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.

The effect of rotor design on sensorless speed estimation using rotor slot harmonics identified by adaptive digital filtering using the maximum likelihood approach

Abstract: Adaptive digital filtering has been demonstrated as an effective technique for extracting a real-time, sensorless, speed signal from rotor slot harmonics (RSHs) embedded in the line current waveform of induction motor drives. It is known that sensorless speed estimation techniques using RSHs may exhibit poor performance with certain motor designs. This paper examines the reasons for that poor performance which reflects differences in the magnitude of the slot harmonic signals consequent upon rotor design. Experimental results for a 30 kW motor with 6 different rotors are presented. The significant parameters are the number of rotor slots, skew and the accuracy of construction. It is clearly shown how inferior performance can arise. Conversely, improvements in reliability of speed estimation and transient response can be obtained by recognising those aspects which provide an enhanced signal, by minimising the background noise of the inverter/machine, or by enhancing the adaptive filter. The recursive maximum likelihood technique is presented as an improved algorithm for tuning the digital filter which aids transient response and reliability of speed estimation. Real time, experimental transient performance is demonstrated for the different rotors used in this paper and the performance failure of a particular slot combination demonstrated.

Resonance-enhanced high-harmonic generation

Abstract: In this paper we present some results of a high-harmonic generation experiment in argon, performed with a Ti sapphire laser (787 nm, 140 fs) and a spatially shaped focus (flat top). The range of intensities is 3-100 TW cm(-2) The intensity dependence of the harmonic signal shows an interesting behaviour of the 13th harmonic, namely an initial suppression followed by a strong enhancement at similar or equal to 85 TW cm(-2), which exceeds the magnitude of the 11th harmonic. This behaviour is a consequence of a resonant atomic process. Numerical calculations were also performed. They partly reproduced the experiment.

Medical ultrasonic diagnostic imaging method and apparatus

Abstract: An improvement to the method for harmonic imaging including the steps of (a) transmitting ultrasonic energy at a fundamental frequency and (b) receiving reflected ultrasonic energy at a harmonic of the fundamental frequency is provided. The transmitting step includes the step of: applying the plurality of waveforms to a respective plurality of transducer elements, a first waveform of the plurality of waveforms characterized by a first value of a harmonic power ratio, waveforms transmitted from the transducer elements and corresponding to the plurality of waveforms summing as an acoustic waveform substantially at the point, the acoustic waveform characterized by a second value of the harmonic power ratio less than the first value. The imaging method can also include a step for subdividing the transmit aperture into two or more subapertures, each subaperture having at least four adjacent transducer elements. The subapertures are phased differently with respect to one another to selectively reduce either fundamental components or harmonic components of echoes from tissue. These techniques can be used to improve contrast agent harmonic imaging as well as tissue harmonic imaging, depending upon the phase shift selected.

Compensation of Dead-Time Effects Based on Adaptive Harmonic Filtering in the Vector-Controlled AC Motor Drives

Abstract: A new dead-time compensation method for vector-controlled ac motor drives is proposed. The method only compensates the fundamental and sixth harmonic component of the inverter-output distortions in synchronous reference frame. The fundamental component is compensated by feedforwardly adding a predetermined compensation signal to the voltage reference of ac motor drive. To compensate the harmonic distortions, the harmonic compensator with all-pass-based adaptive bandpass filter is proposed and builds up the feedback loop with current controllers in order to minimize the distortions due to dead-time effects. The method is software intensive and independent of the polarity of the phase currents and nonlinear-switching characteristics varied with operating conditions of the inverter. It is simulated and implemented on a 750-W laboratory ac motor drive, where its effectiveness is verified

Nonintrusive identification of electrical loads in a three-phase environment based on harmonic content

Abstract: This paper describes a signature construction for identifying loads based upon harmonic content of the current measured at a metering socket. Data gathered from ten loads at a commercial site served to experimentally validate the signature construction. The repeatability of current harmonics was investigated during transients and steady-states of several single, split-phase, and three-phase loads monitored in isolation.