JPH10201285A - Brushless dc motor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To drive the other driving coil on a stator side, by utilizing a voltage obtained by integrating an induction voltage generated in a driving coil on the stator side through rotation of a rotary magnet on the rotor side. SOLUTION: When an induction voltage VA of an A-phase coil 21 and an induction voltage VB of a B-phase coil 22 are integrated through an integration circuit, voltages Vϕ A and Vϕ B proportional to a magnetic flux amount ϕinterlinking to the A-phase coil and B-phase coil are obtained. Since the magnetic flux amount ϕ is generated with a permanent magnet of a rotor 10, its amplitude is, naturally, constant independent of the number of rotations. However, if a sine wave voltage is integrated, a phase is delayed by 90 deg.. Thus, a gate driving voltage GPA obtained by comparison between the voltage Vϕ A which is obtained by integrating VA and a threshold value is used for controlling a semiconductor switch on the B-phase side, and a gate voltage obtained by comparison between the voltage Vϕ B which is obtained by integrating VB and a threshold value is used for controlling a semiconductor switch on A-phase side.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a brushless DC motor, and more particularly, to a brushless DC motor using a voltage obtained by integrating an induced voltage generated in a drive coil on a stator side by rotation of a rotating magnet on a rotor side. And a sensorless brushless DC motor configured to drive another driving coil.

[0002]

[Prior art]

(Structure and operating principle of conventional DC motor)
It is one of the typical motors that have been widely used for more than a hundred years.The rotation speed is determined in proportion to the applied DC voltage, and the speed change is small even if the load torque changes significantly. Most suitable for controlling torque and rotation speed. However, DC motors have only one significant disadvantage. That is, a mechanism for switching the field coil to be energized with the rotation of the rotor, that is, a brush and a commutator (commutator) is required.

[0003] Figure 14 is a diagram for explaining a relationship between a coil of the brush and the commutator and the rotor are welded to the coil C ₁ has its opposite ends a segment S1 of the commutator S4, coils C ₂ is segments S2 and S5, the coil C ₃ at both ends to the segment S3 and S6, are welded. Commutator segments S1 to S6 are:
They are electrically insulated from each other and fixed integrally with the rotor. Also, through the commutator segment,
In order to energize the coil, brushes (carbon + silver particles) B1 and B2 are electrically insulated and fixed to the stator side, and are pressed against the commutator segments by the force of a spring. When a DC voltage V is applied between the brushes B1 and B2, a current flows from the power supply V in the order of brush B1 → segment → coil → segment → brush B2,
As shown in FIG. 15, an electromagnetic force F proportional to the product of the DC magnetic field B generated by the stator and the coil current I is generated, and the rotor of the motor rotates.

When the rotor rotates in the direction of the arrow in FIG.
In turn, the position where there is segment S2 Gamoto segment S1, moves to a position where there is segment S5 Gamoto segment S4, a current flows through the coil C _2. Thus, a current flows through the coil C _2, the interaction of the DC magnetic field stator is made, the driving force is generated in a direction of more rotation of the rotor. This process continues, and the rotor continues to rotate. Since each coil rotates in a DC magnetic field,
When rotating, an induced voltage V _i is generated between the terminals of the coil. When the V _i is the number of turns of the coil and N,

[0005]

(Equation 1)

[0006] φ is the amount of magnetic flux interlinking with the coil, and φ _m is the maximum value (the value of φ when the coil surface is perpendicular to the magnetic field).

[0007]

(Equation 2)

[0008] Here, θ is 0 when the plane is parallel to the coil surface and the magnetic field, and is the angle of the coil measured from here.
If the coil is rotating at a constant angular velocity ω, then θ = ω
Substituting (2) into equation (1)

[0009]

(Equation 3)

## EQU1 ## Therefore, the induced voltage V _i is the angular velocity ω
(Rotational speed). Integrating both sides of equation (3) with t gives:

[0011]

(Equation 4)

From equation (4),

[0013]

(Equation 5)

[0014] next, the coil and the magnetic flux interlinking amount phi, a value obtained by dividing the time integral of the induced voltage V _i in number of turns (integration constant is omitted because it to zero and taking the appropriate integral range).

