DE4427323C2 - Electrical machine with permanent magnets and excitation field windings - Google Patents

Description

The invention relates to an electrical machine with at least one excitation unit has both permanent magnets and excitation field windings.

Permanently excited electrical machines require a high corner power of the An control. The maximum level is particularly high in battery-powered vehicles speed and the maximum moment the machine design. A high river density in the air gap causes - especially at high speeds - high iron losses.

In purely electrically excited machines, the pathogen losses are reduced - especially in partial load operation - the efficiency. Furthermore, due to the good conductivity increased pulsation and surface losses.

From DE-PS 708 038 a large synchronous machine has been higher since 1941 Speed known, the excitation for the most part by rotating permanent magnets and partly due to controllable magnetization currents. As Permanent magnets are used in magnetic steels with low coercive field strengths exhibit. The entire iron body of the runner consists of a hard magnetic Steel. For a constant voltage, the additional electrical magnetization becomes Overcoming anchor reaction and scattering used. The goal is a small Ge importance of runner development. In order to halve the excitation winding effort, it works the additional magnetization not only strengthens the field, but also weakens it. For this, a DC excitation machine with reversing excitation current controller is used, which should also deliver a magnetizing excitation current that measures the magnet steel gnetized.

Ferrite has been on the market in electrical engineering since the 1960s magnets and for high-quality drives the rare earth magnets that have been available since around 1980 enforced. Compared to the no longer used magnet steels, the Magnetic materials common today have significantly higher coercive field strengths. An ent Magnetization through armature cross fields can be within the permissible temperature be excluded. The energy product of rare earth magnets, e.g. B. from SmCo, or NdFeB, is 10 times larger than that of magnetic steels, and their The characteristic curve is a straight line in the entire second square.

DE 34 24 402 C1 describes a converter-fed, self-controlled rotor excited synchronous machine known, one as a counter-excitation to permanent has switched electrical excitation. The only field weakening counter-excitation is characterized by the fact that it increases with increasing speed increases. The max. Excitation field is intended for a stiffness superior to a DC drive  care and is generated solely by the permanent magnets. For this, the Air gap magnets have a high operating point, which also at max. Anchor cross field prevents demagnetization at the pole edges. The size and the set magnet volume corresponds to a purely permanent magnet synchronous machine same standstill torque. During the magnetic losses in the stator sink through the field weakening, high losses occur at high speeds the excitation winding because the magnetic resistance for the electrical excitation field is great. High rotor losses exacerbate heat dissipation problems.

From DE-AS 17 63 317 it is known to demagnetize the permanent prevent magnets in the stator of a disc rotor by making few wire turns can be wrapped directly around the permanent magnets. Because of the low relative Permeability of the magnetic material arranged in the interior of the coils can also be this design only a relatively small adjustment range can be generated. The electrical Electricity is only available in a copper volume that is limited to the pole gap space supply that is poorly used by the wire winding. Enlarged pole gaps reduce the pole cover and thus the magnetic utilization of the machine.

In JP 58-222 765 A an electrical generator is described in which the Lowering the manufacturing costs on the exciter pole area a plastic-bound Ferrite magnet is applied. Plastic-bonded ferrites only reach one river density of approx. 0.15 T. The majority of the pathogen field is from the pathogen wick generated. The magnetic layer itself is only slightly better magnetizable than Air. The desired reduction in manufacturing costs can only be achieved if the additional magnetic layer generates the magnetic resistance for the electrical excitation field not increased. This is only in large generators with relatively large ones Air gaps possible. The weak field of the magnetic layer has an additive effect and a strong one Excitation field against demagnetization must be demagnetized by the armature avoid cross-country. The field winding only has a field-enhancing effect.

From US-PS 4 398 112 is a single phase winding for a radial flux known machine that by cutting axial recesses in a previously wound thin conductor tape is produced.

Furthermore, DE 41 26 019 A1 describes a flat ribbon winding for legs pole machines with radial air gap flow and an exciter from US-PS 41 90 779 unit known for an inner rotor in claw pole design.

