Transformer Transfer Function Research Articles

Does temporal irregularity drive prediction failure in schizophrenia? temporal modelling of ERPs

Schizophrenia subjects often suffer from a failure to properly predict incoming inputs; most notably, some patients exhibit impaired prediction of the sensory consequences of their own actions. The mechanisms underlying this deficit remain unclear, though. One possible mechanism could consist in aberrant predictive processing, as schizophrenic patients show relatively less attenuated neuronal activity to self-produced tones, than healthy controls. Here, we tested the hypothesis that this aberrant predictive mechanism would manifest itself in the temporal irregularity of neuronal signals. For that purpose, we here introduce an event-related potential (ERP) study model analysis that consists of an EEG real-time model equation, eeg(t) and a frequency Laplace transformed Transfer Function (TF) equation, eeg(s). Combining circuit analysis with control and cable theory, we estimate the temporal model representations of auditory ERPs to reveal neural mechanisms that make predictions about self-generated sensations. We use data from 49 schizophrenic patients (SZ) and 32 healthy control (HC) subjects in an auditory ‘prediction’ paradigm; i.e., who either pressed a button to deliver a sound tone (epoch a), or just heard the tone without button press (epoch b). Our results show significantly higher degrees of temporal irregularity or imprecision between different trials of the ERP from the Cz electrode (N100, P200) in SZ compared to HC (Levene’s test, p < 0.0001) as indexed by altered latency, lower similarity/correlation of single trial time courses (using dynamic time warping), and longer settling times to reach steady state in the intertrial interval. Using machine learning, SZ vs HC could be highly accurately classified (92%) based on the temporal parameters of their ERPs’ TF models, using as features the poles of the TF rational functions. Together, our findings show temporal irregularity or imprecision between single trials to be abnormally increased in SZ. This may indicate a general impairment of SZ, related to precisely predicting the sensory consequences of one’s actions.

Detection of probability of occurrence, type and severity of faults in transformer using frequency response analysis based numerical indices

Frequency response analysis (FRA) is mainly used as a tool for detecting mechanical faults (especially displacement and deformation of windings and core) as well as electrical faults (especially short- circuits in windings) of transformers. In the FRA method, the transfer function (TF) of transformer is measured in a wide frequency range and these measurements are compared with the reference TF, to obtain information such as the probability of occurrence, type and severity of the fault; thus, appropriate features must be extracted. In this paper, different transformers are considered, and the transformer TFs are extracted in healthy condition and under different fault conditions such as axial displacement, radial deformation, disc space variation, short-circuits and core deformation. Then, on the basis of statistical and numerical indices, new methods are proposed for fault diagnosis (including detection of occurrence, type and severity of fault). In order to achieve an accurate process and verify the validity of the proposed methods, necessary features are extracted by applying indices to the data obtained from the measurements performed on model transformers. After extracting features, the performance of the proposed methods is evaluated by applying the experimental data obtained from actual transformers. The results show that the proposed methods are more accurate than other well-known methods.

Evaluation of Online Techniques Utilized for Extracting the Transformer Transfer Function

Power transformers have vital importance in the power delivery and, therefore, different diagnostic techniques are proposed for them. The frequency response analysis (FRA) is an effective method which detects the mechanical changes in transformer windings by extracting the transfer function. There are various approaches for obtaining the transfer function online, which is known as the online FRA technique. This paper compares these different mathematical approaches for obtaining the transfer function of a transformer. The comparison is carried out by defining an appropriate model for the transformer and applying these mathematical methods to it. The effect of other power network equipment on the transformer transfer function is also studied in this paper. The results of this contribution determine the proper methods for the online FRA technique, which can be used in the transformer monitoring applications.

Adaptive estimation of the transformer stray capacitances for DC–DC converter modelling

New low cost and accurate estimation method of transformer stray capacitances for wide band DC–DC converter modelling and design is proposed. The Wiener filter (WF) method is applied to estimate the transformer impedance – referred to the selected transformer winding configurations. Laboratory tests are used to adapt the filter, that is to find optimal impedance which minimises mean square error between measured, noise perturbed current and reconstructed current. Transformer transfer function peaks indicate internal LC resonances. Stray capacitances are extracted based on resonant frequencies determination. The method validation is carried out by simulation and experimental analysis, where estimated stray capacitances by WF are compared with measurements of an impedance analyser.

