Harmonic

About: Harmonic is a research topic. Over the lifetime, 44833 publications have been published within this topic receiving 495922 citations. The topic is also known as: overtone & partial.

Harmonic Analysis in Frequency and Time Domain

Abstract: This paper presents a review with a concise description and analysis of the fundamentals, characteristics, analytical details, merits, and drawbacks associated with existing methods in frequency and time domain for harmonic analysis in practical power networks. The description and analysis are centered on methods developed in the harmonic domain, hybrid frequency-time domain, and time domain, respectively. Validation of the reviewed methods for harmonic analysis, against one of the widely accepted digital simulators, such as EMTP, EMTDC, or MATLAB/SIMULINK, is reported in the cited individual contributions.

Analysis of LLC Resonant Converter considering effects of parasitic components

Abstract: Nowadays the trend of power supply market is more inclined to high switching frequency, high efficiency and high power density. To meet this trend, resonant power supply holds more attraction, because it can be operated in high switching frequency with high efficiency. There are many resonant power supplies such as Series-Resonant Converter (SRC), Parallel-Resonant Converter (PRC) and Series-Parallel Resonant Converter (SPRC). Among them, LLC Resonant Converter has a lot of advantages over the conventional SRC and PRC considering relatively narrow switching frequency variation over wide input and load variation and Zero-Voltage-Switching for entire load range. Therefore, the LLC Resonant Converter has been widely used and discussed. However, the conventional analysis of LLC Resonant Converter with Fundamental Harmonic Approximation (FHA) can not explain the practical operation of LLC Resonant Converter. To overcome this limitation, in this paper, analysis and design of the LLC Resonant Converter including parasitic components which are affecting converter operation are proposed using a traditional analysis based on FHA. The effect of each parasitic component is analyzed with simulation results and the design guideline standing on this analysis will be described. Moreover, the experimental results of prototype designing on the basis of the analysis are shown to demonstrate the proposed analysis and design guideline.

Effects of nonlinear loads on optimal capacitor placement in radial feeders

Abstract: The nonlinear portion of electrical loads has increased significantly in recent years. Harmonic currents injected by these loads into the distribution system should be considered when solving the capacitor placement problem in order to assure that the optimal solution does not result in excessive harmonic distortion. A voltage-dependent current injection load model is presented to determine voltage waveform characteristics and additional losses at harmonic frequencies. Computer simulations show that the optimal capacitor sizes and locations depend heavily on the load model used at fundamental frequency and on harmonic signals, especially when limits are imposed on voltage waveforms. >

Voltage harmonics generated by voltage-fed inverters using PWM natural sampling

Abstract: The harmonics generated by natural sampled pulse width modulation are investigated experimentally and by theoretical models for the outputs obtained with triangular and sawtooth carrier signals. These equations are valid for synchronous and asynchronous operation. It is shown that triangular carriers generate less harmonics than sawtooth carriers, and that in synchronous operation with single-phase modulation, the carrier-to-output frequency ratio may be any integer value. >

Native tissue imaging at superharmonic frequencies

Abstract: The second harmonic imaging mode has been adapted to image tissue and shown considerable improvements in image quality in several applications compared to the fundamental mode. The improvements were attributed to the effects of wave distortion due to nonlinear propagation in tissue. However, imaging tissue at the second harmonic frequency only has various drawbacks. Because the energy in the second harmonic frequency band is much lower than that in the fundamental frequency band, there must be excellent sensitivity and dynamic range in the receiving system to achieve an acceptable amount of signal-to-noise ratio. To increase the sensitivity, the spectral overlap between the fundamental and the second harmonic has to be diminished, which in return deteriorates the imaging resolution. Consequently, a trade-off is mandatory between resolution and sensitivity. Using simulations and measurements, we show that, at appropriate scanning acoustic settings, higher harmonics are generated in tissue. The higher harmonics represent additional, relevant information for tissue imaging and characterization. An elegant way to take advantage of the higher harmonics and to bring all the information together is to combine and incorporate all the multiple higher harmonics into a single component that we call the superharmonic component. Using a newly developed array transducer having a wide frequency band, B-mode images of a phantom were made in the superharmonic mode transmitting at 1.2 MHz. These images have exceptionally improved clarity and yield a dramatically cleaner and sharper contrast between the different structures being imaged. In addition to increased signal-to-noise ratio, superharmonic imaging shows better contrast and axial resolution as well as acceptable penetration depth.