JP2000350485A - Brushless motor drive circuit and brushless motor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a brushless motor which is operable over a wide rotational region, while decreasing the number of signal lines by driving the brushless motor in sine wave PWM system at a low speed and driving it in square wave PWM system at high speed. SOLUTION: A drive circuit 10 comprises a speed control circuit 20, performing current control at low speed using the signal from a Hall sensor 70 and performing speed control at a high speed. When the reverse voltage level of a coil increases due to high speed rotation, a brushless motor is driven in square-wave PWM system by detecting the timing of three-phase 120 deg. conduction from the correlation voltage of counter-electromotive force in coils of phase U, phase V and phase W. During low-speed rotation, where the level of counter-electromotive force is low, the coils of the phase U, phase V and phase W are driven in sine wave PWM system respectively different in phase by 120 deg., based on the detection signal of phase U of one Hall sensor 70. According to the arrangement, the brushless motor can be controlled correctly from a high speed to a low speed, using a single Hall sensor and can be driven smoothly over the entire rotational region, while suppressing pulsation.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a brushless motor and a drive circuit for controlling the brushless motor.

[0002]

2. Description of the Related Art A drive circuit for driving a brushless motor at a variable speed is a Hall IC mounted on the brushless motor.
Thus, the timing of the excitation switching of each phase coil is detected.

[0003]

Here, wiring to a Hall IC having three Hall sensors for a three-phase motor is as follows.
Five wires are required for the power line, the ground line, and the signal line of each Hall sensor. That is, in the three-phase motor, five wires for the Hall IC are required in addition to the three power lines.
For this reason, when the DC brushless motor is used for a hand-operated device such as a dental cutting machine (handpiece) used for dental treatment, the operability of the handpiece itself deteriorates due to the large number of wires. In addition, the frequency of failures due to disconnection also increased.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and has as its object to reduce the number of signal lines and to drive a brushless motor in a wide rotation range. It is to propose a brushless motor using a circuit.

[0005]

In order to achieve the above object, according to the present invention, a rotor having a field magnet, a first phase and a second phase for rotating the rotor are provided.
A brushless motor drive circuit comprising: a stator having a phase and a third phase coil; and at least one position detection sensor for detecting a relative position between the rotor and the stator, wherein the brushless motor rotates at a low speed. In some cases,
The first phase, second phase, and third phase coils are respectively set to 1 based on detection signals of the at least one position detection sensor.
It is driven by a sine wave PWM method with different phases by 20 °,
When rotating the brushless motor at high speed, the first
The three-phase 120 ° conduction timing is detected from the correlation voltage of the back electromotive force of the phase, second phase, and third phase coils, and the square wave PW
It is a technical feature that it is driven by the M method.

According to a second aspect of the present invention, in the first aspect, when driving in the low-speed rotation region, the at least one
Detection signals of the position detection sensors, the first phase and the second
A technical feature is that the phases are compared with a sine wave drive signal applied to one of the phase and third phase coils, and torque control is performed based on the phase difference.

[0007] The invention according to claim 3 is the invention according to claim 1 or 2.
In the above, switching between the sine wave drive in the low-speed rotation range and the square-wave drive in the high-speed rotation range is performed at a timing when the back electromotive voltages of the first, second, and third phase coils cross zero. Performing is a technical feature.

According to a fourth aspect of the present invention, in the third aspect, the timing at which the back electromotive force of the first phase, second phase, and third phase coils crosses zero is defined as the first phase, the second phase, and the third phase, respectively. It is a technical feature of the present invention that the voltage component between the coil current and the resistance of the coil is subtracted from the voltage appearing between the phases to detect the voltage.

According to a fifth aspect of the present invention, in the first to fourth aspects, in the square-wave PWM method at the time of high-speed rotation, a speed is detected from a detection signal of the position detection sensor, and a difference between the command speed and the detection speed is calculated. It is a technical feature that the speed is controlled in accordance with the speed.

A sixth aspect of the present invention is characterized in that, in any of the first to fifth aspects, the position detection sensor is a hall sensor.

A seventh aspect of the present invention is characterized in that the driving circuit is used in any of the first to sixth aspects.

