DE10064377A1 - Brushless electrical machine - Google Patents

Abstract

With grooved anchors (stator core), in which the number of stator teeth Z is a multiple of the number of phases m, detent moments occur in brushless electrical machines in the de-energized state, which are a consequence of the magnetic preferred direction of the ferromagnetic teeth. DOLLAR A The cogging torques can be minimized by selecting the number of stator teeth Z with DOLLAR AZ = m È (P / 2 + - C) DOLLAR A, whereby P / 2 should not be divisible by m and C is a constant that, if the number of pole pairs P is even, the following conditions satisfy DOLLAR A 0 <C <P / 2 with DOLLAR AC = (2 È n - 1) if P / 2 is an even number and DOLLAR AC = 2 È n if P / 2 an odd number with n = 1, 2, 3, ..., DOLLAR A with C> 1, P / 2 is not divisible by C DOLLAR A and, if P is odd, DOLLAR A is also the expression (P / 2 + - C) is odd and C satisfies the conditions: DOLLAR AC = 1/2 È (2n - 1) with n = 1, 2, 3, ...,.

Description

The invention relates to a brushless electrical machine with a permanent magnet rotor with P pole pairs, one genu t stand with Z stand teeth and an m-phase stand derwicklungs, the number of stator teeth Z a multiple of Number of phases is m.

Such machines are in particular a multi-pole variant others as direct drives without a reduction gear puts.

A direct drive without a reduction gear offers meh more advantages both in stationary operation and at dy Namely processes compared to a drive with subset reduction gear. A direct drive presupposes the presence ahead of a slow running electrical machine. ever lower the nominal idling speed of the electric machine ne, the larger the number of magnetic rotor poles, if high efficiency, high power-weight ratio Ratio and low manufacturing costs can be achieved. A noise is then characteristic of a direct drive poor behavior in the entire operating area and a excellent controllable behavior.

If the anchors are grooved (stator core), brush them loose electrical machines in the de-energized state Rastmo elements that are a consequence of the magnetic preferred direction of the ferromagnetic teeth are.  

Especially with multi-pole magnetic rotors an electri machine whose magnets are made of neodymium-iron-boron Magnetic material (Nd-Fe-B) exist, strong Rastmo occur ment due to the quadratic value of the remanent production of the magnetic material used.

The minimization of the cogging torque proves to be difficult.

There are various measures to reduce the Rastmo ment known. However, all of these measures ent neither the increase in manufacturing costs nor the reduction machine utilization or they are technical and economically not suitable for multi-pole Machinery.

Examples of known measures for reducing the cogging torque are the following:

• - Use of suitable magnetic pole surfaces and / or for this adapted shapes of the stator teeth, so that the distance between between the two opposing surfaces (pole and tooth area) is smallest in the middle and larger on the outside becomes.

The special shape of the stand teeth and the magnets are included sintered magnet material such as neodymium-iron-boron magnets al but very expensive to manufacture.

Permanent magnet manufacturers offer for economical green the high-energy permanent magnets, such as. B. Neodymium Iron Boron Permanent magnets, in prefabricated form, e.g. B. cuboid or Strips, on. The manufacture of magnetic rotors a high pole electrical machine with cuboid or stripe magnets is the cheaper solution if a ho hes power to weight ratio and a compact design of the machine can be achieved.  

• - Use of magnetic slot wedges.
• - enlargement of the air gap of the electrical machine.
• - Slant of the grooves of the stator core and / or Oblique (displacement) of the permanent magnets.
• - Enlargement of the slot slot angle.

However, the latter measures all reduce the Ma schin utilization.

All of these measures lead to a drastic diminution the instantaneous values of the normal component of the river te (induction) in the air gap of the electrical machine. The The result is a reduced mean induction value in the air gap. This leads to a lower torque or ge lower power output of the machine.

Do you still want such measures in multi-pole electrical use machines, one must expect that the Electricity load of the machine must be increased to the design To achieve torque or electrical power. The leads to drastic warming and a short life duration of the machine.

The only remedy is to enlarge the machine. The is known to lead to higher manufacturing costs and lower power-to-weight ratio of the machine.

The number of stator teeth Z, based on the number of pole pairs 2P of the permanent magnet rotor and the number of phases m of the machine, usually results from the following equations:

Z = m. [2P] (1)

for machines with a number of holes = 1
and

Z = m. [P] (2)

for machines with a number of holes = 1/2

It is also known that the number of teeth at each the rotation of the rotor magnetic poles is equal to the smallest ge common multiples k of Z and 2P and the number equal gears equal to the largest common divisor g of Z and 2P.

For example, join a three-phase machine 2P = 96 magnetic poles and Z = 288 stator teeth according to the equation (1) 288 gears and 96 simultaneous gears with every revolution. The peak values of 96 individual Magnets add up here.

