Total Waveform Research Articles

An online method for the accuracy level evaluation of the phasor measurement units

Online evaluation of the accuracy level of the phasor measurement unit (PMU) is very useful in assessing the accuracy ranges of PMU measurements. Such results can be applied to avoid the misoperation of power system protection and control and enhance the accuracy of power system state estimation. Because the theoretical values are unknown, the evaluation indices defined in the IEEE/IEC standard 60255-118-1, such as the total vector error, frequency error, and rate of change of frequency error, cannot be calculated online. To address this concern, a new index named the total waveform error (TWE) is proposed in this paper. It is defined as a ratio of fundamental root-mean-square (RMS) value to fundamental residual RMS, where harmonic components are excluded in the TWE calculation. For a specific window length, two TWE thresholds are set according to the IEEE standard C37.118.1 to divide the PMU measurement into 3 accuracy levels. Theoretical analysis and simulation tests show that the TWE is effective in accuracy-level evaluation. Two examples are given to illustrate the TWE applications of evaluating accuracy levels of PMU measurements.

A Real-Time Permittivity Estimation Method for Stepped-Frequency Ground-Penetrating Radar by Full-Waveform Inversion

Ground-penetrating radar (GPR) has been widely used in estimating the permittivity of mediums. The radar echo amplitude method is an important method used by GPR in this estimation, the basic step of which is to deduce the magnitude of the permittivity according to the relationship between the reflection coefficient and the permittivity. Based on the basic principle of the radar echo amplitude method, this paper proposes a full-wave inversion real-time permittivity estimation method that can be used for stepped-frequency GPR (SFGPR), which offers high efficiency, accuracy, and generalization ability. The characteristics of this method are mainly reflected in the following four aspects: Using the SFGPR system and introducing a layered media detection model, we can complete waveform compensation optimization with high precision. The distance between the antenna and the surface of the reflective medium is extracted from the time domain waveform without manual measurement, avoiding human measurement errors. The inversion of the total reflection waveform at the required height works under the principle of an electromagnetic field, eliminating the need for repeated metal plate calibration experiments and improving work efficiency and waveform accuracy. In a continuous measurement line, the total reflection waveform inversion on each measurement point can be efficiently completed, and the change of permittivity on the measurement line can be obtained. To evaluate the feasibility of the proposed method, we performed experiments on a wall of known thickness, and the permittivity estimation was basically consistent with that of the dielectric probe, physical model calculation, and wall penetration. We also successfully applied this method to the dielectric property analysis of adobe samples. The results indicate that the proposed method can help grasp the condition of a measured medium, which can ensure the accuracy of detection and improve subsequent data processing efficiency.

Integrated sensing and communication waveform design in the Internet of Vehicles

We design an integrated sensing and communication (ISAC) transmission waveform with total transmission power, waveform similarity, and peak-to-average power ratio (PAPR) constraints in the Internet of Vehicles (IoV). The integrated waveform can complete radar target detection while communicating with downlink cellular users. The design of IoV with ISAC can not only improve the spectrum efficiency, but also further promote the integration of communication and sensing equipment. In this paper, the IoV with ISAC is formally modeled from the communication view and sensing view respectively. On this basis, taking the joint optimization of multi-user interference (MUI) total energy and Cramér Rao Bound (CRB) as the objective function, the transmission waveforms are designed with total transmission power, waveform similarity, and PAPR constraints respectively. To obtain the global optimal solution, we adopt a low complexity algorithm to solve the optimization problem under the total transmit power constraint and the optimization problem based on waveform similarity and PAPR constraints is further transformed into a nonconvex quadratically constrained quadratic programming (QCQP) problem, which is solved by using the semidefinite relaxation (SDR) technique. By ranking one approximation of the constrained optimization problem, it can be transformed into the solution of semidefinite programming (SDP) problems. The numerical results show that the designed ISAC transmission waveform can achieve an efficient tradeoff between sensing and communication performance, and each KPI is superior to one of the only communication and only sensing waveform design schemes. And it can improve the real-time information interaction ability of the IoV.

