Armature Field Research Articles

Research on an online diagnosis for rotating diode faults in three‐phase brushless exciter with two coils

The rotating rectifier is prone to be damaged in the exciter of the brushless excitation system, wherein a diode open-circuit fault which is common can affect the normal and safe operations of a generator. On the basis of the structure of the brushless exciter, this study, analysed the effect that an open-circuit in one and two diodes had on armature current and armature field, and put forward a new online detection method for diode open-circuit fault. In this method, two magnetic field detection coils are installed on the stator iron yoke of the brushless exciter, and the open-circuit fault of the diodes can be reflected by the induced voltage difference of the two detection coils. Using a 16-pole, three-phase brushless exciter as an example, the performance of this new diagnosis method was verified by using a finite element simulation.

Comparison of Radial Force at Modulating Pieces in Coaxial Magnetic Gear and Magnetic Geared Machine

Unlike the coaxial magnetic gear (CMG), the magnetic geared machine (MGM) has the ac armature winding on the inner part or the outer part. Besides, the PM excitation field of the CMG and the ac armature field of the MGM have different space harmonic components of magnetic field from one other. Hence, the flux modulation characteristics in the CMG and the MGM are different, and the resultant magnetic radial forces at the modulating pieces are also occurred differently from one another. Thus, in this paper, first, the flux modulation characteristics of the PM excitation field in the CMG and the ac armature field in the MGM are presented. Second, the characteristics of the magnetic radial forces at the modulating pieces are analyzed, and the causes of the radial force according to the space harmonic components of the magnetic field are compared in the CMG and the MGM.

Magnet Eddy-Current Loss Analysis of Interior PM Machines for Electric Vehicle Application

The magnet eddy-current losses of six interior permanent magnet (IPM) machines are investigated for electric vehicle applications in this paper. The armature field, eddy-current density of magnet, the influence of PM depth, the distance of PM layers, and the number of PM segmentation are studied by finite-element analysis. It is demonstrated that increasing the PM depth of first layer and the distance of PM layers can provide more soft iron space for the armature-reaction flux, which can reduce the magnet eddy-current loss. PM segmentation can effectively reduce the PM eddy-current loss, because the eddy-current paths are divided into smaller loops, increasing the effective resistance. An IPM machine with segmented PM is prototyped to verify the analysis.

An Electromagnet-Assisted Ferrite Magnet Motor

This paper proposes an electromagnet-assisted ferrite magnet motor (EMaFM) with a double air-gap structure. To confirm the principle and validity of the proposed EMaFM, a prototype machine was designed and fabricated. Moreover, the electromagnetic performance of the prototype machine was simulated using a finite-element analysis (FEA) and was supported by experiments. The proposed EMaFM has field regulation capability while utilizing the ferrite magnets. From the FEA and experimental results, it was found that the torque can be controlled widely by the armature current or field current.

A Novel Hybrid Dual-PM Machine Excited by AC With DC Bias for Electric Vehicle Propulsion

This paper proposes a novel hybrid-excited dual-PM machine for electric vehicle propulsion. The key is to use an integrated stator winding to replace the armature winding and the field winding in the conventional hybrid-excited machine. The stator winding is excited by ac current with dc bias, in which the ac component is used to produce the rotating armature field, while the dc bias current is used for the flux regulation. Therefore, the function of the ac and dc windings can be incorporated and realized by using just one set of winding. The torque density and flux regulating capability can be improved, and the winding configuration is also simplified. In addition, dual-PM excitation structure combines the advantage of stator-PM doubly salient machine and rotor-PM magnetic-geared machine, which can further enhance the torque capability. The operating principle and control strategy of the proposed machine are discussed. The electromagnetic performances are studied using the time-stepping finite-element method. A machine prototype is manufactured and experimental tests are conducted to verify the effectiveness of the machine design.

Unbalanced magnetic force prediction in permanent magnet machines with rotor eccentricity by improved superposition method

An improved superposition method accounting for both permanent magnet (PM) and armature field is proposed to predict the unbalanced magnetic force (UMF) of PM machines having static/dynamic eccentricity. It virtually divides the original eccentric machine into a number of sections along the circumferential direction. Then, a series of concentric machine models are established with equivalent air-gap lengths corresponding to those air-gap sections. From the electromagnetic field of each concentric machine predicted by subdomain method, the air-gap field of the original eccentric machine can be synthesised. Finally, the UMF can be easily obtained by the integral of force density along the air-gap circumference. The effectiveness of the proposed method is validated on both rotating asymmetric and symmetrical PM machines by direct finite-element analysis and experiment, with particular emphasis of rotor eccentricity influence on the UMF of later one.