According to the first aspect, when the brushless motor is rotated at a high speed, that is, when the level of the back electromotive voltage of the coil is increased, the correlation between the back electromotive voltages of the first, second and third phase coils is obtained. The timing of three-phase 120 ° conduction is detected based on the voltage, and driving is performed by the square wave PWM method. On the other hand, during low-speed rotation when the level of the back electromotive voltage is low, the first phase, second phase, and third phase coils are shifted by 120 ° each in a different sine based on the detection signal of one position detection sensor. It is driven by the wave PWM method. Therefore, the brushless motor can be appropriately controlled from a high speed to a low speed. In addition, since control is performed based on one position detection sensor, the number of signal lines can be reduced. Further, when the brushless motor is rotated at a low speed (less than a predetermined rotation speed), the brushless motor is driven by a sine wave PWM method, and the brushless motor is rotated at a high speed (more than a predetermined rotation speed).
When the motor is rotated by the square wave PWM method, the brushless motor can be driven smoothly with little torque pulsation in the entire rotation range from low speed (0) to high speed (tens of thousands of rotations).

According to a second aspect of the present invention, at the time of a low speed rotation range, a detection signal of at least one position detection sensor and a sine wave drive applied to one of the first, second and third phase coils. Since the phase with the signal is compared and the torque control is performed based on the phase difference, even if there is a load change, the control can be performed appropriately without step-out.

According to the third aspect, the switching between the sine wave driving in the low-speed rotation region and the square wave driving in the high-speed rotation region is performed by the first method.
Since switching is performed at the timing when the back electromotive voltages of the phase, second phase, and third phase coils cross zero, switching can proceed smoothly.

According to the present invention, the timing at which the back electromotive voltages of the first phase, second phase, and third phase coils cross zero is determined from the voltage appearing between the first phase, second phase, and third phase. Since the voltage component due to the coil current and the resistance of the coil is subtracted and detected, the zero-cross timing can be properly detected.

According to the fifth aspect, at the time of high-speed rotation, the speed is detected from the detection signal of the position detection sensor, and the speed is controlled in accordance with the difference between the command speed and the detected speed, so that the speed can be accurately controlled.

According to the sixth aspect, since a hall sensor is used as the position detection sensor, the configuration can be inexpensive.

According to the present invention, since the brushless motor includes a drive circuit, the number of signal lines can be reduced and the brushless motor can be driven in a wide rotation range.

[0019]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a three-phase brushless motor using a drive circuit according to the present invention will be described below with reference to the drawings. First, a three-phase brushless motor built in the dental treatment handpiece of the first embodiment will be described with reference to FIG. 1 showing a mechanical configuration and FIG. 2 showing a configuration of a drive circuit. The brushless motor 40 is driven at 40,000 revolutions / minute during tooth grinding, and during tooth root treatment.
It is driven at a very low speed of 100 revolutions / minute.

As shown in FIG. 1, a brushless motor 40
Is provided with a stator 60 made of a ceramic sleeve on the outer periphery of a rotor 50 made of a ceramic sleeve.
And form a radial static pressure bearing. On the outer periphery of the rotor 50, four field magnets 5
2, the brushless motor 40 is
It has four poles. On the outer circumference of the stator 60, U
The phase 62, V phase, and W phase coils 62 (see FIG. 2) are attached. Further, a yoke 69 is provided outside the coil 62. Magnets 54A and 54B are arranged at the right end and the left end of the rotor 50 in the drawing, and the movement of the rotor 50 in the thrust direction is restricted by the repulsive force with the magnets 64A and 64B attached to the stator 60 side. You. Note that a Hall sensor 70 (see FIG. 2) for detecting the polarity of the field magnet 52 is attached to the brushless motor. The U-phase detection signal detected by the Hall sensor 70 is sent to the drive circuit 10 via one signal line 78.

As shown in FIG. 2, the drive circuit 10 includes a power supply circuit 12 for supplying power for driving the brushless motor 40 and power for the control circuit, and a PWM control based on a control signal given from the speed control circuit. , A PWM voltage control circuit 14 for controlling a voltage supplied to the three-phase bridge circuit 16, and switching of energization to U-phase, V-phase, and W-phase coils by a control signal from the PWM voltage control circuit 3. A phase bridge circuit 16, an excitation signal generating circuit 18 for switching a control mode from a low speed to a high speed, and a current (torque) at a low speed based on a signal from the Hall sensor 70.
And a speed control circuit 20 for performing speed control at high speed. The three-phase bridge circuit 16 includes a U-phase
Power is supplied to the coil 62 via the three power lines 74 of the phase and the W phase. On the other hand, electric power is supplied from the power supply circuit 12 to the Hall sensor 70 via the power supply line and the ground line 76.

