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This paper presents the modeling and steady-state performance of a novel dual-winding reluctance generator (DWRG) that uses a multiple-barrier (MB) rotor. A simple math-ematical model was developed, and the effects of external parameters (speed, field current, and load) on the steady-state performance were analyzed. Experimental results conducted on a prototype machine were also provided to justify the theoretical approach and performance calculations. The developed model takes into account the magnetic saturation and core loss and enables a quantitative prediction of load characteristics from the no-load test data. Index Terms--Core loss, dual winding, equivalent circuit, magnetic saturation, multiple-barrier (MB) rotor, reluctance generator.

Doubly fed generators have been used as adjustable-speed pumped-storage generator motors and wind turbine generators. Accurate determination of field currents and reactances is important for the design of these machines. We propose a calculation method to obtain the field currents and reactances of machines with rotor duct pieces under any steady-state balanced load condition. The method links two-dimensional static finite-element analysis (FEA) with an approximate calculation to consider three-dimensional (3-D) skin effect in the duct pieces. Its advantage is that the computational time is much smaller than 3-D transient FEA when the slip frequency is not zero. The method will contribute to improvement of the design of doubly fed generators with rotor duct pieces. It was applied to a 395 MVA machine, and the calculated field currents agreed well with the measurements. Variation in the reactances due to saturation is also discussed. Index Terms--Adjustable-speed pumped storage system, cross magnetization, finite-element method, inductance, skin effect, slip.

A simple magnetic circuit of salient-pole synchronous machines is presented. A method for calculating steady-state electrical performances using the circuit is described. Magnetic saturation including the cross-magnetizing phenomenon is considered in the method. The saturated reactances, field currents, and load angles are calculated easily from the method without much computational effort as compared with the finite element method. Despite the simplicity of the magnetic circuit, the calculated reactances at various load conditions using the method are close to the measured and FEM values. Index Terms--Cross-magnetization, magnetic circuit, magnetic saturation, reactances, synchronous machines.

It is important to understand the relationship between leakage flux distributions and machine characteristics for better design of synchronous machines. This paper presents a calculation method for leakage inductances of saturated salient-pole machines with damper circuits. All leakage inductances are divided into the self-leakage, gap leakage, and winding-differential leakage inductances. The leakage inductances correspond directly to the leakage flux distributions in the machines. Cross-magnetizing inductances are also calculated. The method is applied to a 300-MVA class generator. The relationship between the winding distributions, flux distributions, saturation, and inductances is discussed. Weak magnetic influence of the damper circuits on the armature in the d-axis is quantitatively illustrated through values of the winding-differential leakage inductances. The cross- magnetizing inductances, except for the d-axis damper circuits, are relatively large. Variations of the armature self-leakage inductances with saturation are small, and variations of the field and damper self-leakage inductances are larger. Index Terms--Cross-magnetizing effect, damper circuits, finite element methods, leakage inductances, magnetic saturation, salient-pole synchronous machines.

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. [ABSTRACT FROM AUTHOR]

SUMMARY This paper presents a novel type of flux-modulating synchronous machine (FMSM) in which permanent magnets (PMs) are embedded in the stator back-iron. The rotor has neither windings nor PMs. A prototype machine with an outer-rotor configuration was designed and manufactured to validate the operating principle of the FMSM. The characteristics in the motor mode of the prototype machine were also investigated with a vector control system. The results of the investigations show that, as in surface-mounted PM motors, the torque of the FMSM is predominantly generated by the PM flux and can be controlled using the armature current. [ABSTRACT FROM AUTHOR]

This paper investigates the appropriate permanent magnet (PM) arrangement of novel flux-modulating synchronous machines (FMSMs) in which PMs are embedded in the stator back iron. Using finite element analysis (FEA), three types of FMSMs with different PM arrangements are designed, and their performance characteristics are compared. As a result of the investigation, it was found that the FMSM with a V-shaped PM arrangement has a higher torque capability than do other FMSMs. The accuracy of the FEA simulations was confirmed through experiments on a prototype machine. [ABSTRACT FROM AUTHOR]

The output of permanent-magnet-assisted synchronous machines is maximized under constant permanent magnet (PM) volume and machine size by optimizing rotor shape. An automatic shape optimization method combining Rosenbrock's method and adaptive finite-element method is applied for the optimization. Then, a prototype machine is manufactured due to the result of the optimization in order to confirm the validity. It is clarified that the output of the optimized machine significantly increases without decrease in efficiency, increase in PM volume, and increase in machine size compared with that of the conventional machine. [ABSTRACT FROM PUBLISHER]