A Novel Design Method for the Electrical Machines With Biased DC Excitation Flux Linkage

A novel design method for electrical machines with biased dc excitation flux linkage, named biased flux machines (BFMs) is proposed in this paper. The biased current including dc and ac components is applied to drive these machines, in which dc current is used to generate or modulate the exciting magnetic field and ac current is used to generate armature field. To demonstrate this design and control method, a new double salient BFM is proposed. The feasibility of this design is verified by simulations and experiments. The major advantages for this design method could be summarized as: 1) for permanent magnet exciting BFMs, the biased current can be combined with negative d-axis current to realize flexible flux weakening or strengthening control; 2) for hybrid exciting or electrical exciting machines, the biased current can function as the dc windings, which helps to save more space for armature windings and further reduce cost and improve efficiency; and 3) this method is universal, which can be used in all BFMs.

Design Improvement of Three Phase 12Slot-14Pole Outer Rotor Field Excitation Flux Switching Motor

This paper present with design improvement of 12Slot-14Pole outer rotor field excitation flux switching motor (ORFEFSM) from the initial design by implement Deterministic Optimization Method (DOM) which involve 2-dimensional Finite-Element Analysis (FEA). The design improvement starts with the non-active part, rotor and followed with active part, stator which involve the armature coil slot and field excitation coil (FEC) slot. Since it is one of local optimization method, this method involves more than one cycle of improvement depends on the design structure and slot-pole configuration until achieve optimum performance. However, the initial torque and power output of 12Slot-14Pole is 112.95 Nm and 50.46 kW. The main objective is to improve the structure in order to obtain optimum torque and power output. Besides, it is necessary to reduce flux saturation and optimize the flux flow between the rotor teeth and stator arc width. The target torque and power output performance is expected higher than 210 Nm and 123 kW. With the deterministic optimization method technique, the final torque and power output achived are 221.83 Nm and 189kW.

Optimum design and research on novel vehicle hybrid excitation synchronous generator

Hybrid excitation is an organic combination of permanent magnet excitation and electric excitation. Hybrid excitation synchronous generator (HESG) both has the advantages of light quality, less losses and high efficiency like permanent magnet generator and the advantages of good magnetic field adjusting performance like electric excitation generator, so it is very suitable for the vehicle application. This paper presented a novel vehicle HESG which has skew stator core, permanent magnet rotor and both armature winding and field winding in the stator. Using ANSYS software, simulating the electric excitation field and the magnetic field, and finally the main parameters of HESG were designed. The simulation and the test results both show that the novel vehicle PMSG has the advantages of small cogging torque, high efficiency, small harmonic component output voltage and low waveform aberration, so as to meet the design requirements fully.

Comparison of Peak Armature and Field Winding Currents for Different Topologies of 10-MW Superconducting Generators Under Short-Circuit Conditions

This paper studies the peak armature and peak field winding currents for three different topologies of 10 MW partial high temperature superconducting generators (HTSGs) under short-circuit conditions (SCC) by simulation. The investigated partial HTSGs employ copper armature windings and superconducting field windings with different armature and rotor topologies, i.e., iron-cored armature and rotor, air-cored armature and rotor, and iron-cored armature and air-cored rotor. For each HTSG topology, the investigation includes: 1) the field winding current control strategies; 2) the influence of operating field current; and 3) the ratings of circuit breakers for limiting the peak armature and peak field winding currents. The results can provide guidelines for determining the peak armature and peak field currents of HTSGs and also the possibility of limiting them by employing circuit breakers under SCC.

A New Double-Sided HTS Flux-Switching Linear Motor With Series Magnet Circuit

A new double-sided high-temperature superconducting (HTS) linear flux-switching motor for transportation system is proposed in this paper, in which the yokeless iron, armature, and HTS field windings are located in its mover, whereas its double-sided long stator only consist of segmented and low-cost iron. Thus, this type of linear motors exhibit robust and low-cost stator, high efficiency, and high-force capability. First, the general design rule of this kind of motor is proposed. Then, based on the proposed design rule, two double-sided HTS flux-switching linear motors with series and parallel magnetic circuits are investigated and calculated based on the finite-element method. The research results show that the series magnetic circuit motor has the advantages of a more sinusoidal back EMF, high thrust-force density, and high-load capacity.

