BG112818A - Brushless electrical machine with permanent magnetic excitation - Google Patents

Abstract

The electrical machine is designed for operation at increased overloading and rotational speeds, with reduced pulsation of the rotational torque, operating as a generator or motor. The stator (7) has winding (10) from conductors with a rectangular cross-section by two active conductors (Na) in a groove and by three elementary conductors (Nel) in an active conductor (Na) with barreling. The rotor (12) consists of a package, assembled from lightweight sheets with axial channels (14) formed and permanent magnets (15) stuck therein. In the area below the magnets are shaped areas (18) with increased magnetic resistance. The grooves of the stator (7) are bevelled to a size, equal to the distance between the permanent magnets (15). The ratio of the groove division (t4) to the internal diameter (Da) of the stator (7) is limited in the range from 0,039 to 0,048.

Description

BRUSHLESS ELECTRICAL MACHINE WITH PERMANENT MAGNET EXCITATION

FIELD OF THE INVENTION

The invention relates to a brushless electric machine with excitation by permanent magnets, designed to operate at increased overloads and rotational speeds, at reduced torque ripples, operating as a generator and motor in two-zone electrically driven electric motors for electric vehicles, in metal cutting machines digital program control, in automation tools, etc.

BACKGROUND OF THE INVENTION

A brushless electric machine with permanent magnet excitation is known [1], comprising a shaft mounted in front and rear shields by means of front and rear bearings. Between the front and rear shield is a closed housing enclosing a stator. The stator consists of a stator package on the inner surface of which a uniform number of channels are arranged, in which at least one phase winding consisting of three or more phases is laid. The stator comprises a rotor assembly consisting of a set of steel plates comprising a magnetically conductive ring in which axial channels are formed in which permanent magnets are inserted. The magnetically conductive ring of the rotor assembly is fixedly connected to the shaft by means of an intermediate element. The intermediate element is a high value of the magnetic resistance. In the jugular part of the magnetoconducting ring, on the inner wall of the axial channels enclosing the permanent magnets, in the area below the middle of the latter, interruptions are formed with a width not exceeding half the thickness of the permanent magnets. Between each permanent magnet and the outer wall of the axial channel in which the permanent magnet is located, a thin air gap is formed, in which narrow thermal insulation gaskets are inserted between the cut-off parts of the magnetically conductive ring and the permanent magnets. The intermediate element with a high value of the magnetic resistance connecting the magnetically conductive ring is the shaft, can be made as a non-magnetically conductive sleeve or can be made integrally with the magnetically conductive ring.

A disadvantage of the known electric machine is its disturbed compactness, creating the possibility of displacement relative to each other of the two separated halves of the contact surface in the axial channel under the permanent magnet due to forces generated at extreme torque values and detachment of magnets, if the latter are glued, as well as the absence of a compact connection between the permanent magnets and the cutting parts of the rotor, located above the permanent magnets, due to the thermal insulation gaskets, which creates conditions for independent oscillation of the cutting parts.

Another disadvantage of the known electric machine is the formation of significant pulsations in the electromotive voltage created during the rotation of the electric machine due to the structure of the stator and rotor of the electric machine. These pulsations are an obstacle to the electronic control of the operating modes of electric drives.

The disadvantage is also that no appropriate ratios have been selected in the structure of the electric machine with excitation by permanent magnets to provide an acceptable thermal mode of operation.

SUMMARY OF THE INVENTION

The object of the invention is to provide a brushless electric machine with excitation by permanent magnets with increased compactness, reduced pulsations of the electromotive voltage and improved permissible thermal mode of operation.

