Field-circuit Coupling Research Articles

Numerical Simulation and Field Test of the Transient Temperature Rise of HVdc Grounding Electrodes

This paper investigates the temperature rise of vertical/horizontal high-voltage direct current (HVdc) grounding electrodes by simulations and field tests. Based on a field-circuit coupling current distribution model and a three dimensional (3-D) finite element model, a comprehensive methodology is proposed to analyze the transient temperature rise. Since soil resistivity varies with temperature around the electrodes, the temperature-dependent soil resistivity is tested, and then approximated by an empirical formula. Moreover, two practical tests are implemented to validate the simulation model. By ignoring the underground water fluctuations, the calculation results match test results nicely, which demonstrates that the terminal effect of the vertical electrode significantly affects the temperature distribution. But for a horizontal grounding electrode, the current distribution is more uniform than the vertical one. This study provides valuable references for design of HVdc grounding electrodes.

Simulation and analysis of heat losses of in-wheel motor for micro-electric vehicles

Heat losses of in-wheel motor for micro-electric vehicles are computed and analysed, which can enhance the dependability, efficiency, safety and lifetime for in-wheel motor. The theory-practice combination method is adopted. The computational mathematics model of heat losses is set up, which is regarded as the study goal. The field-circuit coupling and the electromagnetic-thermal coupling model are regarded as the breakthrough point, and electromagnetic structures of in-wheel motor are systematically optimised. The control equations of incremental steps alternating solving multiple fields are calculated and analysed. An electromagnetic-thermal coupling calculation model is established. Calculation results are verified to illustrate heat losses principle and uncover the internal mechanism of electromagnetic-thermal coupling field for in-wheel motor. This paper will propose a complete set of integrated modelling method and coupling algorithm of electromagnetic-thermal coupling field, which can provide theoretical and technical support for improving in-wheel motor quality and property of micro-electric vehicles.

Non-uniform Time-Step FLOD-FDTD Method for Multiconductor Transmission Lines Including Lumped Elements

This paper presents a novel non-uniform time-step (NUTS) fundamental locally one-dimensional (FLOD) finite-difference time-domain (FDTD) method for multiconductor transmission lines (MTLs) including lumped elements. The NUTS scheme adopts different (non-uniform) time steps for different periods during simulation, in order to reduce the large errors caused by unconditionally stable FDTD methods with uniform time step larger than Courant-Friedrichs-Lewy limit. It is found that NUTS scheme is potentially unstable for alternating-direction-implicit (ADI) FDTD method, but it is stable for LOD-FDTD method or its implementation based on fundamental (FLOD) scheme. The NUTS FLOD-FDTD method is useful to simulate MTLs with lumped elements including resistor, capacitor, and inductor in series and parallel connections. Moreover, the method based on multiple 1-D approach is also extended to incorporate lumped elements in cross connection to model near-field coupling between the MTLs. While the electric current density is commonly used for field-circuit coupling of parallel connected lumped elements, the magnetic current density will be utilized for field-circuit coupling of series and cross-connected lumped elements. Numerical results for MTLs with lumped elements in series, parallel, and cross connections are provided to show the trade-off between efficiency and accuracy of the proposed NUTS FLOD-FDTD method. Compared with the FLOD-FDTD method with uniform time step, the NUTS FLOD-FDTD method may achieve higher accuracy by using smaller time step for certain periods of simulation.

Harmonic suppression analysis of a harmonic filtering distribution transformer with integrated inductors based on field–circuit coupling simulation

This study analyses and evaluates the feasibility of a harmonic filtering distribution transformer (HFDT) for a harmonic reduction in low-voltage distribution networks. With this new-type transformer, power quality of the distribution systems can be improved by preventing the low-voltage-side harmonic currents from penetrating the higher voltage side. As the physical size of available space in prefabricated substations is strictly limited, necessary low space occupying filtering techniques are needed. Therefore, an HFDT with integrated filtering inductors (IFIs) capable of being implemented in regular air-insulated prefabricated substations is proposed. Two sets of passive filters configured by IFIs and external capacitors are employed for harmonic filtering. Two methods for estimating the inductance parameter are provided. One is the dimension-based method and the other is the reduced-order inductance matrix method. The relevant harmonic reduction analysis is based on simulations with a field–circuit coupling model, which consists of a three-dimensional finite-element electromagnetic model of an HFDT with IFIs and a corresponding electric circuit of a simplified distribution network. These simulations prove that the described HFDT can effectively reduce specific harmonic currents with IFI-based filters. Finally, the successful suppression of harmonics is demonstrated and discussed based on field-test measurements.