In this study we investigate a method for accurately calculating the characteristics of salient-pole synchronous machines assisted by permanent magnets. First, the operating principle of the machines is investigated by using both finite element analysis and a simple magnetic circuit. Then, a theoretical representation of the assist effect on the permanent magnets is derived based on the magnetic circuit. Finally, the measured and calculated results are compared in order to confirm the validity of the proposed calculation method. We show that the load characteristics of the proposed machine can be accurately estimated from the no-load and short-circuit characteristics of the conventional machine without permanent magnets, and the size and magnetization of the inserted permanent magnets. [ABSTRACT FROM AUTHOR]

SUMMARY The flux-modulating synchronous machine (FMSM) is a new type of multipole SM with nonoverlapping concentrated armature and field windings on the stator. This paper compares the output characteristics of two FMSMs through finite element analysis (FEA) and experiments. In both of the FMSMs, the attachment positions of the armature and field windings are swapped. To determine the reason for the discrepancies in their output characteristics, unsaturated inductances were calculated using a d- -q equivalent circuit. In addition, the calculated results of the inductances were confirmed through a visualization of the leakage fluxes using FEA. The results of the study show that the synchronous inductance can be reduced by attaching the armature winding to the air-gap side of the stator teeth and that the reduction leads to an increase in output power. [ABSTRACT FROM AUTHOR]

SUMMARY In designing solid-pole synchronous machines, it is important to take into account the surface eddy-current losses in the field pole cores. In this study, a solid-iron ring specimen is adopted as an approximate model of solid-pole surfaces in order to conduct a fundamental study of the surface losses. The influence of the minor hysteresis loops on the losses under dc-biased magnetization is investigated. The losses in the ring under dc-biased magnetization are measured and analyzed by finite element analysis (FEA). The losses computed by the FEA considering minor loops are nearly the same as those measured. In contrast, the eddy-current losses computed by FEA without considering minor loops are considerably inaccurate because the incremental permeability is overestimated and the skin depth is underestimated. It is important to consider hysteresis for the accurate calculation of the surface eddy-current losses under dc-biased magnetization. [ABSTRACT FROM AUTHOR]

Permanent-magnet-assisted salient-pole synchronous machines (PMa-SMs) are a new type of salient-pole synchronous machines that has PMs between the adjacent pole shoes. The PMs have the ability to improve the output power and the terminal voltage. In this paper, a simple magnetic circuit of PMa-SMs is presented. Using the magnetic circuit, the electric and magnetic basic characteristics of PMa-SMs are calculated. The results are compared with the results by measurements and finite-element analysis (FEA). They have shown that the magnetic circuit calculates the characteristics of PMa-SMs with satisfactory accuracy and that the computational time of the magnetic circuit is much smaller than that of FEA. Influence of the pole-shoe magnetic reluctances on the calculation accuracy by the magnetic circuit is also discussed, and some guidelines to enhance the accuracy have been presented. [ABSTRACT FROM PUBLISHER]

In this paper, the core losses that occur in a 4-kVA flux-modulating synchronous machine (SM) (FMSM) are investigated using 2-D finite-element analysis, and the results are supported by experiments. A method for reducing the core losses is also presented. The FMSM is a new type of multipole SM in which the stator field magnetomotive force is modulated by the air-gap permeance to generate the rotating field. A 2pa-pole three-phase armature winding and a 2pf-pole field winding are centrally wound around individual stator teeth, and a reluctance rotor with 2pr\ (= pa + pf) saliencies is used to provide a magnetic coupling between these windings. As a result of the investigation, it was found that, although the core losses occur in the rotor as well as in the stator, the rotor core loss can be effectively reduced by decreasing the height of the rotor poles. [ABSTRACT FROM AUTHOR]

To improve output performance of salient-pole synchronous machines, permanent-magnet-assisted salient-pole synchronous machines (PMa-SMs) that have permanent magnets (PMs) between the field poles were previously developed. The PM effect of increasing the output power and the terminal voltage has already been confirmed by finite element analysis (FEA) and experiments under steady states. In this paper, demagnetization in the PMs due to sudden three-phase short circuits is evaluated by FEA. The results show that irreversible demagnetization arises in the PMs of a PMa-SM with relatively smaller circumferential PM length. Effects of the PM shape and damper bars on the irreversible demagnetization are also investigated. The results show that making the PM shape a rectangle and adding damper bars on the outer surfaces of the PMs are effective to reduce the demagnetization, while increasing the number of the conventional damper bars is not effective. [ABSTRACT FROM PUBLISHER]

This paper presents a new type of multipole synchronous machine (SM) in which 2pa-pole armature and 2pf-pole field windings are centrally wound around individual stator teeth. The proposed machine operates as a (2pa + 2pf)-pole SM by providing a magnetic coupling between the armature and field windings through a 2pr-pole reluctance rotor. A 4-kVA (32 + 48)-pole prototype machine was designed and built to validate the principle of this structure. Performance characteristics of the prototype machine were simulated using 2-D finite-element analysis (FEA) and were supported by experiments. In addition, the effects of the rotor pole shape on the performance characteristics were studied through 2-D FEA simulations. The results presented provide guidelines for the optimum design of the proposed machine. [ABSTRACT FROM PUBLISHER]

