JP2002078371A - Motor drive circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent generation of uneven rotation and vibration by controlling change of torque of a DC brushless motor. SOLUTION: A logic circuit 20 outputs position signals Ha, Hb, Hc which are detected with the Hall elements 14A to 14C provided to the brushless motor 12 and the switching signals UH, UL, VH, VL, WH, WL based on induced signals Ca, Cb, Cc, based on the phases of the voltages u, v, w induced on each phase to drive a switching element 16 of an inverter circuit 18. In this case, the logic circuit executes switching operation in the 120 deg. power feed system by a signal PWM1 and also continuously executes the switching operation a the signal PWM2 before and after above switching operation, in order to change step by step the voltage applied to each phase of the brushless motor. Thereby, a voltage waveform among these phases can be approximated by a sine wave, and thereby change in the torque during rotation can be controlled.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a motor drive circuit used for driving a DC brushless motor.

[0002]

2. Description of the Related Art There is a DC motor as a drive source excellent in controllability and quietness. A drawback of this DC motor is that it has a rectifying mechanism composed of a brush and a commuter. 2. Description of the Related Art In recent years, brushless motors in which contactlessness is achieved by electronically replacing this rectifying mechanism have been widely used.

An inverter circuit is used as a drive circuit for driving such a brushless motor. For example, when driving a three-phase brushless motor, a three-phase bridge circuit is formed using switching elements such as transistors, and the position of the rotor of the brushless motor is detected using parts such as hall elements. , The switching elements are driven to sequentially supply power to the U, V, and W phases.

In driving a three-phase brushless motor, supply of power to each phase is performed as shown in FIGS.
As shown in (C), a 120 ° energization method in which energization at 120 ° and non-energization at 60 ° are repeated in each phase of U, V, and W is generally used. As a result, as shown in FIG. 7D, a predetermined voltage is applied to, for example, each phase of the brushless motor, and a rotating magnetic field is generated. The rotor provided with the permanent magnet is rotated by the rotating magnetic field. FIG. 7D shows an example of a U-V
Shows a schematic of the voltage V _UV of the phase-to-phase.

[0005]

However, in the driving method based on the 120 ° conduction method in which the electric conduction angle is 120 °, the voltage applied to the coils (stator windings) between the phases greatly differs from the sine wave. Therefore, torque fluctuation may occur, which may cause uneven rotation speed and vibration.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-described circumstances, and has as its object to propose a motor drive circuit that suppresses torque fluctuations of a brushless motor, thereby preventing rotation speed unevenness and vibration. In addition, an object of the present invention is to propose a motor drive circuit that can suppress torque fluctuation of a brushless motor without increasing the number of components for detecting the rotational position of a rotor.

[0007]

SUMMARY OF THE INVENTION In order to achieve the above object, the present invention provides a rotating magnetic field formed by applying a voltage to each of a plurality of stator windings to rotate a rotor. A motor drive circuit that rotationally drives a brushless motor, an inverter circuit that applies a voltage to the stator winding by driving a bridge-connected switching element, and a position detection unit that detects a rotational position of the rotor, A first region in which the switching element is switched in an electrical angle range of 120 ° based on a detection result of the position detection means, and a first region in which the switching device is switched in a predetermined electrical angle range continuously from the first region. 2 is set, and the ON time when the switching element is switched in the second area is switched in the first area. Characterized in that it comprises a first and second driving control means for driving the switching element in each region is shorter than the on-time of Rutoki, the.

According to the present invention, a first region having an electrical angle of 120 ° and a second region continuous with the first region are set, and switching is performed between the first and second regions. Drive the element. At this time, the voltage output from the inverter circuit when switching is performed in the second region is set lower than the output voltage when the switching element is driven in the first region.

Accordingly, the voltage waveform applied between the lines of the DC brushless motor can be changed stepwise as compared with the case where the current is supplied by the 120 ° conduction method, and can be approximated to a sine wave.