In the drive circuit of the brushless motor of the present embodiment, since only the U-phase signal from the Hall sensor 70 is transmitted through one signal line 78, the brushless motor (dental treatment handpiece) 40-drive circuit The number of signal lines between 10 can be reduced by two. For this reason, in addition to facilitating the handling of the dental treatment handpiece, it is possible to reduce the incidence of failure due to disconnection.

In the brushless motor driving circuit of the present embodiment, when the brushless motor rotates at high speed, that is, when the level of the back electromotive voltage of the coil increases, the U phase, V
Phase and W-phase coil correlated voltage of back electromotive force
The timing of 0 ° conduction is detected, and driving is performed by the square wave PWM method. On the other hand, during low-speed rotation when the level of the back electromotive voltage is low, the U-phase, V-phase, and W-phase coils are shifted by 120 ° from each other based on the U-phase detection signal of one Hall sensor 70, and the sine waves having different phases are applied. It is driven by the wave PWM method. For this reason, the brushless motor can be appropriately controlled from a high speed to a low speed by one Hall sensor 70. Furthermore,
When the brushless motor rotates at a low speed (less than a predetermined number of rotations), it is driven by a sine wave PWM method. When the brushless motor rotates at a high speed (more than a predetermined number of rotations), it is driven by a square wave PWM method. Therefore, in the entire rotation range from low speed (0) to high speed (tens of thousands of rotations), the brushless motor can be driven smoothly with little torque pulsation.

The PWM voltage control circuit 14, the three-phase bridge circuit 16, and the excitation signal generation circuit 18 shown in FIG. 2 will be described in further detail below. Here, first, the circuit configuration of the three-phase bridge circuit 16 will be described with reference to FIG. The three-phase bridge circuit 16 includes three upper-stage FET1, FET3, and FET5 connected to the power supply Vcc side, and lower-stage FET2, FET4, and FET6 connected to the ground side.
And a bridge circuit comprising: Six photocouplers FC1 to FC6 for turning on and off the upper and lower FET1 to FET6 are connected to the upper and lower FET1 to FET6, respectively.

The input of the photocoupler FC1 for turning on / off the upper side FET1 is + 15V via the diode D1.
, And the output side of the photocoupler FC1 is connected to the gate side of the FET1. A resistor R1 is connected in series with the photocoupler FC1. This photocoupler FC1 and resistor R1
And a lower-stage FET2 is connected in series with the capacitor C1.

The input of the photocoupler FC2 for turning on / off the lower side FET2 is + 15V via the diode D2.
And the output side of the photocoupler FC2 is connected to the gate side of the FET2 and to the ground through a resistor R2.
The upper FET 1 and the lower FET 2 are connected in series, and are configured so that a current is applied to the U phase of the coil 62 of the brushless motor from the connection point between the FET 1 and the FET 2.

The operation of the three-phase bridge circuit 16 will be described. Here, when a current flows through the W phase-U phase of the stator coil, a signal from the PWM voltage control circuit 14 (at low speed) or the excitation signal generating circuit 18 (at high speed) shown in FIG. The photocouplers FC5 and FC2 are turned on, and the upper FET5 is turned on by the photocoupler FC5 and the lower FE is turned on by the photocoupler FC2.
T2 is turned on, and the power supply voltage Vcc is applied to the W phase-U phase of the stator coil. That is, a current flows in the order of Vcc-FET5-W-phase of coil-U-phase (not shown) -FET2-resistor R7-ground. At this time, + 15V FET
The current from the control voltage line flows to the FET2 side via the diode D1 and the capacitor C1, and the capacitor C1
Stores electric charges of the polarity shown in FIG.

Next, when applying a current to the U-phase to V-phase of the stator coil, the signals from the PWM voltage control circuit 14 or the excitation signal generation circuit 18 cause the photocouplers FC1, FC4
Is turned on. Here, when the photocoupler FC1 is turned on, the electric charge charged in the capacitor C1 when the FET2 is turned on passes through the photocoupler FC1 to the FET1.
To turn on the FET1. On the other hand, when the photocoupler FC4 is turned on, a current from the FET control voltage line of +15 V flows to the ground side via the diode D4, the photocoupler FC4, and the resistor R4, and the potential divided by the resistor R4 is applied to the FET4. Join the gate side,
The FET 4 is turned on. When the FET1 and the FET4 are turned on, the power supply voltage Vcc is applied to the U-phase-V-phase coil. When the FET 4 is turned on, the capacitor C3 is charged to the polarity shown in the figure.