The characteristic improvements of salient-pole synchronous generators by inserting additional permanent magnets are investigated from both results of finite-element analyses and experiments. First, the assist effects of the magnets in a megavoltampere-class generator are analyzed by the finite-element method. It is clarified that the additional permanent magnets have the effects of reducing magnetic saturation at the rotor-pole bodies, as well as the effects of increasing the direct flux linkage of armature windings. It is also clarified that the output of the generator can be increased by more than 20% by inserting the magnets without any increase in total machine size and decrease in efficiency. Finally, the characteristic improvements are validated by the experiment of a small prototype generator. The experimental and calculated results are found to be in good agreement. [ABSTRACT FROM PUBLISHER]

In this paper, we investigate the mechanism of output increase by inserting additional permanent magnets in salient-pole synchronous machines. The machines are modeled not only by finite element methods but also by a simple nonlinear magnetic circuit in order to express the assist effects of permanent magnets by simple theoretical expressions. The no-load saturation curves obtained by the finite element method and the magnetic circuit are compared with those of measurements in order to confirm the validities. It is clarified that the accuracy of the proposed magnetic circuit is nearly identical to that of the finite element method. Furthermore, the mechanism of the output increase by the permanent magnets is revealed by the theoretical expressions derived from the magnetic circuit equations. [ABSTRACT FROM AUTHOR]

In this paper, a new salient-pole synchronous generator (SG) termed the PMa-SG is presented. In the PMa-SG, permanent magnets (PMs) are placed between the pole shoes to reduce the magnetic saturation in the field poles. By using finite element analysis (FEA), the internal magnetic fields and basic characteristics of a 2.8-MVA PMa-SG are compared with those of a conventional SG of the same size, and the reduction effect of the magnetic saturation of the PMs is examined. The FEA simulations are also validated by experiments on a 2.0-kVA prototype machine. The PMs placed between the pole shoes reduce the magnetic saturation in the pole bodies and pole tips and effectively increase the terminal voltage and output power. © 2010 Wiley Periodicals, Inc. Electr Eng Jpn, 174(4): 58-67, 2011; Published online in Wiley Online Library (). DOI 10.1002/eej.21132 [ABSTRACT FROM AUTHOR]

We propose a new method for analysis of the harmonic wave components of magnetic fields in rotating machinery. Using the magnetic permeability obtained by transient analysis of the nonlinear magnetic field, the harmonic wave components of the magnetic field are individually calculated in the spaces of both the rotor and stator subject to the boundary condition that the harmonic wave components obtained by the transient analysis are set on the sliding surface. Mode separation of the magnetic field will contribute to research on reducing harmful harmonic wave components for rotating machinery. © 2010 Wiley Periodicals, Inc. Electr Eng Jpn, 172(2): 55–63, 2010; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.20951 [ABSTRACT FROM AUTHOR]

This paper presents a simple mathematical model for the steady-state analysis of a permanent-magnet-assisted salient-pole synchronous generator (PMa-SG). The PMa-SG is a new type of salient-pole SG that has PMs between the adjacent pole shoes. The developed model takes into account the magnetic saturation and core loss, and enables quantitative predictions of load characteristics from the no-load test data. The validity of the developed model is confirmed experimentally. The effect of the PMs on the performance characteristics of the PMa-SG is also investigated. [ABSTRACT FROM AUTHOR]

In order to evaluate magnetic saturation under subtransient and transient states of a large-sized salient-pole synchronous machine, the currents and leakage inductances after sudden three-phase short circuits are analyzed by a two-dimensional nonlinear transient finite element method (FEM). The currents are calculated both by direct and indirect methods. The direct method uses the FEM and considers fluctuation of the magnetic saturation after the short circuit. The indirect method solves Park's differential equations without fluctuation. Results of the direct method agree well with measurements. When the preshort voltage is large, fluctuation of the leakage inductances after the short is large and it greatly affects values of the short-circuit currents. As the preshort voltage becomes large, the damper leakage inductances saturate at first, then the field leakage inductances, and finally the armature leakage inductances saturate. Although the indirect method considers saturation under the preshort condition, it gives inaccurate results and they are nearly the same as the results by the linear FEM. In general, it is thought that saturation of the leakage flux should be considered when subtransient conditions with large disturbance are analyzed. © 2003 Wiley Periodicals, Inc. Electr Eng Jpn, 145(4): 46–55, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.10240 [ABSTRACT FROM AUTHOR]