In a DC brushless motor, a voltage waveform applied between lines is approximated to a sine wave, whereby a change in torque during rotation is suppressed, and occurrence of rotation unevenness (rotational speed unevenness), vibration, and the like are prevented. .

Further, according to the present invention, the position detecting means is provided on the DC brushless motor at a predetermined phase angle.
First position detecting means using a plurality of Hall elements, and second position detecting means for detecting a position of the rotor from voltages induced in each of the plurality of stator windings by rotation of the rotor. And characterized in that:

According to the present invention, the first position detecting means using three Hall elements provided in the DC brushless motor as the position detecting means, and the voltage induced in the stator winding by the rotation of the rotor. The second position detecting means for detecting the position of the rotor from the second position is used.

In order to change the voltage applied between the stator windings stepwise, it is necessary to detect the position of the rotor finely. At this time, increasing the number of Hall elements provided in the DC brushless motor leads to an increase in the cost and size of the DC brushless motor.However, by detecting the position of the rotor from the voltage induced in the stator winding,
It is not necessary to increase the number of Hall elements.

As a result, the cost and size of the DC brushless motor when the torque change is suppressed are not caused.

Further, the present invention provides a determining means for determining whether or not a voltage induced in the plurality of stator windings exceeds a predetermined value, and the determining means determines whether or not the voltage induced in the plurality of stator windings exceeds a predetermined value. When it is determined that the voltage induced in the switching element is within a predetermined range, the switching element is switched within the range of the electrical angle of 120 °.

According to the present invention, when the voltage induced in the stator winding is low, the switching in the second region is stopped. Thus, in a state where the number of rotations is low, such as at the start of rotation, it is possible to drive the DC brushless motor by the normal 120 ° conduction method.

It is to be noted that not only the switching in the second area is stopped, but also the second
May be narrowed. That is, when the rotation speed of the DC brushless motor is extremely low, the switching in the second region is stopped, but the rotation is increased and the voltage induced in the stator winding is increased, so that the switching is induced. Switching may be performed so as to gradually expand the second region in accordance with the voltage.

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings. [First Embodiment] FIG. 1 shows a schematic configuration of a motor drive circuit 10 according to a first embodiment of the present invention.
This motor drive circuit 10 drives a DC brushless motor (hereinafter referred to as “brushless motor 12”).

A three-phase motor is used as the brushless motor 12. When a voltage of a predetermined phase is applied to each of U, V, and W phases, a rotor as a rotor is rotated by a rotating magnetic field generated in a stator winding. It has a general configuration that rotates. The brushless motor 12 has three Hall elements 14A, 14A as detection means for detecting the rotational position of the rotor.
B, 14C. Hall element 14A, 14
Each of B and 14C outputs position signals Ha, Hb and Hc according to the rotation position of the rotor of the brushless motor 12.

The Hall elements 14A, 14B, 14C
2A to 2C, the position signals Ha, Hb, and Hc are provided such that a phase difference of 120 ° in electrical angle occurs between them.

As shown in FIG. 1, the motor drive circuit 10
Are six switching elements 16U _H , 16U _L , 16V _H , 16V _L , using power MOSFET, IGBT, etc.
16W _H and 16W _L (referred to collectively as “switching element 16”) are bridge-connected to form a three-phase inverter circuit 18. The motor drive circuit 10
In the switching element 16U _H, the output of the 16U _L is connected to U-phase of the brushless motor 12, the switching element 1
6V _H , 16V _L and switching elements 16W _H , 16W _L
Are connected to the V-phase and W-phase of the brushless motor 12, respectively.

The motor drive circuit 10 is provided with a logic circuit 20 as a control circuit for the inverter circuit 18, and is connected to a DC power supply 40 such as a battery. The DC power supply 40 supplies a DC power of a predetermined voltage V _B (for example, DC 12 V) for driving the brushless motor 12 to the motor drive circuit 10.

