JP2007236090A - Method and apparatus for controlling brushless motor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method and an apparatus for controlling a brushless motor which sufficiently control a rotation at a low speed. <P>SOLUTION: In the method, a rotational speed of the brushless motor is detected (step S01), the rotational speed of the brushless motor is compared with a predetermined rotational speed (step S02), a reference voltage Vref is set to a second reference voltage Vref2 lower than a first reference voltage Vref1 if the rotational speed of the brushless motor is lower than the predetermined rotational speed N1 (step S03), the reference voltage Vref is set to the first reference voltage Vref1 if the rotational speed of the brushless motor is higher than the predetermined rotational speed N1 (step S04), an induced voltage Vm of the brushless motor is compared with the reference voltage Vref, and a position of the brushless motor is detected (step S05). A PWM current of the brushless motor is controlled. The rotation control is implemented by changing the reference voltage Vref in response to the rotational speed of the brushless motor. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a brushless motor control method and control apparatus.

  A sensorless DC brushless motor (hereinafter simply referred to as a brushless motor) is widely used as a motor for driving a compressor of various electric appliances, particularly an air conditioner, taking advantage of its power saving.

Conventionally, in controlling the number of rotations of a brushless motor, rotor position information necessary for the control is detected by using a voltage induced in an armature winding of the brushless motor.
The rotor position is estimated by comparing the induced voltage with a reference voltage, and the current flowing through the armature winding of the brushless motor is controlled based on the detected position.

  However, when the rotation speed of the brushless motor is lowered, the voltage induced in the brush winding of the brushless motor is also lowered, which makes it difficult to detect the position of the rotor and thus causes a false detection. As a result, there is a problem that stable rotation control cannot be performed at low speed.

  On the other hand, a brushless motor control method and control device capable of detecting a position at low speed rotation are known (see, for example, Patent Document 1).

  The brushless motor control method and control apparatus disclosed in Patent Document 1 includes a converter that rectifies an AC power supply by double voltage rectification, inverter means that switches the double voltage rectified DC voltage by PWM control, and applies the brushless motor to a position. And a control circuit that calculates the rotational speed based on the position detection signal from the detection circuit, compares the calculated rotational speed with a predetermined value, and determines whether to switch the converter to the double voltage mode.

  When the rotation speed of the brushless motor is low, the power supply voltage is lowered by setting the mode without voltage doubler and the duty of PWM chopping is increased to control the brushless motor to the target rotation speed.

However, the brushless motor control method and control device disclosed in Patent Document 1 has a problem that control is complicated because both the power supply voltage and the duty of PWM chopping are changed.
Japanese Patent Laid-Open No. 11-32498

  The present invention provides a brushless motor control method and control apparatus that can perform sufficient rotation control at low speed.

  The brushless motor control method according to one aspect of the present invention includes a step of detecting a rotation speed of the brushless motor, and a step of changing a reference voltage for detecting the position of the brushless motor according to the rotation speed of the brushless motor. And comparing the induced voltage of the brushless motor with the reference voltage to detect the position of the brushless motor and controlling the rotation of the brushless motor.

  According to another aspect of the present invention, there is provided a method for controlling a brushless motor, the step of detecting the number of rotations of the brushless motor, and changing the carrier frequency of a pulse-width modulated current flowing in the brushless motor according to the number of rotations of the brushless motor. Comparing the induced voltage of the brushless motor with a reference voltage for detecting the position of the brushless motor, detecting the position of the brushless motor, and controlling the rotation of the brushless motor. It is characterized by.

  The brushless motor control device according to an aspect of the present invention includes a rotation speed detection unit that detects the rotation speed of the brushless motor, and a reference voltage for detecting the position of the brushless motor according to the rotation speed of the brushless motor. A reference voltage changing means for changing, and a current control means for detecting the position of the brushless motor by comparing the induced voltage of the brushless motor and the reference voltage to control the rotation of the brushless motor. Yes.

  According to the present invention, it is possible to obtain a brushless motor control method and control apparatus that can perform sufficient rotation control at low speed.

  Embodiments of the present invention will be described below with reference to the drawings.

