High-speed Permanent Magnet Brushless Research Articles

Investigation of Bessel Functions in Analytical Modeling of Rotor Eddy Current Losses in PM Machine Rotor With Copper Shield

In high-speed surface-mounted permanent magnet (SPM) brushless machines, time- and space-harmonic excitations can induce significant eddy currents flowing in the rotor conductive parts. An effective measure to suppress the eddy currents is to employ a copper shield between the magnets and the retaining sleeve. In this article, a Fourier-based analytical model is proposed to evaluate the rotor eddy current losses. The model is set up in the cylindrical coordinate system and is able to compute the eddy current fields and losses in all rotor domains, that is, the sleeve, shield, magnets, and shaft. Although it is generally believed that both ordinary Bessel functions (OBFs) and modified Bessel functions (MBFs) are workable for solving the magnetic vector potential, it is argued in this article that only the MBF-based models are numerically stable when the high-conductivity domain (e.g., the copper shield) exists, while the OBF-based models may result in irrational results. Both the OBF- and MBF-based analytical models for a prototype motor are established and comparatively studied, with verification of the finite-element (FE) method. Moreover, the cause of losing analysis accuracy in the OBF-based models is revealed.

Fault Diagnosis of High-Speed Brushless Permanent-Magnet DC Motor Based on Support Vector Machine Optimized by Modified Grey Wolf Optimization Algorithm

With the development of reliability theory, people realized that “absolutely reliable” machines could not be made. With its incomparable advantages, the high-speed permanent-magnet brushless DC motor is usually used in the symmetrical structure of high-speed operation working systems, which at present are widely used in aerospace and other fields. The structure of the manufacturing process involves a strict processing, but in the process of work failure could still occur. No matter what field the high-speed permanent magnet brushless DC motor is applied to, it is very important to identify states and run fault diagnosis, which is of great significance to maintain the reliability of the motor and its working system. In this study, the fault diagnosis method of a high-speed permanent-magnet brushless DC motor is studied, and a combination model of modified gray wolf optimization algorithm (MGWO) and support vector machine (SVM) have been proposed for the motor fault diagnosis research. Based on the traditional gray wolf optimization (GWO) algorithm, the optimization performance of the algorithm is improved by initializing the population through a tent map and introducing a sine wave dynamic adaptive factor. Then the modified algorithm is used to optimize the internal parameters of SVM to improve the diagnostic accuracy of the model. Through the signal acquisition test, the current signals under different fault states and faultless states were collected, and the current signal data set required for the experiment is obtained. The experimental result showed that, compared with GWO or sailfish optimization (SFO) optimized SVM models, Extreme learning machine and Back Propagation neural network classical classification models, the fault diagnosis accuracy of the proposed model is the highest, proving the excellent classification performance and good robustness of the MGWO-SVM model.

Study on Rotor Eddy Current Losses in High-speed Permanent Magnet Brushless Machines for Aircraft Applications

To improve the power density of aviation electric drive system, the high-speed permanent magnet machines has more and more popular in the air compressor, radial compressor, and electro-hydrostatic actuator applications. Two methods have studied to reduce the rotor eddy current losses in high-speed permanent magnet machines in this paper. Firstly, rotor eddy current losses at different stator slot openings are investigated, the stator core loss are considered simultaneously. Secondly, to reduce the magnet eddy current loss in carbon fiber retaining sleeve, the copper shield is added between permanent and carbon fiber, and the rotor eddy current losses at different copper shield width are studied.

Reduction of Rotor Harmonic Eddy-Current Loss of High-Speed PM BLDC Motors by Using a Split-Phase Winding Method

Low-order harmonic currents in high-speed permanent magnet brushless dc (PM BLDC) motors cause large rotor eddy-current loss, resulting in high temperature rise and even overheating in the rotors, thus their application in the field of high-speed drive is limited. The rotor eddy-current loss can be reduced by using a split-phase winding method. In this paper, various time–space orders of harmonic eddy-current losses in the rotors of the PM motors with and without split-phase winding are quantified. The calculated results indicate that the rotor harmonic eddy-current losses generated by the low-order harmonic currents, which inherently exist in PM BLDC motors, are greatly reduced. Furthermore, associated with the characteristics of harmonic currents of PM BLDC motors, the mechanism of drastically reducing the rotor harmonic eddy-current loss of high-speed PM motors by using the split-phase winding method is revealed and experimentally validated.