The logic circuit 20 includes the switching element 1
6 and the switching element 16
The switching signal for driving is output. That is,
Circuit 20 includes a switching element 16U._H, 16U_L,
16V_H, 16V_L, 16W_H, 16W_LDrive each of
Switching signal U_H, U_L, V_H, V_L, W_H, W _LTo
Output.

The motor driving circuit 10, the switching element _{16U H, 16U L, 16V H} , 16V L, 16W H, 16
W each switching signal U _H of _L, U _L, V _H,
By switching based on V _L , W _H , and W _L , the power supplied from the DC power supply 40 is supplied to the brushless motor 12. Thereby, the brushless motor 12
Is driven to rotate.

Incidentally, the motor drive circuit 10 has a PW
M signal generation circuits (PWM circuits) 22 and 24 are provided, and the PWM circuits 22 and 24 are connected to the logic circuit 20. Further, the motor drive circuit 10 is provided with an oscillation circuit 26, and this oscillation circuit 26 is connected to each of the PWM circuits 22 and 24.

The oscillating circuit 26 generates a signal of a predetermined cycle. When the signal generated by the oscillating circuit 26 is input to the PWM circuits 22 and 24,
The PWM circuits 22 and 24 output a PWM signal when the switching element 16 is switched. In addition, PWM
The circuit 22 outputs the signal PWM ₁ and outputs the signal PWM ₁
Outputs a signal PWM _2.

The logic circuit 20 includes the switching element 1
Signal PW output from the signal PWM ₁ or PWM circuit 24 is output from the PWM circuit 22 when turning on the 6
Outputting one of M _2. Thus, the switching element 16 is switched by one of the signal PWM ₁ or signal PWM _2.

The switching element 16 outputs the signal PWM ₁ while the oscillation circuit 26 is oscillating a signal of a predetermined frequency.
, And outputs a predetermined voltage (for example, voltage V _B / 2). Further, the PWM circuit 24 is provided with, for example, a 1/2 frequency dividing circuit.
When the switching element 16 is switched by the signal PWM ₂ output from the M circuit 24, the output voltage from the switching element 16 is approximately の of the output voltage when switching is performed by the signal PWM ₁ (for example, V _B /
4). That is, the signal PWM
₂ has a duty ratio of approximately １ ／ of the signal PWM ₁ .

This logic circuit 20 includes a Hall element 1
4A, 14B, and 14C are connected, and the Hall element 1
Position signals Ha, Hb, and Hc output by 4A, 14B, and 14C according to the rotational position of the rotor are input.

On the other hand, the motor drive circuit 10 applied to the present embodiment is provided with an induced voltage detection circuit 28.

The induced voltage detecting circuit 28 includes a comparator 30 for each of the U, V, and W phases of the brushless motor 12.
(Comparators 30A, 30B, 30C). The output terminals of the comparators 30A, 30B, 30C are connected to the logic circuit 20, respectively.

The comparators 30A, 30B, 30
One of the input terminals of C is connected to the U, V, and W phases of the brushless motor 12, and the other of the input terminals is connected to the U, V, and W phases of the brushless motor 12 by a resistor 3.
2 are connected. Thereby, the comparator 3
0A, 30B, and 30C are a neutral point voltage V _N and voltages u induced in each phase of U, V, and W by rotation of the rotor,
v and w are input. The resistor 32 has a neutral point voltage V
_N is approximately 1/2 of the voltage V _B of the DC power supply 18 (V _N = V _B / 2)
It is set to be.

Thus, the comparators 30A, 30B,
Each 30C, the induced voltage u, v, when w becomes greater than the neutral point voltage V _N, the induced signals Ca, Cb, C
Output c. The induced signals Ca, Cb, Cc are input to the logic circuit 20. Thereby, the logic circuit 2
At 0, the rotational position can be detected by the induced signals Ca, Cb, Cc.

