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The torque ripple of a switched reluctance motor (SRM) should be taken into account, as it can have negative effects on a connected gearbox and/or load. In this paper a concept and two realization methods for the reduction of the torque ripple are presented. An optimized alignment of the active elements of the stator leads to a reduction of this torque ripple. The first method proposed here is a four-fold segmented motor, which can reduce the torque ripple by 37.3 %. This can be achieved by segmentation in combination with a clever arrangement of active elements. However, this increases the number of necessary inverters, which increases redundancy and therefore leads to more security. A second method of achieving an equal reduction can be obtained by using a “double stator” motor. In this configuration both stators can be powered together. With this concept, the number of converters is halved compared to the first mentioned solution. This saves electronic components and thus reduces the effort. All results referred to in this article are obtained by simulation, or measured on a prototype. [ABSTRACT FROM AUTHOR]

This paper aims to propose a new Vernier reluctance machine (VRM), which integrates the advantages of a robust rotor structure, good torque density, and flexible flux control ability. The key is to establish the excitation field with both stator slot permanent magnets (PMs) and zero-sequence current. Two excitation sources have different pole pair numbers but share a parallel magnetic circuit and contribute to superimposed torque in this machine. Meanwhile, a flexible flux control can be achieved by regulating zero-sequence current, and little demagnetization risk exists for slot PMs during flux control. In this paper, the machine configuration and operation principle are introduced, along with its integrated ac and dc drive method. Electromagnetic performance of this new machine is evaluated by finite-element analysis. Leading design parameters are determined and optimized considering optimal injection ratio of zero-sequence current. A prototype is fabricated, and relevant experiment results demonstrate the feasibility of the proposed solution. [ABSTRACT FROM AUTHOR]

For a marine electrical machine, its high power density and large electromagnetic (EM) load tend to bring high saturation to the magnetic circuit. When the non-linearity of ferromagnetic material is not taken into consideration, large errors will appear in the calculation of air-gap flux density and EM force wave. Considering the radial and tangential EM force waves that cause the stator core to vibrate and deform are the primary sources of EM vibration of a non-salient pole synchronous generator (NSPSG), this paper introduces a semi-analytical method of calculating the radial and tangential EM force waves, with the non-linearity of ferromagnetic material taken into account. The method includes the distributed magnetic circuit method (DMCM), the separation variable method (SVM) and the complex variable conformal transformation method (CVCTM). First of all, the radial air-gap flux density is obtained by using the DMCM to calculate the no-load magnetic circuit of the NSPSG and dealing with the non-linearity of ferromagnetic material by B-H curve. Then, the tangential air-gap flux density is calculated by the SVM and the complex relative air-gap permeance is calculated by the CVCTM to determine the effect of slotting. Finally, the radial and tangential EM force waves are obtained by Maxwell stress tensor method. The proposed semi-analytical method is verified through measuring vibration acceleration of the NSPSG. [ABSTRACT FROM AUTHOR]

In this paper, a position estimation method is proposed to accurately measure the rotor position of a switched reluctance motor equipped with embedded sensing coils under both unsaturated and saturated conditions. This method effectively solves three key problems existing in traditional methods based on embedded sensing coils, which are the mutual induced voltage effect, the main magnetic circuit saturation effect, and low accuracy of the rotational speed estimation in near-zero-speed regions. To address the first problem, the sensing coils are connected into a special designed structure. Then, the sensing coil inductance, which varies with the rotor position, is encoded by some voltage signals. After that, a novel hybrid harmonic filtering algorithm based on a delay filter and a coordinate transformation is proposed to remove the dc, even harmonic, and 3nth harmonic components of the demodulated voltage signals, according to which the rotor position can be estimated continuously and accurately. By applying this hybrid harmonic filter, the main magnetic circuit saturation effect on the position estimation has been indirectly avoided. To solve the third problem, a starting algorithm based on the voltage thresholds is proposed, and a rotational speed estimation method is developed. Detailed experimental results are provided to verify the validity of the proposed methods. [ABSTRACT FROM AUTHOR]

Severe leakage flux is a long-existed drawback in the transverse-flux permanent magnet machines (TFPMs), which results in a low permanent magnet (PM) utilization rate and prominent cogging torque in TFPMs. Aiming to solve this problem, this paper presents a novel consequent-pole transverse-flux machine (CP-TFM). The key is to artificially shift the upper and lower salient-pole rotors with a half-pole pitch and connect them with a ring-shaped core. Therefore, a complementary magnetic circuit is constructed to reduce the flux leakage between the adjacent poles as well as improve the PM utilization rate. To verify the feasibility of design, a 3-D finite-element model is established and its electromagnetic performance is evaluated. With the same peripheral dimension and copper loss, a quantitative comparison is carried out between the proposed CP-TFM and conventional TFPM. Finite-element simulation results reveal that compared to its contrast, the proposed solution can almost double the PM utilization ratio and effectively reduce the cogging torque. [ABSTRACT FROM AUTHOR]

