High-order Harmonic Components Research Articles

A Hybrid Class-E Topology With Constant Current and Constant Voltage Output for Light EVs Wireless Charging Application

Traditional Class-E circuit features fewer components, high reliability, and soft switching. However, due to the unidirectional excitation, the application of such a topology circuit is limited, i.e., usually used in low-power applications. To relieve this issue, this article proposes a switched-capacitor-based Class-E circuit, to extend the operating power range of the Class-E circuit. With the proposed new circuit, both constant current (CC) and constant voltage (CV) output modes can be achieved by switching the branch once without changing the switching frequency or compensation network. Compared with the existing CC and CV charging strategies, the proposed circuit has the advantages of fewer components, simpler implementation, and higher reliability. Moreover, the studied compensation network can also be extended to other inverter topologies. The working principle of the proposed circuit is described in detail, and the variable zero-voltage switching (ZVS) margin is introduced to make an accurate design of parameters. Subsequently, the influence of high-order harmonic components on the circuit and the sensitivity of parameters are analyzed. Finally, the proposed circuit is simulated and experimented on a 180–450-W prototype with CC and CV characteristics to verify the feasibility of the circuit and the accuracy of theoretical analysis.

Phase transitions of the ferroelectric (ND4)2FeCl5·D2O under magnetic field

Due to the strong coupling between magnetism and ferroelectricity, ${({\mathrm{ND}}_{4})}_{2}{\mathrm{FeCl}}_{5}\ifmmode\cdot\else\textperiodcentered\fi{}{\mathrm{D}}_{2}\mathrm{O}$ exhibits several intriguing magnetic and electric phases. In this Letter, we include higher-order onsite anisotropic spin interactions to explain the ferroelectric phase transitions of ${({\mathrm{ND}}_{4})}_{2}{\mathrm{FeCl}}_{5}\ifmmode\cdot\else\textperiodcentered\fi{}{\mathrm{D}}_{2}\mathrm{O}$ in a magnetic field and to produce the large weights of high-order harmonic components in the cycloid structure that are observed from neutron diffraction experiments. Moreover, we predict a new ferroelectric phase sandwiched between the FE II and FE III phases in a magnetic field. By emphasizing the importance of the higher-order spin anisotropic interactions, our work provides a framework to understand multiferroic materials with rich phase diagrams.

High-precision local C–V mapping for ferroelectrics using principal component analysis

Local C–V mapping based on scanning nonlinear dielectric microscopy (SNDM) is a useful tool for characterizing ferroelectric domain dynamics at the nanoscale. In this study, we realized high-precision C–V mapping through an improved measurement system that introduces a digitizer and post-signal processing. Coupled with the high capacitance detection sensitivity of SNDM, nontrivial patterns corresponding to the polarization response were observed even in harmonic images with an order as high as thirty. Using these high-order harmonic components for the C–V curve resynthesis led to improved measurement accuracy. In addition, further improvement was achieved by introducing noise reduction based on principal component analysis. From the C–V curves resynthesized in this manner, parameters that represent the curve features could be extracted and subsequently displayed in two-dimensional maps. Detailed analyses of the datasets obtained with a ferroelectric HfO2 film revealed interesting distributions concerning local polarization switching dynamics.

Analytical Optimization of Electrodynamic Suspension for Ultrahigh-Speed Ground Transportation

Electrodynamic suspension with a permanent magnet Halbach array is suitable for ultrahigh-speed vacuum pipeline transportation. The optimization of a Halbach array is helpful to save cost and increase carrying capacity. Intricate analytical expressions of electromagnetic forces or time-consuming numerical simulation show inherent defects in the structural optimization. To solve the abovementioned problem, this article develops an analytical optimization by two stages. First, a brief approximate analytical expression of electromagnetic forces is established by omitting high-order harmonic components for both the scalar magnetic potential and vector magnetic potential. Second, the lift-to-weight ratio is taken as the optimization index, and the optimal wavelength-to-gap ratio and thickness-to-gap ratios are put forward by seeking extreme values. The numerical simulation is conducted to verify the validation of the analytical optimization, and the result shows that the optimal structural parameters are highly reliable. An experimental rotatory device for electrodynamic suspension with optimal sizes for a Halbach array is built to verify the validation of the analytical expressions of electromagnetic forces.