When a current flows through the V-U phase of the stator coil, the photocouplers FC3 and FC6 are turned on. Here, when the photocoupler FC3 is turned on, the capacitor C3
The FET3 is turned on by the electric charge charged in the FET3. On the other hand, when the photocoupler FC6 is turned on, the FET 6 is turned on.
When the FETs 3 and 6 are turned on, the power supply voltage Vcc is applied to the U-phase to W-phase coils. When the FET 6 is turned on, the capacitor C5 is charged to the polarity shown in the figure. When the above-described W phase is excited by this electric charge, the upper-stage FET 5 is turned on.

As described above, the lower-stage photocouplers FC2, FC4, and FC6 enable the lower-stage FET2,
4. When the FET6 is turned on, the lower FET, FET
4. Capacitors C1 and C connected in series to FET6
3, C5 is charged respectively, and using the charged electric charge,
The upper photocouplers FC1, FC3, and FC5 sequentially turn on the upper FET1, FET3, and FET5. For this reason, in the present embodiment, the upper and lower FETs 1 to 6 of the three-phase power conversion circuit can be controlled by a single power supply (+15 V FET control voltage).

Next, the operation when the brushless motor is stopped will be described. The PWM voltage control circuit 14 shown in FIG. 2 monitors a signal from the Hall sensor 70. Here, the PWM voltage control circuit 14 determines that the signal from the Hall sensor 70 does not change for a predetermined time or more,
When the rotation stop of the brushless motor is detected, the upper photocouplers FC1, FC3, FC5 of the photocoupler three-phase bridge circuit 16 shown in FIG. 2 are all turned off, and the lower photocouplers FC2, FC4, FC6 are turned on, and the motor is turned off. Short-circuit braking. That is, it switches to the charging sequence. Thus, the capacitors C1, C3, and C5 connected in series to the FET2, FET4, and FET6 are all charged.

When the brushless motor is restarted, one of the upper and lower photocouplers is turned on to excite any of the U-phase, V-phase and W-phase coils. Here, in the present embodiment, the upper FET
1. Since the capacitors C1, C3, and C5 for turning on the FET3 and the FET5 are all kept in the charged state during the stop, the upper stage FE is turned on by turning on the photocoupler.
T1, FET3, and FET5 can be immediately turned on.

That is, in the configuration shown in FIG. 2, when the brushless motor is stopped, the lower side FET2, FET4, FET6
Is not switched to the conducting state, the capacitors C1,
The charges stored in C3 and C5 are gradually discharged. Even after the brushless motor is stopped for a long time, even if the photocouplers FC1, FC3, and FC5 floating from the ground are turned on, the FET1, FET3, and FET5 are turned off unless the potential is applied from the capacitors C1, C3, and C5. Cannot turn on. On the other hand, in the power conversion circuit of the first embodiment, the capacitors C1 and C1
3 and C5 are all charged, so that the electric charge stored in the capacitor causes the upper FET1, FET3, F3
Since the ET5 can be turned on, the brushless motor can be quickly restarted even after being stopped for a long time.

Next, the configuration of the excitation signal generating circuit 18 will be described. When the brushless motor rotates at high speed, the excitation signal generation circuit 18 detects the timing of the three-phase 120 ° conduction based on the correlation voltage of the back electromotive voltages of the U-phase, V-phase, and W-phase coils. That is, in a general drive circuit, the Hall IC detects the timing of switching the energization of the U-phase, V-phase, and W-phase coils, whereas in the present embodiment, the U-phase, V-phase, and W-phase are used. The timing of energization switching is detected from the back electromotive voltage of the phase coil. Further, the excitation signal generating circuit 18 switches between sine wave driving in a low speed rotation range and square wave driving in a high speed rotation range. This switching is performed at the timing when the back electromotive voltage of the coil crosses zero.
A voltage component between the coil current and the resistance of the coil is subtracted from the voltage appearing between the phase and W-phase coils, and detected.

The reason for subtracting the voltage due to the coil current and the resistance of the coil from the voltage appearing at the coil will be described below. The reverse voltage of each coil is eu, ev,
ew, the inductance between lines is L, the resistance between lines is R,
The coil supply voltage is Vu, Vv, Vw, and the coil current is i
Assuming u, iv, and iw, the following equations 1 to 3 hold.