A systematic survey for precursory tilt changes at all monitored eruptions in Japan

Volcanic eruptions are sometimes preceded by tilt changes that are an indicator of immediate pre-eruptive processes. In this study, the tilt changes before all monitored eruptions in Japan were surveyed for the first time to address the generality and common features of these signals. An automated procedure was devised to identify tilt changes. The results showed that approximately half of the analyzed eruptions were preceded by tilt changes. Detection ratios depended on station locations, and approximately 10–20% of the total waveforms consisted of detectable tilt changes. Broadband seismic records, when integrated into displacements, showed detection ratios comparable to those of tiltmeter records. The lead times and durations of the tilt changes showed large variations. The durations correlated with amplitudes, although with considerable scatter. Both accelerating and decelerating types of tilt changes were common, and their ratios depended on the volcanoes. These are the first findings on the nature of pre-eruptive tilt changes from many volcanoes, and the waveform analysis procedure proposed in this paper is applicable to other regions. Future works involve extending this study to datasets from other regions, detecting tilt changes from continuous records, applying the proposed method to an early warning system, and detecting longer tilt changes, which require that the proposed approach be improved by subsequent studies.

Terahertz emission from transient currents and coherent phonons in layered MoSe2 and WSe2

Terahertz (THz) time-domain emission spectroscopy was performed on layered 2H-MoSe 2 and 2H-WSe 2. The THz emission shows an initial cycle attributed to surge currents and is followed by oscillations attributed to coherent interlayer phonon modes. To obtain the frequencies of the interlayer vibrations, an analysis of the THz emission waveforms was performed, separating the two contributions to the total waveform. Results of the fitting show several vibrational modes in the range of 5.87–32.75 cm − 1 for the samples, attributed to infrared-active interlayer shear and breathing modes. This study demonstrates that THz emission spectroscopy provides a means of observing these low-frequency vibrational modes in layered materials.

Non-Invasive Blood Pressure Total Waveform Monitoring Using Information Extracted by an Extended Kalman Filter Algorithm from Pulsations in an Oscillatory Cuff

This paper describes a novel approach designed for non-invasive, routine screening of patients for cardiovascular disorders without the complexities of using an electrocardiogram or invasive probes. Specifically, an oscillographic-view of the brachial artery blood pressure waveform, including the dicrotic notch, is extracted from information in the pressure pulsations from an ordinary blood pressure cuff. The novelty of this approach is that the total continuous shape of the waveform, not just two numbers for pressures, is generated. A computer algorithm processes the cuff pressure pulsations and provides a near real-time visual estimate of the continuous shape of the blood pressure waveform to be viewed on oscilloscopes commonly used in hospitals and medical clinics. A model-based Extended Kalman Filter (EKF) algorithm is used to process the information and identify the coefficients of a Fourier transform model for the waveform and the coefficients for an empirical model for artery stiffness. By viewing the total waveform, variations or disorders in the waveform during a series of pulse cycles can be observed and easily recognized. Simulations of two-case studies demonstrate successful convergence of the algorithm for a variety of waveform disorders including arrhythmia, variations in the shape of the dicrotic notch, changing systolic and diastolic pressure levels, and stiff arteries. Experimental verification of this proposed procedure will require invasive pressure measurements while simultaneously processing the algorithm for non-invasive waveform comparisons. Once the algorithm is verified experimentally, the end goal is to use the procedure on patients with known cardiovascular diseases in order to easily create a database of waveform disorders correlated with disorders of specific cardiovascular diseases.

Total loss torque waveform estimation for a turbocharged diesel engine

The indicated (gas) torque is a key parameter for reciprocating engine. It reports on various aspects of the engine, such as the quality of the combustion process, the fuel combustion rate and the average effective pressure. This is a good indicator of the stability of the engine at work. The form of the instantaneous indicated torque is precious information for the control and diagnosis of the engine. The study of the simulation of crankshaft dynamics illustrates the need to know the total loss torque (i.e. the addition of friction torque, auxiliary torque and load torque) to achieve the indicated torque. To date, it has proven difficult to obtain an accurate predictive expression of the instantaneous total loss torque. This expression includes adequate simulation of friction of all moving parts of the engine (piston ring and skirt, crankshaft bearings, valve gear...), auxiliaries and load. Based on experimental results conducted on a four-cylinder turbocharged diesel engine, this work offers a simple and practical solution for estimating the total torque loss. The proposed method makes it possible to successfully estimate total torque losses under a wide range of engine operating conditions. The result prediction has been confronted to experimental data.

