JPS6192150A - Brushless dc motor - Google Patents

Abstract

PURPOSE:To reduce a torque ripple by winding the coil of exciting phase to include the third harmonic wave distribution, and providing the correcting rotor pole of the same number of poles as the third harmonic waves in the rotor, thereby cancelling the variation in the main torque. CONSTITUTION:A semiconductor switch is connected with an exciting coil 13, the position of the main pole of the permanent magnet of a rotor 2 is detected by position sensors H1, H2, and the switch is controlled at a timing so that the combined torque for generating the motor becomes that generated by the exciting phases. The coil 13 is wound on a stator to have the third harmonic wave magnetic flux distribution pole 14, and correcting rotor poles 10 to become triple poles of the same number as the third harmonic waves are integrally provided at the rotor 2. Thus, the variation in the main torque T(T1+T2) can be reduced by the correcting torque T3.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application This invention relates to a brushless DC motor applied to laser printers, polygon scanners for fax machines, and the like.

Conventional configuration and problems The excitation windings are made into multiple phases and a semiconductor switch is connected to each, and the relative position between the rotor, which is made of permanent magnets, and the excitation windings is detected to switch the current direction of the excitation windings. Conventional brushless DC motors that generate torque in a fixed direction by selecting a coil produce inherent discontinuous torque fluctuations when switching the current or selecting the coil.

There are already methods for increasing the inertia of the rotating part in order to average out such inherent torque fluctuations, and for correcting the phase and magnitude of the excitation current by circuit processing in the drive circuit. This invention is an electric motor that reduces torque fluctuation by adding harmonic magnetic flux to the basic magnetic flux distribution and devising the magnetization pattern of the permanent magnets that make up the rotor to generate torque that compensates for the above-mentioned inherent torque. It provides:

A conventional example will be specifically explained below. As a representative example of the conventional example, FIG. 7 shows a brushless morph corresponding to two-phase excitation using so-called AC excitation using transistor switches. In FIG. 7, 1 is a stator, and 2 is a rotor, which are magnetized into two poles, N and S. Although the figure is illustrated using two poles for simplicity, in the case of multiple poles, the electrical angle is 2π as a unit pole pair. The stator 1 has slots 3, and each slot 3 is wound with an excitation coil 4.4', 5.5'. In addition, a DC switch T is connected to each exciting coil 4.4', 5.5'.
r lI+ T r I2. T r 21+ T'r
22 are connected in series and connected to the power source 7 as shown in FIG.

Since the DC switch TrII to T' 22 always conducts current in one direction when it is on, for example, the DC switch Tr
When a current flows into the excitation coil 4 connected to II, the iron core immediately below the coil is excited to N and becomes the same polarity as the rotor pole N shown in the figure. On the other hand, when the DC switch TrI□ is turned on, a current flows into the excitation coil 4', and the iron core immediately below the coil is excited to N, making it different from the rotor pole N shown in the figure. In other words, the polarity immediately below the excitation coil 4 becomes N when the DC switch T r 1) is on, and S when the DC switch T r l□ is on.
The polarity immediately below ' is s when T r 1) is on, N when Tr is on, and substantially represents a single excitation coil in AC excitation.

Excitation coil 5.5' and DC switch T r H, Tr2
The relationship □ is also similar and substantially corresponds to two-phase excitation in AC excitation. Hl, H2, H, , H2 are excitation coils 4.4', 5 to be excited depending on the magnetization polarity of the rotor 2, respectively.
．． Excitation coil 4.4', 5.5 for selecting 5'
' and the position sensor of the rotor 2. For example, using a Hall element, as shown in the figure, as the N pole of the rotor 2 increases, a voltage is induced in the Hall element H1, and the DC switch T rl
1 is turned on, while the induced voltage of and is reduced, and the DC switch Tr1□ is turned off. The same operation is performed for the DC switch T r 2 (, T r 2 □) with a position shift of π/2.

As explained above, this is equivalent to AC two-phase excitation. That is, as the rotor 2 rotates around the shaft 6, the excitation coils 4.4' and 5.5' are sequentially switched. FIG. 8(a) shows the relationship between the excitation coil polarity and the rotor pole at that time. In the figure, the excitation coil 4 is the same as the rotor 2 due to the N pole of the rotor 2 and the turning on of the DC switch Trll by the Hall element H1. It shows the relative position of the polarity of the excitation pole of the second coil when pole-excited, and also represents the relative position between the Hall element and the excitation pole. Figure 8(b)
indicates the torque that occurs over time, and T1 is the first
Torque generated by the excitation coils 4 and 4', T2 is the torque generated by the excitation coil 5.5', which is the second coil, and T1+T2 is the combined torque. This means that the rotation of the rotor 2 extends over π and the excitation coil 4
．． 4' and 5.5' are switched, and the phase difference between the first coil and the second coil of the excitation coil group is π/2. Brushless morphs are said to have π energization.

