Harmonics

About: Harmonics is a research topic. Over the lifetime, 40268 publications have been published within this topic receiving 529716 citations.

New General Formulation and Experimental Verification of Harmonic Clipping Contours in High-Frequency Power Devices

Abstract: This paper presents a novel closed-form solution for the theoretical calculation of harmonic clipping contours when an arbitrary number of harmonics is considered. The clipping contours can be used to design the loads of a high-frequency power device in order to avoid drain current clipping, and hence preventing strong nonlinear effects. For the first time the predicted second harmonic contours are validated thoroughly by means of experimental characterization of GaN HEMT devices. The measured contours result in good agreement with the theory. Moreover, the effect of third harmonic load tuning is also assessed and verified for the first time. These results prove that the clipping contours can be used as a tool for the systematic design of low-distortion power amplifiers.

Modified phase locked loop for grid connected single phase inverter

Abstract: Connecting a single-phase or three-phase inverter to the grid in distributed generation applications requires synchronization with the grid. Synchronization of an inverter-connected distributed generation units in its basic form necessitates accurate information about the frequency and phase angle of the utility grid. Phase Locked Loop (PLL) circuit is usually used for the purpose of synchronization. However, deviation in the grid frequency from nominal value will cause errors in the PLL estimated outputs, and that’s a major drawback. Moreover, if the grid is heavily distorted with low order harmonics the estimation of the grid phase angle deteriorates resulting in higher oscillations (errors) appearing in the synchronization voltage signals. This paper proposes a modified time delay PLL (MTDPLL) technique that continuously updates a variable time delay unit to keep track of the variation in the grid frequency. The MTDPLL is implemented along a Multi-Harmonic Decoupling Cell (MHDC) to overcome the effects of distortion caused by gird lower order harmonics. The performance of the proposed MTDPLL is verified by simulation and compared in terms of performance and accuracy with recent PLL techniques.

Multiple Multiphase Combined Star–Polygon Winding Analysis

Abstract: In order to improve the efficiency and to reduce the field amplitudes of spatial harmonics influencing noise and vibration of electrical machines, three- and five-phase combined star–polygon windings have been suggested in the literature. Besides, the efficiency of an electrical machine is dependent on the fundamental winding factor and the noise/vibration level is related to the winding factors of some higher/lower harmonics. However, there is no systematic method to calculate the winding factor of each spatial harmonic for a multiple topology. This paper deals with proposing different topologies of multiple series multiphase combined star–polygon windings and accordingly with the calculation methods of winding factors for all spatial harmonics and the harmonic leakage factor. The results of winding function approach and symmetrical components of electromotive forces (EMFs) are perfectly in compliance with each other, provided that the fast Fourier transform (FFT) analysis is sufficiently accurate. The results obtained from measurements on an unskewed electrically excited synchronous machine are applied for validating the results given by the sum of EMFs and the proposed calculation formula. The sum of EMFs, considering just one set of a multiple topology, can give the same results as the proposed winding analysis methods for the fundamental or the slot harmonic winding factors.

New Frequency Measurements and Techniques in the 30-THz Region

Abstract: It is proposed that the frequency differences between CO2 laser ines and the harmonics of these differences might be used as intermediate frequencies to bridge the gap between microwave frequency standards and infrared frequencies to simplify absolute measurements of the latter. Tungsten-nickel point-contact diodes would be used as harmonic generators and mixers. The preliminary results of an experimental feasibility study are presented. A description of a novel two-frequency laser, built for this study, is given. It is shown that beat frequencies between differences up to 715 GHz and microwave frequency harmonics up to the twelfth can be observed; interactions with at least the third harmonic of a CO2 frequency difference are possible, producing signals with an S/N of 51 dB in a 2.2-s time constant receiver; attempts to observe a beat between a CO2 frequency and the seventh harmonic of a difference were not successful.

A wind park emitting characteristic and non-characteristic harmonics

Abstract: This paper shows measurements of the emission of harmonics by a small windpark. The spectrum consists of the characteristic harmonics associated with six-pulse converters and a broadband spectrum covering frequencies at which emission normally is not present. These frequencies are caused by the switching pattern of the power-electronics converters. Similar spectra have been reported by other authors and for other types of modern converters. Whereas the actual emission is small, the presence of emission at non-characteristic frequencies could result in voltage distortion limits being exceeded.