The invention had the object of an electrical machine with a perma Magnetic and electrical excitation in such a way that  both in partial load operation as well as low losses at high speeds, the permanent magnet material is good is exploited and the machine both high torques and high speeds can generate, in addition a light and mechanically stable structure and one sufficient cooling and cost-effective production is to be ensured.  

The object is achieved with the characterizing features of claims 1 and 13 solved. Further advantageous configurations are described in the subclaims.

According to the invention, the air gap surface of the excitation unit is made only of a permanent magnet material and insulating material formed, resulting in low surface losses. The Permanent magnets have a high pole coverage and a small thickness in the direction of magnetic flux. As a result, they take a working point close in normal operation their maximum energy product. The permanent magnet segments are flat on soft attached magnetic cores, between which an excitation winding is arranged, which consists of There are ladders with a rectangular cross section and thus have a high fill factor. Depending on the machine design, the excitation windings are designed differently. she ensure high stability and power density due to their compact design.

Passive cooling of the excitation winding due to flat heat sinks is not enough off, there can be an active cooling through cooling channels that are below the pole gaps and run on the end faces of the field winding.

If the excitation unit is in the rotor, the excitation currents are transmitted by slip rings or brushless by controllable transformers, also on a low weight and good use of space is ensured.

The drawings represent advantageous embodiments of the invention.

Fig. 1 shows the magnetization characteristic of a permanent magnet with operating points;

Fig. 2 shows the speed-torque characteristic of an electric machine designed according to FIG. 1;

Fig. 3 shows schematically a manufacturing method for a ribbon excitation field winding of an axial flux machine;

Fig. 4 shows schematically a manufacturing method for a ribbon excitation field winding of a radial flux machine;

Fig. 5 shows an excitation unit of an axial flow machine in Schenkelpolbauform during assembly of the components;

Fig. 6 shows an excitation unit of a radial flux machine with a meandering ribbon coil when assembling the components;

Fig. 7 shows an excitation unit of an axial flow machine in Klauenpolbauform during assembly of the components;

Fig. 8 shows the cross section of an axial flow machine, the excitation unit contains stamped conductor layers.

Fig. 1 shows the magnetization curve 1 of permanent magnets of an inventive electrical machine. The three operating points A _{1-3 shown} result from superimposition of the permanent field by an electrically generated excitation field, where A _{1 represents} the operating point with de-energized excitation winding, A ₂ with maximum positive current and A ₃ with maximum negative current. A positive current means that the permanently excited magnetic field is amplified by the electric field and the flux density in the magnet increases from A ₁ in the direction of A ₂ . In contrast, a negative current weakens the magnetic field and the operating point moves on the characteristic curve in the direction of A ₃ .

In Fig. 2, the speed-torque characteristic line 2 belonging to the machine design of Fig. 1 is shown, wherein the machine can cover only the checkered operating range I with pure permanent excitation by varying the stator currents and voltages. With the stator current still limited, the electric field amplification makes it possible to achieve higher torques, as a result of which the area II shaded from top left to bottom right is added. The electrical field weakening enables higher speeds to be achieved in the area III shaded from bottom left to top right. In normal operation I there are no excitation losses in the machine and, at high speeds III, lower iron losses due to the reduced air gap flux density. Compared to a purely electrically excited machine, the required copper volume of the excitation winding is reduced by approx. 30%. A good use of space also reduces the losses and the weight of the field winding.

There are several manufacturing processes for linear motors, radial and axial flow machines an excitation winding made of flat conductor tape can be used.

In Fig. 3, a variant for producing a two-layer excitation winding in salient pole design for an axial flow machine is shown schematically. Here, the conductor flat strip is first wound from a roll 3 onto a spindle 4 , the cross section of which corresponds to the later pole core cross section. After a coil 5 with twice the conductor length compared to a later single coil 6 has been formed, the cut end is fastened on a second spindle body 7 and half of the conductor flat strip is wound back onto the latter. Coil pairs 8 prefabricated in this way are now placed in two positions in a device offset by one pole pitch. The current flows alternately in pairs of coils of the two layers by changing from a inner coil end 10 to the next coil end 10 ′ on a radial surface of the soft magnetic pole core within a contact rail 9 . The two coils of a pole core thus have an opposite winding direction.