A Novel Vernier Reluctance Fully Superconducting Direct Drive Synchronous Generator With Concentrated Windings for Wind Power Application

In this paper, a novel vernier reluctance fully superconducting (FSC) low-speed direct-drive synchronous generator for a wind power application is proposed. The proposed superconducting (SC) generator is with an external rotor, and both the SC armature and SC dc field windings are in the inner stationary stator. Thus, compared with the existing FSC synchronous generators (FSCSGs), the slip ring is removed, and the cryostat and related refrigerate systems are stationary and greatly simplified. In addition, both the field and armature windings are single tooth-wound concentrated windings with very short end-windings. Compared with the regular FSCSGs, the usage of the SC material is greatly reduced in this proposed topology, as with the total cost. Furthermore, the torque ripple is much lower than that in a regular FSCSG. All these features are evaluated by the finite-element simulations.

Sub-domain analytical model for armature reaction field of permanent magnet vernier machine

Purpose – An analytical sub-domain model is developed for predicting the armature magnetic field in permanent magnet vernier machine (PMVM) which has either non-overlapping or overlapping windings. The developed model accounts for tooth-tips and flux modulation pole slots (FMPs). The paper aims to discuss these issues. Design/methodology/approach – It is obtained by solving Poisson’s and Laplace’s equations in polar coordinates for each sub-domain, i.e. air gap, slots, slot openings at tooth-tips and FMP slots. Armature reaction field distributions in slots, slot openings FMPs, air-gap and magnet region and winding inductances are obtained from the analytical method and compared by finite element analysis. Findings – It is found that the developed model can be employed to accurately predict the armature field and winding inductance for any combination of slots/FMPs/permanent magnets. In addition, it is observed that the winding inductance is high which results in significant armature reaction and poor power factor in PMVM. Originality/value – The main contributions include: first, accurate sub-domain model for PMVM is proposed for armature reaction which is not addressed in literature; second, the model accounts the interaction between FMP and slot; and finally, developed sub-domain model is also used for inductance calculation.

A New Perspective on the Operating Principle of Flux-Switching Permanent-Magnet Machines

The flux-switching permanent-magnet (FSPM) machine attracts increasing attention recently due to its high power density, robust mechanical structure, good flux-weakening capability, and essential sinusoidal back-electromotive-force waveforms. In previous studies, the approach for analyzing FSPM machines is either by using the lumped parameter magnetic circuit models or from the “generator-oriented” perspective. In this paper, the operating principle of FSPM machines is reiterated from a new perspective, viz., the “motor-oriented” perspective. Some interesting findings and essential principles can be unveiled, which include how the stable electromagnetic torque can be developed, how the pole-pair number (PPN) of armature windings, the PPN of PMs, and the synchronous speed of the armature field should be defined, and how to determine the connection of coils for the sake of developing stable electromagnetic torques. This new perspective is more consistent with the classical theory on electric machines. There is no need to consider the polarity of coils when determining the connection of windings. Three typical FSPM machines with different combinations of stator and rotor poles, viz., 12/11-pole, 12/13-pole, and 12/26-pole, are investigated to verify the validity of the proposed analysis approach. Experimental verification concerning the latter two sample machines is also conducted.

Performance of Superconducting Synchronous Generator for Three-Phase Short-Circuit at Its Terminals

In this paper, three-phase short-circuit at the terminals of a superconducting synchronous generator is simulated by using MATLAB. In this simulation, a single screened superconducting generator directly connected to power system is considered and two operating cases are investigated: the first case is that the fault is permanent and the second case is that the fault is cleaned by a protection system. To show the effects of this short-circuit and the performance of the superconducting synchronous generator for both cases, the deviations of armature momentary currents, angular speed and field current are plotted. In order to compare the obtained results, the present simulations for the both cases mentioned above are repeated for a conventional synchronous generator having the same rating as considered superconducting counterpart, which is directly connected to power system, and the deviations of the same variables as considered for the superconducting synchronous generator are also given in the paper.

Fundamental principles of the theory and practice of electric drives with a field-regulated reluctance machine

Special features of electric drives based on a field-regulated reluctance machine (FRRM) supplying high power and regulating characteristics to an electric drive are shown: the feasibility of separate and independent control of the excitation and armature fields, multiphase, waiving schemes of three-phase power circuits, and possibility of the sinusoidal current form. It is shown that independent control of the excitation and armature fields expands the range of options for solving the problem of multicriterion optimization of an electric drive with an FRRM. Calculations show that it is possible to improve the specific values by 30–40% in an electric drive with an ideal transformer due to redistribution of the active materials in the low power electrical machines, but in mediumand high-power electric drives this effect is not so great and does not exceed 10%. Attention is paid to the fact that there are no limitations as concerns commutation conditions in an electric drive with an FRRM, which allows the magnetic flow to be increased during overloading and, therefore, the short-term electromagnetic torque to be increased by from four to eight times as compared to the rated value.