The logic circuit 20 includes the Hall elements 14A to 14A.
14c position signal Ha, Hb, Hc and comparator 3
Induction signals Ca, Cb, Cc output from 0A to 30C
, The switching signal U _H , U _L , V _H , V _L , W _H , and W _L are output from the signal PWM ₁ or the signal PWM ₂ to turn on the switching element 16.

Here, as shown in FIGS. 2D to 2F, the induced signals Ca, Cb, and Cc have a phase difference of 120 °.
It has become. Further, each of the induced signals Ca, Cb, and Cc has an ON interval of 180 °.

As shown in FIGS. 2A to 2F, the position signals Ha, Hb, Hc of the Hall elements 14A, 14B, 14C with respect to such induced signals Ca, Cb, Cc.
The Hall elements 14A, 14A, and 14C have a deviation of 30 degrees in electrical angle from the induced signals Ca, Cb, and Cc.
4B and 14C are attached to the brushless motor 12.

The energization method for driving the brushless motor 12 is generally 120 ° energization. The logic circuit 20 of the motor drive circuit 10 is based on the 120 ° conduction method. To this end, the logic circuit 20
Turns on / off each switching element 16 at an energizing timing based on the 120 ° energizing method. Also, the logic circuit 20 switches the switching element 16 at this timing.
Is turned on, the signal PWM ₁ is output, and the signal PWM ₁
The switching element 16 is switched by (first area).

On the other hand, the logic circuit 20 outputs the signal PWM ₁
After stopping before and the signal PWM ₁ outputs a signal P
And it outputs the WM _2. That is, the logic circuit 20 has the second electrical angle on both sides of the first region in the electrical angle range of 180 °.
The switching element 16 is turned on in this range.

That is, as shown in FIGS. 2G to 2L, the logic circuit 20 includes the switching element 16.
Is turned on by the signal PWM ₂ first, then by the signal PWM ₁ , further by the signal PWM ₂ , and then stops the switching. 2 (G) to 2 (L) show switching elements 16U _H , 16U _L , 1
The switching signals U _H , _UL , V _H , when switching each of 6 V _H , 16 V _L , 16 W _H , 16 W _L ,
V _L , W _H , and W _L are shown, respectively.

Here, a logical expression for generating the switching signals U _H , U _L , V _H , V _L , W _H , and W _L in the logic circuit 20 is shown in Expression 1. Logic circuit 20, the switching signal U _H on the basis of the logical expression (1) ~ (6), U L, V H, V L, W H, and outputs the W _L. Note that Equation 1
In the logical formula shown in FIG. 7, "*" is a logical product, "+" is a logical sum, and "/" is negated (NOT).

[0041]

(Equation 1)

[0042] For example, in the switching element 16U _H, the position signal Ha of the Hall element 14A is turned on, and while the position signal Hb of the Hall element 14B is OFF (Ha * / Hb) becomes the first region , the switching element 16U _H is switched by the signal PWM ₁ in this first region. Further, the second period is between the time when the position signal Ha is off and the induction signal Ca is on (/ Ha * Ca) and the time when the position signal Hb and the induction signal Ca are on (Hb * Ca or Ca * Hb). Area, switching element 1
6U _H is switched by the signal PWM ₂ in this second region.

From this, the logic circuit 20 outputs the switching signal U _H based on the logical expression (1) when switching the switching element 16U _H.

In the motor drive circuit 10 configured as described above, for example, the oscillation circuit 26 starts operating while the logic circuit 20 is operating, or the logic circuit is activated while the oscillation circuit 26 is operating. By the operation of 20, the output of the switching signal is started. That is,
The motor drive circuit 10 starts to output a switching signal when the logic circuit 20 and the oscillation circuit 26 are operated by the operation command of the brushless motor 12.

The logic circuit 20 includes Hall elements 14A-
The switching signal U based on the position signals Ha, Hb, Hc of 14C, the induced signals Ca, Cb, Cc output from the induced voltage detection circuit 28 and the above-described logical expressions (1) to (6).
_{H, U L, V H,} V L, W H, and outputs the W _L. This allows
Switching elements 16U _H , 16 of inverter circuit 18
_{U L, 16V H, 16V L} , 16W H, 16W L is switched.