## EQU1 ## Vu-Vv = L (d (iu-iv) / dt) + R
(Iu-iv) + eu-ev

## EQU2 ## Vv-Vw = L (d (iv-iw) / dt) + R
(Iv-iw) + ev-ew

Vw-Vu = L (d (iw-iu) / dt) + R
(Iw-iu) + ew-eu

FIG. 4 shows the line voltage and the reverse voltage when the motor is driven in the H-type bridge circuit described above with reference to FIG. Here, as described above, the switching between the sine-wave drive in the low-speed rotation region and the square-wave drive in the high-speed rotation region is performed at the timing when the back electromotive voltage of the coil crosses zero. This prevents vibration or the like from occurring in the brushless motor at the time of switching. That is, in the square-wave drive (6-step drive), the rotating magnetic field rotates stepwise at an electrical angle of 60 °. On the other hand, in the sine wave driving, the electric field rotates smoothly based on the driving voltage, and the rotor rotates in synchronization with the rotation. Therefore, in order to switch the driving method at a rotation speed at which there is almost no phase difference between the driving voltage and the coil current,
It is preferable to switch when the rotating magnetic field is at a position created during square wave driving. As a result, the driving method can be switched without torque pulsation. In the present embodiment, the rotation speed of the brushless motor is a predetermined rotation (2000 to 3000 rp).
In m), when the position is related to the rotor (the zero cross point of the back electromotive voltage), the driving method is switched.

In the present embodiment, the following calculation is performed to detect the zero cross point. The reverse voltage is expressed by the above equation
It can be obtained from Equations 4, 5, and 6 obtained by transforming Equation 3.

Eu-ev = Vu-Vv-L (d (iu-iv) / d
t) -R (iu-iv)

Ev-ew = Vv-Vw-L (d (iv-iw) / d
t) -R (iv-iw)

## EQU6 ## ew-eu = Vw-Vu- (d (iw-iu) / d
t) -R (iw-iu)

The back electromotive voltage is obtained by subtracting the voltage generated in the inductance and the voltage generated in the winding resistance from the line voltage as shown in Expressions 4 to 6. Since the brushless motor of the present embodiment has a small inductance and a large coil resistance, the value of the inductance is ignored.

The timing of switching the coil energization based on the back electromotive voltage and the timing of zero crossing of the back electromotive voltage are detected, and the sine wave driving in the low speed rotation region and the square wave driving in the high speed rotation region are performed. Is switched by the excitation signal generating circuit 18 in FIG. The configuration of the excitation signal generation circuit 18 will be described with reference to FIG.

The excitation signal generating circuit 18 detects the current detection value (R
· Two-stage inverting amplifiers OP1 and OP for detecting the voltage dv generated in the coil from
P2 and an operational amplifier OP3 for detecting a voltage of Vv-Vw
An operational amplifier OP4 for detecting a voltage of Vu-Vv,
An operational amplifier OP5 for detecting the voltage of Vw-Vu, and a comparator CP1 for subtracting the output (-dv) of the inverting amplifier OP1 from the output (Vv-Vw) of the operational amplifier OP3.
And a comparator CP2 that adds the output (+ dv) of the inverting amplifier OP2 from the inverted output − (Vu−Vv) of the operational amplifier OP4, and the output (Vw−) of the operational amplifier OP5.
A comparator CP3 that subtracts the output (−dv) of the inverting amplifier OP1 from Vu), a comparator CP4 that adds the output (+ dv) of the inverting amplifier OP2 from the inverted output − (Vv−Vw) of the operational amplifier OP3, From the output (Vu-Vv) of the operational amplifier OP4, the inverting amplifier OP
A comparator CP5 for subtracting the output (-dv) of 1;
It comprises a comparator CP6 for adding the output (+ dv) of the inverting amplifier OP2 from the inverted output-(Vw-Vv) of the operational amplifier OP5, and a CPLD (Complex Programmable Logic Device).