(Defects of DC Motor) Although the structure and operating principle of the DC motor have been described above, the DC motor has significant disadvantages. Since this disadvantage is a problem which the present invention intends to solve, this disadvantage will be described below. (1) While the rotor is rotating, brushes B1 and B2 may come between segments S1 and S2 and between segments S4 and S5 as shown in FIG. At this time, the coil C ₁ and the coil C ₂ is short-circuited through the segments and brushes, transiently large current flows here. This flows between the brush and the commutator segments, causing the rotor to rotate a little more and at the moment the short circuit breaks, creating a spark which damages the commutator surface. In addition, the brush carbon and silver powder enter the insulating plate between the segments, and if the motor is operated for a long time, the insulation between the segments will gradually deteriorate, eventually overheating the segment and reducing the torque of the motor .

(2) Further, when the rotor is rotated at a high speed, a large centrifugal force is applied to the commutator segments and coils, and the commutator is broken apart. This has been the upper limit of the rotation speed of the DC motor up to now.

[0017]

SUMMARY OF THE INVENTION The present invention eliminates the two drawbacks of the DC motor described above, and replaces the highly reliable motor that rotates at an ultra-high speed with a conventional DC motor having a "rotational speed in a wide range. And the speed drop due to the load torque is small ".

[0018]

According to a first aspect of the present invention, there is provided a stator having a plurality of field windings, and a rotor having a permanent magnet rotatably disposed in the stator. In a brushless DC motor in which the permanent magnet rotates by following a rotating magnetic field generated by the field winding by sequentially switching the current flowing through the magnetic winding, the current is generated in the field winding by the rotation of the permanent magnet. An integration circuit that integrates an induced voltage to be generated, and a comparison circuit that compares an integrated output voltage of the integration circuit with a reference voltage and obtains a pulse voltage corresponding to a period when the integrated output voltage exceeds the reference voltage, The pulse voltage is applied as a drive voltage for another field winding.

According to a second aspect of the present invention, in the first aspect of the present invention, there is provided means for advancing the generation timing of the pulse voltage.

[0020]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The role of a commutator of a DC motor is to switch and select a coil for supplying DC according to the rotational position of a rotor. This function can be solved by detecting the rotational position of the rotor and replacing it with a semiconductor switch. In addition, the problem that the coil wound around the rotor is broken apart by centrifugal force can be solved by providing a simple DC magnetic field (permanent magnet) on the rotor side and providing a coil for generating a rotating magnetic field on the stator side.

The above two points have been considered for a long time. For detecting the position of the rotor magnetic pole, two Hall elements are arranged at a 90-degree offset from each other. The method of selecting has been put to practical use. However, this method has a disadvantage that two conductors for passing a constant DC current to the Hall element and four conductors for transmitting the output voltage of the Hall element are required.

The present invention makes it possible to energize a coil corresponding to the position of the rotor without using an additional element for detecting the position of the rotor.

FIG. 1 is a schematic configuration diagram for explaining the operation principle of a DC motor to which the present invention is applied. A-phase and B-phase windings (coils) 21 and 2 are provided inside a stator core 20.
2 is fixed, and a permanent magnet rotor 10 is arranged inside the coil with a gap between the coil and the rotor.
The shaft 11 is located on the central axis of
Are supported by a frame integral with the stator 20 via bearings.

In the motor having the structure shown in FIG.
When 0 rotates, the permanent magnets N and S of the rotor 10 rotate with respect to the coils 21 and 22, so that, as shown in FIG.
An AC voltage is generated in the coils 21 and 22. V _A is a voltage generated in the A-phase coil 21, and V _B is a voltage generated in the B-phase coil 22.

The principle of the voltage induction is as described above. In FIG. 14, since the drive coil is provided on the stator side and the permanent magnet is provided on the rotor side, the arrangement of the magnet and the coil is replaced with that of FIG. 1, but this is a relative one. Are equivalent.

Further, in the case of FIG. 15, when the surface of the coil C ₁ is parallel to the just the magnetic field of the magnet B, the induced voltage V _i in accordance with the rotation of the magnet is maximized in (3), .omega.t = 0 time,
V _i can be easily understood from the fact that the maximum. When the positional relationship between the coil and the magnetic field is as shown in FIG. 15, when the current flows through the coil, the largest driving torque is generated. The reason is that the force F exerted by the magnetic field B on the current I is proportional to the length l (ell) of the conductor crossing the magnetic field and the number of turns N (the magnetic field B, the current I, and the force F are vector quantities),

[0027]

(Equation 6)

(In the arrangement shown in FIG. 15, the force F determined by equation (6) is perpendicular to B and I and is perpendicular to the coil surface, so that the maximum rotational torque is generated).