High-speed Permanent Magnet Brushless DC Motors, Properties and Prospective Applications

Wydawnictwo SIGMA-NOT wydaje czasopisma fachowe informujące swoich czytelników o najnowszych osiągnięciach naukowych i nowoczesnych rozwiązaniach technicznych w Polsce i na świecie, popularyzuje problemy techniczne oraz poszerza wiedzę i kulturę techniczną.

A PLL-Based Novel Commutation Correction Strategy for a High-Speed Brushless DC Motor Sensorless Drive System

Commutation error degrades the operating performance of a high-speed permanent magnet brushless dc motor (BLDC) sensorless drive significantly. It is caused by different kinds of nonideal factors such as low-pass filters (LPFs), digital control delay, and other units in a control loop. This paper analyzes the commutation error caused by different kinds of nonideal factors and points out that the total commutation error is substantially equivalent to the error of an internal power factor (IPF) angle of the BLDC motor. The purpose of the commutation correction in this paper is to regulate the IPF angle to zero. A novel phase-lock loop (PLL)-based commutation correction strategy is proposed and designed in detail in this paper. The proposed PLL consists of a novel PM flux linkage based phase discriminator to detect the IPF angle, an LPF, and an autophase regulator (APR). The function of the proposed PLL is to lock the IPF angle to a reference value. Compared to the conventional scheme, the greatest advantage of the proposed scheme is that the proposed PLL is robust to any kind of phase delay caused by nonideal factors in the control loop, and it is quite important for a high-speed motor drive. Both simulation and experimental results verify the effectiveness and superiority of the proposed correction strategy.

Research on Transient Electromagnetic Field Model of High Speed Permanent Magnet Brushless DC Motor Based on the Theory of Constant Electromagnetic Field

The development of ultra-high speed motor is the development direction of the information industry in the future, and it is also the important guarantee for the production efficiency. Objective: To study the working model of the electromagnetic field of the permanent magnet brushless DC motor in the condition of constant electromagnetic field. Methods: Based on the theory of constant electromagnetic field, the model of a high speed permanent magnet brushless DC motor is derived. Process: Combined magnetic circuit calculation method and finite element method of electromagnetic field, and then use the mathematical model to calculate the electromagnetic. Finally, by using the model simulation to verify its practicability. Conclusion: The inhibiting effect of the ring structure rotor pole and cogging torque ripple can meet the requirements of high-speed motor mechanical and electromagnetic performance, meanwhile, the motor has a good performance in this way. So, it can provide reference for the construction of the transient electromagnetic field model of high speed permanent magnet brushless DC motor in the future.

Amorphous Soft Magnetic Core for the Stator of the High-Speed PMBLDC Motor With Half-Open Slots

Several papers have appeared in recent years on the application of the amorphous soft magnetic materials in the stators of the electric motors. In our previous work, we demonstrated that the replacement of a slotless stator from the FeSi electrical steel with the stator from an amorphous alloy Metglas 2605 SA1 in a high-speed permanent magnet brushless direct current (PMBLDC) motor resulted in a substantial decrease of power losses in this stator, even by three times at the rotary frequency of 70 000 r/min. This paper was concentrated on the development of the cores for stators with half-open slots, which are technologically more difficult to produce than the slotless cores. The cores were made by cutting out suitable amount of $25~\mu \text{m}$ -thick rings from the FeSiB amorphous ribbon by a laser technique, followed by stacking up the rings and their consolidation, and suitable heat treatment of the compressed stacks. Next, the measurements of the magnetic properties of the sample cores with half-open slots were made using the Remacomp C-1200 hysteresisgraph and the Lakeshore 450 Gaussmeter. Based on the results of measurements, the sample cores of different heights (17.5 and 10 mm) were selected for application in a stator of the prototype high-speed PMBLDC motor, 800 W in rated power and with a maximum rotary speed of 60 000 r/min. The preliminary performance tests with this prototype motor showed that after 1 h of uninterrupted operation, the temperature of a motor housing did not exceed 60 °C. It was also found that the operating efficiency of the PMBLDC motor incorporating a stator with half-open slots, made from an amorphous material, was almost 90% over a wide range of torques (from 40 to 140 mN $\cdot \text{m}$ ).

3-D Analytical Model of Helical Winding PM Machines Including Rotor Eddy Currents

Helical windings (or zigzag windings) are used in a number of applications, however, in electrical machines, mainly employed in low-power, high-speed permanent magnet (PM) brushless dc machines due to the cost effectiveness of the winding type while maintaining reasonable performance. Typically, helical windings are used for low-voltage applications due to their spiral form, which makes them most suitable for a small number of turns. In high-speed electrical machines, such a low number of turns are applicable. It is apparent that high-speed PM machines suffer from rotor eddy-current losses, which in some cases may lead to PM demagnetization due to overheating. The performance of the machine is compromised by these losses; hence, they have to be considered during the design procedure. There are many papers analyzing the magnetic field of these machines employing helical windings; however, none of them present a simple and precise electromagnetic model of a machine with the helical winding. This paper presents an analytical approach to model the resulting 3-D magnetic field of the helical winding, considering eddy currents in the conducting media of the rotor. The model is verified with the 3-D finite-element method by means of comparing magnetic field and rotor eddy-current losses.