The inverter circuit 18 includes switching elements 16U _H , 16U _L , 16V _H , 16V _L , 16W _H , 16
W _L is, the switching signal _{U H, U L, V H} , V L, W H, W
By switching by _L , the DC power supply 40
Is supplied to the brushless motor 12.

At this time, if the oscillation frequency of the oscillation circuit 26 is constant, the voltage changes depending on (the duty ratio of) the switching signal (see FIGS. 3A to 3C). For example, as shown in FIG. 3 (A), U-phase voltage U _V (switching elements 16U _H, the output voltage of 16U _L),
Stepwise varies between 0 to V _B.

By switching the switching element 16 in this manner, the voltage applied to the brushless motor 12 becomes as shown in FIGS. 3 (D) to 3 (F). That is, the voltage V _UV between the U and V phases, the voltage V _VW between the V and W phases, and the voltage V _WU between the W and U phases are + V _B to + V _B respectively.
Between −V _B , the voltage changes stepwise according to the output voltage of the switching element 16, and the change in voltage is made closer to a sine wave as compared with the 120 ° conduction method (see FIG. 7D).

In the brushless motor 12, the voltages V _UV , V _VW , and V _WU applied between the phases are each approximated to a sine wave, thereby suppressing a change in torque during rotation. Thereby, the rotation speed of the brushless motor 12 is stabilized, and the occurrence of vibration due to uneven rotation speed is prevented.

On the other hand, when the voltage applied between the phases of the brushless motor 12 is changed stepwise so as to approximate a sine wave, there is a method of increasing the number of Hall elements for detecting the rotational position of the rotor. However, increasing the number of Hall elements increases the cost and size due to an increase in the number of components when forming the brushless motor 12.

On the other hand, in the motor drive circuit 10,
An induced voltage detecting circuit 28 is provided as a second position detecting means, and the rotational position of the rotor is detected from a change in voltage induced in each coil of the brushless motor 12. Thus, the brushless motor 12 only needs to be provided with three Hall elements 14A, 14B, and 14C.
The change in torque of the brushless motor 12 and the occurrence of uneven rotation and vibration caused by the change in torque can be suppressed without increasing the cost and size of the brushless motor 12 as compared with the case where 120 ° conduction is performed.

In the motor drive circuit 10, when a DC power supply 40 is used, such as a battery provided in a vehicle such as an automobile, having a constant output voltage, the brushless motor 12 Can be increased. Thereby, in the motor drive circuit 10, the output of the brushless motor 12 can be increased as compared with the conventional 120 ° conduction system.

In the first embodiment described above, the voltage applied to the brushless motor 12 when switching is performed by the signal PWM ₂ is set to approximately １ ／ of the voltage when switching is performed by the signal PWM ₁ . not limited to, as long as it was lower than the output voltage when the switching by at least signals PWM _1.

In the first embodiment, the angle of 120 °
Switching within 30 ° of the electrical angle before and after the power
However, for example, when the signal P is between 30 ° and 150 °,
WM ₁0-30 ° and 1 when switching at
Signal PWM within the range of 50 ° to 180 °₁Switch by
Signal PWM so that_TwoBy switch
Anything can be used. [Second Embodiment] Hereinafter, a second embodiment of the present invention will be described.
Will be described. The basic configuration of the second embodiment is as follows.
The second embodiment is the same as the first embodiment described above.
In the embodiment, the same components as those in the first embodiment have the same reference numerals.
And description thereof is omitted.

FIG. 4 shows a schematic configuration of a motor drive circuit 50 according to the second embodiment. The motor drive circuit 50 is provided with an operation determination circuit 52 as determination means.