  A first embodiment of the present invention will be described with reference to FIGS. FIG. 1 is a circuit diagram showing the configuration of a brushless motor control device according to the present embodiment, FIG. 2 is a timing chart showing the operation of the brushless motor, FIG. 3 is a flowchart showing a control method of the brushless motor, and FIG. FIG. 5 is a diagram showing the effect of this embodiment in comparison with the conventional example.

  As shown in FIG. 1, the motor control device 10 according to the present embodiment compares the induced voltage Vm of the brushless motor 11 with the reference voltage Vref to detect the position of the brushless motor 11, and according to the position of the brushless motor 11. Current control means 12 for controlling the current flowing through the brushless motor 11, rotation speed detection means 13 for detecting the rotation speed of the brushless motor 11, and reference voltage variable means 14 for changing the reference voltage Vref according to the rotation speed of the brushless motor 11. It is equipped with.

  The brushless motor 11 includes a rotor (not shown) having a permanent magnet and, for example, Y-connected electric windings U, V, and W. The rotor rotates by applying a direct current whose phase is shifted by 120 ° to the electric coil windings U, V, and W.

  The rotation speed of the brushless motor 11 is controlled by applying a pulse width modulated current (hereinafter referred to as a PWM current) by intermittently applying a direct current to the electric windings U, V, W at a predetermined carrier frequency. This is done by changing the duty of the PWM current.

  The current control means 12 includes an inverter circuit 15 that supplies a PWM current to the armature windings U, V, and W of the brushless motor 11, a reference voltage generation circuit 16 that generates a reference voltage Vref, and an induced voltage Vm of the brushless motor 11. And the reference voltage Vref, a position signal detection circuit 18 for detecting the position of the brushless motor 11 from the output of the comparator 17, a predetermined carrier frequency determined by the time constant of the capacitor C1 and the resistor R1, and a predetermined duty The PWM control part 19 which generate | occur | produces the PWM signal which has these, and the inverter control part 20 which generates the drive signal which drives the inverter circuit 15 with a PWM signal are comprised.

  In the inverter circuit 15, three series circuits of two transistors, for example, IGBTs (Insulated Gate Bipolar Transistors), are connected in parallel to the power source V0.

  The transistor Ua and the transistor X are connected in series, and the connection point 22 is connected to the electric element winding U of the brushless motor 11. The transistor Va and the transistor Y are connected in series, and the connection point 23 is connected to the electric winding V of the brushless motor 11. The transistor Wa and the transistor Z are connected in series, and the connection point 24 is connected to the electric winding W of the brushless motor 11.

The gates of the transistors Ua, Va, Wa, X, Y, and Z are connected to a driver circuit (not shown) of the inverter control unit 20, respectively.
Further, free-wheeling diodes D1 to D6 are connected in parallel between the collectors and emitters of the transistors Ua, Va, Wa, X, Y, and Z, respectively.

  The reference voltage generation circuit 16 has a series circuit of a resistor R2 and a resistor R3 connected between a power source V0 that drives the brushless motor 11 and a reference potential GND. A connection point 25 between the resistors R2 and R3 is connected to the negative input terminal of the comparator 17.

  The power supply voltage Vo is divided by the resistors R2 and R3, and the reference voltage Vref is generated. The resistors R2 and R3 are set so that the reference voltage Vref is ½ of the power supply voltage V0.

One ends of resistors R4, R5, and R6 are respectively connected to the armature windings U, V, and W of the brushless motor 11, and the other ends of the resistors R4, R5, and R6 are commonly connected to the resistor R7.
A common connection point 26 of the resistors R4, R5, R6 and the resistor R7 is connected to the positive input terminal of the comparator 17.

Since the coil windings U, V, and W of the brushless motor 11 are open at one end when the PWM current is not flowing, an induced voltage proportional to the rotation speed is generated by electromagnetic induction with the rotor.
The induced voltage is divided and combined by the resistors R4, R5, R6 and the resistor R7, and the induced voltage Vm of the brushless motor 11 is obtained.

  The rotational speed detection means 13 receives a signal corresponding to the rotational speed from a rotational speed output circuit (not shown) in the inverter control unit 20, and outputs “H” when the rotational speed is larger than a predetermined rotational speed N1, When the rotational speed is smaller than N1, “L” is output.