Reconstruction of the aortic pressure waveform using a two-level adaptive transfer function strategy

Existing studies cannot estimate the high-frequency components of the aortic pressure waveform (APW) practically and reliably. To solve this problem, a two-level adaptive transfer function (ATF) strategy was proposed. Two ATFs were derived from raw and normalized brachial and aortic pressure waveforms. The APW was reconstructed with the amplitude and pulsatility information from the two ATFs. Experimental results showed that our method achieved lower errors for total waveform, diastolic blood pressure, the pressures at the start-systolic and dicrotic-notch points, and three high-frequency-dependent indices including the pressure at inflection point, augmentation index and the time interval from foot to inflection points (3.11 versus 4.24 mmHg, 1.74 versus 1.94 mmHg, 2.56 versus 2.75 mmHg, 6.94 versus 7.47 mmHg, 3.35 versus 3.80 mmHg, 9.56 versus 10.48 % and 24.64 versus 27.73 ms, respectively) compared with traditional generalized transfer function. The proposed method can accurately estimate both the shape and high-frequency components of APW.

Strategies for improving the force performance of a superconducting linear synchronous motor

Combined with superconducting technology, an electrodynamic suspension train can reach a higher traveling speed by taking advantage of the strong magnetic field generated by high-temperature superconducting (HTS) magnets. However, a HTS linear synchronous motor (LSM) in a propulsion system typically uses an air-core structure to reduce the normal force. As a result, excessive propulsive force ripple occurs due to magnetic circuit divergence and a large air gap, which leads to an uncomfortable ride and unexpected mechanical resonance. To reduce this ripple, this study first improves the traditional short-pitch winding structure of the stator. By staggering the double-layer coils of the stator, the ripples of the magnetic flux density generated by the upper and lower coils change from superposition to suppression. Then, the propulsive force of a pair of pole magnets of the HTS-LSM under this structure is analyzed, and its primary ripple frequency is 6 times the fundamental frequency. By installing two pairs of magnets in a bogie and staggering them by a 30° electrical angle, the peak and valley of the propulsive force of the two magnets are staggered so that the total propulsive force waveform of the bogie can be smoothed as much as possible. Concurrently, the AC loss generated by the alternating magnetic field on the HTS magnets can be reduced. Also, this study investigates the influence of the short pitch factor on the propulsive force, and the ripple can be suppressed by reducing the factor.

Two Novel Approaches for Identification of Synchronous Machine Parameters From Short-Circuit Current Waveform

In this article, two novel approaches for identifying the synchronous generator (SG) parameters are presented. The proposed approaches use an experimentally obtained armature current during the short-circuit test as input data. Both approaches are simple, cost-effective, and practical since they do not require any additional equipment for signal generation nor applying any of the advanced control techniques. The first approach relies on fitting the analytical total armature current waveform with the experimental one, while the second approach relies on matching the observed waveform with an analytical waveform of asymmetrical and alternating components. Instead of traditional graphical methods typically used in standardized procedures, this article also proposes a novel hybrid metaheuristic algorithm to identify the SG's parameters. The experimental verification of the proposed methods is carried out on 100 MVA SG at the Bajina Basta hydropower plant in Serbia.

Results of plasma radiative compression investigation in the PF-24 device operated with D2, Ar and (100%-x)D2+x%Ar mixtures obtained using the 5-phase Lee model code

The article presents new results for plasma radiative compression in high-current discharges in the z-pinch configuration. The results are based on the 113 discharges performed in the plasma-focus PF-24 device operated with D2, Ar and (100%-x)D2+xAr mixtures, with Ar pressure fractions x ≈ 3–60% (mole fractions). The constant initial total pressure is about 2.9 mbar and the constant initial pressure of Ar is 1.2 mbar. Each experimental discharge was simulated individually using the 5-phase Lee model code to carry out the fitting procedure of the total discharge current waveform. The results from these 113 computed discharges fitted to the corresponding 113 experimental discharges show that the increase of the effective atomic number of the gas mixture increases the probability of occurrence of plasma radiative compression phenomenon. Relatively weak radiative compression was found for part of the discharges in 15–60% range of Ar mole fractions and in Ar, while the stronger radiative compression occurred for part of discharges in Ar only. This is because there was too little total x-ray line radiation emission during the equilibrium pinch lifetime related to the very small amount of swept up mass and the low current flow through pinched plasma, represented by the decreasing values of model parameters as the Ar mole fraction increases. The results show that the main pinch parameters influencing the occurrence and strength of radiative compression are: total x-ray line emission yield, effective atomic number, initial pinch radius, initial pinch ion number density and initial pinch ion/electron temperature.