Acoustic Waves Radiated From Two Degrees-of-Freedom Nonlinear Rigid Oscillator Systems Immersed in Unbounded Compressible Fluid

Abstract This paper is concerned with the nonlinear behaviors of acoustic waves produced by two degrees-of-freedom rigid oscillators containing nonlinearities and immersed in infinite fluid medium. The vibrations of the oscillators are computed by both the harmonic balance method (HBM) and the direct-time integration scheme, whereas the linearized Euler equations (LEEs) of the acoustic fluid are discretized by a fourth-order dispersion-relation-preserving (DRP) scheme in space and a four-level explicit time marching scheme in time. A constrained moving least-squares (CMLS) immersed boundary method (IBM) is used to enforce the boundary conditions on the common interfaces of the rigid oscillators and the Cartesian grid of the acoustic fluid. A serially staggered procedure is adopted to solve the governing equations of the oscillators and the acoustic fluid as a coupled system. The perfectly matched layer (PML) technique is utilized to damp out the out-going acoustic waves on the boundaries of the truncated computational domain to approximate the nonreflecting wave conditions. Physical insights into the mechanism of the nonlinear acoustic waves induced by super-harmonic resonances, principal resonances, internal resonances, and combination resonances of two degrees-of-freedom nonlinear oscillator systems are provided. The interference fringes of the acoustic waves due to the nonlinear vibration of the system are also discussed. Numerical results show that the sound fields radiated from the vibration system with the above nonlinear behaviors exhibit more complicated interference phenomena since the high-order harmonic components are introduced.

Vortex generator design and numerical investigation for wake non-uniformity and cavitation fluctuation pressure reduction

Aiming at the problem that the exciting force induced by the propeller is excessive and the hull vibration noise exceeds certain limits for a certain surface ship, a type of triangular vortex generator is designed in this paper which is installed on the surface of ship stern to improve the quality of ship wake and solve the vibration problem. Firstly, the size and installing position of the vortex generator are designed based on the ship body lines. Then, the numerical calculation is conducted both for the bare hull and “hull-propeller-vortex generator” system to investigate the effectiveness of the vortex generator. With the installation of the vortex generator, the wake changes mainly occur in the region near the 12 o'clock. The velocity in the high wake area gains effective acceleration and the circumference transition of wake becomes more moderate which contributes to the smooth transition of the blade unsteady cavitation in circumference direction. What's more, the changes of wake can delay the circumference angle of the blade cavitation collapse. It increases the distance between the positions where the blade cavitation collapsed and the ship bottom shell. It is also beneficial to reduce the amplitude of fluctuating pressure. The calculated results show that the fluctuation pressure energy is spread from 1st, 2nd to 3rd or more high-order harmonic components with help of vortex generator. So, the level of fluctuation pressure drops significantly for the 1st and 2nd harmonic components which are the main exciting sources for the hull vibration.

Is the Combination of Linearized Theoretical Analysis and Sand Column Experiment Always Suitable for Estimating the Complex Effective Porosity?

AbstractGroundwater hydrodynamics are significantly affected by the capillary effect when groundwater table approaches sand surface. A complex effective porosity was suggested to replace the specific yield to represent the capillary effect based on varieties of sand column experiments, and its estimation is based on the assumption that the response of time‐varying groundwater table is a simple harmonic motion. Nevertheless, groundwater hydrodynamics always consist of multiple harmonic components, which should be further examined. In this study, we first conducted laboratory sand column experiments with respect to different periodic oscillation conditions. Then, a fast Fourier transformation algorithm was applied to analyze the measured groundwater table, upon which the high order harmonic components under high frequency wave conditions was demonstrated. Subsequently, based on a perturbation approach, we presented a third order analytical solution of time‐varying groundwater table under a simple harmonic oscillation. The gradient descent method was applied to estimate the complex effective porosity by fitting the high order analytical solution to the experimental data. In addition, effects of various parameters, representing different driving head conditions and sediment properties, were testified through parametric studies, which demonstrates high order harmonic components should not be neglected under the conditions of large relative amplitude of driving head, short period oscillation, and the ratio of hydraulic conductivity to dynamic effective porosity being around 1 m/s, for example, in the scenarios of wave‐dominant swash zone. These new findings are of great importance to extend our understandings of the capillary effect on groundwater hydrodynamics.