  The reference voltage varying means 14 has an inverter 21 to which the output of the rotation speed detecting means 13 is supplied, a gate G1 connected to the output terminal of the inverter 21, and a drain D1 connected to a resistor R2 and a resistor R3 via a resistor R8. 25, and an insulated gate field effect transistor M1 (hereinafter referred to as a MOS transistor) having a source S1 connected to a reference potential GND.

When the output of the rotation speed detection means 13 is “H”, the output of the inverter 21 is “L”, so that no voltage is applied to the gate G1 of the MOS transistor M1, and the MOS transistor M1 is turned off.
When the output of the rotation speed detection means 13 is “L”, the output of the inverter 21 is “H”, so that a voltage is applied to the gate G1 of the MOS transistor M1, and the MOS transistor M1 is turned on.
When the MOS transistor M1 is on, a parallel circuit of the resistor R3 and the resistor R8 is formed, and the voltage dividing ratio of the power source V0 to the resistor R2 changes, so that the reference voltage Vref is changed.

Specifically, as shown in FIG. 2, the reference voltage Vref when the rotation speed of the brushless motor 11 is higher than the rotation speed N1 is set as the first reference voltage Vref1, and the reference voltage Vref when the rotation speed is lower than the rotation speed N1 is set as the second voltage. Assuming that the reference voltage Vref2 is used, the first reference voltage Vref1 and the second reference voltage Vref2 are expressed by the following equations.
Vref1 = V0 × R3 / (R2 + R3)
Vref2 = V0 × Ra / (R2 + Ra), Ra = R3 × R8 / (R3 + R8)
Here, Ra is a parallel resistance of R3 and R8.

  Next, rotation control of the brushless motor 11 will be described using a timing chart. The brushless motor control device 10 first outputs a predetermined drive signal from the inverter control circuit 20 to the inverter circuit 15 to start the brushless motor 11, and then detects the position of the brushless motor 11 to perform rotation control.

  As shown in FIG. 3, the position of the brushless motor 11 is detected by comparing the voltage appearing at the connection point 26 including the induced voltage Vm induced in the non-energized coil with the reference voltage Vref. The position signal detection circuit 18 extracts only the output corresponding to the target position detection signal from the output of the comparator 17.

  The position of the rotor is detected based on the position detection signal, and the energized phase is switched 30 ° after this position detection. Note that “after 30 °” is, for example, a time calculated and predicted by the position detection interval time × 30/360.

  Specifically, when the intersection point 31 between the terminal voltage (induced voltage Vmu) of the armature winding U and the reference voltage Vref is detected, the energization of the Wa phase (transistor Wa) to the energization of the Ua phase (transistor Ua) after 30 °. Switch to. Here, the PWM waveform is displayed only on the terminal voltage of the armature winding U and a part of the transistor Ua.

  When the intersection 32 between the terminal voltage (induced voltage Vmw) of the armature winding W and the reference voltage Vref is detected, the energization of the Y phase (transistor Y) is switched to the energization of the Z phase (transistor Z) after 30 °.

  When the intersection 33 between the terminal voltage (induced voltage Vmv) of the armature winding V and the reference voltage Vref is detected, the energization of the Ua phase (transistor Ua) is switched to the energization of the Va phase (transistor Va) after 30 °.

  When the intersections 34, 35, 36 between the terminal voltages (induced voltages) of the armature windings U, V, W and the reference voltage Vref are detected again, the energized phases are switched after 30 °.

  Similarly, the brushless motor 11 can be rotationally controlled by repeatedly switching the energized phase of the brushless motor 11 based on the position detection signal.

  Here, the voltage applied to the brushless motor 11 can be changed by changing the duty of the PWM current flowing through each of the transistors Ua, Va, Wa, X, Y, and Z.

  Therefore, by detecting the rotational speed of the brushless motor 11 by the rotational speed detection means 13 and changing the duty of the PWM current by the inverter drive unit 20, the brushless motor 11 can be controlled to a target rotational speed.

