Fundamental frequency

About: Fundamental frequency is a research topic. Over the lifetime, 8941 publications have been published within this topic receiving 131583 citations.

Control of square-wave inverters in high power hybrid active filter systems

Abstract: This paper presents a new control scheme for a hybrid parallel active filter (HPAF) system intended for high-power applications-up to 100 MW nonlinear loads-to meet IEEE 519 recommended harmonic standards. The active filter inverter is realized with small-rated (1%-2% of the load rating) square-wave inverters operating at the dominant harmonic frequencies. The proposed system achieves harmonic isolation at desired dominant harmonic frequencies, such as the fifth and seventh, even in the presence of supply voltage harmonic distortions. A novel method of active filter inverter DC-bus control, as proposed here, achieves power balancing by exchanging energy at the fundamental frequency and at the dominant harmonic frequency (such as the fifth). The proposed square-wave inverter-based HPAF system provides improved filtering characteristics as compared to the conventional passive filter and is expected to be cost effective for high-power nonlinear loads compared to the conventional passive filter or other active filtering solutions. The concept of harmonic isolation at dominant harmonic frequencies by square-wave inverters with the proposed control scheme is validated by simulation results.

p-q Theory power components calculations

Abstract: The "generalized theory of the instantaneous reactive power in three-phase circuits", proposed by Akagi et al., and also known as the p-q theory, is an interesting tool to apply to the control of active power filters, or even to analyze three-phase power system in order to detect problems related to harmonics, reactive power and unbalance. In this paper it will be shown that in three phase electrical systems the instantaneous power waveform presents symmetries if 1/6, 1/3, 1/2 or 1 cycle of the power system fundamental frequency, depending on the system being balanced or not, and having or not even harmonics (interharmonics and subharmonics are not considered in this analysis). These symmetries can be exploited to accelerate the calculations for active filters controllers based on the p-q theory. In the case of the conventional reactive power or zero-sequence compensation, it is shown that the theoretical control system dynamic response delay is zero.

On a New Method for the Generation of Sound-Waves

Abstract: Pressure variation along a high-velocity air jet, produced by a pressure of 0.9 to 5 atm. above normal, was determined with a simple Pitot tube, and the periodic intervals of instability were located (Figs. 2 and 5).New Source of Sound; Resonator Actuated by a High-Velocity Air Jet.---It was found that the intervals of instability referred to above can be used for the generation of sound. (1) Bulb form. When the small orifice to a bulb is placed in one of these intervals so that the particles of air move in and out of the opening, pulsations like those of a siren are produced, the tones not being pure. The fundamental frequency depends on the volume of the bulb, the size of the orifice and the position in the jet, and may readily be varied from 1/10 to 5,000 per second. (2) Cylindrical form. When a simple cylindrical resonator is placed with one end in an interval of instability, pure tones are produced except in certain positions when overtones may be present. The frequency is the fundamental of the resonator and may be made as high as 125,000 per second by using a very short tube, about 0.5 mm. in length and in bore. With a hydrogen jet, the frequencies are, of course, 3.8 times as high. The efficiency of such sources is remarkable, intensities that are painful being readily produced. Practical forms of these generators are illustrated (Figs. 3 and 4).

Pulse generation in fiber lasers with frequency shifted feedback

Abstract: Lasers with frequency shifted feedback may spontaneously generate periodic trains of short optical pulses. Frequency shifts as small as several kilohertz per roundtrip are shown to sustain pulsing at the cavity fundamental frequency in Er/sup 3+/- and Nd/sup 3+/-fiber lasers with intracavity acousto-optic frequency shifters. A numerical model based on the split step Fourier method suggests that this pulse mode of operation may be attributed to the Kerr-type nonlinearity of the optical fiber. >

Second-harmonic generation from metal nanoparticles: resonance enhancement versus particle geometry.

Abstract: We demonstrate that optical second-harmonic generation (SHG) from arrays of noncentrosymmetric gold nanoparticles depends essentially on particle geometry. We prepare nanoparticles with different geometrical shapes (L and T) but similar wavelengths for the polarization-dependent plasmon resonances. In contrast to recent interpretations emphasizing resonances at the fundamental frequency, the T shape leads to stronger SHG when only one, instead of both, polarization component of the fundamental field is resonant. This is explained by the character of plasmon oscillations supported by the two shapes. Our numerical simulations for both linear and second-order responses display unprecedented agreement with measurements.