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.

Combined System for Harmonic Suppression and Reactive Power Compensation

Abstract: In this paper, a combined system of static Var compensator (SVC) and active power filter (APF) was proposed. The system has the function of power factor correction, voltage stability, and harmonic suppression. The SVC, which consists of delta-connected thyristor-controlled reactor (TCR) and Y-connected passive power filter (PPF), is mainly for voltage stability and power factor correction. The small rating APF is used to filter harmonics generated by the nonlinear load and the TCR in the SVC and to suppress possible resonance between the grid and the PPFs. The configuration and principle of the combined system were discussed first, and then, the control method of the combined system was presented. An optimal nonlinear proportional-integral control was proposed to improve the dynamic response and decrease the steady-state error of the SVC. Harmonic detection with precompensation method and improved generalized integrator control were proposed to improve the performance of APF. The new combined system is compared to classical SVC. It is implemented in a 200-kVA prototype in the laboratory. Simulation and experimental results show that the proposed combined configuration can effectively stabilize system voltage, correct power factor, and suppress harmonic currents.

Suppression of harmonics in Wilkinson power divider using dual-band rejection by asymmetric DGS

Abstract: In this paper, we present an effective technique of second and third harmonic suppression for a Wilkinson power divider by using an asymmetric spiral defected ground structure (DGS). With the proposed technique, a single asymmetric DGS provides two different resonance frequencies because of the different sizes of spiral-shaped defects on the ground plane. The transfer function of the asymmetric DGS shows signal rejection characteristics at two different resonance frequencies and the characteristics of asymmetric DGS is modeled by two parallel RLC resonance circuits in cascade. With the insertion of asymmetric spiral DGS into a quarter-wave line of the Wilkinson power divider, the second and third harmonics are suppressed simultaneously. In experimental results, 18-dB suppression for the second harmonic and 15-dB suppression for the third harmonic, respectively, are achieved. Using asymmetric DGS, the size of a quarter-wave line is reduced by 9.1% compared to that of the conventional divider without a DGS.

An Adaptive Prefiltering Method to Improve the Speed/Accuracy Tradeoff of Voltage Sequence Detection Methods Under Adverse Grid Conditions

Abstract: This paper deals with the improvement of the transient response and harmonic, subharmonic, and dc-offset voltage rejection capability of a grid voltage sequence detection scheme based on a second-order generalized integrator (SOGI). To perform that, the SOGI structure is first analyzed in deep, emphasizing both its tradeoff limits between settling time and harmonic attenuation and the sensitivity to grid subharmonics and dc-offset voltage. Then, a study of the effect of grid voltage harmonics and subharmonics in SOGI and in the SOGI-FLL and MSOGI-FLL structures is introduced. Hence, to overcome these problems, a new structure based on the use of the SOGI filter as prefilter for the previous structures is proposed to achieve a faster time response and higher harmonic rejection. This structure is used in a sequence detection scheme for the detection of the grid voltage components in the αβ-frame and it is applied in a three-phase PV system. Experimental and comparative results are shown to validate this proposal.

Active filtering of harmonic currents in three-phase, four-wire systems with three-phase and single-phase nonlinear loads

Abstract: A novel active harmonic-neutralizing filter is proposed which eliminates current harmonic effects, caused by any configuration of nonlinear loads in a three-phase, four-wire systems. The authors present proposed filter topologies and simulation results verifying the concept. Theoretical analysis of the circuit is included to facilitate a detailed converter design. The proposed topology is shown to have distinct advantages over traditional approaches to the problem, particularly over the three single-phase inverter approach. >

Dynamics of MEMS resonators under superharmonic and subharmonic excitations

Abstract: We present an analysis and simulations for the dynamics of electrically actuated microbeams under secondary resonance excitations. The presented model and methodology enable simulation of the transient and steady-state dynamics of microbeams undergoing small or large motions. The microbeams are excited by a dc electrostatic force and an ac harmonic force with a frequency tuned near twice their fundamental natural frequencies (subharmonic excitation of order one-half) or half their fundamental natural frequencies (superharmonic excitation of order two). In the case of superharmonic excitation, we present results showing the effect of varying the dc bias, the damping and the ac excitation amplitude on the frequency–response curves. In the case of subharmonic excitation, we show that, once the subharmonic resonance is activated, all frequency–response curves reach pull-in, regardless of the magnitude of the ac forcing. We conclude that the quality factor has a limited influence on the frequency response in this case. This result and the fact that the frequency–response curves have very steep passband-to-stopband transitions make the combination of a dc voltage and a subharmonic excitation of order one-half a promising candidate for designing improved high-sensitive RF MEMS filters. For both excitation methods, we show that the dynamic pull-in instability can occur at an electric load much lower than a purely dc voltage and of the same order of magnitude as that in the case of primary-resonance excitation.