High Frequency Harmonic Components Research Articles

Design Voltage Controller of Bipolar SPWM Voltage Source Inverter

This paper presents single phased VSI (Voltage Source Inverter) type bipolar SPWM. The main purpose of this system is generating a constant sinusoidal output waveform without affected by load (resistive) demand. Its concept is to get reference voltage from PI control and compare it with modulated triangular carrier for controlling inverter’s switches. The system is also represented by a LCL output filter. The LCL filter is employed to reduce the high frequency harmonic components in current waveform due to PWM switching and to reduce the output current THD. Simulation result and analysis are bravely presented to verify the effectiveness of proposed approach.

Harmonic suppression and uniformity improvement of plasma density in capacitively coupled plasma

A method for improving plasma uniformity in capacitively coupled plasma (CCP) is developed. Plasma contains harmonics due to the nonlinear characteristics of the sheath. Because high-frequency harmonic components in the plasma have short wavelengths, high-frequency harmonics components have a bad influence on plasma uniformity. This is because the electromagnetic standing wave effect (SWE) is severe at high frequencies. To improve plasma uniformity, a CCP using a parallel capacitor that is connected to the powered electrode is developed. By adjusting the capacitance of the parallel capacitor, a parallel resonance between the parallel capacitor and the reactor, which is net inductive, is generated. As the parallel loop approaches the parallel resonance, the currents of other harmonic frequency components in the plasma are greatly reduced. Therefore, the waveform of the plasma bulk current also becomes sinusoidal, and the amplitude of the plasma current becomes almost constant, regardless of the radial position at the parallel resonance condition. Moreover, the voltage applied across the plasma is greatly increased. Consequently, plasma uniformity and the voltage applied to the plasma along the electrode are significantly improved under the parallel resonance condition due to a greatly reduced SWE.

Effects of Long-Term Vibration on Cellulose Degradation in an Oil-Impregnated Pressboard under Simultaneous Thermal–Electrical–Mechanical Stress Aging

Due to the complex operation conditions in a power transformer, an oil-impregnated pressboard (OIP) simultaneously suffers from thermal, electrical, and mechanical stress. Since most research studies have paid much attention to thermal or electrical aging of OIPs, this paper analyzes the effects of long-term mechanical vibrations on cellulose degradation in OIPs under simultaneous multi-stress. The aging experiments were firstly conducted at 130 °C, with a DC electric voltage of +6 kV, vibration amplitude of 10–50 μm, and vibration frequency of 100–300 Hz. The finite element analysis (FEA) of the pressboard vibration model was then performed on Abaqus to investigate the time–frequency domain characteristic parameters of compressive stress on the pressboard under varied vibration frequencies and amplitudes. The FEA results reveal that compressive stress on the pressboard in a multi-stress aging experiment coincided with the axial compressive stress on the insulation spacers in an SZ-50000/110 transformer. Moreover, combined with the degree of polymerization (DP) of cellulose, the effects of long-term vibration on cellulose degradation are reflected in two ways: the increase in compressive stress on the pressboard generates more links available for degradation, while more high frequency harmonic components in compressive stress accelerate the reaction rate in cellulose degradation.

Effect of magnetic slot wedge on the performance of bulb tubular turbine generator

Purpose Owing to the salient pole structure and stator slots of hydro-generator, the air gap magnetic field in the generator is unevenly distributed. High-frequency harmonic components contained in the inhomogeneous air gap magnetic field will have a negative impact on the generator performance. The purpose of this paper, therefore, is to improve the distribution of air gap magnetic field by using appropriate magnetic slot wedge, thereby improving the generator performance. Design/methodology/approach Taking a 24 MW, 10.5 kV bulb tubular turbine generator as an example, the 2 D electromagnetic field model of the generator is established by finite element method. The correctness of the model is verified by comparing the finite element calculation data with the experimental data. The influences of the permeability and thickness of the magnetic slot wedge on the generator performance are studied. Findings It is found that the intensity and harmonic content of the air gap magnetic field will change with the permeability of slot wedge and then the performance parameters of the generator will also change nonlinearly. The relationship between the eddy current loss, torque ripple, output voltage and other parameters of the generator and the permeability of slot wedge is confirmed. In addition, the variation of losses and torque with wedge thickness is also obtained. Originality/value The influence mechanism of magnetic slot wedge on the performance of hydro-generator is revealed. The presented results give guidelines to selecting suitable magnetic slot wedge to improve generator performance.

