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Moment of inertia of motor with external rotor is much higher than this moment for motor with internal rotor and identical power rating. This characteristic may be utilized for designing kinetic energy storage using electric motor. Problems occurring when brushless dc motor (PM BLDC) with external rotor is employed as kinetic energy storage are discussed in the paper. Design recommendations for reducing these problems are also given. The analysis is supported by results of laboratory tests run with motor manufactured to scale

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 $\cdot \text{m}$ ).

PurposeWhen phase windings of brushless DC motor are switched, additional voltage drops across inductances of main circuit appear. These drops lead to, among other effects, increase of torque‐speed curve slope. The discussed research has been aimed at working out a simple and precise method of identifying torque‐speed characteristic of PM BLDC motor. The elaborated method takes into account the influence of windings switching and motor inductances on motor torque‐speed characteristic. In order to assess the results, extensive test simulations of models implemented in Matlab/Simulink software have been run. Results of analysis and test simulations have been compared with lab test results of two real PM BLDC motors.Design/methodology/approachAnalytical calculations take into consideration phenomena occurring during windings switch‐overs and impact of inductance on emerging voltage and rotational speed drops. It has been pointed out that on account of main circuit inductance, the average value of source current is less than average value of equivalent current generating electromagnetic torque. For analysis sake it has been assumed when windings are being switched‐over the current is kept constant; the motor parameters have also been assumed to be constant.FindingsA novel and accurate method of determining torque‐speed characteristics of PM BLDC motor has been worked out. This method has been investigated with the help of motor computer models implemented in Matlab/Simulink software and the obtained results have been subsequently compared with results of laboratory tests of two commercially available PM BLDC motors.Research limitations/implicationsThe object of the research was brushless DC motor with permanent magnet excitation. The impact of windings switch‐overs on torque‐speed curves of the motor has been analysed. Analytical method which makes it possible to determine torque‐speed curve of this motor very easily has been elaborated. Computer model of PM BLDC motor for Matlab/Simulink software has also been worked out. Extensive simulations helping to verify the proposed method have been run. Results of analysis and simulation tests have been verified by means of laboratory tests of two commercially available PM BLDC motors.Practical implicationsPM BLDC motors are used more and more widely. The new method of determining PM BLDC motors torque‐speed curves will facilitate analysis and design of drive systems utilizing these motors and will also speed up calculations.Originality/valueThe presented method of determining torque‐speed curves of PM BLDC motor is novel and much more precise than methods commonly used nowadays. Recognized methods usually neglect impact of inductance on motor properties.

This paper presents results of a research work related to the development of the production technology of the amorphous cores designed for application in permanent magnet brushless direct current (PMBLDC) motors. The cores were made from the Metglas 2605 SA1 amorphous ribbon, from which rings of the specific external and internal diameters were cut using a laser technique. Next, the rings were stacked up so as to form a core of a required height, subjected later to the consolidation by pressing, followed by an appropriate heat treatment. Finally, the cores were coated with an epoxy resin to protect them against delamination and used as stators in a prototype high-speed electric motor, 1 kW in rated power and 70 000 rpm in a rotary speed. The motor incorporating these amorphous cores was subjected to the performance tests, which confirmed their proper operation and satisfactory mechanical characteristics and efficiency. It was found that power losses in the stators from the amorphous material were considerably smaller than those in the conventional stators from the silicon steel, and they did not exceed 7 W. Therefore, an application of the amorphous soft magnetic materials in the high-speed PMBLDC motors may contribute to eliminating the need of using additional cooling systems in these motors.

PurposeThe purpose of this paper is to elaborate a method of computer analysis of high‐speed motor with specific parameters and verifying the obtained results, i.e. computer models by experimental (laboratory) tests.Design/methodology/approachIn order to determine motor properties from the viewpoint of energy conversion, a model using FEM was worked out with the help of Maxwell software. To determine static and dynamic properties of both motor and drive, Matlab/Simulink models were used; one of these models was a built‐in (library) model, the other one was proposed by the authors.FindingsThe new analysis method and model of high‐speed motor have been carried out.Research limitations/implicationsThe permanent magnet brushless direct current high‐speed motor was the subject of the research. In the first part of the research, the properties of the motor were determined by using finite element method.Practical implicationsThe laboratory prototype can be a starting point in establishing the production of the high‐speed motors with rotational speed in the range of 50,000‐100,000 rpm.Social implicationsAt this moment, there are several possible application of the high‐speed motor and it should be expected that other new applications can appear in near future after the start of the production.Originality/valueThe paper shows that the computer‐based analysis method determines the motor properties accurately. It is also pointed out that a motor with half‐open slots has advantageous properties. The new simulation model of high‐speed motor has been carried out. This model allows taking into account some imperfections caused by slots and rectangular cross‐section magnets.

Two constant current models of Permanent Magnet Brushless Direct Current Motor (PM BLDC) are presented in the paper. In the first part of the paper principle of operation, basic properties and mathematical equations describing PM BLDC models are given. Then, two different constant current models of PM BLDC motor are considered: In the first model, PM BLDC motor is approximated with dc motor; in the second model, modified constant current model is applied with additional block, which is used to take into account the impact of inductance on torque-speed characteristics. In order to verify these models, torque-speed characteristics have been determined and compared for different motor supply voltages. After running a series of simulation and laboratory tests, we have found that this modified model (which makes allowance for the influence of inductance on torque-speed characteristics) ensures obtaining torque-speed characteristics identical to those of the real motor. Therefore, this model may be recommended for those simulation tests which do not consider effects occurring inside the electronic commutator-motor circuit. However, approximation of PM BLDC motor with dc motor is not recommended in computer tests.

In practice we often meet with electrical drives, where it is necessary to operate with higher speed, while load torque is less than rated torque. This type of operation is called ldquoconstant power operationrdquo and may be defined as second range of natural motor torque-speed characteristic. In case of motors excited with permanent magnets magnetic flux is constant, and while supply voltage remains constant, motor speed is also (approximately) kept constant. In practice, different solutions are attempted in order to achieve increased rotating speed of brushless motors at decreased torque. One of the methods, which make possible PM BLDC motor operation at increased speed and decreased torque, is use of electronic commutator with switchable bridge-half-bridge structure. The investigation presented in the paper has been aimed at estimation of losses and efficiency in the drive consisting of brushless motor operating with variable structure commutator. Results of theoretical analysis, computer simulations and laboratory tests have shown that application of electronic variable structure commutator, which makes possible operation in the second speed range without increasing motor power and supply source power, causes an insignificant decrease in overall drive efficiency.