High Frequency Model Research Articles

High Frequency Modeling of Smart Sensor for Precise Power Quality Assessment Using Fuzzy Logic

Power Quality Assessment (PQA) is a critical issue both in transmission and distribution networks. Therefore, it is necessary to precisely classify the disturbances in shortest possible time to prevent the malfunction or increase of losses in the electrical equipment through appropriate remedial techniques. This paper proposes a highly accurate method of PQA through data acquisition using smart sensors, the Rogowski coils (RCs). RCs with wide band width and linear characteristics allow faithful reproduction of high-frequency (HF) signals. In the proposed method, simulated disturbance signals are applied to RC. The output signals are subjected to multilevel wavelet decomposition and then computation of the energy difference in the detailed components between the disturbance signal and the pure sinusoidal waveform is performed to design a fuzzy logic Power Quality Classifier. The classifier is tested by varying the magnitude, frequency and duration of the disturbance and found to be accurate to 98.38%. The classification accuracy depends mainly on the performance of sensors at HFs. Thus, with RCs as sensors instead of conventional instrument transformers, it is found that the precision of power quality classification is greatly improved.

금융 및 특수시계열 모형의 조망

Contrasted with the standard linear ARMA models, financial time series exhibits non-standard features such as fat-tails, non-normality, volatility clustering and asymmetries which are usually referred to as “stylized facts” in financial time series context (Terasvirta, 2009). We are accordingly led to ad hoc models (apart from ARMA) to accommodate stylized facts (Andersen et al., 2009). The paper aims to give a contemporary overview on financial and special time series models based on the recent literature and on the author’s publications. Various models are illustrated including asymmetric models, integer valued models, multivariate models and high frequency models. Selected statistical issues on the models are discussed, bringing some perspectives to the future works in this area.

Forecasting of Surface Currents via Correcting Wind Stress with Assimilation of High-Frequency Radar Data in a Three-Dimensional Model

This paper details work in assessing the capability of a hydrodynamic model to forecast surface currents and in applying data assimilation techniques to improve model forecasts. A three-dimensional model Environment Fluid Dynamics Code (EFDC) was forced with tidal boundary data and onshore wind data, and so forth. Surface current data from a high-frequency (HF) radar system in Galway Bay were used for model intercomparisons and as a source for data assimilation. The impact of bottom roughness was also investigated. Having developed a “good” water circulation model the authors sought to improve its forecasting ability through correcting wind shear stress boundary conditions. The differences in surface velocity components between HF radar measurements and model output were calculated and used to correct surface shear stresses. Moreover, data assimilation cycle lengths were examined to extend the improvements of surface current’s patterns during forecasting period, especially for north-south velocity component. The influence of data assimilation in model forecasting was assessed using a Data Assimilation Skill Score (DASS). Positive magnitude of DASS indicated that both velocity components were considerably improved during forecasting period. Additionally, the improvements of RMSE for vector direction over domain were significant compared with the “free run.”

A Simplified High Frequency Model of Interleaved Transformer Winding

A Simplified High Frequency Model of Interleaved Transformer Winding

High frequency modeling of a shielded four-core low voltage underground power cable

Underground low voltage (LV) power cables have a long life span, and so far minimum effort was put in methods for condition assessment. However, a slow but steady increase in the amount of faults is being observed and future de-central power generation may further put pressure on the reliability of the LV grid. Therefore, condition monitoring for LV cable systems is under investigation. With the occurrence of intermittent faults, fast transients from discharges may be observed before an outage occurs. To estimate if such signals are measurable, a model of the cable valid up to 50 MHz was derived. Numerical simulations have been used to obtain the parameters of the multi-conductor transmission line model, with special consideration of the copper screen configuration. Measurements on a 60 m cable segment have been performed to verify the model, showing good agreement. This model will be used to investigate signal propagation through a LV grid with focus on the feasibility to base LV condition monitoring on signals which may originate from upcoming cable faults.