As shown in FIG. 5, the operation determination circuit 52
Is constituted by dead zone detection units 54A, 54B, 54C provided for the U, V, and W phases of the brushless motor 12 and a determination unit 56. Note that the dead zone detection unit 5
4A to 54C have the same configuration, and will be described below as the dead zone detection unit 54.

The dead zone detecting section 54 has a comparator 58A for detecting an upper limit and a comparator 58B for detecting a lower limit. One of the input terminals of the comparators 58A and 58B has induced voltages u, v,
w is input, and the upper limit reference voltage Hv or the lower limit reference voltage Lv is input as a reference voltage to the other input terminals of the comparators 58A and 58B.

The dead zone detecting section 54 is provided with a reference voltage generating circuit 66 formed by connecting three resistors 60, 62 and 64 in series. This reference voltage generation circuit 66
When a predetermined voltage (eg, voltage V _B ) is applied, a lower-limit reference voltage Lv is generated between the resistors 62 and 64, and an upper-limit reference voltage Hv is generated between the resistors 60 and 62. The resistor 62 is a variable resistor.
By varying the second resistance value, an upper limit reference voltage Hv and the lower limit reference voltage Lv (Hv across the neutral point voltage V _N>
Has been to V _N> Lv) be able to set.

As shown in FIG. 6A, for example, the induced voltage u depends on the rotation of the brushless motor 12 (rotation of the rotor).
It changes according to. At this time, when the rotation speed is low, the voltage u also decreases (shown by a broken line in FIG. 6A), and as the rotation speed increases, the voltage u also increases (shown by a solid line in FIG. 6A).

Thus, in the dead zone detecting section 54A, for example, when the voltage u is lower than the upper limit reference voltage Hv and higher than the lower limit reference voltage Lv (Hv> u and Lv <u), the comparators 58A and 58B either Also off (output L
o level) (shown by a two-dot chain line in FIG. 6 (A)).

On the other hand, as shown by the solid line in FIG. 6A, when the voltage u exceeds the upper limit reference voltage Hv (u> H
In v), the output of the comparator 58A turns on (Hi level), and when the output drops below the lower limit reference voltage Lv (u <Lv), the comparator 58B turns on. As a result, FIG.
As shown in the figure, the output of the dead zone detection unit 54 (54A) is
Turns on / off according to voltage u.

As shown in FIG. 5, comparators 58A,
An output terminal of the OR circuit 68 is connected to an input terminal of the OR circuit 68, and an output terminal of the OR circuit 68 provided in each of the dead zone detection sections 54 </ b> A to 54 </ b> C is connected to an OR
It is connected to the input terminal of the circuit 70.

Thus, the judging section 56 determines that all of the voltages u, v, w induced at a low rotation speed (rotor rotation speed), such as when the brushless motor 12 is started, are equal to the upper limit reference voltage Hv and the upper limit reference voltage Hv. When the voltage does not exceed the lower limit reference voltage Lv, the output becomes Lo level (off), and the voltage u,
Either v or w is the upper reference voltage Hv or the lower reference voltage L
When the voltage exceeds v, the output becomes Hi level (ON).

OR circuit 70 which is the output terminal of determination section 56
Is connected to a logic circuit 20A provided in place of the logic circuit 20, whereby the determination result of the operation determination circuit 52 is input to the logic circuit 20A as a determination signal REV.

The logic circuit 20A includes a Hall element 14A
~ 14C position signals Ha, Hb, Hc and induced signal C
When switching of the switching element 16 is performed based on a, Cb, Cc, voltages u, v,
If all of w do not exceed the upper limit reference voltage Hv and the lower limit reference voltage Lv, energization is performed by the 120 ° energization method. That is, when the electrical angle is in the range of 120 °, the signal PWM ₁
The switching using is performed.

[0066] Further, the logic circuit 20A, a voltage is induced u, v, when one of w exceeds the upper limit reference voltage Hv and lower limit reference voltages Lv, adding switching using signal PWM _2. As a result, the voltage applied to the brushless motor 12 approaches a sine wave.

