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.

Broadband vibration-based energy harvesting improvement through frequency up-conversion by magnetic excitation

Abstract: Traditional vibration-based energy harvesters are designed for a specific base excitation frequency by matching its fundamental natural frequency. This work presents the modeling and analysis of a nonlinear, magnetically excited energy harvester that exhibits efficient broadband, frequency-independent performance utilizing a passive auxiliary structure that remains stationary relative to the base motion. This system is especially effective in the regime of driving frequencies well below its fundamental frequency, thus enabling a more compact design solution over traditional topologies. A model based on Euler–Bernoulli beam theory is coupled to a linear circuit and a model of the nonlinear, magnetic interaction to produce a distributed parameter magneto-electromechanical system. This model is used in both harmonic and stochastic base excitation case studies. The results of these simulations demonstrate multiple-order-of-magnitude power harvesting performance improvement at low driving frequencies and an insensitivity to time-varying base excitation. Furthermore, the proposed system is shown to outperform an optimally designed, standard energy harvester in the presence of broadband, random base excitation.

Optimal PWM based on real-time solution of harmonic elimination equations

Abstract: Pulse-width modulation of DC/AC power converters (PWM) based on the elimination of low-order harmonics necessitates solving systems of nonlinear equations. Conventional implementations of this technique based on storing off-line calculated solutions have the common problem that the system flexibility is very limited, especially for applications that require both amplitude and frequency control. A new implementation scheme based on real-time solution of nonlinear harmonic elimination equations using a digital signal processor DSP56001 is reported in this paper. With this digital signal processor (DSP), optimal pulse patterns having 15 switching angles in each quarter fundamental period can be determined within 2.15 ms. Details of the system hardware and software are described. New theoretical results concerning the solvability of harmonic elimination equations are also presented.

Feed-Forward Scheme for an Electrolytic Capacitor-Less AC/DC LED Driver to Reduce Output Current Ripple

Abstract: In order to achieve high-efficiency, high-power-factor, high-reliability, and low-cost, a flicker-free electrolytic capacitor-less single-phase ac/dc light emitting diode (LED) driver is investigated in this paper. This driver is composed of a power-factor-correction (PFC) converter and a bidirectional converter. The bidirectional converter is used to absorb the second harmonic component in the output current of the PFC converter, thus producing a pure dc output to drive the LEDs. The spectrum of the output capacitor voltage of the bidirectional converter is analyzed, indicating that the output capacitor voltage contains harmonic components at multiples of twice the line frequency apart from the dc component and second harmonic component. A feed-forward control scheme with a series of calculation operation is proposed to obtain the desired modulation signal, which contains the corresponding harmonic components, to ensure the bidirectional converter fully absorb the second harmonic current in the output of the PFC converter. Finally, a 33.6 W prototype is fabricated and tested in the lab, and the experiment results show that the proposed control scheme greatly reduces the ripple of the LED driving current.

Generation of Ultrasonic Second and Third Harmonics Due to Dislocations. I

Abstract: By representing the effective-tension term of a dislocation (string model) as a power series in displacement gradients, and retaining the first nonlinear term, expressions for the amplitudes of the second and third harmonics of an ultrasonic wave introduced into a solid containing mobile dislocations are obtained. In the case of the second harmonic, a lattice term, a dislocation term, and a cross term contribute to the amplitude and all three terms can be of comparable magnitude. In the case of the third harmonic, in a solid containing a reasonable density of mobile dislocations, the dislocation contribution to the amplitude is dominant and usually lattice effects can be neglected. Except in special circumstances, it is difficult to separate the three terms that contribute to the amplitude of the second harmonic, and dislocation dynamics, therefore, are more easily studied through the generation of third harmonics.

Evaluation of harmonic detection methods for active power filter applications

Abstract: In the attempt to minimize the harmonic disturbances created by the non-linear loads the choice of the active power filters comes out to improve the filtering efficiency and to solve many issues existing with classical passive filters. One of the key points for a proper implementation of an active filter is to use a good method for current/voltage reference generation. There exist many implementations supported by different theories (either in time- or frequency-domain), which continuously debate their performances proposing ever better solutions. This paper gives a survey of the common used theories. Then, the work here proposes a simulation setup that decouples the harmonic reference generator from the active filter model and its controller. In this way the selected methods can be equally analyzed and compared with respect to their performance, which helps anticipating possible implementation issues. The conclusions are collected and a comparison is given at the end, which is useful in deciding the future hardware setup implementation. The comparison shows that the choice of numerical filtering is a key factor for obtaining good accuracies and dynamics for an active filter.