JP2000287480A - Control method of brushless motor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To eliminate ripple components of a reluctance torque which are contained in an induced voltage and avoid erroneous position detection in the position detection of a brushless motor which generates also a reluctance torque. SOLUTION: A DC power supply is switched by a plurality of transistors of a transistor matrix unit 3 and applied to a brushless motor 4 to control the rotation of the brushless motor 4. At that time, in a position detection circuit 10, an induced voltage (imaginery neutral voltage) generated in the non- current-application phase of the motor 4 is obtained by a synthesizer circuit 5a, and the induced voltage is applied to a low-pass filter 10a to eliminate the ripple components of a reluctance torque. The induced voltage is then compared with a reference voltage generated by a voltage generating circuit 5b by a comparison circuit 5c, and the comparison result is outputted to a control circuit 6 as a position detection signal.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a position detecting technique for detecting the position of a rotor using an induced voltage generated in a non-energized phase of a brushless motor, and more particularly, to a position detecting technique for detecting a position of a rotor in response to generation of reluctance torque. The present invention relates to a control device for a brushless motor that performs appropriate position detection by removing a ripple superimposed on a voltage.

[0002]

2. Description of the Related Art Inverter control of a brushless motor requires, for example, an apparatus shown in FIG.
Is converted to DC by an AC / DC converter 2, and this converted DC power is switched by a transistor matrix unit 3 and supplied to a brushless motor 4 as a three-phase AC. Further, the position of the rotor is detected by a position detection circuit 5, and a signal of the position detection is input to a control circuit (microcomputer) 6, and the control circuit 6 drives the transistors of the transistor / matrix section 3 to drive the stator. Switch the winding current.

As a method of detecting the position, for example, there is a method of detecting a zero cross point from a back electromotive force (induced voltage) waveform induced in a non-energized phase, and detecting the position of the rotor based on the zero cross point. Therefore, the position detection circuit 5 combines the terminal voltages of the armature windings U, V, and W with the combining circuit 5a.
The voltage is divided to obtain a voltage waveform (virtual neutral point voltage) corresponding to the neutral point voltage of the motor, and the virtual neutral point voltage (that is, the induced voltage) and a predetermined voltage (reference voltage) generated by the voltage generating circuit 5b. ) Is compared by a comparison circuit 5c, and the comparison result is output to a control circuit (microcomputer) 6 as a position detection signal.

When the PWM control method is adopted, the control circuit 6 generates a PWM waveform for switching the energization of the armature winding based on the position detection signal.
The drive signal of the WM waveform is output to the transistor matrix unit 3 via the drive circuit 7. As a result, each of the transistors Ua, Va,
Wa, X, Y, and Z are turned on and off in a predetermined manner, and the energization of the armature winding of the brushless motor 4 is switched.

By the way, as a brushless motor, not only the magnet torque but also the magnet torque is required from the viewpoint of increasing the efficiency of the motor.
One that also uses reluctance torque has been proposed.
For example, a magnetic path from one q-axis to the other q-axis from the stator is secured in consideration of the shape and arrangement of the magnet embedded in the rotor, and a slit is formed along the magnetic path to form d.
If the difference between the axis and the q-axis inductance is increased, reluctance torque can be generated.

[0006]

However, when the reluctance torque is used in the brushless motor, ripples (higher harmonics) are superimposed on the induced voltage due to the interaction between the slots of the stator 1 and the reluctance torque. An induced voltage including a ripple which is a pulsating component of the reluctance torque is generated (see FIG. 6A). For this reason, erroneous position detection due to ripple occurs (because erroneous energization switching is performed), which hinders smoothness of motor rotation control and causes the worst step-out. For example, when 24 slots are used as a stator in a three-phase four-pole motor, as shown in FIGS.
It can be seen that the ripple included in the induced voltage is the eleventh harmonic (eleventh harmonic).

The present invention has been made in view of the above problems, and has as its object to remove ripples (higher harmonics) superimposed on an induced voltage due to the influence of reluctance torque.
An object of the present invention is to provide a brushless motor control method capable of preventing erroneous position detection.

[0008]

SUMMARY OF THE INVENTION In order to achieve the above object, the present invention provides a brushless motor that generates at least reluctance torque by comparing an induced voltage generated in a non-energized phase with a reference voltage by a comparing means. A method of controlling a brushless motor that obtains a detection signal, detects a position of a rotor by the position detection signal, and switches energization of an armature winding of the brushless motor, and removes a ripple that is a pulsating component of the reluctance torque. For this purpose, a low-pass filter is provided in a stage preceding the comparing means to remove a ripple included in the induced voltage.

According to the present invention, a position detection signal is obtained by comparing a reference voltage with an induced voltage generated in a non-energized phase of a three-phase four-pole brushless motor that generates at least reluctance torque, and a position detection signal is obtained. A method of controlling a brushless motor that switches the energization of an armature winding of the brushless motor by detecting a position of a rotor, wherein the comparing means removes a high-order harmonic that is a pulsating component of the reluctance torque. And a cut-off frequency of the low-pass filter is set so as to remove at least the eleventh harmonic.