An alternative method for producing a field winding of conductor ribbon shown in FIG. 4, except that a meander coil 11 is pre-manufactured for a Radialflußmaschine. The rolled out of a drum 12 thin conductor flat strip 13 first passes through an automatic beam cutting system 14 , in which the recesses 15 for the pole segments are worked out. Alternatively, a punching machine could also be used. Then a baking varnish is applied evenly in a coating system 16 and the cut and coated tape 17 is rolled onto a device 18 . After the baking lacquer has hardened, the device is removed and the pole cores and a yoke ring are pushed on axially (see FIG. 6).

Axial flux machines can also be designed with meandering ribbon windings are, but the flat strip is to be rolled spirally.

Furthermore, a programmable jet cutting system also enables parallel strips with a meandering course to be cut from the flat conductor strip in one operation. After to which insulation layers have been applied in the direction of the groove width, tape packs are made exchanged two production machines working with different rolling directions, axially pushed into each other and electrically connected at their ends. Several meander coils then lie axially flat against one another and are connected in series.

Through this and similar, preferably fully automatic processes, pathogen wick lungs, which despite small conductor cross-sections and long conductor lengths are right corner-shaped conductor cross-sections have a very high slot filling factor and by avoiding Bending radii have relatively short connection paths in the end windings.

Fig. 5 shows an excitation unit 20 with a flat tape reels 21 in Schenkelpolbauform for a 18-pole axial flow machine during assembly. The structurally identical pole cores 22 with permanent magnets 23 glued or applied on the air gap surface are inserted into the ribbon coils 21 and pushed radially from the outside into the grooves 24 of a soft magnetic yoke ring 25 . In this single-layer excitation winding, the series connection of the ribbon coils 21 takes place only after assembly, for. B. by laser soldering.

In FIG. 6, an excitation unit 26 is shown a zwölfpöligen Radialflußmaschine during assembly. First, the axial insertion of each second pole core 27 into a soft magnetic yoke ring 29 provided with grooves 28 . Then a ready-made flat ribbon meander coil 30 is pressed on and finally the second half of the pole cores 31 with oppositely magnetized permanent magnets 32 are also inserted axially. The permanent magnetic field supports the cohesion of the excitation unit 26 .

In the case of axially short radial flow machines or annular axial flow machines, this takes place Design of the excitation winding preferably in the form of claw poles.

Fig. 7 shows such an excitation unit 33 for a 24-pole axial flow machine during assembly. After winding up a flat conductor strip to form a ring reel 34 , both the inner claw pole segments 35 can be inserted axially from the air gap side and the outer claw pole segments 36 36 radially from the outside. For optimal use of the magnetic material, the magnetic segments 37 occupy the entire air gap surface except for narrow pole gaps 38 , whereby they protrude somewhat tangentially beyond the claw pole segments 35 , 36 . This reduces the leakage flux of the electrically excited field. While the effort for prefabricating the ring reel 34 is low, the more complex claw pole segments 35 , 36 can preferably be produced as sintered parts based on a cobalt iron alloy.

In a multi-pole axial flux machine 40 , the field winding 41 - as shown in FIG. 8 Darge - also advantageously consist of stamped conductor plates. In order to keep the manufacturing outlay and the amount of space of the insulating material low, only a small number of layers are realized and the control voltage is reduced by a wave transformer 42 . To compensate for the axial magnetic forces, the axial flow machine has two air gaps 43 , two axial thin-ring bearings 44 near the inner winding heads 45 ensuring a constant distance between the rotor disk 46 and the two stator halves 47 . Both stator halves are made of structurally identical multi-phase layer windings 48 which, together with their grooved soft magnetic bodies 49, are each pressed into a housing half 50 a, b. The magnetic field flows through the rotor disc 46 only in the axial direction, with permanent magnets 51 on pole cores 52 made of grain-oriented sheets being arranged on both air gap surfaces. A liquid or gaseous coolant circulates in cooling channels 53 arranged under the pole gaps and above the winding heads. In addition to the magnetic forces, the rotor disk is held together by two plastic bodies 54 a, b, which are hooked together on the radial surfaces and fill the pole gaps. A fiber-reinforced bandage 55 on the outer circumference of the rotor disc absorbs the centrifugal forces.