  Here, the pulse-like output included in the output of the comparator 17 is due to the current flowing during the ON period of the free-wheeling diodes D1 to D6. Since the position signal detection circuit 18 recognizes this and rejects it, it does not affect the rotation control of the brushless motor 11.

  Next, a method for controlling the brushless motor 11 using the brushless motor control device 10 of the present embodiment will be described using a flowchart.

As shown in FIG. 4, the brushless motor 11 is first activated by a predetermined drive signal (step S00).
Next, after the brushless motor 11 is started and the rotation is stabilized, the rotation number detecting means 13 detects the rotation number of the brushless motor 11 (step S01), and the obtained rotation number and a predetermined predetermined rotation number N1. Are compared (step S02).

When the rotation speed of the brushless motor 11 is smaller than the predetermined rotation speed N1 (Yes in Step S02), the reference voltage Vref is set to the second reference voltage Vref2 smaller than the first reference voltage Vref1 by the reference voltage varying means 14. (Step S03).
On the other hand, when it is larger than the predetermined rotation speed N1 (No in step S02), the reference voltage variable means 14 sets the reference voltage Vref to the first reference voltage Vref1 (step S04).

  Specifically, as shown in FIG. 2, if the rotation speed is larger than a predetermined rotation speed N1, for example, 50 rpm, the first reference voltage Vref1 = V0 / 2 (neutral point voltage) is set. If the rotation speed is smaller than the predetermined rotation speed N1, The second reference voltage Vref2 is, for example, V0 / 4.

  Next, the induced voltage Vm and the reference voltage Vref are compared by the comparator 17, and the intersections 31 to 36 between the induced voltage Vm and the reference voltage Vref are detected to detect the position of the flashless motor 11 (step S05).

  Next, according to the detection position of the flashless motor 11, each transistor Ua, Va, Wa, X, Y, Z of the inverter circuit 15 is turned on and off to control the PWM current flowing in the electric element windings U, V, W. (Step S06).

  Next, the presence / absence of an operation stop command for the brushless motor 11 is checked (step S07). If there is no operation stop command (No in step S07), the process returns to step S01 and steps S01 to S06 are repeated. On the other hand, when there is an operation stop command (Yes in step S07), the operation of the brushless motor 11 is stopped.

  FIG. 5 is a timing chart showing the effect of this embodiment in comparison with the conventional example. FIG. 5A shows the case of this embodiment, and FIG. 5B shows the case of the conventional example. The figure shows the case of the armature winding U.

  As shown in FIG. 5, the induced voltage Vmu of the brushless motor 11 is proportional to the rotation speed of the brushless motor 11, so that the induced voltage Vmu decreases as the rotation speed of the brushless motor 11 decreases.

In this embodiment, the reference voltage Vref is changed and set to the second reference voltage Vref2, so that the comparator 17 detects the intersection 37 and the intersection 38 between the induced voltage Vmu of the brushless motor 11 and the second reference voltage Vref2. Can do.
As a result, the rotation of the brushless motor 11 can be controlled by detecting the position of the brushless motor 11 at low speed.

  On the other hand, when the conventional first reference voltage Vref1 is maintained without changing the reference voltage Vref, there is no intersection between the induced voltage Vmu of the brushless motor 11 and the first reference voltage Vref1, so the position of the brushless motor 11 Cannot be detected. As a result, rotation control of the brushless motor 11 cannot be performed at low speed.

  FIG. 6 is a diagram showing a semiconductor integrated device in which the brushless motor control device 10 of this embodiment is monolithically integrated on the same semiconductor chip.

  As shown in FIG. 6, the semiconductor integrated device 40 includes a current control unit 12 that controls the current of the brushless motor 11, a rotation number detection unit 13 that detects the rotation number of the brushless motor 11, and a reference that changes the reference voltage Vref. The voltage variable means 14 is monolithically integrated on the same semiconductor chip 41.

Furthermore, bonding pads 42 a to 42 g for connecting the semiconductor integrated device 40 to the outside are formed on the semiconductor chip 41.
The power supply Vdd is supplied to the semiconductor integrated device 40 through the bonding pad 42a, and is connected to the common potential GND through the bonding pad 42b.
A PWM current is supplied to the electric windings U, V, and W of the brushless motor 11 through the bonding pads 42c to 42e, and an induced voltage Vm of the brushless motor 11 is input.
A power supply V0 applied to the brushless motor 11 is supplied to the semiconductor integrated device 40 through the bonding pads 42f and 42g.