Simultaneous adaption of the gain and phase of a generalized transfer function for aortic pressure waveform estimation

GoalThis paper proposes and validates a completely adaptive transfer function (CATF) based on an autoregressive exogenous (ARX) model which adjusts the gain and phase of a generalized transfer function (GTF) simultaneously to estimate the aortic pressure waveform from a brachial pressure waveform. MethodsInvasive aortic and brachial pressure waveforms were recorded from 34 subjects for the validation of the proposed method. Individual transfer functions (ITFs) were trained based on the pressure waveforms using an ARX model. The GTF was derived by averaging the ITFs. CATF was then obtained by adjusting both the gain and phase of the GTF using regression formulas calculated from the ITFs and brachial hemodynamic parameters. Meanwhile the quantitative contributions of the adaption of gain and phase of the GTF were investigated respectively. The root-mean-square-error of the total waveform and absolute errors of common hemodynamic indices including systolic and diastolic blood pressures (SBP and DBP, respectively), pulse pressure (PP) and augmentation index were used to evaluate the performance of the proposed method in the data divided into low, middle and high PP amplification groups. ResultsThe CATF achieved lower errors for DBP and PP in the low PP amplification group (1.79 versus 2.10 mmHg and 5.08 versus 6.23 mmHg, respectively, both P < 0.05) and PP in the middle amplification group (1.43 versus 1.92 mmHg, P < 0.05) compared with the GTF. SignificanceThe proposed method provides a step towards the development of an improved and clinically useful non-invasive approach for estimating the aortic pressure waveform from a peripheral pressure waveform.

An analysis of voltage source inverter switches fault classification using short time Fourier transform

&lt;p&gt;The dependability of power electronics systems, such as three-phase inverters, is critical in a variety of applications. Different types of failures that occur in an inverter circuit might affect system operation and raise the entire cost of the manufacturing process. As a result, detecting and identifying inverter problems for such devices is critical in industry. This study presents the short-time Fourier transform (STFT) for fault classification and identification in three-phase type, voltage source inverter (VSI) switches. TFR represents the signal analysis of STFT, which includes total harmonic distortion, instantaneous RMS current, RMS fundamental current, total non harmonic distortion, total waveform distortion and average current. The features of the faults are used with a rule-based classifier based on the signal parameters to categorise and detect the switch faults. The suggested method's performance is evaluated using 60 signals containing short and open circuit faults with varying characteristics for each switch in VSI. The classification results demonstrate the proposed technique is good to be implemented for VSI switches faults classification, with an accuracy classification rate of 98.3 percent.&lt;/p&gt;

POWER BALANCING TOPOLOGY FIVE-LEVEL CASCADED H-BRIDGE INVERTER WITH PHASE SHIFT TECHNIQUE FOR PHOTOVOLTAIC SOURCES

This research paper proposes a power balance optimization topology for a five-level cascaded H-bridge inverter with a phase shift technique. This topology uses two phase-shifted sine waveforms 180 degrees apart to modulate the two triangular waveforms. These two triangular waveforms are assigned a 90-degree phase shift. When the outputs of the two H-bridge inverters are connected in series, the total output waveform is 5 levels. The principles and methods of this research will focus on a cascaded H-bridge inverter with photovoltaic sources. Two independent units are connected in series to allow linear and non-linear loads at a maximum one-kilowatt rating. However, the researcher will create a prototype mechanism to test the power balance and power distribution efficiency of the two inverters compared with the simulation results using MATLAB/Simulink. Nevertheless, the results showed that the power balance efficiency could be improved, resulting in the mean efficiency of both inverters of 96%. When the harmonics were measured, the load was not Linear produced third- and fifth-order harmonics greater than linear load. This research confirms that the simulation with MATLAB/Simulink program and the prototype is correct and acceptable.

The effect of left ventricular contractility on arterial hemodynamics: A model-based investigation.