While a profiled wire 57 with a small conductor cross section is inserted in the stator-side transformer core half 56 b, the core half 56 a arranged in the shaft 58 contains a coiled conductor flat strip 59 . The excitation current multiplied by the wave transformer 42 is rectified by Schottky diodes 60 , current reversal being made possible by a bistable power relay 62 controlled by an optocoupler 61 .

Claims (15)

1. Electrical machine with at least one excitation unit ( 20 , 26 , 33 ), which has excitation poles with alternating polarity in the direction of movement, the excitation unit having both permanent magnets ( 23 , 32 , 37 , 51 ) and at least one excitation field winding ( 21 , 30 , 34 , 41 ) with soft magnetic pole cores ( 22 , 27 , 31 , 35 , 36 , 52 ) and current switching elements are provided for changing the current direction through the excitation winding, the permanent magnets ( 23 , 32 , 37 , 51 ) being flat on the to the air gap facing surface of the excitation poles are arranged and have a working point (A1) with approximately half the residual flux density (B _R ) near their maximum energy product when the excitation field winding ( 21 , 30 , 34 , 41 ) is without current. 2. Electrical machine according to claim 1, wherein the excitation field winding ( 21 , 30 , 34 , 41 ) arranged between the pole cores ( 22 , 27 , 31 , 35 , 36 , 52 ) consists of conductors with a rectangular cross section. 3. Electrical machine according to claim 1, wherein the soft magnetic pole cores ( 22 , 27 , 31 , 35 , 36 , 52 ) reduce their cross section in the flow direction to 0.3 to 0.5 times the pole surface. 4. Electrical machine according to claim 1, wherein at least one ring of a thin conductor flat band ( 21 ) is arranged around each pole core ( 22 ). 5. Electrical machine according to claim 1, wherein the pole cores ( 35 , 36 ) form claw poles, which together encompass an excitation field winding ( 34 ) made of wound flat ribbon. 6. Electrical machine according to claim 1, wherein between the pole cores ( 27 , 31 , 51 ), the conductors of the field winding ( 30 , 41 ) are arranged in meandering circumferential layers. 7. Electrical machine according to claim 1, wherein electrically isolie in the pole gaps between the excitation poles material or magnetized magnet segments in the direction of movement are ordered.   8. Electrical machine according to one of the preceding claims, wherein the permanent magnets ( 37 ) have a greater width in the direction of movement than the pole pieces of their pole cores ( 35 , 36 ). 9. Electrical machine according to one of the preceding claims, wherein the pole cores ( 22 , 27 , 31 ) on the side facing away from the permanent magnets ( 23 , 32 ) are fastened in an annular soft magnetic yoke ring ( 25 , 29 ). 10. Electrical machine according to one of the preceding claims, wherein the pole cores ( 52 ) on two opposite sides each have a permanent magnet ( 51 ). 11. Electrical machine according to one of the preceding claims, wherein the excitation winding ( 41 ) is fed via a transformer ( 42 ) which multiplies the excitation current. 12. Electrical machine according to one of the preceding claims, wherein under half of the pole gaps and on the end windings ( 45 ) cooling channels ( 53 ) run in which a coolant circulates. 13. A method of manufacturing an electrical machine according to claim 1, wherein thin hard magnetic layers applied to soft magnetic pole cores and then into a prefabricated winding with a rectangular shape Conductor cross section can be used. 14. A method of manufacturing an electrical machine according to claim 13, wherein the thin hard magnetic layers by laser sintering or plasma fuel zen can be applied to the soft magnetic pole cores. 15. A method of manufacturing an electrical machine according to claim 13, wherein a conductor flat strip first through a beam cutting or punching machine runs in which cutouts for the pole cores are worked out, and then before winding in a coating system with a thin adhesive and Insulating layer is provided.