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 Vibrational Frequencies: Scaling Factors for HF, B3LYP, and MP2 Methods in Combination with Correlation Consistent Basis Sets

Abstract: A least-squares approach has been used to determine multiplicative scaling factors for harmonic vibrational frequencies to facilitate comparison with experimentally observed frequencies. The harmonic frequencies were calculated using several of the most popular quantum chemical methods (HF, MP2, and B3LYP) and the correlation consistent family of basis sets (cc-pVxZ and aug-cc-pVxZ, where x = D(2), T(3), or Q(4)). Calculations were performed on 41 organic molecules for which fundamental frequencies are well established. When the derived scaling factors are applied, the percentage of calculated frequencies that deviate less than 3% from the experimental frequencies is 93−97% for B3LYP and 88−92% for MP2 when quadruple-ζ level basis sets are used. Similarly, scaling factors were determined for computing the vibrational components of the thermal contributions to enthalpy and entropy. An additional set of molecules was used in calculating scaling factors for the zero-point vibrational energy.

An instantaneous active and reactive current component method for active filters

Abstract: A shunt active filter based on the instantaneous active and reactive current component i/sub d/-i/sub q/ method is proposed. This new control method aims to compensate harmonics and first harmonic unbalance. To evaluate its relative performance, it is compared with the instantaneous active and reactive power p-q method under various mains voltage conditions and for different harmonic injection high-pass filters. Both methods are completely frequency-independent, however under distorted mains voltages the proposed method presents a better harmonic compensation performance. The system synthesis and implementation are performed. Simulation and experimental results are presented.

Multiple-Complex Coefficient-Filter-Based Phase-Locked Loop and Synchronization Technique for Three-Phase Grid-Interfaced Converters in Distributed Utility Networks

Abstract: Synchronization with the utility networks is crucial for operating three-phase grid-interfaced converters. A challenge of synchronization is how to fast and precisely extract the fundamental positive and negative sequences under the distorted and unbalanced conditions. Many phase-locked loop (PLL) and synchronization techniques have been presented in the past decades. Most of them make a tradeoff between the accuracy and dynamic response under severe distorted and unbalanced conditions. In this paper, a multiple-complex coefficient-filter-based PLL is presented, and its unique feature lies in the accurate and rapid extraction of the positive and negative sequence components from the polluted grid voltage, and the harmonic components can also be estimated precisely, which has the potential use for selective compensation in active filter applications. Another advantage of the proposed method is its flexibility for simplifying its structure in some specified conditions. Results of continuous-domain simulations in MATLAB and discrete-domain experiments based on a 32-b fixed-point TMS320F2812 DSP are in good agreement, which confirm the effectiveness of the proposed method.

Harmonic optimization of multilevel converters using genetic algorithms

Abstract: In this letter, a genetic algorithm (GA) optimization technique is applied to determine the switching angles for a cascaded multilevel inverter which eliminates specified higher order harmonics while maintaining the required fundamental voltage. This technique can be applied to multilevel inverters with any number of levels. As an example, in this paper a seven-level inverter is considered, and the optimum switching angles are calculated offline to eliminate the fifth and seventh harmonics. These angles are then used in an experimental setup to validate the results.