Design of Variable-Flux Permanent-Magnet Machines Using Alnico Magnets

This paper proposes a novel design for variable-flux machines with Alnico magnets. The proposed design uses tangentially magnetized magnets to achieve high air-gap flux density and to avoid demagnetization by the armature field. Barriers are also inserted in the rotor to limit the armature flux and to allow the machine to utilize both reluctance and magnet torque components. An analytical procedure is first applied to obtain the initial machine design parameters. Then, several modifications are applied to the stator and rotor designs through finite-element analysis (FEA) simulations to improve machine efficiency and torque density. A prototype of the proposed design is built, and the experimental results are in good correlation with the FEA simulations, confirming the validity of the proposed machine design concept.

Comparison of Methods for Permanent Magnet Eddy-Current Loss Computations With and Without Reaction Field Considerations in Axial Flux PMSM

This paper presents an analytical solution of the eddy currents in the permanent magnets (PMs) in the axial flux PM synchronous machine using a coupled solution of Maxwell’s equations and electric circuit network. This is based on calculating the axial field in an accurate way on the surface of the PM. This method is able to consider the effect of armature field and slots. The eddy currents are obtained by imposing this solution on the PM which is modeled by a simple electric network. This network is composed of simple resistances and inductances. The inductances are used to model the reaction field effect of the eddy currents flowing through the PM and also the skin effect. To show this effect, the machine is excited with different sources at different speeds. In addition, a variant of the model is made that neglects the inductances, in order to show in which conditions this low-frequency approximation is acceptable. It is concluded from this paper that inclusion of the reaction field is necessary when the machine is excited by a pulsewidth modulated (PWM) current, while for a sinusoidal excitation, the reaction field effect has minor contributions to the total eddy losses. In addition, the reaction field has major influence at higher speeds rather than lower speeds for PWM injection. In conclusions, for a preliminary design, the resistance model without the reaction field computation would be enough for the calculation of the PM losses. The circuit model is also capable of obtaining the solution with PM segmentation. In this paper, different PM segments were studied from the circuit model and the finite-element (FE) model point of view. Compared with the FE model, the circuit model has the advantage of flexibility in geometrical machine parameters, less CPU time, and accurate results for the PM losses up to 10%.

Characteristics of Rotating Armature Type High Temperature Superconducting Generators With Dual Field Windings for the Wind Turbine

We proposed an HTS wind power generator that has armature windings in the rotor. Field windings in the stator make a slightly higher magnetic field than the field windings in the rotor if both windings have same size of armature windings and field coils. In addition, we split the field windings into two and installed one of the split ones inside the armature, i.e., the so-called dual field windings. This structure is mechanically complex because the armature windings rotate between two stationary field windings. However, the output voltage of the 10-MW generator is 12% higher than that of the rotating field with this structural modification. We set up six different types of field winding arrangement and analyze the field magnitudes and field distributions in the armature and field windings of each one. Finally, the output voltages are calculated by a finite-element method at full load.

Analysis of Novel Multi-Tooth Variable Flux Reluctance Machines With Different Stator and Rotor Pole Combinations

Novel multi-tooth variable flux reluctance machines (VFRMs), which adopt doubly salient stator and rotor structure with nonoverlapping stator ac armature and dc field windings, are investigated in this paper. The rotor pole number can be any integer except the phase number and its multiples. Meanwhile, to obtain symmetrical bipolar phase flux-linkage and back electromotive force waveforms, the ratio of stator pole number to the greatest common divisor of stator- and rotor-pole numbers should be even integers. Furthermore, under the same rated copper loss and stator outer radius as well as 6-pole stator, 4-tooth per stator pole VFRMs in which the stator and rotor pole number determined by N r = nN s ± 1 (n is the number of small teeth per stator pole) exhibit the highest average torque. Moreover, compared with the optimal 6/7 stator/rotor pole single-tooth VFRM, the 6/25 stator/rotor pole 4-tooth VFRM has more sinusoidal and larger back EMF, negligible cogging torque, lower torque ripple, and higher torque capability at relatively low copper loss. Similar to single-tooth VFRMs, 4-tooth VFRMs with N r = nN s ± 1 exhibit more sinusoidal back EMF and larger torque than that of VFRMs with N r = nN s ± 2. The analyses are experimentally validated by several prototype machines.