Ventricular-arterial coupling is a major determinant of cardiovascular performance, however, there are still inherent difficulties in distinguishing ventricular from vascular effects on arterial pulse phenotypes. In the present study, we employed an extensive mathematical model of the cardiovascular system to investigate how sole changes in cardiac contractility might affect hemodynamics. We simulated two physiologically relevant cases of high and low contractility by altering the end-systolic elastance, Ees, (3 versus 1 mmHg/mL) under constant cardiac output and afterload, and subsequently performed pulse wave analysis and wave separation. The aortic forward pressure wave component was steeper for high Ees, which led to the change of the total pressure waveform from the characteristic Type A phenotype to Type C, and the decrease in augmentation index, AIx (-2.4% versus +18.1%). Additionally, the increase in Ees caused the pulse pressure amplification from the aorta to the radial artery to rise drastically (1.86 versus 1.39). Our results show that an increase in cardiac contractility alone, with no concomitant change in arterial properties, alters the shape of the forward pressure wave, which, consequently, changes central and peripheral pulse phenotypes. Indices based on the pressure waveform, like AIx, cannot be assumed to reflect only arterial properties.

Radar altimeter waveform simulations in Antarctica with the Snow Microwave Radiative Transfer Model (SMRT)

Radar altimeters are important tools to monitor the volume of the ice sheets. The penetration of radar waves in the snowpack is a major source of uncertainty to retrieve surface elevation. To correct this effect, a better understanding of the sensitivity of the radar waveforms to snow properties is needed. Here, we present an extension of the Snow Model Radiative Transfer (SMRT) to compute radar waveforms and conduct a series of simulations on the Antarctic ice sheet. SMRT is driven by snow and surface roughness properties measured over a large latitudinal range during two field campaigns on the Antarctic Plateau. These measurements show that the snowpack is rougher, denser, less stratified, warmer, and has smaller snow grains near the coast than on the central Plateau. These simulations are compared to satellite observations in the Ka, Ku, and S bands. SMRT reproduces the observed waveforms well. For all sites and all sensors, the main contribution comes from the surface echo. The echo from snow grains (volume scattering) represents up to 40% of the amplitude of the total waveform power in the Ka band, and less at the lower frequencies. The highest amplitude is observed on the central Plateau due to the combination of higher reflection from the surface, higher scattering by snow grains in the Ka and Ku bands, and higher inter-layer reflections in the S band. In the Ka band, the wave penetrates in the snowpack less deeply on the central Plateau than near the coast because of the strong scattering caused by the larger snow grains. The opposite is observed in the S band, the wave penetrates deeper on the central Plateau because of the lower absorption due to the lower snow temperatures. The elevation bias caused by wave penetration into the snowpack show a constant bias of 10 cm for all sites in the Ka band, and a bias of 11 cm, and 21 cm in the Ku band for sites close to the coast and the central Plateau, respectively. Now that SMRT is performing waveform simulations, further work will address how the snowpack properties affect the parameters retrieved by more advanced retracking algorithms such as ICE-2 for different snow cover surfaces.

The Incidence of Peripheral Artery Disease in Patients with Rheumatoid Arthritis

Objectives: The basic aim of this study was to find the expression of PAD in a group of Rheumatoid arthritis participants but with no record of any cardiovascular diseases. Methods: On Ninety subjects with no record of considerable CVD but with RA a prospective observational non-experimental studywas performed. Doppler spectral waveform analysis and Ankle Brachial Pressure Index for vascular judgment was performed. Place and Duration: In the Medicine Department of Aziz Fatima Medical and Dental College Faisalabad for one-year duration from April 2020 to April 2021. Results: In this study total 90 of participants were selected out of which 18 were males and 72 were females. The mean age for this study and time period of RA was 62 ±9.01 and 11.8±11.2 years respectively. It was noticed that seventy five percent of the subjects had triphasic waveforms in the Right foot while sixty percent had in the Left foot when examined the posterior tibial or PT artery. In sixty-eight percent of the total participants triphasic waveforms of the Dorsalis Pedis Arteries were found. Biphasic right was present in thirty percent subjects while biphasic left was present in thirty five percent subjects. Biphasic Dorsalis Pedis was found in forty percent participants of both feet. Only one subject was found with discontinuous monophasic PT of both feet. Conclusions: Results show that ABPI index was discovered normal in majority of patients but waveform analysis was found suboptimal or biphasic in total of one-third of the participants. These results indicatethat to find patients with early PAD the judgment of peripheral arterial perfusion should use both modes. Keywords: Rheumatoid arthritis, ankle brachial pressure value, CVD risks hazards, screening.