Modeling and nonlinear dynamics analysis of a rotating beam with dry friction support boundary conditions

A nonlinear dynamic model of a rotating beam with dry friction support boundary conditions is developed, and the effectiveness of this model is verified by comparing it with the relevant literature. In the proposed model, a macro-slip friction model of the contact interfaces at the root of the beam with a dovetail tenon is established to characterize the friction on the beam. Furthermore, a time-domain solution and a linearization method of nonlinear friction force are proposed. The dynamic differential equations of the rotating beam are obtained conveniently by means of Chebyshev polynomials theory. Based on the developed model, the effect of the harmonic number on calculations is discussed by incremental harmonic balance method (IHBM). Moreover, the influences of friction coefficient, excitation amplitude, and rotational speed on the amplitude-frequency response of the system are analyzed. The results indicate that the higher-order harmonic components have significant influence on the nonlinear dynamic response of the tenon-mortise connected beam, which must be considered in the frequency-domain computation. When the contact interface slips, the contact stiffness decreases and the contact damping increases. With the rise of friction coefficient, rotational speed or the decreases of excitation amplitude, the range of slip zone narrows. The variation of amplitude-frequency curves is well explained from the perspective of contact stiffness and contact damping.

ACTIVE ELECTRICITY METERS ERROR ANALYSIS IN CASE OF HARMONICALLY DISTORTED VOLTAGES AND CURRENTS

High order harmonic components in voltage and current signals are nowadays more prevalent in power grids at any voltage level, therefore demands for accurate measurements of the system’s parameters go beyond the performance of instruments under pure sine wave conditions. This topic is highly challenging, especially in domain of electricity meters intended for legal metrology purposes, i.e. for billing in the regulated trade of electrical energy. Test procedures for examination of electricity meters’ output in case of harmonically distorted signals are proposed in several international standards and recommendations. The drawbacks of the signals presented in these documents are the lack of complexity and random behavior of single harmonic component’s amplitude and phase shift. Because many types of electricity meters are used worldwide, different output is expected for instruments based on different measurement principles. For faithful presentation of meters’ errors in case of harmonics, several devices are about to be tested with random distorted signals, by using different currents and phase shifts.

A 20–80 MHz Continuously Tunable Gm-C Low-Pass Filter for Ultra-Low Power WBAN Receiver Front-End

This paper presents a third-order Butterworth low-pass filter (LPF) with continuously tuning capability to be used in the receiver front-end for Wireless Body Area Network (WBAN). To realize the bandwidth tuning for multi-standard operation in WBAN receivers with ultra-low power consumption and minimized area, a novel transconductor-capacitor (Gm-C) filter is proposed. The proposed transconductor core uses an additional gain stage with regulated cascode structure to control the transconductance ( $G_{m}$ ) by tuning the drain-source voltage $V_{ds}$ of the input transistors operating in linear region. Based on fundamental analysis, $V_{ds}$ should be reduced to attenuate the nonlinear effects caused by higher-order harmonic components. This proposed transconductor circuit enables the $G_{m}$ tuning and widens the tuning range while maintaining good linearity with negligible power and area consumption. This work is then implemented into a third-order Butterworth LPF. Measurements show that with external control voltage varying from 450 mV to 550 mV, the cutoff frequency of the LPF can be continuously adjusted from 20 MHz to 80 MHz. This design is implemented in 40 nm CMOS process with 1.1 V supply voltage. The total power consumption of this work is below 2 mW with an active area of 0.0105 mm 2 . Its low power consumption and good area efficiency makes this LPF suitable for WBAN applications.