[0010] The cutoff frequency of the low-pass filter may be varied according to the number of revolutions of the brushless motor. Thereby, regardless of the number of rotations of the brushless motor, the ripple included in the induced voltage can be appropriately removed.

According to the present invention, at least a position detection signal is obtained by comparing an induced voltage generated in a non-energized phase of a brushless motor generating reluctance torque with a reference voltage, and a position detection signal is obtained by the position detection signal. A brushless motor control method for switching the energization of an armature winding of the brushless motor by detecting a ripple, which is a pulsating component of the reluctance torque. Using variable resistance means for varying the input resistance of the active filter circuit, switching the resistance value of the variable resistance means according to the rotation speed of the brushless motor, and varying the cutoff frequency of the active filter circuit. Wherein the ripple contained in the induced voltage is removed. There.

Further, information for varying the cutoff frequency in accordance with the rotational speed is empirically obtained in advance and stored in a storage means, and a predetermined time is required for detecting the position of the rotor by the position detection signal. When masking the position detection, the cutoff frequency may be switched in a region of the same mask. Thereby, switching of the cutoff frequency of the active filter circuit is performed without adversely affecting the rotation control.

According to the present invention, a position detection signal is obtained by comparing an induced voltage generated at least in a non-energized phase of a brushless motor generating reluctance torque with a reference voltage, and a position detection signal is obtained based on the position detection signal. And a brushless motor control method for switching the energization of an armature winding of the brushless motor, wherein a low-pass switched capacitor IC is provided before the comparing means in order to remove a ripple which is a pulsating component of the reluctance torque. The cut-off frequency of the switched capacitor IC is varied according to the number of revolutions of the brushless motor to remove a ripple included in the induced voltage.

Further, in order to vary the cut-off frequency of the switched capacitor IC, the clock frequency is empirically determined in advance and stored in a storage means in the form of a table, and the switched capacity is referred to in accordance with the rotation speed by referring to the table. The cutoff frequency of the filter IC may be changed. Thereby, regardless of the number of rotations of the brushless motor, the ripple included in the induced voltage can be appropriately removed.

When the brushless motor is started, it is preferable to control the low-pass filter, the active filter circuit, or the switched capacitor IC so that the cut-off frequency is obtained empirically and stored in the storage means. As a result, even when the brushless motor is started, the ripple superimposed on the induced voltage is removed, and there is no failure in starting, so that the starting can be performed accurately.

[0016]

FIG. 1 is a block diagram showing an embodiment of the present invention.
This will be described in detail with reference to FIG. In FIG. 1,
The same parts as those in FIG. 5 are denoted by the same reference numerals, and redundant description will be omitted. See FIG. 6 for the induced voltage waveform generated in the non-energized phase of the brushless motor 4.

FIG. 1 is a schematic block diagram of a control device for a brushless motor according to a first embodiment of the present invention.
In FIG. 1, the control device compares the induced voltage waveform (virtual neutral point voltage waveform) with a reference voltage to obtain a position detection signal, and a ripple of a pulsation component due to reluctance torque is provided before a comparison circuit 5c. A position detection circuit 10 having a low-pass filter 10a to be removed is provided.

As described in the conventional example, when the brushless motor 4 is a three-phase four-pole motor (stator; 24 slots) that generates reluctance torque, the frequency component of the reluctance torque can be represented by FIG. That is, the frequency component (twice the rotation speed of the motor) appears as an eleventh harmonic (eleventh harmonic) (see FIG. 6B).

Further, the envelope of the harmonic component constituting the induced voltage waveform has the form shown by the dashed line in FIG. Therefore, the cutoff of the low-pass filter 10a is set to the form shown by the solid line in FIG. 2, that is, the cutoff is set so as to cut high-order harmonics.

In the position detection circuit 10, at least the eleventh harmonic is removed by passing the induced voltage obtained by the combined resistance circuit 5a through a low-pass filter 10a. That is, the ripple included in the induced voltage due to the influence of the reluctance torque is removed.

Therefore, the comparison circuit 5c compares the induced voltage not including the ripple with the reference voltage and outputs a position detection signal, and the control circuit 6 determines an accurate position detection timing based on the position detection signal. As a result, erroneous position detection due to ripples of high-order harmonic components can be prevented.

When the present invention is applied to a variable speed control inverter, it is necessary to change the cutoff frequency of the low-pass filter 10a according to the rotation speed. Therefore, as shown in FIG. 3, a control device for a brushless motor to which the second embodiment of the present invention is applied includes a low-pass active filter circuit 20a in place of the low-pass filter 10a of the previous embodiment and a preceding stage of the comparison circuit 5c. 1 and a position detection circuit 20 using a variable resistance means (attenuator) 20b as an input resistor of an active filter circuit 20a.
And a control circuit (microcomputer) 21 for changing the cutoff frequency of the active filter circuit 20a by switching the resistance value of the attenuator 20b according to the rotation speed of the brushless motor 4 in addition to the function of the control circuit 6 shown in FIG. I have.