  As described above, in this embodiment, the reference voltage Vref for detecting the position of the brushless motor 11 is changed according to the rotation speed of the brushless motor 11.

  As a result, the position of the brushless motor 11 can be detected by detecting the intersection between the induced voltage Vm of the brushless motor 11 and the reference voltage Vref. Therefore, sufficient rotation control can be performed at low speed.

Although the case where the resistor R8 is connected in parallel to the resistor R3 and the reference voltage Vref is changed has been described here, the resistor R3 and the resistor R8 may be switched by a switch 45 as shown in FIG. As a switching element of the switch 45, a MOS transistor or a mechanical relay can be used.
This has the advantage that the resistors R3 and R8 can be set independently without affecting each other.

  Moreover, although the case where the reference voltage Vref is changed to two stages of the first reference voltage Vref1 and the second reference voltage Vref2 has been described, the number of stages may be further increased. If the number of stages is increased, there is an advantage that the rotation control of the brushless motor 11 can be performed more finely.

Furthermore, although the case where the rotation speed detecting means 13, the reference voltage varying means 14, the resistors R1 to R9, and the capacitor C1 are all incorporated in the semiconductor integrated device 40 has been described, they may be externally attached.
According to this, it is easy to quickly provide a brushless motor control device adapted to the specifications of the brushless motor and the purpose of use of the user.

  Although the case where the armature windings U, V, and W of the brushless motor 11 are Y-connected has been described, rotation control can be similarly performed even in the case of delta connection.

  A second embodiment of the present invention will be described with reference to FIGS. FIG. 8 is a circuit diagram showing the configuration of the brushless motor control device according to the present embodiment, FIG. 9 is a diagram showing changes in the carrier frequency of the PWM current, FIG. 10 is a flowchart showing a brushless motor control method, FIG. 11 and FIG. 12 is a diagram showing the effect of the present embodiment in comparison with the conventional example.

  In the present embodiment, the same components as those in the first embodiment are denoted by the same reference numerals, description thereof will be omitted, and only different portions will be described.

  The difference between the present embodiment and the first embodiment is that the carrier frequency of the PWM current is changed according to the rotational speed.

That is, as shown in FIG. 8, the brushless motor control device 50 of this embodiment includes a carrier frequency varying means 51.
The carrier frequency varying means 51 has an inverter 52 to which the output of the rotation speed detecting means 13 is supplied, a gate G2 connected to the output terminal of the inverter 52, and a drain D2 connected to the resistor R1 of the PWM controller 19 via the resistor R9. The MOS transistor M2 is connected to one end and the source S2 is connected to the reference potential GND.

When the output of the rotation speed detection means 13 is “H”, the output of the inverter 52 is “L”, so that no voltage is applied to the gate G2 of the MOS transistor M2, and the MOS transistor M2 is turned off.
When the output of the rotation speed detection means 13 is “L”, the output of the inverter 52 is “H”, so that a voltage is applied to the gate G2 of the MOS transistor M2, and the MOS transistor M2 is turned on.
As a result, a parallel circuit of the resistor R1 and the resistor R9 is formed, and the CR time constant (τ = 1 / ωCR) of the PWM control unit 19 is changed, so that the PWM carrier frequency f can be changed.

Specifically, as shown in FIG. 9, since the PWM carrier frequency f is proportional to the inverse of the CR time constant τ, the CR time constant τ when the rotation speed of the brushless motor 11 is higher than the rotation speed N1 is set to τ1, If the carrier frequency f at that time is the first carrier frequency f1, the CR time constant τ is smaller than the rotation speed N1, and the carrier frequency f at that time is the second carrier frequency f2, then the first carrier frequency f1 and the second carrier frequency f2 are expressed by the following equations.
f1∝1 / τ1 = ωC1R1
f2∝1 / τ2 = ωC1Rb
Here, Rb is a parallel resistance of R1 and R9. From this, the second carrier frequency f2 lower than the first carrier frequency f1 can be obtained.

