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Nowadays the efficient use of energy is a major issue in applications such as electric vehicles. However, there are some phenomena that affect electric vehicle performance. One of those phenomena is the torque ripple of electric motors, which interferes with traction and the suspension system (causing vibration that stresses this system), and it can also introduce electric current harmonics into the battery, reducing its life, since torque ripple is partly a consequence of non-sinusoidal back EMF. For those reasons this is a topic worth investigating. The torque ripple of permanent magnets (PM) motors can be reduced in design or through control. Since control techniques have been reviewed and design methods have not, this paper presents a comparison of several design techniques to reduce torque ripple by different approaches and categorize them to show the characteristics of each group. A discussion is then made about the advantages and disadvantages of the designs, in general, as well as some comments about the missing, but important information, in the papers, such as the effects on efficiency. The study shows that a combination of methods provide the best results, although it complicates fabrication and suggests that this is a promising line of future investigation on torque ripple reduction methods. [ABSTRACT FROM AUTHOR]

In this paper, the analysis and design methodology of a high-frequency self-oscillating (SO) electronic ballast with lamp current control are presented. SO electronic ballasts have two important drawbacks: First, the lamp current varies according to the ac input voltage, causing undesired effects in the lamp brightness, and second, the design method lacks precision at very high frequency operation (greater than 200 kHz) mainly due to the Cgs parasitic capacitance. The ballast is modeled by using the descriptive function method and the extended Nyquist criterion; the model of the ballast includes a control circuit and takes into account the high-frequency effect of the MOSFET parasitic capacitance Cgs. Finally, experimental results of a 38-W SO electronic ballast prototype with lamp current control for high-intensity discharge lamps are presented to validate the analysis and the proposed methodology. The switching frequency is selected at 2 MHz in order to avoid the acoustic resonance problem. [ABSTRACT FROM AUTHOR]

In this paper, the dimming and frequency effects on stability, current crest factor (CCF), and power factor (PF) of high-intensity discharge lamps fed with square waveforms are experimentally evaluated. For this evaluation, the lamp was stabilized using resistances. The resistances were varied in function of the impedance of the lamp. The effects of dimming and frequency variation were observed for two types of lamps of different nominal powers. The results indicate the ranges in which the lamp is stable and the frontier values in which the lamp becomes unstable. The CCF and PF remain close to unity, and no acoustic resonances were observed during the applied tests. [ABSTRACT FROM AUTHOR]