From DE-T 38 87 011 a brushless electrical machine is already known, the cogging torques are to be minimized by assigning the number of stator teeth to the number of magnetic poles. The number of teeth Z is the equation

Z = (P ± N) .m are sufficient, where

P the number of pole pairs
N is a natural number and
M the phase number
is. The condition should apply that

0 <N <P - 2P / m, so that Z <2P.

Even with this version, however, add up at certain the rotor angles depending on the choice of the number N, so that residual moments remain.

The invention has for its object the occurrence of Reduce cogging torque, even when using high quality  Permanent magnets, e.g. B. from neodymium-iron-boron Magnetic materials, also in the form of cuboids or stripes fen can exist.

According to the invention, the object is achieved by the features of claim 1.

Starting from equations (1) and (2), one can generally write:

Z = m.2P.q (3)

with q as the number of holes

With equation (3) the following applies for q = 1:

Z = m.2P. [2P / 2P] (4)

And for q = 1/2, equation (3) turns into

Z = m.2P. [P / 2P] (5)

The expression in the square brackets indicates the number of holes the machine. The numerator or even the denominator is ge the largest common part in standard versions of Z and 2P. As here in equations (4) and (5) the counter is equal to the number of poles or the number of poles of the machine and reflects the largest common divisor (g) again. It is also the largest common divisor of 2P and the amount [Z - 2P]. The denominator gives the number of poles of the Ma seem.

If, however, the counter in the square brackets is an uneven one is an even number, there is no simultaneous occurrence of the Peak values of the individual magnets are possible and therefore only given a low cogging torque.  

According to the invention, the electrical machine is therefore designed with the following number of stator teeth Z:

Number of holes q = [Matching odd number / 2P]

q = [P / 2 ± C] / 2P (6)

Z = m.2P. [P / 2 ± C] / 2P

respectively.

Z = m. (P / 2 ± C) (7)

With
Z = number of stator teeth
m = number of phases
P = number of magnetic rotor poles
P / 2 is chosen as not divisible by m.

C is a constant that must meet the following conditions:

• 1. P is an even number
  0 <C <P / 2 (8)
  With
  C = (2.n - 1) (9)
  if P / 2 is an even number
  and
  C = 2.n (10)
  if P / 2 is an odd number
  with n = 1, 2, 3,. , ,
  such as
  at C <1
  is [P / 2 + C] not by [C] (11)
  divisible.
• 2. P is odd
  C = 1/2. ( 2 n - 1 ) with n = 1, 2, 3,. , ., in which
  the expression (P / 2 ± C) is also chosen to be odd.

If a certain minimum distance between two between the individual magnetic poles and the fulfillment of the glide chung (7) under conditions (8 to 11) Cogging torque vanishingly small, even when using mag netpolen made of magnetic material with very high remanent inductance on.

A hole number of less than 0.5 advantageously results. This also increases the number of coils in the stator winding number range is smaller and it is a technologically one multiple winding of the coils around the stator teeth of the machine possible.

The tooth widths can be with the invention in a tech nisch advantageous area to be run. Find it Machines with sinusoidally induced voltages (synchron machines) or with rectangular or trapezoidal induced Voltages (brushless DC machines) application.

For the number of stator teeth of the respective stand, for Machines with rectangular or trapezoidal induced chip preferably low values and for machines with a sinusoidal shape  induced voltages preferably higher values selected.

This results in a three-phase version of the machine for example a number of 2P poles, the ≧ 16 as well are divisible by 4 but not by 3.

The number of teeth is expediently kept larger than that Number of pole pairs.

The invention is for both outrunner and for In internal rotor machines applicable.

The invention is intended below with reference to exemplary embodiments play will be explained in more detail. In the associated drawings gen show

Fig. 1 is a partial view of an extended as an external rotor motor electric machine formed according to the invention,

Fig. 2 shows a detail from Fig. 1 in an enlarged scale;

Fig. 3 is a partial view of a second variant of the machine elekt step,

Fig. 4 shows a detail from Fig. 3 in an enlarged scale;

Fig. 5 shows the discrete curve of the detent torque of the Maschi ne according to the first variant, depending on the rotor position,

Fig. 6 shows the discrete curve of the detent torque of an e lektrischen machine according to the prior art with the same number of stator teeth in dependence on the rotor position,

Fig. 7 shows the discrete course of the cogging torque of an inventive machine according to the second variant depending on the rotor position and

Fig. 8 shows the discrete course of the cogging torque of a machine according to a third variant.

Fig. 1 shows a first embodiment of the machine according to the Invention. Fig. 2 gives an indication of the necessary distance between the individual magnetic poles (pole gap). All magnetic poles have the same dimensions. The gaps between the individual magnets also have the same dimensions.

The machine shown has a machine part designed as a permanent magnet rotor, here designated as a rotor 111 , and a second machine part designed as a stand 222 .