Next, the control method of the brushless motor 11 of the present embodiment will be described using a flowchart.
As shown in FIG. 10, the rotational speed of the brushless motor 11 is compared with a predetermined rotational speed N1 (step S02), and the rotational speed of the brushless motor 11 is smaller than the predetermined rotational speed N1 (Yes in step S02). Then, the carrier frequency changing means 51 sets the carrier frequency f to the second carrier frequency f2 smaller than the first carrier frequency f1 (step S13).

  On the other hand, if it is greater than the predetermined rotation speed N1 (No in step S02), the carrier frequency variable means 51 sets the carrier frequency f to the first carrier frequency f1 (step S14).

  FIG. 11 is a diagram showing the effect of this embodiment in comparison with the conventional example. FIG. 11A shows the case of this embodiment, and FIG. 11B shows the case of the conventional example. The figure shows the case of the armature winding U.

  As shown in FIG. 11, in the present embodiment, the PWM carrier frequency f is lowered and set to the second carrier frequency f2, so that the induced voltage Vmu of the brushless motor 11 is increased, and the first reference voltage Vef1 is reduced. The intersections 55 and 56 can be detected by the comparator 17. Thereby, the position of the brushless motor 11 can be detected and the rotation control of the brushless motor 11 can be performed.

  On the other hand, in the conventional example, since the carrier frequency f of the PWM current remains the first carrier frequency f1, there is no intersection between the induced voltage Vmu of the brushless motor 11 and the first reference voltage Vref1, and the position of the brushless motor 11 is detected. I can't. As a result, the rotation control of the brushless motor 11 cannot be performed.

  Further, FIG. 12 is an enlarged view showing the vicinity of the intersection 55 of the induced voltage Vmu and the reference voltage Vref1 in FIG. 11, FIG. 12 (a) is the case of this embodiment, and FIG. 12 (b) is the case of the conventional example. .

  As shown in FIG. 12, since the armature windings U, V, W of the brushless motor 11 are inductive loads, the induced voltage Vm of the brushless motor 11 rises later than the PWM current, and the waveform has a waveform with respect to the PWM waveform. It's slowing down.

  However, since the PWM waveform on-period t2 is long in this embodiment, the induced voltage Vm of the brushless motor 11 can rise to a level exceeding the first reference voltage Vref1 during the PWM waveform on-period.

  On the other hand, since the on period t1 of the PWM waveform is short in the conventional example, the induced voltage Vm of the brushless motor 11 cannot rise to the level of the first reference voltage Vref1 during the on period of the PWM waveform.

  As described above, in this embodiment, the carrier frequency f of the PWM current flowing through the brushless motor 11 is changed according to the rotation speed of the brushless motor 11.

  As a result, the time during which the induced voltage Vm of the brushless motor 11 is generated becomes longer and the induced voltage Vm increases, so that the position of the brushless motor 11 can be detected by detecting the intersection with the reference voltage Vref. Therefore, sufficient rotation control can be performed at low speed.

  Although the case where the carrier frequency f of the PWM current is changed to two stages of the first carrier frequency f1 and the second carrier frequency f2 has been described here, the number of stages may be further increased. If the number of stages is increased, there is an advantage that the rotation control of the brushless motor 11 can be performed more finely.

  Further, although the case where the carrier frequency f of the PWM current is controlled by charging / discharging by the resistor R1 and the capacitor C1 has been described, other control methods may be used. In this case, the carrier frequency varying means must be adapted to other control methods.

  A third embodiment of the present invention will be described with reference to FIGS. FIG. 13 is a circuit diagram showing the main configuration of the brushless motor control apparatus according to the present embodiment, FIG. 14 is a flowchart showing a control method of the brushless motor, and FIG. 15 is a diagram showing the control operation of the brushless motor.

  In the present embodiment, the same components as those in the first embodiment are denoted by the same reference numerals, description thereof will be omitted, and only different portions will be described.

  The difference between the present embodiment and the first embodiment is that both the reference voltage Vref and the carrier frequency f are changed according to the rotational speed.