This task is solved by means of a brushless electric machine with excitation by permanent magnets, including a shaft mounted in front and rear shields by front and rear bearings, between the front and rear shields is a closed housing comprising a stator consisting of a stator package, on the inner surface of which a uniform number of channels are arranged, with a width t4 of channel division along the inner diameter of the stator, in which a phase winding consisting of three or more phases with conductors of rectangular cross-section is laid. The stator is a movable rotating rotor kit comprising a magnetically conductive ring composed of a set of steel plates in which axial channels are formed in which permanent magnets are inserted. The gaps between the inner surface of the channels and the permanent magnets are filled with an adhesive substance. The magnetically conductive ring of the rotor assembly includes an outer magnetically conductive ring and an inner magnetically conductive ring connected to the shaft by means of intermediate elements with a high value of the magnetic resistance. The outer magnetic ring forms the excitation magnetic field in the air gap between the rotor and the stator, and includes cut-offs located above the permanent magnets and narrowed sections of equal radial size hl and total tangential size tl outside the permanent magnets. The outer and inner magnetic rings in the areas between the permanent magnets are connected to each other by radial stripes with a width included in the size tl. The inner magnetic ring is composed of prismatic shapes, each of which is located below the adjacent halves of the permanent magnets and has a maximum radial size below the zones between the permanent magnets and a decreasing radial size to the centers of the permanent magnets. According to the utility model, the prismatic shapes under the media of adjacent permanent magnets are connected by narrow strips with radial size h2 <1mm and tangential size t3, which satisfies the inequality 3,5h2 <t3 <5h2. The plurality of grooves on the inner surface of the stator are inclined to form on the inner cylindrical surface of the stator a size t3 corresponding to the condition 0.9tl <t2 <1.1 tl, and the ratio of the width t4 of the channel division on the inner surface of the stator to the diameter Da on the inner surface of the stator is determined by the condition 0,039 <t4 / Da <0,048 | The number of active conductors Na in the channel is equal to 2, and the number of elementary conductors Nel in one active conductor Na is 3. The three elementary conductors Nel of two active conductors Na, which are part of one section group, are transposed by covering one of another.

An advantage of the brushless electric machine with excitation by permanent magnets, according to the utility model, is that while maintaining the monolithicity of the magnetic system of the rotor, the resistance of the permanent magnets against demagnetization is increased at reduced mass of the permanent magnets. Another advantage is that the value A of the pulsations of the electromotive voltage of the electric machine is greatly reduced. It is also an advantage that through the formulated ratios and parameters of the structure of the brushless electric machine with permanent magnets, the heat fluxes emitted by the stator winding are limited and in the operating modes a permissible heating temperature range is provided.

BRIEF DESCRIPTION OF THE ATTACHED FIGURES

The invention is illustrated in more detail by the accompanying figures, where:

FIG. 1 is a longitudinal partial section through the middle of a permanent magnet of the rotor assembly of the brushless electric machine with excitation by permanent magnets according to the invention.

FIG. 2 is a partial cross-sectional view of the rotor of the brushless electric machine.

FIG. 3 is a view of part of the inner surface of the stator of the brushless electric machine.

FIG. 4 shows a map of the magnetic flux pathways.

EXAMPLES OF EMBODIMENT OF THE INVENTION

The exemplary embodiment of the brushless electric machine with excitation by permanent magnets according to the invention shown in FIG. 1 comprises a shaft 1 mounted in a front shield 2 and a rear shield 3 by means of a front bearing 4 and a rear bearing 5. Between the front shield 2 and the rear shield 3 is a closed housing 6 comprising a stator 7. The stator 7 is composed of a stator package 8 , on the inner surface of which are arranged evenly a plurality of grooves 10. A winding 11 is arranged in the grooves. The stator 7 movably encloses a rotor assembly 12 comprising a magnetically conductive ring 13 composed of a set of steel plates in which axial grooves 14 are formed, in which permanent magnets 15 are inserted. The magnetically conductive ring 13 of the rotor assembly 12 includes an outer magnetically conductive ring 16 and an inner magnetically conductive ring 17 connected to the shaft 1 by means of intermediate elements 18 with a high value of magnetic resistance. The electric machine is equipped with a control sensor 19.