Analysis and Experimental Validation of Dynamic Performance for Slotted Limited-Angle Torque Motor

Field-circuit coupling method is increasingly drawing attention from researchers who engage in electric machine design. It is worth mentioning that no related field-circuit coupling methods have been presented to investigate the dynamic performance for slotted limited-angle torque motor (LATM). Hence, this paper presents a simplified field-circuit coupling method to evaluate the dynamic performance including position tracking ability and operating temperature for slotted LATM during its design optimization process. All magnetic saturation problems including nonlinear torque characteristic and inductance parameter variation with rotor position can be taken into account, which is completely consistent with the actual operation condition. The simplified field-circuit coupling method contains a thermal resistance network (TRN) module which can be applied to estimate the slotted LATM operating temperature in accordance with the accurate winding current and copper loss information. Therefore, whether the slotted LATMs meet design requirements should be evaluated before manufacturing prototypes. Related experiments for the slotted LATM are carried out to validate the field-circuit coupling method cooperating with TRN module.

Nonlinear Analysis of Microwave Limiter Using Field-Circuit Coupling Algorithm Based on Time-Domain Volume-Surface Integral Method

This letter presents the nonlinear analysis of the physical characteristic of a microwave positive intrinsic-negative diode limiter using the field-circuit coupling algorithm based on a time-domain volume-surface integral equation method. In order to accelerate the Newton iteration solution of the nonlinear field-circuit coupling equations, an improved solution scheme of a matrix equation is used here. Moreover, the basic diode charge-control model employed contains both a forward and reverse process as well as emitter recombination. Experimental and numerical results are given to demonstrate the accuracy and the efficiency of the proposed method for the nonlinear analysis of commercial limiter.

Analysis of the super high‐speed permanent magnet generator under unbalanced load condition

In this paper, the 117 kW, 60,000 r/min super high-speed permanent magnet generator (SHSPMG) under unbalanced load condition is studied. First, the influence mechanism of the unbalanced load on the generator was revealed, and by using field-circuit coupling method and at rated load, the current unbalance factor (CUF) was determined. Second, through the time-stepping finite element method, the generator air-gap flux was obtained and decomposed in virtue of the principle of Fourier transform. The influence of the unbalanced load on air-gap flux was studied, and the eddy current loss and torque ripple with different CUFs were calculated and analysed. Finally, based on the calculation results of two-dimensional transient electromagnetic field, the negative sequence current was extracted by using the symmetrical component method. The research showed that the harmonic content of air-gap flux density increases when the generator is connected to unbalanced load, and the eddy current loss and the torque ripple increases with the increase of the load unbalance degree. The experimental platform was established and the test data were in good agreement with the model calculated results, which verified the correctness of the model. The research could provide some useful conclusions for the research of the SHSPMG.

Simulation on Transient Characteristics of Inter-Turn Short Circuit Fault of Dry-type Air-Core Reactor Based on ANSYS Maxwell

Transient characteristic analysis of inter-turn short circuit fault has been done which is paramount for detecting the earlier fault of dry-type air-core reactor. Dynamic physical process of inter-turn short circuit is theoretically analyzed for dry-type air-core reactor from normal running condition to inter-turn short circuit fault condition. Using ANSYS Maxwell, transient field circuit coupling calculation model is set up and the transient characteristic of inter-turn short circuit fault is simulated, which is also verified by experiments. The study shows that the short circuit ring causes a sudden change of magnetic field at the position of short circuit which can be detected by the detecting coils installed on the package of reactor. Inter-turn short circuit fault can be detected in the earlier fault period by the method proposed in this paper.

A Consistent Simulation of Electrothermal Transients in Accelerator Circuits

Transient effects occurring in a superconducting accelerator circuit can be correctly simulated only if the models consistently account for the electrothermodynamic coupling between the magnets, the protection systems, and the remaining network. We present a framework based on the idea of cosimulation. The core component is a coupling interface exchanging information between the independent models. Within the framework, we simulate selected parts of a magnet and the electrical network, combining appropriately different commercial tools. This modularity gives the possibility of integrating new tools in the framework, to provide further insights on different physical domains as mechanics or fluid dynamics. The workflow is applied to the field-circuit coupling of an LHC main dipole magnet.

A Hybrid Volume–Surface Integral Spectral-Element Time-Domain Method for Nonlinear Analysis of Microwave Circuit

This letter presents a field–circuit coupling method for analysis of microwave circuit included with nonlinear physical-model-based semiconductor devices. The electromagnetic field is analyzed by the time-domain volume–surface integral equation (TD-VSIE) and the physical-model-based semiconductor is solved by spectral-element time-domain method. The discrete Newton–Raphson method is employed to solve the proposed field–circuit coupling equations. Compared to the traditional field–circuit coupling method in TD-VSIE, the proposed method can analyze not only the equivalent-model-based semiconductor circuit, but also the physical-model-based one. Finally, numerical results are given to demonstrate the accuracy and efficiency of the proposed method.