Numerical and experimental investigation of a spur gear pair with unloaded static transmission error

PurposeThe purpose of this paper is to investigate the dynamic responses of a spur gear pair with unloaded static transmission error (STE) excitation numerically and experimentally and the influences of the system factors including mesh stiffness, error excitation and torque on the dynamic transmission error (DTE).Design/methodology/approachA simple lumped parameters dynamic model of a gear pair considering time-varying mesh stiffness, backlash and unloaded STE excitation is developed. The STE is calculated from the measured tooth profile deviation under the unloaded condition. A four-square gear test rig is designed to measure and analyze the DTE and vibration responses of the gear pair. The dynamic responses of the gear transmission are studied numerically and experimentally.FindingsThe predicted numerical DTE matches well with the experimental results. When the real unloaded STE excitation without any approximation is used, the dynamic response is dominated by the mesh frequency and its high order harmonic components, which may not be result caused by the assembling error. The sub-harmonic and super-harmonic resonant behaviors are excited because of the high order harmonic components of STE. It will not certainly prevent the separations of mesh teeth when the gear pair is under the condition of high speed and heavy load.Originality/valueThis study helps to improve the modeling method of the dynamic analysis of spur gear transmission and provide some reference for the understanding of the influence of mesh stiffness, STE excitation and system torque on the vibration behaviors.

Harmonic current suppression method with adaptive filter for permanent magnet synchronous motor

ABSTRACT Due to the distortion of air gap magnetic field and the inherent non-linear characteristics of the inverter, the stator current of permanent magnet synchronous motor (PMSM) contains a large number of high order harmonic components, which distorts the current waveform and generates torque ripple, limiting the application of the PMSM in high speed and precision situations. To solve this problem, a harmonic current suppression method is proposed based on synchronous rotating coordinate transformation theory and adaptive filtering algorithm. The PMSM harmonic mathematical model is established and the coordinate transformation method is used to extract the 5th and 7th harmonic currents. On the basis of the original double closed-loop control system, the harmonic current loop is added, and the harmonic components are suppressed by injecting harmonic voltages. In order to improve the filtering effect and reduce the harmonic content, an adaptive filter is designed to replace the conventional low pass filter in the process of harmonic current extraction. According to the results of coordinate transformation, the adaptive filter continuously adjusts the parameters online through the least mean square (LMS) algorithm to extract the harmonic current. The simulation and experimental results proved the correctness and effectiveness of the proposed method.

Experimental investigation on the VIV of a slender body under the combination of uniform flow and top-end surge

In order to investigate the effect caused by floating bodies on vortex-induced vibration (VIV) of risers, a composite pipe with the aspect ratio of 250 is tested under coupled uniform and shear oscillatory flow, with Reynolds number ranging from 2000 to 24000. The characteristics of VIV amplitude and frequency of the model under uniform flow are compared and analyzed comprehensively, alongside experimental results from literature, validating the reasonability of the test devices and methods. The key characteristics of VIV under coupled top-end surge and uniform flow are then discussed. Some phenomena involving time-varying frequency, mode transition, amplitude modulation and so on are induced by the oscillation of flow, which also promotes the generation of high-order and low-order harmonic components in cross-flow and in-line frequencies. When combined with uniform flow, the identification of time-varying frequency and amplitude modulation is significantly enhanced by uniform flow with lower velocities while the top-end surge mainly affects the vibration instability in higher-velocity uniform flow. The oscillation amplitude and frequency of the top-end surge mainly change the values of cross-flow vibration amplitude, but affect the in-line amplitude both for trend and values, inducing the increase of values in the range of medium and low reduced velocities and the changing of the distribution of reduced velocity corresponding to the local maximums in the higher range. The combination of the top-end surge related to the movement of floating body and the background flow is responsible for the high-order harmonics of VIV frequency and the enhancement of VIV amplitude under certain reduced velocities, which may induce additional fatigue damage of riser. It is suggested that the movement of floating body should be taken into account in the evaluation of VIV of risers.

