Xiaojun Zhao

Analysis of the DC Bias Phenomenon by the Harmonic Balance Finite-Element Method

An Epstein frame-like core model is set up to study the dc-biased problem of the power transformer. The harmonic phenomenon of the model under the dc bias condition is investigated by using the harmonic-balance finite-element method (HBFEM). The harmonic-balance finite element equation is coupled with the external electric circuit. Each harmonic component of the magnetizing current and magnetic field can be calculated directly in the harmonic frequency domains. Comparing the calculated results with the experimental data shows consistency. The dc bias effects on the magnetizing current and the magnetic induction are analyzed through the harmonic solutions.

Characteristics Analysis of the Square Laminated Core under dc-biased Magnetization by the Fixed-point Harmonic-balanced FEM

The ferromagnetic core of power transformer is susceptible to dc bias and has special nonlinear and hysteretic characteristics under dc-biased magnetization. The dc-biasing magnetization curve of a square laminated core (SLC) can be obtained by dc bias test. The harmonic-balanced finite-element method (HBFEM) combined with the fixed-point technique is used to calculate the dc-biasing magnetic field in the SLC based on the measured dc-biasing magnetization curve. A locally convergent method in harmonic domain is presented to determine the fixed-point reluctivity, which can speed up the convergence of harmonic solution. The dc-biasing magnetic fields are computed by using the basic and dc-biasing magnetization curves respectively. The results indicate the dc-biasing magnetization curve is more reasonable than the basic one in the analysis.

Analysis of the saturated electromagnetic devices under DC bias condition by the decomposed harmonic balance finite element method

The modified harmonic balance finite element method was applied to investigate the DC biased problem in the saturated electromagnetic devices. The electromagnetic field was solved by the block Gauss-Seidel algorithm combined with the relaxation iterative method. The DC bias effects on magnetizing current and magnetic induction was analyzed by means of harmonic solution in multi-frequency domain. The computation is more efficient than the time-domain FEM and harmonic analysis can be achieved.

An Effective Method of Solving Anisotropic Nonlinear Periodic Electric Field in Oil-Paper Insulation under the AC-DC Hybrid Voltage

In this paper, the frequency finite element method, combined with fixed point method and linearization method, is adopted to compute the anisotropic nonlinear periodic electric field in oil-paper insulation under the AC-DC hybrid voltage, which contains many high order harmonics. The field equation is derived based on the qua-static field theory, and the formula of selecting fixed-point conductivity is proposed. The proposed algorithm is used to analyze the anisotropic nonlinear periodic electric fields of an typical model of converter transformer under the AC-DC hybrid voltage and the results show that the anisotropism of the oil-immersed paper has significant effects on the distributions of potential.

Fixed-Point Harmonic-Balanced Method for DC-Biasing Hysteresis Analysis Using the Neural Network and Consuming Function

The magnetic flux includes dc component and ac component in the square laminated core (SLC) under dc-biased magnetization. Hysteresis loops are distorted by dc component of magnetic field intensity in ferromagnetic core and exhibit asymmetrical and special nonlinearities. A neural network (NN) is trained on the basis of the experimental data to model hysteresis effects in the limb-yoke of the SLC. Hysteresis effects in the mitered-joint region are modeled by the consuming function combined with the dc-biasing magnetization curve. The global fixed-point magnetic reluctivity is properly determined in harmonic-balanced finite-element method (HBFEM) to ensure globally convergent computation. The magnetic field in the SLC under dc-biased magnetization is computed by the proposed method taking account of the dc-biasing hysteresis effects.

Harmonic Analysis of the DC biased Epstein Frame-like core model by the Harmonic Balance Finite Element Method

The DC biased problem of the Epstein Frame-like core model is investigated by using the Harmonic Balance Finite Element Method (HBFEM). It considers coupling between the electric circuit and the magnetic field. The magnetizing current and its harmonic components can be calculated directly in the harmonic domain. Comparing the calculated results with the experimental data shows consistency. The DC bias effect on the harmonic components of the exciting current is analyzed directly with the distribution of the magnetic flux visually observed through the harmonic solutions.