Design of Experiments Predictive Models as a Tool for Lifespan Prediction and Comparison for Enameled Wires Used in Low-Voltage Inverter-Fed Motors

Since the development of power electronic components, which allowed the manufacturing of reliable and efficient inverters, variable speed drives using inductive motors have become more and more popular. The pulsewidth modulation (PWM) technique has proven to be a very effective method of rotational speed control. However, the fast-changing voltage pulses, with very steep slopes (in the order of a few kilovolt/microsecond), have brought new hazards for the electrical insulation system of such motors. Very high frequency harmonic components of PWM voltage will result in significant overvoltage due to an impedance mismatch between the cable and the motor. As an effect, the voltage seen by some parts of the insulation system may exceed the partial discharge inception voltage stating the localized partial discharges activity. The aim of this article is to investigate and analyze the aging process of the enameled wire exposed to different factors and to propose a method allowing them to predict their lifespans in given conditions. This study introduces a prediction based on the design of experiments method and the statistical Weibull distribution. Thanks to the model obtained with short multistress aging tests, it is possible to predict the results of significantly longer ones. Moreover, the adopted methodology is proposed that allows us to predict the scatter of the long tests based on the short-time results dispersion. The same approach is used to compare different products between each other and rank them. All model predictions are compared with the experimental data in order to prove the model accuracy.

Обеспечение когерентности цифровой обработки сигналов токов и напряжений электроэнергетических систем при снижении частоты дискретизации

The development of Russia’s electric power industry includes, as one of important objectives, step by step intellectualization of the electric power system under the conditions of decentralized generating capacities and wide use of facilities on the basis of renewable energy sources. The Smart Energy System of Russia national project implies construction of digital substations equipped with state of the art relayprotection and automatic control devices, which exchange instantaneous values of currents and voltages. In implementing such exchange, a need may arise to decrease or increase the signal sampling frequency for optimally suiting to the process tasks. The results from analyzing the effects of digital processing involving loss of coherence of power frequency voltage and current signals, which arise in decreasing the sampling frequency, are presented. It is shown that, if the coherence requirements are not complied with in decimation, this will result in significant errors in estimating the signal parameters. It is also shown that for determining the current and voltage signals sine wave distortion degree due to loss of coherence in processing, it is advisable to use a normalized mutual correlation ratio. It has been demonstrated based on simulation results that for signals containing high frequency harmonic components, incoherent samplingaggravates the distorting effect; it is also pointed out that in analyzing distortion effects on power frequency signals, it is important to take into account the initial phases of high frequency harmonic components.

Positional stability and radial dynamics of sonoluminescent bubbles under bi-harmonic driving: Effect of the high-frequency component and its relative phase

The use of bi-frequency driving in sonoluminescence has proved to be an effective way to avoid the spatial instability (pseudo-orbits) developed by bubbles in systems with high viscous liquids like sulfuric or phosphoric acids. In this work, we present extensive experimental and numerical evidence in order to assess the effect of the high frequency component (PAcHF) of a bi-harmonic acoustic pressure field on the dynamic of sonoluminescent bubbles in an aqueous solution of sulfuric acid. The present study is mainly focused on the role of the harmonic frequency (Nf0) and the relative phase between the two frequency components (φb) of the acoustic field on the spatial, positional and diffusive stability of the bubbles. The results presented in this work were analyzed by means of three different approaches. First, we discussed some qualitative considerations about the changes observed in the radial dynamics, and the stability of similar bubbles under distinct bi-harmonic drivings. Later, we have investigated, through a series of numerical simulations, how the use of high frequency harmonic components of different order N, affects the positional stability of the SL bubbles. Furthermore, the influence of φb in their radius temporal evolution is systematically explored for harmonics ranging from the second to the fifteenth harmonic (N=2–15). Finally, a multivariate analysis based on the covariance method is performed to study the dependences among the parameters characterizing the SL bubble. Both experimental and numerical results indicate that the impact of PAcHF on the positional instability and the radial dynamics turns to be progressively negligible as the order of the high frequency harmonic component grows (i.e. N≫1), however its effectiveness on the reduction of the spatial instability remains unaltered or even improved.

Improved Control Strategy for DFIG Wind Turbines for Low Voltage Ride Through

This paper presents an improved control strategy for both the rotor side converter (RSC) and grid side converter (GSC) of a doubly fed induction generator (DFIG)-based wind turbine (WT) system to enhance the low voltage ride through (LVRT) capability. Within the proposed control strategy, the RSC control introduces transient feed-forward compensation terms to mitigate the high frequency harmonic components and reduce the surge in the rotor currents. The proposed GSC control scheme also introduces a compensation term reflecting the instantaneous variation of the output power of the rotor side converter with consideration of the instantaneous power of grid filter impendence to keep the dc-link voltage nearly constant during the grid faults. To provide precise control, non-ideal proportional resonant (PR) controllers for both the RSC and GSC current regulation are employed to further improve dynamic performance. Simulations performed in Matlab/Simulink verify the effectiveness of the proposed control strategy.