Assuming that the air gap length is uniform and there is no reluctance torque, the torque generated during excitation of each excitation coil 4.4', 5.5'- is as follows: Excitation magnetic flux distribution is Bs5i per unit axial length
nθ The magnetic flux distribution of the rotor magnet is B Ral per unit axial length
n (θ-wt-ψ). θ is the spatial distribution angle, B is the maximum value of the excitation distribution, w
t is the rotational angular velocity, BR is the maximum value of the rotor magnetization distribution, and ψ is the initial position or load angle of the stator and rotor. The magnetic energy W stored in the air gap is W = (B5sinθ+B R51n (θ−
wt-ψ)) ”R...1 formula where R is magnetic resistance.

Therefore, generated torque = -2πRBS BRsin (w t+ψ)...
...Equation 2 If there is a spatially harmonic magnetic flux distribution in the magnetic flux distribution, then from the progression of Equations 1 and 2, torque is generated only when there is a harmonic magnetic flux distribution of the same order.

To=-2πRnB5. BR1) Blnn (w
t+ψ)...3 Formula Here, BSo is the maximum value of the n-th excitation distribution, and BRn is the maximum value of the n-th rotor magnetization distribution.

The above is a case where DC continues to flow through the excitation coils 4.4' and 5.5', so each excitation coil is excited with DC by each of the Hall elements H1 to H2, which are rotor position sensors. It holds true in the area where it is. That is, in the case of π energization, the relationship between each exciting coil and the rotor is established in the energization period of 0 to π.

Figure 9 shows the relationship between the excitation coil and the rotor, π
/2 energization The Hall elements H1 to H2 are arranged so that when a specific excitation coil is energized, the current in other excitation coils is turned off, and the logic of switching on and off is taken.
This shows the torque of so-called π/2 energization in which the excitation coils are sequentially and exclusively excited during a period of /2. In any case, the torque has inherent torque fluctuations at intervals of π/2 in two-phase excitation.

Figure 10 shows the relationship equivalent to three-phase excitation in AC excitation as well as two-phase excitation. shows the case where the polarity matches the polarity of the first coil pole.At this time, the same (Hall element H1~group of C1

constitutes an excitation distribution as shown in FIG. 10(a).

This is so-called π energization. Figure 10 (d+ is π/3
Hall element H1~dan when energized. This is the case where each coil is exclusively energized and the energization period is set to π/3 using the logic of . The figure (Q) shows the torques T, , T2 ., generated by each excitation coil group at that time. The torque is generated as time passes sequentially for each π/3 period of 'r3. Although the torque in the case of π energization is not shown, it is clear that it is the sum of the torques generated by the respective excitation coils. In any case, the torque has inherent torque fluctuations at intervals of π/3 in three-phase excitation.

OBJECTS OF THE INVENTION An object of the present invention is to provide a brushless DC motor that can reduce torque fluctuations and effectively level out torque ripples.

Structure of the Invention The brushless DC motor of the present invention is a brushless DC motor having a position sensor that connects a semiconductor switch to an excitation coil, operates the excitation coil with the semiconductor switch using a d-wave magnet, and selects the semiconductor switch. In a brushless DC motor whose switching operation is timed so that the composite torque generated by the motor is the torque itself generated by each excitation phase, the coil of each excitation phase is wound so as to include the third harmonic distribution,
On the other hand, the rotor magnet is characterized by coaxially coupling a magnet having main rotor poles having the same number of poles as the main driving magnetic poles and correction rotor poles having three times the same number of poles as the third harmonic. . Since the torque generated between the correction rotor pole and the third harmonic magnetic flux distribution generated in the coil acts to cancel the fluctuations in the main torque, the fluctuations in torque can be reduced.

DESCRIPTION OF THE EMBODIMENTS An embodiment of the present invention will be described with reference to FIGS. 1 to 6. In other words, this brushless DC motor has a position sensor that connects a semiconductor switch to the excitation coil and selects the excitation coil switch by actuating the excitation coil switch using a permanent magnet in the rotor. The timing is such that the resultant torque generated by each excitation phase is itself the torque generated by each excitation phase.

Each phase excitation coil is wound around the stator so as to include the harmonic magnetic flux distribution, while the rotor is coaxially coupled with magnets having the same number of poles as the harmonic distribution poles (correction rotor magnetic poles).