  That is, as shown in FIG. 13, the brushless motor control device 60 of this embodiment includes a rotation speed detection means 61, a reference voltage variable means 14 that changes the reference voltage Vref according to the rotation speed of the brushless motor 11, and a carrier frequency. Carrier frequency varying means 51 for changing f is provided.

The rotational speed detection means 61 outputs “H” to the carrier frequency variable means 51 when the rotational speed of the brushless motor 11 is larger than the predetermined rotational speed N1, and outputs “L” when the rotational speed is smaller than the predetermined rotational speed N1. "Is output.
Further, the rotation speed detection means 61 outputs “H” to the reference voltage variable means 14 when the rotation speed of the brushless motor 11 is larger than the predetermined rotation speed N2 (N1> N2), and the predetermined rotation speed. When it is smaller than N2, “L” is output.

Next, the control method of the brushless motor 11 of the present embodiment will be described using a flowchart.
As shown in FIG. 14, the rotational speed of the brushless motor 11 is compared with a predetermined rotational speed N1 (step S02), and when the rotational speed of the brushless motor 11 is smaller than the predetermined rotational speed N1 (Yes in step S02). The carrier frequency changing means 51 sets the carrier frequency f to the second carrier frequency f2 smaller than the first carrier frequency f1 (step S23).

  On the other hand, when the rotation speed of the brushless motor 11 is greater than the predetermined rotation speed N1 (No in step S02), the carrier frequency f is set to the first carrier frequency f1 by the carrier frequency variable means 51 (step S24).

  Next, the rotational speed of the brushless motor 11 is compared with a predetermined rotational speed N2 (step S25), and when the rotational speed of the brushless motor 11 is smaller than the predetermined rotational speed N2 (Yes in step S25), the reference voltage is variable. The reference voltage Vref is set to the second reference voltage Vref2 smaller than the first reference voltage Vref1 by the means 14 (step S26).

  On the other hand, when the rotation speed of the brushless motor 11 is greater than the predetermined rotation speed N2 (No in step S25), the reference voltage variable means 14 sets the reference voltage Vref to the first reference voltage Vref1 (step S27).

As shown in FIG. 15, the induced voltage characteristic 62 at the first carrier frequency f1 cannot rise sufficiently because the on-period of the PWM waveform is short, and shows a low value.
For this reason, when the rotational speed is lower than N1, the position of the brushless motor 11 cannot be detected and rotation control cannot be performed.

  Therefore, by changing the carrier frequency f to the second carrier frequency f2 at the predetermined rotation speed N1, the induced voltage characteristic 63 at the second carrier frequency f2 can be obtained, so that the brushless motor has a rotation speed between N1 and N2. 11 positions can be detected and rotation control can be performed. However, if the rotational speed is further lower than N2, the position of the brushless motor 11 can be detected and rotation control cannot be performed.

  Therefore, by changing the reference voltage Vref from the first reference voltage Vref1 to the third reference voltage Vref3 higher than the second reference voltage Vref2 at a predetermined rotation speed N2, the brushless motor 11 has a rotation speed between N2 and Nmin. Rotation control can be performed. Here, Nmin is the minimum number of rotations that requires rotation control.

  Since the reference voltage Vref is as close to ½ of the power supply voltage V0 as possible, the objectivity of the detection position of the brushless motor 11 is maintained, so that smoother rotation control can be performed.

  As described above, in this embodiment, both the reference voltage Vref and the carrier frequency f are changed according to the rotation speed of the brushless motor 11. As a result, there is an advantage that smoother rotation control can be performed at low speed.

Although the case where the reference voltage Vref is set to the third reference voltage Vref3 higher than the second reference voltage Vref2 has been described here, the reference voltage Vref may be set to the second reference voltage Vref2.
According to this, there is an advantage that the position of the brushless motor 11 can be detected even at a lower rotational speed and the rotation can be controlled.

  Moreover, although the case where the reference voltage Vref is changed after changing the carrier frequency f has been described, the carrier frequency f may be changed after changing the reference voltage Vref.