Reducing Identification Error Using Over-Sampling Technique

In this paper, a method of identification is introduced which is based on the so-called output over-sampling scheme. When analyzing the frequency domain properties of the over-sampling scheme, it is found that the error of the frequency response is pushed away from the frequency band of the plant. The method first identifies a high frequency model using low-pass filtering and then convert the model to the original sampling frequency. Simulations show that the model parameter variance can be made much smaller than the Cramer-Rao bound of the model identified from the data of the original sampling frequency.

Transformer Winding Modeling based on Multi-Conductor Transmission Line Model for Partial Discharge Study

To study and locate partial discharge(PD) and analyze the transient state of power transformer, there is a need for a high frequency model of transformer winding and calculation of its parameters. Due to the high frequency nature of partial discharge phenomenon, there is a need for an accurate model for this frequency range. To attain this goal, a Multi-Conductor Transmission Line (MTL) model is used in this paper for modeling this transformer winding. In order that the MTL model can properly simulate the transformer behavior within a frequency range it is required that its parameters be accurately calculated. In this paper, all the basic parameters of this model are calculated by the use of Finite Element Method (FEM) for a 20kV winding of a distribution transformer. The comparison of the results obtained from this model with the obtained shape of the waves by the application of PD pulse to the winding in laboratory environment shows the validity and accuracy of this model.

Unrestricted Mixed Data Sampling (MIDAS): MIDAS Regressions with Unrestricted Lag Polynomials

SummaryMixed data sampling (MIDAS) regressions allow us to estimate dynamic equations that explain a low frequency variable by high frequency variables and their lags. When the difference in sampling frequencies between the regressand and the regressors is large, distributed lag functions are typically employed to model dynamics avoiding parameter proliferation. In macroeconomic applications, however, differences in sampling frequencies are often small. In such a case, it might not be necessary to employ distributed lag functions. We discuss the pros and cons of unrestricted lag polynomials in MIDAS regressions. We derive unrestricted-MIDAS (U-MIDAS) regressions from linear high frequency models, discuss identification issues and show that their parameters can be estimated by ordinary least squares. In Monte Carlo experiments, we compare U-MIDAS with MIDAS with functional distributed lags estimated by non-linear least squares. We show that U-MIDAS performs better than MIDAS for small differences in sampling frequencies. However, with large differing sampling frequencies, distributed lag functions outperform unrestricted polynomials. The good performance of U-MIDAS for small differences in frequency is confirmed in empirical applications on nowcasting and short-term forecasting euro area and US gross domestic product growth by using monthly indicators.

고주파모델링을 위한 이중게이트 FET의 열잡음 파라미터 추출과 분석

본 논문에서는 이중게이트 FET를 고주파회로에 응용하기 위해 필요한 열잡음 파라미터를 추출하여 그 특성을 분석하였다. 이중게이트 열잡음 파라미터를 추출하기 위해 튜너를 이용해 잡음원의 임피던스를 바꿔가며 잡음특성을 측정하였으며, open과 short 더미를 이용해서 패드의 기생성분을 제거하였다. 측정결과 일반적인 캐스코드구조의 FET와 비교해서 5GHz에서 약 0.2dB의 잡음 개선효과가 있음을 확인하였으며, 시뮬레이션과 소신호 파라미터 분석을 통해 드레인 소스 및 드레인 게이트간 캐패시턴스의 감소에 의해 잡음지수가 줄어들었음을 확인하였다. In this paper, noise parameters for high frequency modeling of dual-gate FET are extracted and analyzed. To extract thermal noise parameter of dual gate, noise characteristics are measured by changing input impedance of noise source using Tuner, and the influence of pad parasitic elements are subtracted using open and short dummy structure. Measured results indicated that the dual-gate FET is improved the noise figure by 0.2dB compared with conventional cascode structure FET at 5GHz, and it confirmed that the noise figure has dropped due to reduction of capacitances between the drain and source, gate and drain by simulation and analysis of small-signal parameters.