In a general motor, it is ideal that the magnetic flux distribution by the excitation winding is arranged in a sinusoidal wave, but in many cases the winding is simple due to size reasons or to simplify manufacturing. Generally, if one coil is used for each main coil pole, the third harmonic magnetic flux distribution will be extremely large in the excitation flux distribution when winding at full pitch or extreme short pitch. This third
Expressed differently from the harmonic magnetic flux distribution, it can be considered that an excitation winding having three times the number of poles as the basic number of poles coexists. As can be seen from the Fourier series expansion, there is a distribution of odd harmonic poles, but as mentioned above, the distribution of third harmonic poles is large as a component. Since this harmonic pole is associated with the fundamental power, the direction of the excitation current is switched to keep the torque always in a predetermined direction depending on the relative position of the fundamental power of the rotor and the fundamental power of excitation by the stator excitation winding. When the polarity is reversed, the third harmonic pole is also reversed. Now, if a permanent magnet with the same number of poles as the third harmonic excitation distribution pole is provided in the rotor 2 in combination with or in conjunction with the basic permanent magnet pole, torque of each component will be generated. This relationship is illustrated in terms of torque per hour, stator excitation polarity, and rotor permanent magnet magnetization polarity as shown in FIGS. 1, 4, and 5.

In the case of two-phase π/2 energization shown in Fig. 1, the same figure (al indicates the generated torque, T is the composite torque of the basic magnetic flux T1゜T2, T1 is the basic excitation pole of the first phase and the rotor basic T2 is the torque due to the basic excitation pole of the second phase and the rotor basic control, T3 is the third harmonic magnetic flux T I-3, T2
-3 composite torque, T1-3 is the torque due to the correction rotor magnetic pole 10 of the rotor 2 corresponding to the concomitant third harmonic pole of the first phase, T2-3 is the concomitant third harmonic pole of the second phase This is the torque due to the correction rotor magnetic pole 10 of the rotor 2 corresponding to .

The same figure (bl is the excitation pole 13 of the first coil (first phase) 1) and its associated harmonic pole 14 and the second coil (second phase) 12
FIG. It is a developed view showing the relationship between the basic rotor 15 which is the main rotor pole of the rotor 2 and the correction rotor magnetic pole 10 of the rotor 2 with reference to the same figure (C1 is the first coil 1). Hl.

H2, group 1. f12 indicates a sensor that detects the relative position between the excitation pole 13 and the rotor base 15 and switches the excitation direction, and its position.

The condition for most leveling out the composite torque T+T3 of the basic torque and associated torque is 1-T3=0.707+0.707T3T3/T1=0, assuming that the maximum torque due to the basic excitation pole of each phase is the reference 1.
．． 172...It is to satisfy the relationship of formula 4.

Torque component element 1. 'r3 is the product of the excitation fl east distribution and the corresponding magnetic flux distribution of each rotor magnet.

(Example 1) If the stator excitation magnetic flux distribution is a π square wave distribution, by Fourier expansion, the maximum fundamental wave excitation magnetic flux of each phase Bs1 = 1
(standard), the maximum value of the third harmonic excitation flux B53 = 1/
3B, 1=0.333B, 1, because they share the magnetic path T3/”r1=nBS 3 BR3/BS I BR1
・・・・・・Equation 5 Here, n is the adjoint harmonic order (n='3), Bs
1 is the maximum value of each phase excitation basic magnetic flux distribution, BRI is rotor 2
13sa is the maximum value of the accompanying third harmonic magnetic flux distribution of each phase excitation, and BR3 is the maximum value of the magnetic flux distribution of the correction rotor magnetic pole 10 of the rotor 2.

BS 1 =1. Use BR1=' as the unit standard T
3 / T 1 = n °k S 3 °kR3kS
3 = BS 3 /B'S 1 = 0.333 with π full-pitch excitation kR3 = BR3/BR1 When the rotor magnetic poles are magnetized to have a rectangular magnetic flux distribution of the sheet pitch for the π-pitch excitation of the stator, the rotor FIG. 2 is a plot of the ratio of magnetization pitch, fundamental torque, and third harmonic torque.

From the figure, the magnetization pitch approximated by equation 4 is 140°. That is, the torque can be leveled by short-pitch rectangular wave magnetization including a non-magnetized band.

(Example 2) A triple-polarity magnet is added to the basic magnet of the rotor, and the magnitude of the third harmonic magnetization flux distribution BR3 is corrected to satisfy Equation 4.

The stator has a π square wave distribution.