Compared with dc magnetic bearings, an ac magnetic bearing has obvious advantages in cost savings and reducing power consumption. For more precise control of the ac magnetic bearing, it is particularly important to build a correct mathematical model of radial suspension forces. Due to the working principle of the ac magnetic bearing, it has similarities to the suspension subsystem of a bearingless motor, thus the modeling method for radial suspension forces of the bearingless motor could be referenced for modeling the radial suspension forces of the ac magnetic bearing. This paper presents a new modeling method based on the Maxwell tensor method for radial suspension forces of the ac magnetic bearing. Compared with existing methods, the invention method designed specially for the ac magnetic bearing overcomes inaccuracy and possesses advantages of directness and universality. Taking the ac hybrid magnetic bearing (ac HMB), for example, this paper presents the mathematical modeling process of radial suspension forces with the proposed method. The comparison result between the models established by the equivalent magnetic circuit method (the most classical modeling method for magnetic bearings currently) and by the proposed method shows the high uniformity in their forms of expression (the only difference is the coefficient between them). Being different from the traditional modeling method, we do not need the detailed derivation and complex theoretical computation based on the particular magnetic circuit analysis for this particular case but simply modify several key expressions representing magnetic circuit features in the modeling process with this method. Therefore, the proposed method invented especially for the ac magnetic bearing has the greater advantage of directness and universality than previous modeling method. To illustrate the precision of the proposed modeling approach, the verification experiment is designed and the encouraging experimental results show that the model based on the Maxwell tensor method is more close to the test results comparing with equivalent magnetic circuit method. Thus, the proposed modeling method makes the modeling results on radial suspension forces of the ac magnetic bearing more accurate, universal, and direct. [ABSTRACT FROM PUBLISHER]

This paper proposes and implements a new single-phase magnetless flux switching machine (FSM) for rooftop wind power generation. The key is to integrate an outer-rotor FSM and an inner-rotor FSM with shared stator yoke and stator drum windings. In such a way, this proposed machine can not only realize flux switching function to regulate magnetic flux effectively, but also incorporate the field and armature windings within one stator to reduce the copper losses and improve the overall machine efficiency. Meanwhile, the structure is compact and rotors can be directly driven by blades to capture the wind power. The machine design guidelines from both magnetic and electric aspects are illustrated, the machine characteristics are analyzed by using time-stepping finite-element method, and the system performances are evaluated based on mathematical modeling. Both simulation and prototyping test are conducted to verify the validity of the proposed machine and system. [ABSTRACT FROM AUTHOR]

This paper presents a new topology of parallel hybrid excitation machine (PHEM), which integrates permanent-magnet synchronous motor (PMSM) and variable-reluctance machine, namely, doubly salient electromagnetic machine (DSEM), and provides a solution to better field-regulating capability. The configuration and the operation principle of the proposed PHEM are introduced. The combination criterion and design consideration are discussed. The performances of the two axial sections (PMSM and DSEM) are studied by 2-D finite-element analysis (FEA), respectively, to achieve reasonable integration. The field and voltage regulation capability of the PHEM is further investigated by 3-D FEA. A prototype PHEM is designed, manufactured, and tested. The measured results verify structural validity and finite-element predictions. The loss is predicted, and the measurement of short-circuit current illustrates the capacity of deexcitation at fault. The results confirm that the PHEM achieves effective power superposition of two different brushless machines. Bidirectional field-regulating capability facilitates a wide field regulating range of 6.5:1 under no load. [ABSTRACT FROM PUBLISHER]

The need for testing magnetic materials used in electric machine laminations and measurements under a rotating field is of importance in machine design. In order to obtain satisfactory experimental data, the design of the measurement apparatus deserves particular attention. The purpose of this paper is to propose a novel design of a magnetic circuit based on the Halbach array, which generates a uniform flux density inside the test specimen for the measurement of rotational core loss. The proposed design is simulated and prototyped, and experimental tests are performed on two different samples of M19 gauge-24 and M36 gauge-29 silicon steel at three different frequencies (60 Hz, 400 Hz, and 1 kHz). The field-metric method is used in this work to evaluate the rotational core losses. [ABSTRACT FROM PUBLISHER]

This paper presents a new signature for detection of rotor faults in induction motors, such as eccentricity and broken rotor bars, that uses the external magnetic field analysis. The proposed method is based on the variations of axial flux density in the presence of these faults. The low frequency part of the magnetic field spectrum is particularly analyzed. The analysis is realized through a machine modeling based on permeance circuit under eccentricity fault and also by machine modeling based on coupled magnetic circuit theory under broken rotor bars fault. Analytical relations which describe the machine operation under broken bars fault highlight the influence of speed variation to modify the low frequency components of the external magnetic field. The theoretical results have been validated by experimental measurements. In particular, an inverse stator cage induction machine have been used to measure the bar currents under healthy and faulty cases. [ABSTRACT FROM PUBLISHER]

This paper proposes a novel radial hybrid magnetic bearing (RHMB), which has integrative magnetic pole boards and continuous working air gaps that reduce the hysteresis and eddy-current losses of the traditional homopolar structure. Its configuration and working principle are introduced. The bias and control magnetic circuits of the RHMB are analyzed with the equivalent magnetic circuit method. Mathematical models, from which the force-displacement and force-current relationships are derived, are built. The method for the rudimentary design of RHMB parameters is illustrated, through which a prototype RHMB for a reaction flywheel system is designed and assembled. Its performance and characteristics are calculated and analyzed with the obtained models and relationships. The results show that in its air gaps, the novel RHMB can generate a continuous and uniform bias magnetic field, which reduces the hysteresis and eddy-current losses and enhances the radial load capacity and axial passive resilience. The bias fluxes of all poles are decoupled from each other at all times. Although the control fluxes of the two channels are slightly coupled when the rotor is not in the central position, the coupling force-current stiffness is very low and can be ignored. These attributes simplify the design of the control system. The novel RHMB is especially suitable for high-speed and low-loss circumstances. A pair of RHMBs are used for the reaction flywheel, and for maintaining suspension of the rotor at the spin speed of 0–6000 rpm. [ABSTRACT FROM AUTHOR]