In FIG. 2 shows a partial cross-section of a rotor assembly 12 with an outer magnetically conductive ring 16, including cut-off portions 20 and narrowed sections 21 with the same radial size h1 and a total tangential size t1. The outer magnetically conductive ring 16 is connected to the inner magnetically conductive ring 17 by radial ribs 22. The inner magnetically conductive ring 17 is connected to the shaft 1 by means of intermediate elements 18 with high magnetic resistance. The inner magnetic ring 17 is composed of prismatic bodies 23 which are interconnected by narrow strips 24 which have a radial size h2 <1mm and a tangential size t3, such as 3,5hl <t3 <5hl.

In FIG. 3 shows a view of the inner surface of the stator. The channels 10 are inclined tangentially to the one forming the inner cylinder of the stator 7, the two ends of the channels 10 being displaced tangentially to each other at a distance t2, which satisfies the inequality 0.9tl <t2 <ltl.

In FIG. 4 shows a map of the paths of the magnetic fluxes Fml created by adjacent halves of the adjacent permanent magnets 15 and of the magnetic fluxes Fwl, Fw2 and Fw3 generated by the stator winding 11. Fwl is a magnetic flux closing in a pole division and intersecting at different directions of the two halves of the permanent magnet 15 and closing through the narrow strip 24 located below the middle of the permanent magnet 15. Fw2 is the magnetic flux passing in different directions through the radial ribs 22 surrounding the permanent magnet 15 and having common areas with Fwl above channels 10 and under the permanent magnet 15. Fw3 is a magnetic flux closing through the intermediate element 18 is increased magnetic resistance and having common areas in the radial ribs 22 with magnetic flux Fw2. The size t4 of the channel division and the size Da of the inner diameter of the stator 7 are in a ratio determined by the inequality 0.039 <t4 / Da <0.048. It is shown that in the channel 10 of the stator 7 there are two active conductors Na and each active conductor Na is composed of three elementary conductors Nel with a rectangular cross section.

In another embodiment of the invention, the stator 7 may be closed between the front shield 2 and the rear shield 3, ie the electric machine can be realized in the same way as described above, but without a housing 6.

ACTION OF THE INVENTION

When an alternating voltage is applied to the stator winding 11, coordinated in value and frequency, an electric current flows through the stator winding 11, which interacts with the magnetic fluxes Fml creating torque. The electric current creates its own transverse current in the area of each magnet 15. Depending on the paths through which it passes, this magnetic flux is divided into three types of parts - Fwl, Fw2 and Fw3. The Fwl parts pierce the two halves of the permanent magnets 15 in different directions and in one half are opposite to the magnetic fields Fml created by the permanent magnets 15 and act demagnetizing. The parts Fw2 pass outside the permanent magnets 15 through the radial ribs 22. In the zones below the permanent magnets 15, the magnetic fluxes Fw1 and Fw2 pass together through the strips 24 formed below the media of the permanent magnets 15 as parts of the inner magnetic ring 17. the value and the demagnetizing action of the flow Fwl. And the flow Fw3 allows most of the flow Fw2 to be directed to the strips 24 to reduce the flow Fwl. This increases the resistance of the permanent magnets 15 against demagnetization.

The ripple in the voltage induced by the permanent magnets 15 and its deviation from the sinusoidal shape are minimized due to the bevel of the value t2 of the channels 10 of the stator 7. Thus, the pulsations of the torque are limited. In this way, the harmonic components in the current, generating additional electrical losses, are removed.

By limiting the values of the ratio t4 / Da, the number of active conductors Na in channel 10 and the number of parallel elementary conductors Nel in one active conductor Na, the heat fluxes generated by the stator winding 11 are limited, while the values are also limited. of the thermal resistances in the emission of these flows. In particular, the value of the FILD coefficient, which determines the ratio of additional eddy current losses to the main electrical losses, is limited. The selected structure of the active conductors Na, in which the elementary conductors Nel are covered from each other, reduces the values of the circulating currents, creating additional losses in the elementary conductors Nel and high values of the efficiency in a wide range of loads. This ensures the operation of the electric machine in the allowable heat range, and the increase of the ohmic resistance and the main electrical losses in the copper conductors is limited.

