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61.
Unity PF current-source rectifier based on dynamic trilogic PWM 总被引:12,自引:0,他引:12
One remaining step in perfecting the stand-alone, unity power factor, regulated current-source pulse-width-modulated (PWM) rectifier is to reduce cost, by bringing the twelve-valve converter (consisting of three single-phase full bridges that operate with two-level or bilogic PWM) to the six-valve bridge. However, the six-valve topology requires a three-level or trilogic PWM strategy that can handle feedback signals. A general method of translating three-phase biologic PWM signals into three-phase trilogic PWM signals is presented. The method of translation retains the characteristics of the bilogic PWM, including the frequency bandwidth. Experiments show that the trilogic PWM signals produced by the method can handle not only stabilizing feedback signals but also signals for active filtering 相似文献
62.
Research studies of symmetrical spiral inductors for silicon technology have become very important and challenging. In this article, we attempt to give a detailed explanation of how symmetrical spiral inductors help to improve the quality factor (Q) as compared to conventional nonsymmetrical inductors. The experimental results are presented to verify our theory. © 2005 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2005. 相似文献
63.
Many jurisdictions in the United States are currently preparing total maximum daily load (TMDL) programs for stream segments that come under Section 303(d) of the Clean Water Act. Among the options being considered by many state pollution control agencies is that of permit trading, otherwise known as permit transfers, transferable permits, emissions trading, bubbles, pollution rights, marketable effluent permits, and transferable discharge permits. Under such programs, a permit to discharge into a watercourse, issued as part of a wasteload allocation program, is treated as a marketable commodity. This paper presents a qualitative discussion of the strengths and weaknesses of permit trading in the context of a TMDL program, and discusses the circumstances that favor it. The paper also presents hypothetical quantitative findings to illustrate the circumstances under which a regional administrator might wish to adopt a program of permit trading, and if so, what type of permits would suit it best. 相似文献
64.
65.
Multiple-wavelength integration in InGaAs-InGaAsP structures using pulsed laser irradiation-induced quantum-well intermixing 总被引:1,自引:0,他引:1
In this paper, we present the characteristics of a quantum-well intermixing technique using pulsed-photoabsorption-induced disordering. Photoluminescence, micro-Raman spectroscopy, and transmission electron microscopy were used to characterize the process. Using this technique, a differential wavelength shift between the intermixed and nonintermixed regions of over 160 nm has been observed from InGaAs-InGaAsP heterostructures. It was found from the micro-Raman measurements that a spatial resolution of better than 2.5 /spl mu/m can be achieved. A theoretical model has been developed to estimate the spatial resolution limit. Theoretical analysis has also been performed to investigate the effect of laser irradiation on the degree of intermixing in InGaAs-InGaAsP structures. To verify the capability of this process in monolithic photonic integration, high-quality bandgap tuned lasers, two-section extended cavity lasers, and multiple-wavelength laser chips have been fabricated. 相似文献
66.
Consider a multipath signal whose individual signals are deterministic known increasing or decreasing pulses. The problem is to estimate the amplitudes and delay times of individual signals. Several methods have been devoted to the solution of these unknown parameters. The maximum likelihood (ML) estimation and the estimate maximize (EM) algorithm are commonly used, but they are computationally intensive and still insufficient to obtain accurate estimations. The method can provide a quick and accurate estimate of the amplitudes and arrival (delay) times, even in the closely spaced multipaths and heavy noise. 相似文献
67.
A single-phase controlled-current PWM rectifier 总被引:9,自引:0,他引:9
The analysis and test results are given for an experimental single-phase controlled-current PWM (pulse-width-modulated) rectifier that operates at unity power factor with near sinusoidal current waveform and that has power reversal capability. The twice-line-frequency AC power is identified as a source of voltage harmonics in the DC link. The harmonics enter into the voltage regulation feedback loop to distort the AC current waveform. These undesirable harmonics can be removed by a low-pass filter. It is noted that the overall design must address the possibility of instability due to the low-pass filter in the feedback path 相似文献
68.
The advantages of using multiple modules of the current-source, sinusoidal pulse-width-modulated (SPWM), three-phase, six-valve converters as the power conditioner for the superconducting magnetic energy system are highlighted. A high degree of controllability is obtained by using dynamic SPWM trilogic as the operating strategy. Very low switching losses are assured by using two carrier triangles per modulated cycle. By partial connection of converter modules, and by phase-shifting the triangle carriers, the following are obtained: increasing the current capacity to the level required by the superconducting magnet; reducing conduction losses; meeting harmonic standards, without the need of an expensive filter, by harmonic cancellation; and achieving a high frequency bandwidth 相似文献
69.
Because the impedance-modeling technique is such a convenient tool, it is used often (and sometimes incorrectly) for the prediction of forces in electrodynamic levitation systems. In spite of its widespread applications, the technique rests on flimsy theoretical foundations. This paper presents force formulas, derived from the dynamic circuit theory, which establish both the validity and the limitations of the technique. The cases of a holonomic and a nonholonomic guideway are treated. The method of equivalencing frequency to velocity is found to be incorrect algebraically. The extent to which approximate equivalencing of frequency to velocity can be relied on, is demonstrated by numerical examples. 相似文献
70.
Boon-Teck Ooi Om Jain 《IEEE transactions on magnetics》1979,15(3):1102-1108
Theoretical predictions of the moments and the force density distributions on the superconducting magnet and on the conducting sheet guideway are given for the reference levitation system design proposed for the Canadian Maglev vehicle. The theoretical method is based on the Lorentz force,tilde{J} times tilde{B} and the solution follows from a combination of the dynamic circuit theory and the EM field theory already developed. Very good correlations are found with the moments measurements already published. The data from the predictions are important for vehicular mechanics analysis and for mechanical structural design of fastenings and bracings. 相似文献