The circuit diagram which shows the structure of the control apparatus of the brushless motor which concerns on Example 1 of this invention. The figure which shows the change of the reference voltage which concerns on Example 1 of this invention. 3 is a timing chart showing a control operation of the brushless motor according to the first embodiment of the invention. 1 is a flowchart showing a method for controlling a brushless motor according to Embodiment 1 of the present invention. The figure which shows the effect which concerns on Example 1 of this invention compared with a prior art example. 1 is a diagram illustrating a semiconductor integrated device in which brushless motor control devices according to Embodiment 1 of the present invention are integrated on the same chip. FIG. FIG. 3 is a circuit diagram showing another reference voltage variable circuit according to the first embodiment of the present invention. The circuit diagram which shows the structure of the control apparatus of the brushless motor which concerns on Example 2 of this invention. The figure which shows the change of the carrier frequency which concerns on Example 2 of this invention. The flowchart which shows the control method of the brushless motor which concerns on Example 2 of this invention. The figure which shows the effect which concerns on Example 2 of this invention compared with a prior art example. The figure which shows the effect which concerns on Example 2 of this invention compared with a prior art example. The circuit diagram which shows the principal part structure of the control apparatus of the brushless motor which concerns on Example 3 of this invention. 10 is a flowchart illustrating a method for controlling a brushless motor according to a third embodiment of the invention. The figure which shows control operation of the brushless motor which concerns on Example 3 of this invention.

Explanation of symbols

10, 50, 60 Brushless motor control device 11 Brushless motor 12 Current control means 13, 61 Rotation speed detection means 14 Reference voltage variable means 15 Inverter circuit 16 Reference voltage generation circuit 17 Comparator 18 Position detection circuit 19 PWM control section 20 Inverter control section 21, 52 Inverters 31 to 38 Intersection point of induced voltage and reference voltage 40 Semiconductor integrated device 41 Semiconductor chips 42a to 42g Bonding pad 45 Switch 51 Carrier frequency variable means 62 Induced voltage characteristic at first carrier frequency 63 At second carrier frequency Induced voltage characteristics R1 to R9 Resistor C1 Capacitor V0 Power supply Vm Induced voltages U, V, W Electron windings Ua, Va, Wa, X, Y, Z Transistor Vref Reference voltage Vref1 First reference voltage Vref2 Second reference voltage V ef3 third reference voltage f carrier frequency f1 first carrier frequency f2 second carrier frequency M1, M2 MOS transistors N1, N2 rpm

Claims (5)

Detecting the number of rotations of the brushless motor;
Changing a reference voltage for detecting the position of the brushless motor according to the number of rotations of the brushless motor;
Detecting the position of the brushless motor by comparing the induced voltage of the brushless motor and the reference voltage, and controlling the rotation of the brushless motor;
A control method for a brushless motor, comprising: Changing the reference voltage comprises:
When the rotational speed of the brushless motor is greater than a predetermined rotational speed, the reference voltage is set to a first reference voltage;
2. The method of controlling a brushless motor according to claim 1, wherein when the rotational speed of the brushless motor is smaller than a predetermined rotational speed, the brushless motor is set to a second reference voltage lower than the first reference voltage. Detecting the number of rotations of the brushless motor;
Changing the carrier frequency of the pulse-width modulated current flowing in the brushless motor according to the number of rotations of the brushless motor;
Detecting the position of the brushless motor by comparing the induced voltage of the brushless motor and a reference voltage for detecting the position of the brushless motor, and controlling the rotation of the brushless motor;
A control method for a brushless motor, comprising: Changing the carrier frequency comprises:
When the rotational speed of the brushless motor is greater than a predetermined rotational speed, the carrier frequency is set to a first carrier frequency;
4. The method of controlling a brushless motor according to claim 3, wherein the carrier frequency is set to a second carrier frequency lower than the first carrier frequency when the rotational speed of the brushless motor is smaller than a predetermined rotational speed. . A rotational speed detecting means for detecting the rotational speed of the brushless motor;
Reference voltage variable means for changing a reference voltage for detecting the position of the brushless motor according to the number of rotations of the brushless motor;
A current control means for detecting the position of the brushless motor by comparing the induced voltage of the brushless motor and the reference voltage, and controlling the rotation of the brushless motor;
A brushless motor control apparatus comprising:

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