Design, Modeling, Fabrication, Back-to-Back Test of a Magnetic Bearing System for High-Speed BLDCM Application

This paper describes in detail the design, construction, and testing of an active magnetic bearing (AMB) system for high-speed permanent magnet (PM) brushless DC motor (BLDCM) application. A back-to-back (BTB) test setup which consists of two BLDCMs connected by a high-speed flexible coupling is designed and built: the first one acts as the motor and the other one acts as the generator with resistive load. The dynamic model of the rigid rotor supported by AMBs, and its electromagnetic and feedback control design aspects are also provided. Mechanical design aspects are rotor assembly, radial AMB (RAMB), and thrust AMB (TAMB). Finally, full-loaded test results of the AMBs are given using the BTB experimental test setup that adopts two 100 kW electric machines supported by AMBs.

Application of Rapidly Quenched Soft Magnetic Materials in Energy-Saving Electric Equipment

The rapidly quenched soft magnetic materials have found many practical applications in power electronics, electric engineering, telecommunications, and other industrial sectors. The aim of this paper was to present the results of a research on fabrication technology of the amorphous and nanocrystalline cores intended for: 1) soft magnetic cores for the stators of the high-speed permanent magnet brushless direct current (PMBLDC) motors; 2) nanocrystalline soft magnetic cores for application in high-frequency power conversion; and 3) three-limb amorphous cores for the three-phase distribution transformers. The cores intended for the stator of the high-speed PMBLDC motor were made from the Metglas 2605 SA1 ribbon and then subjected to the performance tests in a model of an electric motor. The research on soft magnetic materials for high-frequency high-power conversion was concentrated on the Finemet rectangular cores with a gap and the composite ones with distributed gap, and the comodified Finemet cores with the induced transverse magnetic anisotropy. The three-limb cores for 400 kVA three-phase distribution transformer were made from the Metglas 2605 SA1 ribbon and subjected to the performance tests in electricity distribution network. It was found that all the amorphous and nanocrystalline cores fabricated under this paper enable considerable reduction in power losses.

Analytical Calculation of Slotless Permanent Magnet Motor Based on Soft Ferrite

High-speed slotless permanent magnet brushless motor based on soft ferrite adopts a large effective air gap structure. For the large effective air-gap, the air-gap flux distribution becomes uneven and the end leakage flux significantly increases. Thus, the traditional analytical method of the phase EMF is inapplicable. This paper deduces the analytical expression of the phase EMF based on the analytical calculation of the air-gap field and analyzes the distribution of the end leakage flux by 3D finite elements methods. Then the end leakage flux is considered by a correction factor of the core length. Finally the analytical calculation method is proved to be feasible by the comparison between the finite elements results and the prototype test results.

Reduction of Rotor Eddy Current Loss in High Speed PM Brushless Machines by Grooving Retaining Sleeve

Eddy currents might be significant in the rotor of a high speed permanent magnet brushless machine, especially when a metal retaining sleeve is applied. Various methods have been used to reduce the eddy currents. In this paper, a simple method, by grooving the retaining sleeve, is proposed, such that the flowing path of the eddy currents is obscured and the energy loss is thus suppressed. Circumferential, axial and comprehensive grooving are comparatively studied, particularly on the aspects of loss reduction, sleeve mechanical strength, rotor dynamic balance, and manufacture process complexity. It is proved that the circumferential grooving is the most effective for overall performance improvement and the simplest for practical manufacture with little extra cost.

Core Loss Calculation in Step Magnetic of High-Speed Motor Stator

According to the reduction for efficiency of high-speed permanent magnet brushless DC motor (High-speed PM BLDC motor) by core loss of stator in the design process, the accurate calculation for stator core loss is very important.2-D finite element method is used to analyze the alternating magnetic field and magnetic field of the stator core of which a rotational speed of 27000rpm high-speed BLDC motor. Harmonic analysis is used for the step magnetic field of high-speed BLDC motor, Based on the model of Bertotti iron loss calculation, superposition of various frequency loss will be calculated, the calculation accuracy was validate to increase.