On-Chip Single Tone Pseudo-Noise Generator for Analog IP Noise Tolerance Measurement

A single tone pseudo-noise generator with a harmonic-eliminated waveform is proposed for measuring noise tolerance of analog IPs. In the waveform, the harmonics up to the thirteenth are eliminated by combining seven rectangular waves with 22.5- degree spacing phases. The proposed waveform includes only high region frequency harmonic components, which are easily suppressed by a low-order filter. This characteristic enables simple circuit implementation for a sine wave generator. In the circuit, the harmonic eliminated waveform generator is combined with a current controlled oscillator and a frequency adjustment circuit. The single tone pseudo-noise generator can generate power line noise from 20MHz to 220MHz with 1MHz steps. The SFDR of 40dB is obtained at the noise frequency of 100MHz. The circuit enables the measurement of frequency response characteristics measurements such as PSRR.

Synchronization of stochastic bistable systems by biperiodic signals

We study the nonlinear response of a noisy bistable system to a biperiodic signal through experiments with an electronic circuit (Schmitt trigger). The signal we use is a biharmonic one, i.e., a superposition of low and high frequency harmonic components. It is shown that the mean switching frequency (MSF) of the system can be locked at both low and high frequencies. Moreover, the phenomenon of MSF locking at the lower frequency can be induced and enhanced by the higher frequency excitation. Thus high frequency bias can control synchronization at the low frequency.

Nonlinearity in piezoelectric ceramics

The paper presents an overview of experimental evidence and present understanding of nonlinear dielectric, elastic and piezoelectric relationships in piezoelectric ceramics. This topic has gained an increasing recognition in recent years due to the use of such materials under extreme operating conditions, for example in electromechanical actuators and high power acoustic transducers. Linear behaviour is generally confined to relatively low levels of applied electric field and stress, under which the dielectric, elastic and piezoelectric relationships are described well by the standard piezoelectric constitutive equations. Nonlinear relationships are observed above certain ‘threshold’ values of electric field strength and mechanical stress, giving rise to field and stress-dependent dielectric (e), elastic (s) and piezoelectric (d) coefficients. Eventually, strong hysteresis and saturation become evident above the coercive field/stress due to ferroelectric/ferroelastic domain switching. The thermodynamic method provides one approach to describing nonlinear behaviour in the ‘intermediate’ field region, prior to large scale domain switching, by extending the piezoelectric constitutive equations to include nonlinear terms. However, this method seems to fail in its prediction of the amplitude and phase of high frequency harmonic components in the field-induced polarisation and strain waveforms, which arise directly from the nonlinear dielectric and piezoelectric relationships. A better fit to experimental data is given by the empirical Rayleigh relations, which were first developed to describe nonlinear behaviour in soft magnetic materials. This approach also provides an indication of the origins of nonlinearity in piezoelectric ceramics, in terms of ferroelectric domain wall translation (at intermediate field/stress levels) and domain switching (at high field/stress levels). The analogy with magnetic behaviour is also reflected in the use of Preisach-type models, which have been successfully employed to describe the hysteretic path-dependent strain-field relationships in piezoelectric actuators. The relative merits and limitations of the different modelling methods are compared and possible areas of application are identified.

Significance of harmonic changes and noise components in hoarseness.

Acoustic Analysis and synthesis of hoarseness by sound spectrography suggests that the acoustic properties of hoarseness are mainly determined by the interactions of the following three factors: 1) noise components in the main formant of each vowel, 2) high frequency noise components above 3000 Hz, and 3) the loss of high frequency harmonic components. These three findings are more pronounced in the vowels /α/, /ε/, and /i/ than in /u/ and /ɔ/. With the progression of the severity of hoarseness, these three abnormal patterns become more prominent and exaggerated. On the basis of these findings, a classification of four types of hoarseness was presented using sonagram tracings.

On the different effect of sound absorption on the tone of new and old violins

The “Theory of Residue” explains how the absorption of high frequency harmonicschanges the tone quality and loudness of old violins less than that of modern ones. Indeed, following this theory, the high frequency harmonic components directly contribute to the sensation of fundamental sound. Therefore in new violins, rich in high partial components, the room absorption makes itself felt not only in these, but also in the fundamental component sensation.