Electrode-less measurement of cell layers impedance.

This paper is devoted to yet unpublished electrode-less methods (ELM) of cell layers impedance measurement based on transformer principle. The main advantage of ELM is elimination uncertainties caused by interface between electrodes and measured electrolyte. The method of avoiding distortion caused by non-ideal transformer transfer function ("deconvolution") and errors caused by residual voltage is described. The modification of original transformer based method allowing to measure an impedance of inserted object is proposed. Results of several calibration measurements confirming the proper function of ELM including example of transepithelial resistance of cells layer are presented. Crucial parts of measuring system and recommendation for their realization are included.

Advanced transformer winding deformation diagnosis: moving from off-line to on-line

On-line monitoring and diagnosis of transformers have been investigated and discussed significantly in last decade. This study has concentrated on issues arising while on-line transformer winding deformation diagnosis is going to be applied on transformers with various kinds of techniques. From technical perspective, before replacing off-line methods by on-line methods and eventually by intelligent approaches, practical challenges must be addressed and overcome. Hence, available off-line transformer winding deformation diagnosis methods are discussed precisely. Mathematical calculation in on-line short circuit impedance measurement is investigated. On-line transformer transfer function measurement setup is presented. A profound insight to the problems pertaining on-line transformer winding deformation recognition methods, characterizes existing online methods, explains the concepts behind online measurements and striving to open the discussion doors towards challenges are discussed. In the end a 400 MVA step up transformer has been taken as a case in order to clarify the capability of Frequency Response Analysis (FRA) method in fault detection while short circuit impedance could only demonstrate some rough understanding about transformer condition.

A Vector-based Approach to Discriminate Radial Deformation and Axial Displacement of Transformer Winding and Determine Defect Extent

The transfer function is a well-known method to detect mechanical defects of transformer windings. After measurement of transfer functions, they must be evaluated to detect any anomaly in transformer windings. One of the main problems in this stage is lack of transparency. This article tries to solve this problem through a vector space-based perspective to diagnose radial deformation and axial displacement of transformer windings. To determine the severity of the winding deformation or displacement, the angular proximity index is used. The measurement results show the effectiveness of this index. Based on the verified model of the transformer, a dimensionality reduction technique is applied to transformer's transfer function to map it from its original high-dimensional vector space to a lower-dimensional one. It is shown that transfer functions of radially deformed and axially displaced windings are well separated visually in the reduced space.

Microwave photonic quadrature filter based on an all-optical programmable Hilbert transformer

A microwave photonic quadrature filter, new to our knowledge, based on an all-optical Hilbert transformer is presented. It is based on mapping of a Hilbert transform transfer function between the optical and electrical domains, using a programmable Fourier-domain optical processor and high-speed photodiodes. The technique enables the realization of an extremely wide operating bandwidth, tunable programmable bandwidth, and a highly precise amplitude and phase response. Experimental results demonstrate a microwave quadrature filter from 10 to 20 GHz, which achieves an amplitude imbalance of less than ±0.23 dB and a phase imbalance of less than ±0.5°.

変圧器の伝達関数計算ソフトウエアの数値計算レシピおよび評価用テストデータ

変圧器の伝達関数計算ソフトウエアの数値計算レシピおよび評価用テストデータ

Maximum likelihood estimation of transformer high frequency parameters from test data

A methodology for the development of transformer high-frequency models is presented. Time constants of the transformer transfer function are estimated from frequency response measurements by using the nonlinear least-squares method in the frequency domain. Then, the time response of transfer functions is used in conjunction with the maximum-likelihood method to estimate the transformer model parameters. As a case study, a high-frequency model of a 15 kVA, 7620/240 V single-phase distribution methodology. >

Equiripple magnitude approximation for low‐pass IIR digital filters with prescribed group delay

AbstractAn efficient algorithm is proposed for approximating the magnitude of the low‐pass IIR digital filter with prescribed group delay in equiripple. Prescribed group delay characteristics can be realized by placing in the denominator of the transfer function a polynomial expression designed to have such characteristics. For amplitude characteristics we approximate it to obtain equiripple using a linear‐phase polynomial in the numerator.Equiripple magnitude approximation is done separately for the passband and for the stopband and all the characteristics are made equiripple by several times of iterations.In this simple method the auxiliary complex plane is utilized and in each the transformed transfer function is expressed as the sum of objective magnitude 1 and the error function for it. By assigning an all‐pass function to an approximation function of the error function, equiripple characteristics are realized.By approximation in the stopband, good equiripple characteristics can be obtained even if all the degrees of freedom are used. On the other hand, since the approximation in the passband deviated largely from equirippleness, a method is presented for improving ripple characteristics by reducing the degree of freedom by one. As a design example, a filter of order 10 is given.