The rotor 111 consists essentially of a rotor yoke 11 , which is made of solid soft magnetic material and the permanent magnetic field magnets 11 to 140 , which are in the form of strips of neodymium-iron-boron magnetic material and are arranged on the inner wall of the rotor yoke 11 ,

The arrangement of the field magnets 11 to 140 with alternating magnetization are indicated in the drawing by the letters N (north pole) and S (south pole).

The stand 222 , which is provided with a stator core 22 with 33 stander teeth 2 ₁ to 2 ₃₃ and 33 grooves 4 ₁ to 4 ₃₃ , is formed from a laminated soft magnetic material (laminated core).

The stator tooth surfaces 21 ₁ to 21 ₃₃ and the field magnets 1 ₁ to 1 _{40 of} the rotor 111 are separated by an air gap 5 . Around the stator teeth 2 ₁ to 2 ₃₃ , 33 coils 3 ₁ to 3 _{33 are} wound.

The number of rotor poles 2 P = 40 for the stator 222 was selected. The equation (6) results in the number of teeth Z = 33. The number of holes is therefore q = 11/40. An experimentally constructed machine with a rotor 111 made of neodymium-iron-boron magnetic material in the form of strips with a remanent induction of 1.23 Tesla has a standstill torque per axial length of 1520 Nm / m.

Fig. 5 shows the discrete course of the cogging torque of the machine. The peak value of the cogging torque per axial length is 0.62 Nm / m. This corresponds to 0.04% of the machine's standstill torque.

In order to be able to compare the height of the peak values of the cogging torque, the machine was compared with a conventional machine with a number of stator teeth Z = 33 and with a magnetic pole number 2P = 44. The field magnets were also made of neodymium-iron-boron magnetic material with a remanent induction of 1.23 Tesla in the form of strips. The standstill torque per axial length is 1600 Nm / m. Fig. 6 shows the discrete course of the cogging torque as a function of the rotor position . With this machine version, the peak value of the cogging torque per axial length is 100 Nm / m. This corresponds to 6.25% of the standstill torque. This high peak value of the cogging torque is typical of electrical machines whose magnetic poles made of neodymium-iron-boron magnets with a ratio of stator teeth to rotor poles ratio Z / 2P = 3/4 or 3/2.

The second embodiment of the machine according to the invention has a rotor pole number 2P = 64 and was carried out according to equation (7) with a stator with a number of teeth Z = 51. The number of holes is q = 17/64. The machine has a standstill torque per axial length of 1750 Nm / m. Fig. 7 shows the discrete course of the cogging torque per axial length as a function of the rotor position . The maximum value of the cogging torque per axial length is 1.16 Nm / m. However, this maximum value is very small and corresponds to 0.066% of the machine's standstill torque. The machine shown in Fig. 3 corresponds in construction to the first embodiment. The number of field magnets 1 ₁ to 164 is 2P = 64, that of the stator teeth 1 ₁ to 1 ₅₁ is Z = 51. The field magnets 1 ₁ to 1 ₆₄ are made of neodymium-iron-boron magnetic material and have the form of strips.

Fig. 4 gives an indication of the necessary distance between the individual magnetic poles (pole gap).

With the same rotor, i.e. the number of magnetic poles 2P = 64 a machine was carried out with a stand whose Number of teeth according to equation (7) Z = 57.

Fig. 8 shows the course of the detent torque per axial length of the machine in dependence on the rotor position. From the drawing it can be seen that the maximum value of the locking torque per axial length is 1.7 Nm / m. It is therefore higher than in the machine according to the second variant with a stand, the number of teeth of which is 51 . With this value, however, the machine still runs smoothly at very low speeds.

LIST OF REFERENCE NUMBERS

111

runner

222

stand

11

rotor yoke

1 ₁

-

1 _n

field magnets

22

stator core

2 ₁

-

2 _n

stator teeth

4 ₁

-

4 _n

groove

21 ₁

-

21 _n

Stator tooth surfaces

5

air gap

3 ₁

-

3 _n

Do the washing up
N north pole
S South Pole

Claims (2)

1. Brushless electrical machine with a permanent magnet rotor with P pole pairs, a grooved stator with Z stator teeth and an m-phase stator winding, where the number of stator teeth Z is a multiple of the number of phases m
characterized in that
the number of stator teeth Z with
Z = m. (P / 2 ± C)
is selected, where P / 2 should not be divisible by m and C is a constant which, provided P is an even number, satisfies the following conditions:
0 <C <P / 2 with
C = (2.n - 1) if P / 2 is an even number and
C = 2.n if P / 2 is an odd number with n = 1, 2, 3,. , .,
if C <1, P / 2 is not divisible by C.
and, if P is odd,
the expression (P / 2 ± C) is odd and C satisfies the conditions:
C = 1/2. (2n - 1) with n = 1, 2, 3,. , .,. 2. Brushless electrical machine according to claim 1, characterized in that the number of phases is chosen to be m = 3.