Application of Synchronous Brushless Motors in Electric Hand Tools
In the paper, the possibilities to apply synchronous brushless motors in the electric hand tools are considered. The potential of such motors is estimated in a wide range of characteristics. In particular, estimation is made for the electric hand plane with a synchronous motor having outer rotor and excitation from permanent magnets.
The authors consider the possibilities to synthesise metamodels for the analysis and optimisation of brushless synchronous motors. The metamodels are presented for new designs of the outer-rotor permanent magnet synchronous motor and the outer-rotor reluctance motor. The metamodels are synthesised based on the results obtained by the numerical calculations of magnetic field taking into account magnetic saturation. Analysis of the results for the motor magnetic field and tests of the metamodels at the selected and intermediate points shows that these can be synthesised with acceptable accuracy using numerical calculations instead of expensive real experiments.
This paper focuses on studying the synchronous reluctance motors as an alternative to low-power commutator motors. Analysis is done for the improved design of synchronous reluctance motor with a segmental external rotor. Relevant equations and a suitable method are proposed for calculating characteristics of the synchronous reluctance motors operating in a specific mode with electronic commutation as switched reluctance motors. It is concluded that synchronous reluctance motors in this mode can provide a wide range of characteristics and are quite competitive with commutator motors used in low-power devices.
The paper focuses on studying the external-rotor synchronous reluctance motor. The analysis is performed to estimate the influence of the number of stator slots and non-magnetic areas in the rotor (i.e., flux barriers) on the electromagnetic torque and torque ripple of the studied motor. It is concluded that the increase in the number of stator slots Z = 6 to Z = 18 causes an approximately twofold decrease in the ripple factor, but torque increases by 5 %. Electromagnetic torque will be increased approximately by 24 %, if non-magnetic flux barriers are created in the rotor of the studied synchronous reluctance motor.
The paper presents new designs for synchronous reluctance motors that have external rotor (segment-shaped rotor, rotor with additional non-magnetic space to the quadrature axis of the rotor, and rotor with several flux barriers). Impact of the external rotor configuration on the electromagnetic torque and torque ripple is analysed. Electromagnetic torque ripple factor is calculated for each studied motor using the results of magnetic field numerical calculations.
The authors consider the features and operation specifics of the synchronous permanent magnet motors and the synchronous reluctance motors with electronic commutation in servomotor operation modes. Calculation results show that mechanical and control characteristics of studied motors are close to a linear shape. The studied motor control is proposed to implement similar to phase control of induction servomotor; it means that angle θ (angle between vectors of the supply voltage and non-load electromotive force) or angle ε (angle between rotor direct axis and armature magnetomotive force axis) is changed. The analysis results show that synchronous electronically commutated motors could be used as servomotors.
A new design of synchronous reluctance motor with segment-shaped outer rotor is presented and investigated in this paper. In order to obtain correct recommendations for optimal design of the studied synchronous reluctance motor, analytical relations of motor electromagnetic parameters and geometrical dimensions (also known as metamodels) have been synthesized. Electromagnetic parameters, which have been used for metamodels synthesis, are obtained by means of magnetostatic field numerical calculations with finite element method using software QuickField.
The paper includes the analysis of the studied synchronous reluctance motor geometrical parameters (stator outer diameter, height and overlap angle of rotor’s segment-shaped packages) influence on the electromagnetic torque per unit volume. Testing of synthesized metamodels shows that relative difference between the results obtained by numerical calculations and those obtained with the help of synthesized metamodels does not exceed eight percent at experimental points and intermediate points as well. The proposed optimal design of the segment-shaped outerrotor synchronous reluctance motor obtained with the help of synthesized metamodels has been compared with a salient-pole outer-rotor synchronous reluctance motor having ferromagnetic yoke with the same value of the electromagnetic torque. The comparison results of both motors show that the highest value of electromagnetic torque per unit volume can be achieved with the proposed new design of the synchronous reluctance motor with segment-shaped outer rotor.
The authors analyze the advantages and disadvantages of brushless synchronous electric machines with radially and non-radially mounted rectangular permanent magnets. The results show that the proposed nonradial mounting of permanent magnets considered in the paper, in several cases (e.g. multi-pole brushless generators with tooth windings of the armature) allows achievement of the following advantages: better technology of manufacturing the electric machine owing to simple packing of the stator winding in the stator open slots, which also increases the copper slot fillfactor; reduction in the mass-and-size of permanent magnets at least twice; significantly lower cost of the electric machine; and, finally, its greater specific power.
The paper presents an overview of brushless electric motors used in hand electric tools and household appliances. Analysis of the motor types has shown that synchronous reluctance motors are the most reliable for lowpower drives of such tools and appliances due to their simple design, long service life and low cost of production. Solutions are proposed for significant decrease in the quadrature-axis magnetic flux of the synchronous reluctance motor. The motors are shown to develop the specific electromagnetic torque up to 0.35÷0.4 Nm/kg.
The paper presents the comparison of two synchronous reluctance motors with the inner rotor and the outer one. The aim of the research is to determine the influence of motor type on electromagnetic torque and ripple factor. The results indicate that a maximum value of electromagnetic torque and the amplitude of the first harmonic of electromagnetic torque increase for the motor with the inner rotor, and the value of ripple factor increases as well. If both motor types with equal rated power, rotation frequency and current density are compared, the results show a possibility to reduce the volume of motor with the inner rotor by 15 %.