Low sensitivity digital LDI ladder filters with elliptic magnitude response

A method of designing elliptic LDI [I] type switched-capacitor filters is known [2], [3]. However, this method cannot be extended directly to digital filter design and implementation. Preliminary results involving the design of a fifth-order digital LDI ladder filter have been proposed 141. In this contribution a complete design method for low sensitivity digital LDI ladder filters which have elliptic magnitude response is presented. A relationship between the bilinear and LDI transformed impedances is investigated. A precompensation procedure together with the bilinear transformation are applied to transform an elliptic analog ladder filter into a realizable digital LDI ladder filter. A voltage-current signal flowgraph ( <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">V/I</tex> SFG) simulation method is adopted in this design procedure. The design procedure provides a method of realizing the bilinear transformed transfer function using the LDI as a building block. An example of fifth-order elliptic LDI low-pass filter design is given. The effects of multiplier coefficient quantization on both the digital elliptic LDI ladder filter and an equivalent wave digital ladder are compared.

Simplification of z-transfer function via Padé approximation of tangent phase function

Simplification of <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">z</tex> -transfer function is performed in the bilinear-transformed domain via approximating tangent phase function by a Padé technique. A modification has been given to the transformed transfer function so that the reduced <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">z</tex> -transfer function has the same zero initial responses as the original system. The simplified <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">z</tex> -transfer function is always stable and minimum phase.

On the synthesis of lattice parameter digital filters

The synthesis of lattice parameter digital filters from a given <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">z</tex> -transform transfer function is considered. Included are several versions of AR, MA, and ARMA structures. The approach is based upon partial fraction expansions and leads to numerical algorithms for parameter calculation which are numerically robust in terms of zeros and poles close to the unit circle as well as self-correcting for finite precision coefficients.

Entropy power factors for linear discrete systems

The change in entropy of an ergodic signal ensemble that passes through a linear discrete filter is written in terms of the <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">z</i> -transform transfer function of the system and expressed as the entropy power factor of the filter. The entropy change in the first order continuous amplitude distribution is separated from the sequential component that results from the effect of the system on the correlation function and power spectrum of the ensemble. A new entropy power factor is defined which expresses the change in entropy associated with the sequential redundancy alone. The results are used to calculate the information transmission rate of a signal ensemble with a given autocovariance function.

Noise analysis of switched capacitor networks

Noise generated in switched capacitor (SC) networks has its origin in the thermal fluctuations of charged particles in the channels of the MOS switch transistors on one hand, in the operational amplifiers on the other hand. Using a SC integrator as vehicle, it is shown that the output noise spectrum consists in general of a broad-band component due to a continuous-time noise signal and of a narrow-band contribution predominating in the baseband of the SC network resulting from a sampled-data noise signal. The ratio of undersampling is introduced and it is shown that the latter noise contribution can be evaluated by sampled-data techniques using the <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">z</tex> -transform transfer function. These results are applied to the SC integrator and excellent concordance to the measurements made on a laboratory model is established.

Parasitic insensitive toggle-switched capacitor and its applications to switched-capacitor networks

A new parasitic insensitive toggle-switched-capacitor scheme is presented along with its applications to the synthesis of switched-capacitor networks. The scheme can be used to obtain a recently reported5 first-order inverting bilinearly transformed transfer function. The advantage of this technique is that, for the realisation of a lowpass filter, it requires only three capacitors and no matching conditions.

Digital-filter precorrection for zero-order hold distortion

A second-order linear phase z transform transfer function is presented which precorrects for the amplitude distortion, introduced by the zero-order hold, over a specified frequency range. For this function, optimum coefficient values are given graphically which yield a minimum equal-ripple error characteristic.