T3/TI=3X0.333kR3=0.172,-,
kR3, = 0.2 Fundamental rights 15 in Figure 1 (C) as in Figure 3 + a)
If the correction rotor magnetic poles 10 and 10 are made of the same material and share the same magnetic path, the magnetization pattern of the rotor 2 will be axially B R1 sin θ + B R3 sln 3 θ = B R1 (
slnθ+0, 2 sin 3θ). If it is normalized with BR1=1 and plotted at a pitch of π/2, a magnetized pattern including a non-magnetized band shown in FIG. 2(b) will be obtained.

In the case of two-phase π current flow shown in FIG. 4, the relationship between two generated torques and an hour is shown in FIG. In the case of π energization, the torques generated by the combinations of each phase and each harmonic order are superimposed. Therefore, the maximum value and minimum value of the fundamental combined torque T1+T2 and the third harmonic pole combined torque T1-30T2-3 coincide with each other, and there is no correction effect.

In the case of three-phase π/3 energization shown in FIG. 5: FIG. 5(a).

(bL (C1 shows the generated torque, the polarity relationship of the stator phase coils, the polarity relationship of the rotor magnet poles, and the relationship of the rotor position sensor to the stator excitation coil. The symbols are the same as in Fig. 1, and the third coil (3rd phase) is added. T3 is the torque, and T3-3 is the harmonic torque. As can be seen from Fig. 5 (a), the condition for the flattest torque is 0.866 = 1 -T3 T3/T1=0.134 ・・・・・・6
If the stator excitation magnetic flux distribution is a π rectangular wave distribution, the fundamental wave of each phase (■ Maximum magnetic flux value BS Emi 1
(standard), the maximum value of the third harmonic excitation flux B33#0
．． 333B, 1, and from Equations 5 and 6, k, 3 = 0.134 = 0.1 When the rotor 2 is magnetized in a rectangular magnetic flux distribution with short pitch, the magnetization pitch width is approximately from Equation 6 and Figure 2. 135°, and in a homogeneous magnet, with the magnetic flux BR1=1 of the basic magnet as a reference, the composite pattern of magnetization in the axial direction including a non-magnetized band as shown in FIG. 6 is obtained.

In the case of 3-phase π energization: As in the case of 2-phase π energization, the maximum value and the minimum value of the fundamental combined torque and the 3rd harmonic combined torque match, so there is no correction effect.

Effects of the Invention According to the present invention, the torque ripple can be easily leveled by providing a correction rotor magnetic pole corresponding to the third harmonic excitation component of the excitation coil.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram of the case of two-phase π/2 energization in one embodiment of the present invention, and FIG. 2 is an explanatory diagram showing the relationship between the ratio of fundamental wave torque and third harmonic torque with respect to the magnetization pitch of the rotor. , Fig. 3 is an explanatory diagram showing the magnetization pattern of the rotor in two-phase π/2 energization, Fig. 4 is a torque waveform diagram in two-phase π energization, and Fig. 5 is an explanation for three-phase π/3 energization. Figure, 6th
The figure is an explanatory diagram of the magnetization pattern of the rotor, Fig. 7 is an explanatory diagram of the conventional example, Fig. 8 is an explanatory diagram showing the relationship between excitation and torque, and Fig. 9 is an explanatory diagram of the magnetization pattern in the case of two-phase π/2 energization. The explanatory diagram, FIG. 10, is an explanatory diagram in the case of three phases. l... Stake, 2... Rotor, 10... Correcting rotor magnetic pole, 13... Excitation pole (excitation coil), 14...
...Harmonic distribution pole, 15... Fundamental right (main rotor pole) 2nd r (b (C - τ - 埜 - F dimension 0': 51 Fig. 6 (b) (C) Fig. 5' Part 8 Figure 7 N S
1st coil (Yu 1st) (a) S
N S 2nd coil (2nd phase) S N
S 3rd film 'Yuu 3 phase) 1st
0 [Li [To[]==≦] Note 1 14th item) 9th
mouth

Claims (2)

[Claims] (1) A brushless DC motor that connects a semiconductor switch to an excitation coil, operates the excitation coil with the semiconductor switch by a rotor magnet, and has a position sensor that selects the semiconductor switch, and the switching operation is controlled by a synthetic torque generated by the motor. In a brushless DC motor whose timing is such that is the torque itself generated by each excitation phase, the coil of each excitation phase is wound so as to include the third harmonic distribution, while the rotor magnet has the same polarity as the main excitation pole. A brushless DC motor, characterized in that a magnet having a number of main rotor poles and a correction rotor pole having three times the same number of poles as the third harmonic is coaxially coupled. (2) The brushless DC motor according to claim 1, wherein the main rotor pole and the correction rotor magnetic pole are the same magnet, and are formed by a magnetized pattern including a non-magnetized zone.