From the above, it can be understood that the torque flowing through the coil can be maximized by flowing the current when the electromotive force of the coil is at the maximum phase. For that, FIG.
(A), the a and the induced voltage V _A generated in the coil of the motor and the threshold voltage V _th, the comparator is inputted to the (comparator), V _A> V _th interval (between theta ₁ through? ₂₎ FIG.
The output shown by the solid line in (B) is taken out,
This is applied to the gate of the positive voltage half-wave semiconductor switch of the A-phase semiconductor switch SA shown in FIG. The gate of the A-phase negative voltage half-wave semiconductor switch has a negative half-wave of the A-phase induced voltage, in which the range of | _VA |> | _Vth | is satisfied (θ ₁ + π).
During (θ ₂ + π) (shown by a broken line in FIG. 3B), the output of the negative-side comparator is output, and the output is applied to the gate of the semiconductor switch for negative voltage half-wave.

The semiconductor switch SA shown in FIG. 4 is a bridge type switch combining the semiconductor switch for positive half wave and the semiconductor switch for negative half wave. A similar semiconductor switch SB is also provided on the B-phase side, and the voltages applied to the A-phase coil and the B-phase coil are as shown in FIGS. 5A and 5B.

In principle, this may be as described above, but in an actual case, the rotational speed of the motor must be controlled from a low value to a high value. Therefore, as shown in FIG.
When comparing the induced voltage of each phase coil with the threshold _Vth , the amplitude of both the induced voltage and the threshold voltage _Vth is proportional to the rotation speed, so when the rotation speed must be controlled in a wide range. , Circuit operation is difficult. The present invention eliminates this drawback.

[0032] Now, when integrating the A-phase coil induced voltage V _A and the B phase coil induced voltage V _B shown in FIG. 2 through the integration circuit, a voltage proportional to the amount of magnetic flux φ interlinking to the A-phase coil and B phase coil V _φA and _VφB are obtained. This has already been shown by equation (5). Since the amount of magnetic flux φ is created by the permanent magnet of the rotor, its amplitude is naturally constant irrespective of the rotation speed. However, when the sine wave voltage is integrated, the phase is shifted by 90 ° as shown in FIG. Therefore, the gate drive voltage G _PA obtained by comparing the voltage V _φA obtained by integrating _VA with the threshold value is used to control the semiconductor switch on the B-phase side, and the voltage V _φB obtained by integrating V _B is used. The gate voltage obtained by comparing the threshold voltage and the threshold value is used to control the semiconductor switch on the A-phase side. FIG. 7 shows the induced voltages V _A , V _B
The following shows an example of an electric circuit for obtaining V _φA and V _φB by integrating.

The waveforms of the induced voltages V _A and V _B of the coils of the respective phases are significantly distorted because a driving short-wave voltage is applied. Figure 8 is a diagram showing a circuit example for taking out successfully this, E _i in FIG. 8 (A) is a induced voltage of each phase coil, r is the internal resistance of each phase coil, L is the coil inductance , R are external resistors inserted between each phase coil and the power supply voltage E ₀ . FIG. 8B shows only one phase.

As shown in FIG. 8, X point, Y point,
The voltages between the point Z and the ground are V ₁ , V ₂ , and V ₃ , respectively.
And the current flowing into the coil from the power supply is i, according to Kirchhoff's law,

[0035]

(Equation 7)

Holds. Since the inductance L is small and ignored,

[0037]

(Equation 8)

Is obtained. Therefore, the internal resistance r of the coil
And the external resistance R are measured, V ₁ , V ₂ , and V ₃ are calculated by the arithmetic circuit of FIG. 8B, and the coil induced voltage _Ei can be detected as shown in equation (8). it can. FIG.
The reason why (B) divides V ₁ , V ₂ , and V ₃ into 1/6 by resistance division is to prevent an excessive input from being applied to the operational amplifiers A ₁ , A ₂ , and A _3. Not something.

[0039] Note that the comparator for comparing a voltage V _phi proportional to the magnetic flux waveform obtained by integrating the coil induced voltage E _i and the threshold V _th, as shown in FIG. 9, FIG. 10, the output is OFF
When it is turned ON from, and when it is turned OFF from ON,
There is some difference (hysteresis) ε. Therefore, the phase of the comparator output wave is not symmetrical about the peak value of the magnetic flux waveform, and is slightly delayed by (ε / 2).

In addition, a transient phenomenon occurs in which the rotation of the rotor rapidly decreases when a load is suddenly applied. In such a case, it is desirable that the phase of the gate drive voltage (comparator output) is slightly ahead of the magnetic flux waveform.
As described above, the phase relationship between the gate drive voltage and the magnetic flux waveform can be adjusted slightly arbitrarily as follows.