That is, the logic circuit 20A outputs the switching signals U _H , _UL , V _H , V _L , W _H , and W _L based on the logical expressions (7) to (12) shown in Expression 2.

[0068]

(Equation 2)

The motor driving circuit 50 thus configured
Then, when the rotation drive of the brushless motor 12 is instructed, the logic circuit 20A causes the Hall elements 14A to 14C
Position signals Ha, Hb, Hc input from the control unit and induced signals Ca, C input from the induced voltage detection circuits 28A to 28C.
The switching element 16 is driven based on b, Cc, and the determination signal REV input from the operation determination circuit 52.

Here, in the motor driving circuit 50, when the rotation driving of the brushless motor 12 is started, the rotation frequency of the brushless motor 12 is increased by gradually increasing the oscillation frequency of the oscillation circuit 26.

On the other hand, since the rotation speed of the brushless motor 12 at the start of rotation (at the time of starting) is low, U,
Voltages u, v, and w induced in each of the V and W phases are low.

The operation judging circuit 52 generates a voltage u induced in each phase by a dead zone detecting section 54 provided for each phase,
It is determined whether or not v and w exceed the upper reference voltage Hv and the lower reference voltage Lv, respectively. At this time, if the voltages u, v, w induced in each phase do not exceed the upper reference voltage Hv and the lower reference voltage Lv, the operation determination circuit 5
4 is at the Lo level (off).

Thus, when the output of the operation determining circuit 52 is turned off, the logic circuit 20A sets the electrical angle to 1
Only the switching using the signal PWM ₁ in the range of 20 ° is performed.

When the rotation speed of the brushless motor 12 is low,
In the induced voltage detection circuit 28 provided for detecting the rotation position of the rotor of the brushless motor 12, the voltages u, v, w input to the comparator 30 are low and the change is unclear. Therefore, the induced signals Ca, Cb, and Cc output from the induced voltage detection circuit 28 may be unstable.

From this, the logic circuit 20A calculates the induced signals Ca, Cb, C from the signal REV of the operation determination circuit 52.
c is determined to be in an unstable state, and induced signals Ca, C
When it is determined that b and Cc are unstable, the Hall elements 14A are used without using the induced signals Ca, Cb and Cc.
Switching using only the position signals Ha, Hb, and Hc by .about.14C is performed.

Thus, in the motor drive circuit 50, the switching elements 16 of the inverter circuit 18 are switched so that the brushless motor 12 is driven by the 120 ° conduction method, and the switching timing of the switching elements 16 of the inverter circuit 18 is switched. In this way, it is possible to reliably prevent the deviation from occurring.

After the driving of the brushless motor 12 is started by the 120 ° conduction method in this way, if the induced voltages u, v, w increase due to the increase in the rotation speed of the brushless motor 12, the operation determination circuit 52 becomes Hi level (ON), and the logic circuit 2
0A, in addition to switching using signals PWM _1,
Switching using the signal PWM ₂ is started.

As a result, the voltage waveform applied between the phases of the brushless motor 12 approaches a sine wave, and the brushless motor 12 is driven to rotate stably.

As described above, in the motor drive circuit 50A,
As in the case of starting the rotation of the brushless motor 12, for example, the range in which the number of rotations is low and the voltages u, v, w induced in each phase do not exceed predetermined voltages (upper reference voltage Hv and lower reference voltage Lv). As the dead zone, the induced voltages u, v, w
Is within this dead zone, the induced voltage u,
By not performing the position detection using v and w, the timing of switching the switching element 16 is shifted, thereby causing problems such as unstable rotation of the brushless motor 12. Thus, the brushless motor 12 can be driven stably from the low rotation state to the rated rotation state.

Also, in the motor drive circuit 50, the output signal REV of the operation determination circuit 52 gradually increases the on-time as the rotational speed increases (the induced voltages u, v, w increase). Since the switching time by the signal PWM ₂ can be gradually increased, the torque change can be suppressed in accordance with an increase in the rotation speed of the brushless motor 12.