Voltage Regulation System of Doubly Salient Electromagnetic Generator Based on Indirect Adaptive Fuzzy Control

In this paper, a voltage regulation system based on indirect adaptive fuzzy (IAF) control for doubly salient electromagnetic generator (DSEG) is proposed to improve the robustness of the system and reduce output voltage ripple. The operating principle of IAF controller is described in detail subsequently and the stability condition of the system is deduced by Lyapunov function based on the mathematical model and working principle of the generator. Moreover, the selection method of parameters and control strategy are determined with the adaptive fuzzy control law. Finally, a field-circuit coupling simulation model of voltage regulation system for DSEG using IAF controller is constructed by finite element analysis technique and transient solver of control circuit. The simulation results show that DSEG using IAF controller has good static characteristics, high robustness, and low output voltage ripple.

Influence of Rectifiers on Permanent Magnet Wind Generator Electromagnetic and Temperature Fields

Power rectifiers are very necessary in the wind power generation systems since they are the necessary channels that link the generator and power gird together. However, they have some effects on the permanent magnet wind generator due to their work on fast on-off transitions. Taking an 8kW 2000r/min wind-driven permanent magnet generator as an example, the system model and external circuit were established. Firstly, based on the field-circuit coupling calculation method, the voltage and current harmonics have been studied respectively when the generator was connected to rectifier loads and pure resistance loads, so did the total harmonic distortion. The mechanism of harmonic impacted by rectifiers was revealed. Secondly, combined the harmonic electromagnetic field theory, the stator core loss, armature winding copper loss and rotor eddy loss were analyzed when the generator connected different loads. Furthermore, according to the definition of nonlinear circuits PF, the numerical analysis method was adopted to calculate the power factor when the generator connected two loads respectively. The change mechanism of PF impacted by rectifiers has been revealed. In addition, the temperature field model has been established and the generator temperature was also analyzed. The temperature distributions were obtained when the wind generator was connected to different loads. Then, the relationship between losses and temperature was combined, the change rules of permanent magnet temperature by the eddy current loss were studied under different load. At last, it can prove that the rectifiers have influences on both electromagnetic field and temperature field through comparing the simulation results with experimental test data.

Influence of Void Transposition Structure on the Leakage Magnetic Field and Circulating Current Loss of Stator Bars in Water-Cooled Turbo-Generators

In the design of stator bar structure, void transposition is an important way of reducing circulating current loss in water-cooled turbo-generators. The different void transposition structures have a great influence on circulating current loss. However, the influences of void transposition structure on the leakage magnetic field and circulating current loss are not definite. A 600-MW water-cooled turbo-generator is taken as an example. A three-dimensional (3-D) physical model of transposition bars in a single slot is established, and the field-circuit coupling method is used in 3-D numerical calculation of the leakage magnetic field and circulating current loss. The influences of segment number and length of the void transposition on the slot leakage magnetic field, current, and circulating current loss are obtained. The relationship between the slot leakage magnetic field distribution along the axial direction and circulating current loss based on different void transposition structures is clarified. The numerical calculation accuracy is validated with the current test experiment. New strategies and theoretical basis will be provided for the optimal design and technology of the transposition bars.

Fast Steady-State Field-Circuit Model for SMPM-BLdc Motors Driven From 120° and 180° Quasi-Square Wave Inverters

A consistent and computationally efficient finite-element model for the simulation of the steady-state operation of surface-mounted permanent magnet brushless dc motors driven from quasi-square wave inverters is presented. The methodology combines the magnetostatic finite-element and the steady-state time-periodic circuit models with time averaging. A weak field-circuit coupling is established through the effective constant current and lumped parameters estimated at various loading conditions. The performance characteristics, determined via the proposed model for two different motors, are comparable with those obtained from the comprehensive time-stepping finite-element model, with the execution time being approximately a hundred times shorter for the former.

Optimization of a Stern–Gerlach Magnet by Magnetic Field–Circuit Coupling and Isogeometric Analysis

Stern–Gerlach magnets are used to magnetically separate a beam of atoms or atom clusters. The design is difficult, since both the magnetic field gradient and its homogeneity should be maximized. This paper proposes the numerical optimization of the device’s pole-shoe shapes, starting from a reference geometry given in the literature. The main contributions of this paper are the generalization of a magnetic field–magnetic circuit coupling and the application of isogeometric analysis (IGA), which are shown to reduce the computational complexity and increase the accuracy. The field–circuit coupling significantly reduces the size of the field model part, in which the IGA’s spline-based framework enables a highly accurate evaluation of local field quantities, even across elements.