Research on High Frequency Model of Hybrid Vehicle Battery

The application of motor and converter in hybrid vehicle can lead to a significant increase in electromagnetic compatibility. The influence of traction batteries as part of the electromagnetic interference path was not well considered. In this study, high frequency circuit models of single cell, cells connected in series and cells connected in parallel were proposed and developed based on their impedance characteristics and their structure features. Finally, values calculated based on the models and dates measured actually were compared and analyzed. The results show the calculation high frequency losses and the simulation as interference path.

Partial discharge modeling: an improved capacitive model and associated transients along medium voltage distribution cables

The presence of partial discharges is one of the most prominent indicators of defects and ongoing degradation processes of electrical insulation. As a high percentage of failures are associated with partial discharges, the need for the classification, extraction and evaluation of partial discharge signals is essential. Consequently, an electrical model of a breakdown void, modeled as part of the power system, is more than a necessity. In this paper an improved capacitive model of void based on streamer concepts is proposed for the study of the transients generated at the void location. Further, the high frequency model of the cable is employed in order to examine the propagated partial discharge simulated transients of the improved capacitive model. The simulated transients of both models are compared and discussed on a theoretical basis.

A High Frequency Equivalent Circuit and Parameter Extraction Procedure for Common Mode Choke in the EMI Filter

Power converters with high switching frequency generate conducted electromagnetic interference (EMI) noise. EMI filters are thus widely used to reduce these conducted noises for the compliance with electromagnetic compatibility standards. In this paper, a high-frequency (HF) equivalent circuit model for common mode (CM) chokes used in EMI filters is proposed together with its parameter extraction procedure. This procedure is based on impedance measurements and it incorporates an iterative rational function approximation fitting algorithm to extract the parameters in the model. The proposed model and procedure is applied to a planar CM choke which is used to realize an EMI filter. The simulated results of the filter show good agreement with the experimental ones. This extraction procedure is quite general and it can also be extended to identify the HF model of other passive components.

Asymptotic long wave models for a pre-stressed elastic layer with elastically restrained boundaries

Long wave dispersion phenomena is investigated in respect of a pre-stressed incompressible elastic layer subject to elastically restrained boundary conditions (ERBC). Such conditions can be treated as a generalisation of classical free and fixed-face boundary conditions, allowing investigating of the transition between the Neumann and Dirichlet statements of the problem. Symmetric elastically restrained boundary conditions are introduced, followed by both a numerical investigation and a multi-parameter asymptotic analysis of the dispersion relations. All possible asymptotic regimes are grouped into classes based on the magnitude of the associated restraint parameter. A long wave low frequency model is developed to describe motion associated with the fundamental modes for small values of the restraint parameters. Four high frequency models are developed describing asymptotic regimes connected with vibration within the vicinity of the thickness resonances.

High frequency modelling and validation of railway dampers

This paper presents and validates an appropriate physical damper model to predict the dynamic behaviour of a railway damper for frequencies of up to 200 Hz. The model is computationally efficient and, therefore, appropriate for implementation in NVH-CAE models used to study the transmission of vibration paths to the train body. The model parameters are related to the physical characteristics of the damper (volume of the chambers, piston rod sections, characteristics of the valves, etc.). However, it is shown that in the absence of internal constructive information, which is most often the case, the model parameters can be fitted from a few tests carried out at low frequency (0–20 Hz), based on its theoretical background.

Design of Wide Band CMOS VCO with Common Source Transformer Feedback Topology

This paper demonstrates wide-band CMOS VCO based on the transformer feedback from traditional circuit to our proposed work. The start up condition of the traditional cross-coupled pair is expressed by the high frequency model. The wide band technique of this structure is derived with the help of the high frequency model of the transistor. Therefore, the wide band CMOS VCO based on the common source transformer feedback topology can achieves the high performance in the low voltage and low phase noise. The measurement result of the VCO exhibits the figure of merit, core power consumption and output power at supply voltage 0.8 V are –193.1 dBc/Hz, 4.4 mW and –2.3 dBm, respectively. The phase noise is –124.3 dBc/Hz at 1 MHz offset under the operation frequency 5.8 GHz. And the tuning range of the circuit can obtain 28%, this VCO is fabricated in TSMC 0.18 μm 1P6MCMOS process.