Method of dynamic mode decomposition and reconstruction with application to a three-stage multiphase pump

Helico-axial multiphase pumps are significant equipment in the exploitation of petroleum resources in offshore platforms, and in-depth understanding of gas-liquid flow fields is beneficial for the design and optimization. The method of dynamic mode decomposition and reconstruction is introduced and applied to study gas-liquid flow characteristics in a three-stage multiphase pump. Firstly, the theoretical relation between decomposed results and DMD parameters is investigated. Then, the dominant frequency and corresponding coherent structures inside the multiphase pump are revealed, which are induced by rotor-stator interaction and gas-liquid flow patterns. The reconstruction residual versus mode number represents a stepped curve, and the minimum residuals are below 10−5 governed by linear combination approximation. Comparison among reduced-order reconstruction, full-order reconstruction, and raw data shows that reduced-order reconstruction fields are effective in reflecting main flow characteristics, but fail to capture high order harmonic components, which is related to complex flow in diffuser passages and following vaneless areas.

Direction Finding Based on Time-Modulated Array With Multiharmonic Analysis

Direction finding with time-modulated array (TMA) has attracted considerable attention recently. In this communication, a multiharmonic analysis for direction finding based on TMA is proposed. The linear regression model of the two-element direction-finding system is established, and its noise covariance matrix is also analyzed. With the best linear unbiased estimator (BLUE), the high-order harmonic components which were previously ignored in the estimation can be effectively utilized to improve the direction-finding accuracy. Compared with conventional single harmonic analysis, simulation results are provided to demonstrate validation of the proposed method for improving the direction-finding accuracy. An experimental system based on two-element TMA is constructed and implemented to verify the feasibility of the proposed method.

Higher-order crystal field and rare-earth magnetism in rare-earth– Co5 intermetallics

Crystal-field (CF) effects on the rare-earth (RE) ions in ferrimagnetic intermetallics NdCo$_5$ and TbCo$_5$ are evaluated using an ab initio density functional + dynamical mean-field theory approach in conjunction with a quasi-atomic approximation for on-site electronic correlations on the localized 4$f$ shell. The study reveals an important role of the high-order sectoral harmonic component of the CF in the magnetism of RECo$_5$ intermetallics. An unexpectedly large value is computed in the both systems for the corresponding crystal-field parameter (CFP) $A_6^6 \langle r^6 \rangle$, far beyond what one would expect from only electrostatic contributions. It allows solving the enigma of the non-saturation of zero-temperature Nd magnetic moments in NdCo$_5$ along its easy axis in the Co exchange field. This unsaturated state had been previously found out from magnetization distribution probed by polarised neutron elastic scattering but had so far remained theoretically unexplained. The easy plane magnetic anisotropy of Nd in NdCo$_5$ is strongly enhanced by the large value of $A_6^6\langle r^6 \rangle$. Counter-intuitively, the polar dependence of anisotropy energy within the easy plane remains rather small. The easy plane magnetic anisotropy of Nd is reinforced up to high temperatures, which is explained through $J$-mixing effects. The calculated ab initio anisotropy constants of NdCo$_5$ and their temperature dependence are in quantitative agreement with experiment. Unlike NdCo$_5$, the $A_6^6 \langle r^6 \rangle$ CFP has negligible effects on the Tb magnetism in TbCo$_5$ suggesting that its impact on the RE magnetism is ion-specific across the RECo$_5$ series. The origin of its large value is the hybridization of RE and Co states in a hexagonally coordinated local environment of the RE ion in RECo$_5$ intermetallics.

Detecting abandoned farmland using harmonic analysis and machine learning

It is critical to inventory abandoned farmland soon after it is generated, to better manage agricultural resources and to prevent negative consequences that would otherwise follow. This study aims to distinguish abandoned farmlands from active croplands—rice paddy and agricultural fields—by discerning the phenological trajectories over a short-term period of three years (Jan. 2016 to Dec. 2018) in Gwanyang City in South Korea. For Support Vector Machine (SVM) classification, we fully utilized parameters derived from harmonic analyses of the three vegetation indices (VIs: NDVI, NDWI, and SAVI) extracted from Sentinel-2A imagery. The harmonic analyses proved that higher-order sinusoid components produced better fitting to explain the trajectory of the VIs—the maximum adjusted R2 was 95.23%—and the multiple VIs diversified the attributes for the classifications. Consequently, the higher-order harmonic components and the additional VIs increased the accuracy when used in SVM classification. The best performing classification was achieved with a composite of harmonic terms derived from the three VIs, yielding overall accuracy of 90.72%, Kappa index of 0.858, and user’s accuracy for abandoned farmland of 93.40%. The proposed method here would greatly improve the process of detecting abandoned farmland, despite a relatively short observation period, and enable a rapid response to the occurrence of abandonment.