EXPERIMENTAL RESULTS IN THE STUDY OF AN EXPERIMENTAL MODEL IMPLEMENTING THE USEFUL MODEL

A physical experimental sample made in accordance with the invention and a virtual sample with some characteristic differences from the patent at the same nominal power of 45 KW, the same nominal torque of 150 Nm, twice the maximum power, torque and speed of rotation, with practically the same dimensions are compared: stator length with winding about 200 mm and stator diameter less than 200 mm, equal voltages and liquid cooling.

For the physical sample, the number of active conductors Na is 2 and the number of elementary conductors Nel is 3, the value of the ratio t4 / Da is between 0.039 and 0.045, at 12 poles. The total losses are 2100 W and the efficiency is 95%. Coil temperature at coolant temperature is 130 degrees.

For the virtual sample, the number of active Na conductors in a channel is 4, the number of elementary conductors Nel is 1, the value of the ratio t4 / Da is 0.058 at 6 poles. The total losses are 4000 W and the efficiency is 0.91%. The coil temperature in S1 mode and the coolant temperature of 85 degrees is over 200 degrees.

Comparing the above results, it was found that the total losses of the experimental sample were reduced by almost half, and the temperature of the stator winding was significantly reduced - from over 200 degrees to 130 degrees.

REFERENCES

1. Patent application in Bulgaria ent. № 112317 dated 09.06.2016. BRUSHLESS ELECTRICAL MACHINE WITH EXCITATION BY PERMANENT MAGNETS

Claims (1)

A brushless electric machine with excitation by permanent magnets, comprising a shaft mounted in front and rear shields by means of front and rear bearings, a housing enclosing a stator enclosed by a stator package, the inner part of which is composed of a stator package a number of channels are arranged evenly on the surface, with a width t4 of channel division along the inner diameter of the stator, in which a phase winding consisting of three or more phases with rectangular conductors is laid, and the stator is movably covered by a rotor set containing a magnetically conductive ring. consisting of a set of steel plates in which axial grooves are formed in which permanent magnets are inserted, the gaps between the inner surface of the axial grooves and the permanent magnets are filled with an adhesive substance, and the magnetically conductive ring of the rotor assembly includes an outer magnetoconductive ring. an inner magnetically conductive ring connected to the shaft by means of intermediate e elements with a high value of magnetic resistance, the outer magnetic ring forming the excitatory magnetic field in the air gap between the rotor and the stator, and includes cutting parts located above the permanent magnets and narrow sections of equal radial size hl and total tangential size tl outside the permanent magnets, the outer and inner magnetic rings in the areas between the permanent magnets being connected by radial ribs of width included in the size tl, and the inner magnetic ring being composed of prismatic shapes, each of which is located below the adjacent halves of the permanent magnets; has a maximum radial size below the zones between the permanent magnets and a decreasing radial size to the media of the permanent magnets, characterized in that the prismatic shapes (23) located below the media of the adjacent permanent magnets (15) are connected by narrow strips (24 ) with radial dimension h2 <1mm and tangential dimension t3 that satisfy the unequal 3.5h2 <t3 <5h2, and the plurality of grooves (10) on the inner surface of the stator (7) are inclined with respect to the forming on the inner cylindrical surface of the stator (7) at a distance t2 corresponding to the condition 0.9t 1 <t2 < 1.1 tl and the ratio of the width t4 of the channel division along the inner surface (9) of the stator (7) to the diameter Da of the inner surface (9) of the stator (7) is determined by the condition 0.039 <t4 / Da <0.048, at which the number of active conductors Na in the channel (10) is equal to 2, and the number of elementary conductors Nel in Hellenic active conductor Na is 3, as the three elementary conductors Nel of the two active conductors Na, which are part of one section group, are transposed by covering from each other.