High-frequency equivalent model of AC motor for electric vehicle drive system

The application of the motor drive system in electric and hybrid–electric vehicles can lead to a significant increase in electromagnetic compatibility. The AC motor as an important part of motor drive system must be considered. In this paper, a high frequency modelling method of the AC motor is presented. The modelling method consists of deriving the motor model parameters from mathematical resolution of the electrical circuit equations and observation of the variations of the motor impedance with the frequency. All parameters of the proposed models are obtained by differential mode (DM) and common mode (CM) impedance measurement in the frequency domain. The model is verified by impedance measurement of a synchronous motor. The method proposed can be used to obtain a high–frequency equivalent circuit of an AC motor and predict conducted electromagnetic interference in a motor drive system.

Analysis of Wireless Power Transfer System Based on 3-D Finite-Element Method Including Displacement Current

With the advent of electronic technology, researchers are devoting increasing interests to wireless power transfer methods. Generally finite-element method (FEM) is a powerful tool for numerical simulation of such systems. Due to the relatively high operating frequency, the presence of inductance and distributed capacitance in the system as well as eddy current and displacement current become two essential issues in the study of electromagnetic field distribution in wireless power transfer systems. One of the major problems to be addressed is the gap between low and high frequencies as conventional low frequency methods cannot include displacement current, while common high frequency methods focus mainly on the ultrahigh frequencies, such as in antenna studies. In this paper, a 3-D FEM including displacement current is developed to model wireless power transfer system to include displacement current and eddy current and close the gap of high and low frequency modeling methods. No frequency sweeping, which is required in conventional studies, is necessary in the proposed algorithm. Hence the computing time of the proposed algorithm requires only 1.5% of the normal time domain FEM method and this is a significant accomplishment for the electromagnetic community.

HF induction motor modeling using automated experimental impedance measurement matching

High-frequency (HF) models of electrical motors and power converters are greatly important for electromagnetic compatibility characterization of electrical drives and for electromagnetic interference (EMI) filter design. In this paper, an accurate and effective method for the characterization and tuning of HF models (150 kHz-30 MHz) for induction motors has been proposed based on experimental measurements of the motor impedance. Impedance measurements have been taken in three different configurations: between all the six winding terminals which are shorted and grounded; between the three input terminals which are shorted and grounded (common mode); and between one input terminal and the other two which are shorted (differential mode). Once an HF motor model structure has been chosen and modeled using a state-space representation, its parameters have been tuned using genetic algorithm to match the real impedance in each corresponding configuration. Comparison between the experimental impedance measurements and the model impedance estimate are shown for all the tested configurations, in order to validate the model within the frequency range of interest for EMI.

High frequency model of EMI filter

The EMI filters are usually used for suppression of electromagnetic conducted interference of range 9 kHz-30 MHz. The efficiency of electromagnetic interference filter is described by attenuation characteristics. The value of attenuation of EMI filter depends on main parameters of filter’s elements and its parasitic parameters. Therefore the high frequency model of electromagnetic interference filter is analyzed in this paper.

High Frequency Modeling and Parameter Extraction for Vertical-Cavity Surface Emitting Lasers

Accurate modeling and efficient parameter extraction of the equivalent circuit model of high-speed vertical-cavity surface emitting lasers (VCSELs) for high-frequency operation based on the rate equations are presented in this paper. The model is versatile in that it permits dc, small signal, and large signal to be performed, and can be easily on commercial circuit software. An analytical method, along with closed-form solution, to determine parasitic elements, intrinsic model parameters and rate equation model parameters of the VCSELs is developed and experimentally verified using on wafer measurement of electronic and optical performance. Modeled and measured results for the input reflection coefficients and modulation responses exhibit good agreement over a wide range of bias points under cutoff and above-threshold biased condition in the frequency range of 50 MHz-20 GHz for an oxide-confined AlGaAs VCSELs.