Harmonic Analysis of Nonlinear Magnetic Field Under Sinusoidal and DC-Biased Magnetizations by the Fixed-Point Method

The laminated core is tested under sinusoidal and dc-biased magnetizations. The measured data are manipulated by the proposed modified iterative method to obtain dc-biasing hysteresis loops accurately. The hysteresis model, based on a consuming function, is used to simulate the hysteresis effects of the iron core under different magnetizations. The fixed-point technique is combined with the harmonic-balanced method to compute exciting currents and magnetic fields simultaneously by considering the hysteresis effects. The global convergent strategies are presented to guarantee the convergence of harmonic solutions. The hysteretic characteristics and iron loss of the laminated core are analyzed on the basis of harmonic solutions of the magnetic field.

Analysis of the saturated electromagnetic devices under DC bias condition by the modified harmonic balance finite element method

The modified harmonic balance finite element method was applied to investigate the DC biased problem in the saturated electromagnetic devices. The electromagnetic field was solved by the block Gauss-Seidel algorithm combined with the relaxation iterative method. The DC bias effects on magnetizing current and magnetic induction was analyzed by means of harmonic solution in multi-frequency domain. The computation is more efficient than the time-domain FEM and harmonic analysis can be achieved.

Stray-field loss and flux distribution inside magnetic steel plate under harmonic excitation

Purpose n n n n nThis paper aims to investigate an efficient approach to model the electromagnetic behaviors and predict stray-field loss inside the magnetic steel plate under 3D harmonic magnetization conditions so as to effectively prevent the structural components from local overheating and insulation damage in electromagnetic devices. n n n n nDesign/methodology/approach n n n n nAn experimental setup is applied to measure all the magnetic properties of magnetic steel plate under harmonic excitations with different frequencies and phase angles. The measurement and numerical simulation are carried out based on the updated TEAM Problem 21 Model B+ (P210-B+), under the 3D harmonic magnetization conditions. An improved method to evaluate the stray-field loss is proposed, and harmonic flux distribution in the structural components is analyzed. n n n n nFindings n n n n nThe influence of the harmonic order and phase angle on the stray-field loss in magnetic steel components are noteworthy. Based on the engineering-oriented benchmark models, the variations of stray-field losses and magnetic field distribution inside the magnetic components under harmonic magnetization conditions are presented and analyzed in detail. n n n n nResearch limitations/implications n n n n nThe capacity of the multi-function harmonic source, used in this work, was not large enough, which limits the magnetization level. Up to now, further improvements to increase the harmonic source capacity and investigations of the electromagnetic behaviors of magnetic steel components under multi-harmonic and DC-AC hybrid excitations are in progress. n n n n nOriginality/value n n n n nTo accurately predict the stray-field loss in magnetic steel plate, the improved method based on the combination of magnetic measurement and numerical simulation is proposed. The effects of the frequency and phase angle on the stray-field loss are analyzed.

Harmonic balance FEM and its application in power system and renewable energy systems

Power system harmonic distortion is mainly caused by non-linear loads and power electronics used in the electrical power system and distributed renewable energy systems and Microgrids. The presence of non-linear loads and the increasing number of distributed renewable energy systems in electrical grids contribute to changing the characteristics of voltage and current waveforms in power systems. Such electrical loads which introduce non-sinusoidal current consumption patterns (current harmonics) can be found in power electronics. In addition, the harmonics can be generated in high voltage (HV) DC power systems, distributed renewable energy systems and Microgrids, and in HV power system caused by Geomagnetic Disturbances (GMDs) and Geomagnetic Induced Currents (GICs). This paper introduces and develops harmonic balance finite element method (HBFEM) and its application in power system and distributed renewable energy systems and Microgrids.