The Influence of Transposition Angle on 3-D Global Domain Magnetic Field of Stator Bar in Water-Cooled Turbo-Generator

Reasonable transposition structure of stator bars in water-cooled turbo-generators could reduce circulating current of strands, and related factors on distribution change of circulating current are complex and diverse. Transposition angle is one of the most important influencing factors, and its influencing degree on circulating current is still unclear. A 600 MW water-cooled turbo-generator is set as an example, a 3-D physical model of transposition bars in a single slot is established, and a field-circuit coupling method is used in 3-D numerical calculation. The optimization of transposition angle is researched, and the distribution changes of 3-D global domain magnetic field, maximum current, and circulating current loss in different transposition angles are obtained. Finally, the calculation results are compared with that of the improved analytical algorithm to validate the accuracy of the solving model.

Numerical calculation for circulating current in stator transposition bars of large water-cooled turbo-generators

Accurate calculation of circulating current is one of the key problems for stator transposition bars in the design of turbo-generators. Aimed at limitation that analytical algorithm of circulating current could not reflect the local electromagnetic field distribution and difficulty that overlaps easily exist in solid modeling process of stator transposition bars, a simplified physical model of transposition bars is established. A three-dimensional (3-D) numerical method for circulating current in stator transposition bars of large water-cooled turbo-generators is investigated, which is combined with field-circuit coupling method. Taking stator bars less than 540° transposition with void model of a 600-MW water-cooled turbo-generator as the research object, the magnetic flux density distribution, current density distribution and circulating current distribution of transposition strands are obtained by numerical calculation. Compared with calculation results of the improved analytical algorithm, the correctness of the numerical calculation for circulating current is demonstrated, the calculation value difference for the maximum current of strands is obtained. The numerical calculation for circulating current will provide an appropriate basis for the reasonable calculation of local overheating of stator transposition bars and the design of safety margin for turbo-generators.

Negative-sequence Component Analysis of an AP1000 Nuclear Turbo-generator in an Internal Short-circuit Condition

—This article analyzes the fault location, negative-sequence component, and current harmonic content of the first AP1000 third-generation 1250-MVA nuclear half-speed (four-pole) turbo-generator with internal phase faults. To this end, the internal armature winding fault of an AP1000 turbo-generator is systemically explored by using both an experimental method and the field-circuit coupling simulation method. The internal phase short circuit is one of the worst faults that a generator can experience; such a fault may have serious consequences for nuclear power large-capacity turbo-generators because of the severe mechanical and heat damage caused by the high current. To understand these problems, the possible position of the internal short circuit is investigated in detail according to the winding arrangement of the AP1000 turbo-generator, and the internal short-circuit faults of two branches from different phases are calculated. Furthermore, the negative-sequence current can be captured by analyzing each harmonic of the short-circuit current. In addition to the calculations, the steady-state negative-sequence component and degree of asymmetry of the internal phase short-circuit current in different fault locations are also obtained. The results significantly enhance the accuracy assessment of a large-capacity generator imbalance and provide a theoretical reference for the protection of a large-capacity generator system.

Eddy Currents and Non-Conforming Sliding Interfaces for Motion in 3-D Finite Element Analysis of Electrical Machines

This paper presents non-conforming sliding interfaces for motion in 3-D finite element simulations. Sliding interfaces are favorable, especially for field circuit coupling in comparison to other approaches such as the Lockstep method because an arbitrary position of the rotor is possible. A previously presented approach by the authors is extended to take eddy-currents into account. The sliding interfaces approach utilizes specific Lagrange multiplier to handle the relative motion between stator and rotor which require a magnetic scalar potential formulation. The formulation is presented as well as methods to compute the mandatory cohomology basis functions.

Study on Harmonics Characteristics of Magnetic-Valve Controllable Reactor Based on the Finite Element Method

Magnetic-valve controllable reactor (MCR) has been widely applied in many kinds of industries, such as power systems and ferrous metallurgy. As electrical equipment, MCR can adjust its reactance smoothly and continuously, which has advantages like low dissipation and maintenance costs, high reliability. In this paper, a precise 2-D field-circuit coupling model of MCR is established by the finite element analysis software-ANSYS, and then the analysis of the harmonic characteristics of this model is presented in detail. Compared with the conventional numeric method, the proposed method could obtain more practical and accurate results and also has the ability to analyze electromagnetic field. Meanwhile, an experimental platform of a 2200 VA/380 V MCR is built. This paper provides detailed harmonic characteristics analysis of simulation and experiment. The simulation and experimental results verify that the proposed method is more accurate than using conventional ways.