Accurate Rectifier Characterization and Improved Modeling of Constant Power Load Wireless Power Transfer Systems

Wireless power transfer (WPT) is an emerging technology deployed for a wide range of applications. Various design challenges need to be addressed at both circuit and system levels. However, the conventional modeling methods either require impractical assumptions or only focus on the coil-to-coil part. This article presents a system-level model for WPT applications, including all the critical interior blocks, such as power amplifier, transmitter coil, receiver coil, matching networks, and rectifier. An accurate characterization method is proposed to obtain the rectifier impedance as a realistic load condition. Then, through frequency harmonic analysis, the power capabilities along the power flow path are analytically derived for both the fundamental and higher order harmonic components. The system efficiency and the power loss at each block can be accurately estimated. As a result, this model can not only optimize the system performance, but also help improve the thermal design for WPT products. With the assistance of this improved model, a practical design methodology is introduced to optimize the system parameters. An experimental prototype is built to validate the proposed model and the design methodology. Good correlations are observed between the calculations and experiments in both the time-domain and frequency-domain results.

A novel fault diagnosis method for rotor rub-impact based on nonlinear output frequency response functions and stochastic resonance

The rub-impact fault of the rotor system is the research object in this paper, and the system is modeled by the finite element method. In the process of the study, the high-order harmonic components appear in the output response of the rotor system, which imply that the rotor system is nonlinear. Nonlinear output frequency response functions (NOFRFs) solve nonlinear problems in the frequency domain and explain these nonlinear phenomena. Based on NOFRFs, a method named weighted contribution rate of NOFRFs (WNOFRFs) is used to improve the weak high-order harmonic components proposed by the authors. In this paper, the multi-parameter optimized genetic algorithm is used to calculate the obstacle parameters of the stochastic resonance (SR) which is used to enhance weak signal components. In view of the fact that both WNOFRFs and SR can improve the weak signal components, a new method of weighted contribution rate of NOFRFs incorporating stochastic resonance (WNS) algorithm is proposed in this paper. Based on the algorithm, the variations of index WS show a trend of approximately linear growth, which indicates that index WS has certain advantages for the fault diagnosis of the rotor rub-impact.

Effect of positional errors on the accuracy of multi-probe roundness measurement methods

Multi-probe roundness measurement methods can be used to measure cross section roundness profiles and dynamic behaviour of large flexible rotors such as paper machine rolls. Other roundness measurement methods are not suitable for such measurements, since the rotors are too large to be measured on precision spindles and the center point of the measured profile can move in an unpredictable and unrepeatable way during the measurement. Multi-probe roundness measurement methods can, to a limited extent, separate the center point movement (commonly also called error motion) and the roundness profile of a cross section of a rotating workpiece.This study compares the effect of positional errors and center point movement on the accuracy of three different multi-probe roundness measurement methods. The research included quantification of the effects of probe noise, positional errors and center point movement on the accuracy of the roundness profiles produced by the different methods. A novel method for generating continuous random center point movement is presented. Signals of a rotating workpiece with center point motion were simulated, and following GUM handbook supplement 1 guidelines, the Monte Carlo method was used to obtain distributions for the harmonic components of the methods. Distributions for different errors and their effects on roundness parameters are presented separately for each roundness measurement method.The results of this research only show minor differences in lower order harmonic components between the methods. The results also show that diameter sampling is immune to horizontal positional errors although it is particularly sensitive to angular positional errors of the probes, which lead to more errors accumulating in the phases, not the amplitudes of the harmonic components. With higher order harmonic components, the obtained error distributions were observed to correspond well with theoretical error propagation rates for harmonic sensitivity.