiTAID, a general Fitting Tool for Arrays of Interrelated Datasets.     

Synthesis of cogging-torque waveform from analysis of a single stator slot

A simple analytical technique is proposed to synthesize the cogging-torque waveform of a permanent-magnet brushless machine from the cogging torque, which is associated with a single stator slot. An analytical expression is derived, which reveals the relationship between the two. It is then applied to two motors, which have a fractional number of slots per pole. It is shown that the resultant cogging-torque waveform can be synthesized to a high accuracy, as confirmed by both finite-element analysis and measurements. It is also shown that not all the cogging-torque harmonics that exist in the cogging-torque waveform due to a single slot will be present in the resultant cogging torque, and that the most significant components can be identified analytically.     

Development and Experimental Demonstration of a Self-Powered ETO (SPETO)

This paper presents the design and experimental demonstration of a superior high-power-device self-powered emitter turn-off thyristor (SPETO). Different from conventional high-power devices which require external power input for their gate drivers, the SPETO achieves optically controlled turn on and turn off, and all of the internal power required is self-obtained. A low-loss gate-drive circuit is implemented which allows the simple power-up operation. During a normal switching operation, the SPETO obtains a power for the gate drive during its turn-on operation. A novel switching strategy is also introduced to minimize the gate-drive power requirement. The SPETO greatly reduces costs and increases the reliability of power converters since no external power supply for device gate drive is required. Therefore, the SPETO is suitable for high-power high-frequency voltage-source-converter applications     

晶闸管控制的单相–三相变换器

提出一种单相电源供电时适用于异步电机传动的单相–三相变换器。由于仅采用7个晶闸管和1个移相电容,该变换装置具有造价低、结构简单的特点。分析该变换器的工作原理及开关过程,并提出一种基于开环变压变频(variable voltage variable frequency,VVVF)和变压恒频(variable voltage constant frequency,VVCF)控制的单相–三相离散跳频控制策略,用于电机的起动和稳态运行控制,一方面保证了电机在低频阶段足够大的起动力矩,另一方面可使电机稳步起动到额定转速。仿真和实验结果表明了该控制策略的有效性以及系统方案的可行性。     

基于能流循环的电力机车辅助逆变器试验系统

提出了一种新型的电力机车辅助逆变器试验系统,采用PWM整流器代替原有的风机负载,调节其交流侧电流来完成各种工况下的试验任务,并实现能量循环流动.系统采用预测电流控制算法,使电感电流跟踪指令电流.该方法响应速度快,并可分别调节各相电流,以模拟辅助逆变器的缺相、不平衡、过载等故障工况.实验表明,试验系统运行稳定可靠,具有节能降噪的优越性能.     

An evidential reasoning approach to transformer condition assessments

This paper presents an evidential reasoning (ER) approach to the transformer condition assessment. An ER algorithm is briefly introduced which is used to combine evidences and deal with uncertainties. The methodology of transferring the transformer condition assessment problem into a multiple-attribute decision-making (MADM) solution under an ER framework is then presented. Several solutions to the transformer condition assessment problem, using the ER approach, are then illustrated, highlighting the potential of the ER algorithm. Based on the outputs of the ER approach, system operators can obtain an overall evaluation of the observed unit's condition; also, several units may be ranked in order of severity for system maintenance purposes. It can be seen from the results developed that the ER approach is a suitable solution to tackle the MADM problem of transformer condition assessment.     

Sensorless flux-weakening control of permanent-magnet brushless machines using third harmonic back EMF

The sensorless control of brushless machines by detecting the third harmonic back electromotive force is a relatively simple and potentially low-cost technique. However, its application has been reported only for brushless dc motors operating under normal commutation. In this paper, the utility of the method for the sensorless control of both brushless dc and ac motors, including operation in the flux-weakening mode, is demonstrated.     

Experiments and simulations of short-pulse laser-pumped extreme ultraviolet lasers

Recent experimental work on the development of extreme ultraviolet lasers undertaken using as the pumping source the VULCAN laser at the Rutherford Appleton Laboratory is compared to detailed simulations. It is shown that short duration (/spl sim/picosecond) pumping can produce X-ray laser pulses of a few picosecond duration and that measurement of the emission from the plasma can give an estimate of the duration of the gain coefficient. The Ehybrid fluid and atomic physics code developed at the University of York is used to simulate X-ray laser gain and plasma emission. Two postprocessors to the Ehybrid code are utilized: 1) to raytrace the X-ray laser beam amplification and refraction and 2) to calculate the radiation emission in the kiloelectronvolt photon energy range. The raytracing and spectral simulations are compared, respectively, to measured X-ray laser output and the output of two diagnostics recording transverse X-ray emission. The pumping laser energy absorbed in the plasma is examined by comparing the simulations to experimental results. It is shown that at high pumping irradiance (>10/sup 15/ Wcm/sup -2/), fast electrons are produced by parametric processes in the preformed long scalelength plasmas. These fast electrons do not pump the population inversion and so pumping efficiency is reduced at high irradiance.