The above-described embodiment does not limit the configuration of the present invention. For example, in the present embodiment, if switching is performed so that a voltage lower than that at the time of 120 ° conduction is continuously applied to each phase of the brushless motor 12 before and after switching by the 120 ° conduction method. Any configuration can be applied.

[0082]

As described above, according to the present invention, the voltage applied between the lines of each phase can be approximated to a sine wave, so that the torque fluctuation of the brushless motor can be suppressed and the torque fluctuation caused by the torque fluctuation can be suppressed. Vibration can be reduced. Further, when the voltage of the power supply for driving the brushless motor is the same, the effective voltage applied to the brushless motor can be increased as compared with the conventional 120 ° conduction method, so that the output of the brushless motor can be increased. .

Further, the present invention has an excellent effect that the torque fluctuation of the brushless motor can be suppressed at low cost without increasing the number of components for detecting the rotational position of the rotor.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of a motor drive circuit applied to a first embodiment.

FIGS. 2A to 2C are diagrams schematically illustrating position signals of a Hall element, respectively, and FIGS. 2D to 2F are schematic diagrams of induced signals based on voltages induced in respective phases. The diagrams (G) to (L) are diagrams schematically illustrating switching signals.

FIGS. 3A to 3C are diagrams schematically illustrating voltages applied to respective phases, and FIGS. 3D to 3F are diagrams schematically illustrating voltages applied between respective phases.

FIG. 4 is a schematic configuration diagram of a motor drive circuit applied to a second embodiment.

FIG. 5 is a schematic configuration diagram illustrating an example of an operation determination circuit provided in a motor drive circuit according to a second embodiment.

6A is a diagram schematically showing a voltage induced in each phase of the brushless motor, and FIG. 6B is a diagram schematically showing an output of a dead zone detection unit based on the diagram of FIG. 6A; It is.

FIGS. 7A to 7C are diagrams schematically showing voltage changes applied to U, V, and W phases in a conventional 120 ° conduction system, and FIG. FIG. 3 is a diagram illustrating an example of a voltage to be applied.

[Explanation of symbols]

10,50 motor driving circuit 12 brushless motor 14A~14C Hall element (position detecting means, the first position detection _{means) 16 (16U H, 16U L} , 16V H, 16V L, 16
W _H , 16 W _L ) Switching element 18 Inverter circuit 20, 20A Logic circuit (setting means, drive control means) 28 Induced voltage detection circuit (position detection means, second position detection means) 40 DC power supply 52 Operation determination circuit (determination) means)

Claims (3)

[Claims] 1. A motor drive circuit for rotating a DC brushless motor by applying a voltage to each of a plurality of stator windings to form a rotating magnetic field and rotating the rotor, comprising a bridge connection. An inverter circuit that applies a voltage to the stator winding by driving the switching element, a position detection unit that detects a rotational position of the rotor, and an electric circuit that electrically connects the switching element based on a detection result of the position detection unit. A first region in which the angle is switched in a range of 120 ° and a second region in which the switching element is switched in a range of a predetermined electrical angle continuously from the first region is set, and the switching is performed in the second region. The on-time for switching the element is shorter than the on-time for switching in the first region, and the first and second regions are switched. A motor drive circuit which comprises a driving control means for driving the switching elements in each of. 2. The method according to claim 1, wherein the position detecting means comprises: first position detecting means using three Hall elements provided at a predetermined phase angle in the DC brushless motor; 2. The motor drive circuit according to claim 1, further comprising: second position detection means for detecting a position of the rotor from a voltage induced in each of the stator windings. 3. 3. A determining means for determining whether or not a voltage induced in the plural-phase stator windings exceeds a predetermined value; and a voltage induced in the plural-phase stator windings by the determining means. 3. The motor drive circuit according to claim 1, wherein when it is determined that is within a predetermined range, the electric element switches the switching element within a range of 120 °. 4.