Adiabatic waveforms for extreme mass-ratio inspirals via multivoice decomposition in time and frequency

We compute adiabatic waveforms for extreme mass-ratio inspirals (EMRIs) by ``stitching'' together a long inspiral waveform from a sequence of waveform snapshots, each of which corresponds to a particular geodesic orbit. We show that the complicated total waveform can be regarded as a sum of ``voices.'' Each voice evolves in a simple way on long timescales, a property which can be exploited to efficiently produce waveform models that faithfully encode the properties of EMRI systems. We look at examples for a range of different orbital geometries: spherical orbits, equatorial eccentric orbits, and one example of generic (inclined and eccentric) orbits. To our knowledge, this is the first calculation of a generic EMRI waveform that uses strong-field radiation reaction. We examine waveforms in both the time and frequency domains. Although EMRIs evolve slowly enough that the stationary phase approximation (SPA) to the Fourier transform is valid, the SPA calculation must be done to higher order for some voices, since their instantaneous frequency can change from chirping forward ($\stackrel{\ifmmode \dot{}\else \textperiodcentered \fi{}}{f}&gt;0$) to chirping backward ($\stackrel{\ifmmode \dot{}\else \textperiodcentered \fi{}}{f}&lt;0$). The approach we develop can eventually be extended to more complete EMRI waveform models---for example, to include effects neglected by the adiabatic approximation, such as the conservative self-force and spin-curvature coupling.

Window Optimisation of Power Quality Signal Detection using Gabor Transform

This paper presents power quality analysis on different signal characteristics, namely instantaneous sag, momentary sag, temporary sag, instantaneous swell, momentary swell, and temporary swell. Power quality signals were analyzed using linear time-frequency distribution (TFD) namely short-time Fourier transform (STFT) and proposed Gabor transform (GT), and the best technique for power quality detection was determined based on the performance analysis of varied window length. Optimum window length for different signal characteristics which are effective and reliable for developing real-time monitoring system was employed using MATLAB. From a time-frequency representation (TFR) results based on STFT and GT, parameters such as instantaneous RMS voltage, VRMS(t) and instantaneous total waveform distortion, VTWD(t) had been extracted. In finding the best technique for power quality, the TFDs had been compared in terms of accuracy, memory and computational complexity of the analysis. Based on the performance analysis conducted, GT was able to compute with high accuracy with 94% averagely as well as low memory size by 6% compared to STFT. Hence, GT is considered as the best TFD, and recommended for low cost PQ monitoring system.

An implementation of Short Time Fourier Transform for Harmonic Signal Detection

Power electronic components has the tendency to induce a non-linear signal called harmonic distortion. Without proper monitoring tools, harmonic distortion can harm sensitive electronic equipment, and in worse case scenarios, may lead to unreliable operation of controller and misalignment of motoring unit. This matter can be compromised by taking safety precaution, by identifying the level of harmonic rise in the electrical system. This paper presents analysis on different characteristics of harmonic signal using frequency distribution technique, namely Fourier transform (FT), and proposal of time-frequency distribution (TFD) technique, which is a short time Fourier transform (STFT). The novelty of utilizing STFT is the analyzed signal is represented in both time and frequency marginals, hence providing extra information of the spectral over the time. Simulation was carried out using MATLAB, by means the results consisting of the magnitude of multi-frequency components signal were represented in time-frequency representation (TFR). From the TFR, parameters such as instantaneous RMS fundamental voltage, V1RMS(t), instantaneous RMS voltage, VRMS(t), instantaneous total waveform distortion, VTWD(t), instantaneous total harmonic distortion, VTHD(t) and instantaneous total nonharmonic distortion, VTnHD(t) had been extracted. The performance of different harmonic signals such as normal, single-level harmonic, multi-level harmonic, short duration harmonic and interharmonic had been analyzed. The performance based on absolute percentage error (APE) index indicated average of 93% of correctness using 256 window length in STFT measurement.