The CPLD switches between synchronous operation and sensorless driving based on a command from the microprocessor. The switching is performed at a timing at which the voltage obtained by subtracting the voltage drop due to the resistance and the current from the inter-phase voltages of the first phase, the second phase, and the third phase crosses zero. In the present embodiment, the rotation speed of the brushless motor is 2000 to 3000 r.
When the speed is equal to or less than pm, the synchronous operation by the sine wave PWM signal is performed. On the other hand, when the rotation speed becomes equal to or higher than 2000 to 3000 rpm, the output is switched to the output of the excitation signal generation circuit 16 and the sensorless driving is performed. When the switching is performed, the CPLD performs the following operation based on FIG. (1) Wait until CP1 becomes H, and when it becomes H, Se
The excitation signal of ction2 is output, and the process proceeds to the next (2). (2) Wait until CP2 becomes H, and when it becomes H, Se
The excitation signal of ction3 is output, and the process proceeds to the next (3). (3) Wait until CP3 becomes H, and when it becomes H, Se
The excitation signal of ction4 is output, and the process proceeds to the next (4). (4) Wait until CP4 becomes H, and when it becomes H, Se
The excitation signal of ction5 is output, and the process proceeds to the next (5). (5) Wait for CP5 to become H, and when it becomes H, Se
The excitation signal of ction6 is output, and the process proceeds to the next (6). (6) Wait for CP6 to go high, and when it goes high, Se
The excitation signal of ction1 is output, and the process returns to the first step (1). The calculation of the back electromotive voltage for determining the commutation point has the relationship shown in FIG. 7 in one section. The excitation data shown in FIG. 7 is Tr6, Tr5, Tr4, Tr
3, ON / OFF of Tr2 and Tr1.
1 is ON and 0 is OFF. Numerical values in [] are data represented by hexadecimal numbers.

Subsequently, the operation of the PWM voltage control circuit 14 will be further described. The PWM voltage control circuit 14
The control signals of the square wave PWM method at high speed and the sine wave PWM method at low speed are formed. This operation will be described with reference to the waveform diagram of FIG. First, the control operation of the drive circuit at the time of high-speed rotation of the brushless motor will be described. The brushless motor drive circuit performs speed feedback control by detecting the number of rotations based on a signal from the hall sensor 70 at the time of high-speed rotation exceeding 3000 rotations / minute. At this time, a current is applied to the coil using a square wave PWM method based on a three-phase 120 ° conduction type.

That is, the PWM voltage control circuit 14 inputs a signal (the number of rotations of the brushless motor) by which the Hall sensor 70 detects the polarity of the field magnet 52 and a speed command value via the speed control circuit 20, and Is generated to generate a DA signal obtained by converting the rotation speed of the brushless motor into a voltage value. Then, the DA signal is compared with a triangular wave from a triangular wave generating circuit (not shown), and FIG.
A square wave PWM signal as shown in (b) is generated. When the actually measured speed is equal to the target speed at a constant cycle T (20 KHz), a rectangular wave having a short wave width t1 is output as shown in FIG. When the actual measurement speed is low, a long rectangular wave having a wave width t1 'is output as shown in FIG.

The excitation signal generation circuit 18 sets the timing of conducting to the coil 62 based on the above-mentioned back electromotive force by 120 °.
A drive signal for the three-phase bridge circuit 16 is generated based on the conduction type, and based on the PWM output from the PWM voltage control circuit 14 shown in FIGS. At the time of high rotation, since the number of rotations is directly detected and feedback is performed, high rotation accuracy can be realized.

Next, the operation of the PWM voltage control circuit 14 during ultra-low speed rotation of the brushless motor (several rotations / minute) will be described. The brushless motor drive circuit is 2000 to 30
At the time of low-speed rotation of less than 00 rotations / minute, the brushless motor is controlled by switching from the above-described square-wave PWM method of speed feedback control at the time of high-speed rotation to a sine-wave PWM method of torque feedback control. That is, the load is detected based on the phase difference between the magnetic pole position and the coil excitation voltage waveform (for the U phase), and the PWM duty ratio is adjusted according to the phase difference (load) so that the phase difference does not exceed 60 °.

Here, the PWM voltage control circuit 14 detects the load based on the phase difference between the magnetic pole position and the coil excitation voltage waveform at low speed rotation, and excites the coil of the brushless motor so that the phase difference does not exceed 60 °. I do. At this time, the PWM voltage control circuit 14 combines two sine waves and a triangular wave as shown in FIG.
A sine wave PWM signal shown in (f) is generated. This sine wave PWM signal has three phases, each having a phase difference of 120 °. The PWM signal directly controls the control of the three-phase bridge circuit 16. In the first embodiment, since the load is detected and feedback is performed so as to control the torque by flowing a current corresponding to the load, it is possible to prevent a step-out that easily occurs at low rotation speed. In the present embodiment, since the sine wave PWM signal is applied, the rotation can be performed smoothly, and no step-out occurs.