[0041] Between the A-phase voltage V _A and the B phase voltage V _B, FIG. 1
As shown in FIG. 1, since there is a phase difference of 90 °, V _A is V _B
Of -k times the sum (as voltage, also added as a vector), the than V _A

[0042]

(Equation 9)

The phase advances only by one.

The amount of phase shift θ is constant regardless of the rotation speed (ie, frequency), which is very convenient. Another method, for example, a phase shift circuit consisting of R and C is
Since the frequency dependency is severe, it cannot be used in a wide frequency (rotational speed) range.

Although the description so far has been directed to the case of a two-phase drive motor, as shown in FIG. 11, the voltages (vectors) having different phases are vector-composited by appropriately multiplying the coefficients. This method of generating a voltage of an arbitrary phase regardless of the frequency (rotation speed) can also be used in the case of three-phase driving.

That is, as shown in FIG.
Phase, V _A to the coil induced voltage of phase C, V _B, by integrating the V _c, A, B, _C phases of the magnetic flux waveform voltage _V φA, V φB, V φc
Make any two of For example, if you make a V _.phi.A and V _{[phi] B,} by combining these two vectors, it is possible to make V _A, V _B, V _c and phase voltage.

The coefficients k _1A , k _1B , k _2A ,
k _2B , k _3A , and k _3B are all coefficients and, in terms of the circuit, are values determined by the ratio of resistance division. In the vector synthesis in the figure, the sum of the voltages may be obtained by an adder in terms of a circuit.
Integrating the coil induced voltages of the two phases to produce a magnetic flux waveform voltage interlinking with the coils of the two phases allows the addition circuit to create a voltage for producing a gate drive signal of each phase. Since this voltage has a constant phase and voltage with respect to a large change in frequency (rotational speed), an appropriate gate drive voltage can always be obtained as a comparator output by a constant threshold value. Stable motor rotation can be realized by controlling the phase semiconductor switches.

[0048]

According to the present invention, the commutator can be prevented from being broken or disassembled, which is a drawback of the conventional DC motor.
To realize a highly reliable motor that rotates at an ultra-high speed without impairing the advantages of the conventional DC motor: the rotational speed can be varied over a wide range and the speed drop due to load torque is small. Can be.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram for explaining the operation principle of a DC motor to which the present invention is applied.

FIG. 2 is a diagram for describing a force and an induced voltage generated in a coil.

FIG. 3 is a diagram for explaining a relationship between an induced voltage generated in a coil and a threshold.

FIG. 4 is a diagram for explaining a method of applying a drive voltage of a motor.

FIG. 5 is a diagram for explaining a waveform example of a drive voltage applied to a motor.

FIG. 6 is a diagram for explaining a motor drive voltage according to the present invention.

FIG. 7 is a diagram illustrating an example of a circuit that integrates an induced voltage.

FIG. 8 is a diagram illustrating an example of a motor drive voltage generation circuit.

FIG. 9 is a diagram for explaining hysteresis of a comparison circuit.

FIG. 10 is a diagram for explaining a drive voltage based on the hysteresis shown in FIG. 9;

FIG. 11 is a diagram illustrating an example of a phase shift (phase advance).

FIG. 12 is a diagram illustrating an example of a phase shift (phase advance).

FIG. 13 is a diagram illustrating an example of a phase shift (phase advance).

FIG. 14 is a view for explaining the operation principle of a conventional DC motor.

FIG. 15 is a diagram for explaining a force and an induced voltage generated in a coil.

FIG. 16 is a diagram for explaining a problem of a conventional DC motor.

[Explanation of symbols]

10 ... roller (permanent magnet), 11 ... rotary shaft, 20 ... stator, 21 ... winding, B _1, B ₂ ... brush, C ₁ ~
C ₃ ... coil, S ₁ ~S ₆ ... segment, M ... motor.

Claims (2)

[Claims] A stator having a plurality of field windings; and a rotor having a permanent magnet rotatably disposed in the stator, wherein a current flowing through the field windings is sequentially switched. In a brushless DC motor in which the permanent magnet rotates following a rotating magnetic field generated by a field winding, an integration circuit for integrating an induced voltage generated in the field winding by rotating the permanent magnet; A comparison circuit that compares an integrated output voltage of the integration circuit with a reference voltage and obtains a pulse voltage corresponding to a period in which the integrated output voltage exceeds the reference voltage, and compares the pulse voltage with another field winding. A brushless DC motor, wherein the DC voltage is applied as a drive voltage. 2. The brushless DC motor according to claim 1, further comprising means for accelerating the generation timing of the pulse voltage.