Motor noise generation and prediction for high spinning speed hard disk drive

The acoustic level of a hard disk drive is an important specification. This is especially so for enterprise HDD which is required to operate under a high spinning speed. In order to reduce the acoustics level of a HDD, an in depth understanding behind the mechanisms whereby the noise is being generated in a HDD should be established. This paper will study the acoustics characteristics of a high speed permanent magnet brushless DC motor (PM BLDC) and investigate the physics underlying the generation of noise associated with a motor. An analysis procedure of the PM BLDC motor noise generating mechanisms is proposed. Through finite element analysis and experimental verification, the results indicate that the major noise source for the high speed PM BLDC motor is due to the presence of electromagnetic (EM) torque ripples. Furthermore, it has been observed that the noise radiated by a HDD can be amplified when its structural dynamics are close to the frequency components of the noise source. Finally, a methodology which discusses the steps involved in the prediction of motor radiated noise will be presented.

Study on rotor structure with different magnet assembly in high-speed sensorless brushless DC motors

High-speed permanent magnet (PM) brushless DC motors have gained more and more interests for many applications. The technique of detecting the electromotive force (EMF) zero-crossings is a common method in sensorless operation of PM brushless DC motors. However, the zero-crossings of the phase EMF will be obscured and the sensorless control will be malfunctioned, since the free-wheeling diode conduction can last more than 30 elec-degs under high-speed condition. Therefore it is supposed that the utilisation of third-harmonic EMF is more preferable, as it is not influenced by the free-wheeling diode conduction. Some design features for the high-speed sensorless operation are presented, primarily focusing on the rotor structure with different magnet assembly. The influence of the pole-arc to pole-pitch ratio on the third-harmonic airgap field will be analysed with both finite-element method and analytical model. Based on these analyses, another method which can improve both the third harmonic and fundamental components in the airgap field, by segmenting the parallel-magnetised PMs, is employed and studied. Motor prototypes are then designed and fabricated, and the experimental results confirm the validity of the proposed design method.

A Magnetic-Geared Outer-Rotor Permanent-Magnet Brushless Machine for Wind Power Generation

This paper presents a new permanent-magnet (PM) brushless machine for wind power generation. This machine adopts an outer-rotor topology, aiming at capturing wind power directly. In order to achieve high power density, a high-speed PM brushless generator is artfully integrated with a coaxial magnetic gear. The design details, with emphasis on the special constraints of wind power generation, are elaborated. By using the time-stepping finite element method, the static characteristics as well as no-load and on-load operations are simulated. A prototype is also built for experimentation. Both simulation and experimental results are given to verify the validity of the proposed machine. Finally, a quantitative comparison is made to justify that the proposed machine is of smaller size, lighter weight, and lower cost than its counterparts.

Design aspects of a high-speed sensorless brushless dc motor using third harmonic back-emf for sensorless control

There is increasing interest in high-speed permanent magnet (PM) brushless dc motors for a wide range of applications. Back-emf is often utilized for sensorless operation of permanent magnet brushless dc motors, by detecting the emf zero crossings. However, in high-speed motors, the free-wheeling diode conduction can last more than 30edeg. This can obscure the zero crossings of the phase EMF; therefore, it is preferable to utilize the third harmonic emf instead of the phase emf. In this paper, some design aspects related to this high-speed sensorless operation are presented, including a special nonoverlapping winding arrangement and magnet segmenting technique. Finally, the experimental results confirmed the validity of the proposed design method.

Study of Retaining Sleeve and Conductive Shield and Their Influence on Rotor Loss in High-Speed PM BLDC Motors

Rotor eddy-current loss is usually significant in high-speed permanent magnet brushless dc (PM BLDC) motors. On the other hand, the rotor is usually protected with a nonmagnetic retaining sleeve. The influence of the conductivity of the retaining sleeve on the rotor eddy-current loss is analyzed in this paper. Furthermore, utility of a conductive copper shield between the sleeve and magnets is demonstrated. Although eddy current is induced in the copper shield, causing additional loss, its magnetic field can smooth the varying field in the rotor and reduce the overall eddy-current loss dramatically. The relationship between the thickness of copper shield and the rotor eddy-current loss is also examined

Influence of control strategy on stator and rotor losses in high-speed permanent magnet brushless motors

The stator iron loss and rotor eddy current loss which results in a high-speed permanent magnet brushless motor when operated in brushless dc and ac modes, on both open-circuit and at rated load, with four different current control strategies, is investigated by finite element analysis. It has highlighted the significant influence of the phase current wave form. It has also shown that, on load, the rotor eddy current loss can be the dominant loss component, particularly in brushless dc mode.