In this embodiment, the Hall sensor 7
Although the U phase is detected using 0, the above operation can also be realized by detecting the V phase or the W phase. Further, in the present embodiment, the Hall sensor is used to detect the relative position between the stator and the rotor, but various sensors capable of detecting the position may be used instead.

[0048]

As described above, according to the present invention, since the control is performed based on at least one position detection sensor, the number of signal lines can be reduced. Further, when the brushless motor rotates at a low speed (less than a predetermined number of rotations), the brushless motor is driven by a sine wave PWM method. When the brushless motor rotates at a high speed (more than a predetermined number of rotations), a square wave PWM method is used. Therefore, the brushless motor can be driven smoothly with little torque pulsation in the entire rotation range from low speed (0) to high speed (tens of thousands of rotations).

[Brief description of the drawings]

FIG. 1 is a sectional view showing a configuration of a brushless motor according to a first embodiment.

FIG. 2 is a block diagram of a brushless motor drive circuit according to a first embodiment of the present invention.

FIG. 3 is a circuit diagram of the three-phase bridge circuit shown in FIG.

FIG. 4 is a waveform diagram of a line voltage and a back electromotive voltage.

FIG. 5 is a block diagram of an excitation signal generation circuit shown in FIG. 2;

FIG. 6 is a waveform diagram showing a signal for sine wave PWM control and a signal for square wave PWM control formed by the PWM voltage control circuit shown in FIG. 2;

FIG. 7 is a chart showing rules for determining commutation points.

[Explanation of symbols]

 Reference Signs List 10 brushless motor drive circuit 12 power supply circuit 14 PWM voltage control circuit 16 three-phase bridge circuit 18 excitation signal generation circuit 20 speed control circuit 40 brushless motor 62 coil 70 Hall sensor 78 signal line

 ────────────────────────────────────────────────── ─── Continuing from the front page (72) Inventor Takehiro Higuchi 1-1, Ibikawa-cho, Ibi-gun, Gifu Prefecture F-term (reference) in the north factory of Ibiden Co., Ltd. 5H560 BB04 BB08 DA02 DA13 DA17 EB01 EC01 EC07 UA02 XA03 XA05 XA12

Claims (7)

[Claims] 1. A rotor having a field magnet, a stator having first, second, and third phase coils for rotating the rotor, and at least detecting a relative position between the rotor and the stator. A brushless motor drive circuit comprising: one position detection sensor, wherein when the brushless motor rotates at a low speed, the first phase and the second phase are detected based on a detection signal of the at least one position detection sensor. When the two-phase and third-phase coils are each driven by a sine wave PWM method having a different phase by 120 °, and the brushless motor is rotated at a high speed, the first
The three-phase 120 ° conduction timing is detected from the correlation voltage of the back electromotive force of the phase, second phase, and third phase coils, and the square wave PW
A brushless motor drive circuit characterized by being driven by the M system. 2. When driving in the low-speed rotation range, a detection signal of the at least one position detection sensor and the first signal
2. The brushless apparatus according to claim 1, wherein a phase is compared with a sine wave drive signal applied to one of the phase, second phase, and third phase coils, and torque control is performed based on the phase difference. 3. Motor drive circuit. 3. The method according to claim 1, wherein the switching between the sine-wave driving in the low-speed rotation region and the square-wave driving in the high-speed rotation region is performed by the first switch.
3. The brushless motor driving circuit according to claim 1, wherein the driving is performed at a timing when the back electromotive voltages of the phase, second phase, and third phase coils cross zero. 4. The timing at which the back electromotive force of the first phase, second phase, and third phase coils crosses zero based on the voltage appearing between the first phase, second phase, and third phase. 4. The brushless motor driving circuit according to claim 3, wherein a voltage component based on the current and the resistance of the coil is subtracted and detected. 5. In the square wave PWM method at the time of high-speed rotation, a speed is detected from a detection signal of the position detection sensor,
5. The brushless motor driving circuit according to claim 1, wherein the speed is controlled in accordance with a difference between the command speed and the detected speed. 6. The brushless motor driving circuit according to claim 1, wherein the position detection sensor is a Hall sensor. 7. The brushless motor according to claim 1, wherein the drive circuit is used.