If the resistance value R of the attenuator 20b is equal to the resistance R1 of the operational amplifier circuit 20c (R = R1), the active filter circuit 20a
The gain of c is 1, and the cutoff frequency is determined by the capacitor C1 and the resistor R1 (= R). Also,
If the resistance value R of the attenuator 20b is different from the resistance R1,
Since the gain of the operational amplifier circuit 20c is no longer 1 and the break point (so-called cut-off frequency) of the tangent of the gain (frequency characteristic) is different from the case of the gain 1, the cut-off frequency changes depending on the resistance value R.

Therefore, an optimum cut-off frequency is empirically determined in advance in accordance with the rotation speed of the brushless motor 4, and the resistance value of the attenuator 20b is set so that the cut-off frequency of the active filter circuit 20a becomes the determined cut-off frequency. Are stored in a table format in the internal memory (storage means) of the control circuit 21.

The control circuit 21 calculates the switching timing of the energization of the brushless motor 4 based on the position detection signal, switches the energization, calculates the number of revolutions, reads out the data in the internal memory, and controls the attenuator 2.
0b is sequentially switched.

As a result, the cut-off frequency of the active filter circuit 20a becomes optimal for removing ripples in accordance with the number of revolutions of the brushless motor 4, that is, it is possible to appropriately remove the eleventh harmonic which is a pulsating component due to reluctance torque. Thus, erroneous position detection can be prevented.

Since the position detection is the zero-cross point detection, even if the gain of the operational amplifier circuit 20c slightly changes, the position detection is not adversely affected. In this case, since the noise at the time of switching the energization of the brushless motor 4 is superimposed on the position detection signal because the transient response at the time of switching the cutoff frequency is easily affected, the position detection for a predetermined time is masked. The area of the mask is used. That is, in the area of the mask,
The resistance value of the attenuator 20b is switched to change the cutoff frequency of the active filter circuit 20a.

As shown in FIG. 4, a control device for a brushless motor to which the third embodiment of the present invention is applied includes a low-pass switched capacitor filter IC 30a instead of the active filter circuit 20a of the previous embodiment and a comparison circuit 5c.
In addition to the functions of the position detection circuit 30 provided in the preceding stage and the control circuit 6 shown in FIG. 5, the clock frequency (clock signal of a predetermined cycle) of the switched capacitor filter IC 30a is changed, and the cutoff frequency is changed to And a control circuit (microcomputer) 31 that can be varied according to the number of rotations.

In this case, an optimum cutoff frequency is previously empirically determined according to the rotation speed of the brushless motor 4, and the switched capacitor filter is set so that the cutoff frequency of the switched capacitor filter IC 30a becomes the determined cutoff frequency. Data for changing the clock frequency of the IC 30a is stored in a table format in the internal memory (storage means) of the control circuit 31.

The control circuit 31 calculates the switching timing of the energization of the brushless motor 4 based on the position detection signal, switches the energization, calculates the number of revolutions, reads the data in the internal memory, and switches the switched capacitor. The frequency of the clock signal output to the filter IC 30a is sequentially switched.

As a result, the cut-off frequency of the switched capacitor filter IC 30a becomes optimal for removing ripples according to the rotation speed of the brushless motor 4. That is, the eleventh pulsation component due to the reluctance torque
The second harmonic can be appropriately removed, and detection of an erroneous position can be prevented.

As in the previous embodiment, the frequency of the clock signal of the switched capacitor filter IC 30a is switched in the region of the position detection mask because the transient response at the time of switching the cutoff frequency may adversely affect the operation. , Switched capacitor filter I
The cutoff frequency of C30a may be switched.

As the above-mentioned filter, DPS
Or a high-speed arithmetic device such as In this case, the virtual neutral point voltage (induced voltage) waveform of the brushless motor 4 is A
The resulting induced voltage is digitally filtered to appropriately remove the eleventh harmonic which is a pulsating component (ripple) of the reluctance torque.

In the above three embodiments, the case where the brushless motor 4 is rotating has been described.
The same applies when the brushless motor 4 is started.

In this case, similarly to the above-described embodiment, a cutoff frequency for appropriately removing a ripple at the time of startup is obtained, and the cutoff frequencies of the active filter circuit 20a and the switched capacitor IC 30a are used as the obtained cutoff frequencies. Control data for the control circuits 21 and 31
Is stored in the internal memory (storage means). When the brushless motor 4 is started, the cut-off frequency of the active filter circuit 20a and the cut-off capacitor IC 30a is switched according to the data in the internal memory.
As a result, it becomes possible to start the job properly without starting the job.

In the above-described embodiment, the case where the terminal voltages of the three-phase armature windings U, V, and W are filtered has been described. However, when the energization switching timing is obtained by using the one-phase terminal voltage. Is also applicable. The present invention is also applicable to a case where a position detection (energization switching) timing is obtained using a voltage waveform (induced voltage waveform) obtained by combining three-phase terminal voltages.

[0037]

According to the present invention described above, the following effects can be obtained. According to the present invention, an induced voltage generated in a non-energized phase of a brushless motor that also contributes to reluctance torque is passed through a low-pass filter and compared with a reference voltage, and the comparison result is used as a position detection signal. In particular, a three-phase four-pole motor (24 slots) In the case of (1), since the cutoff frequency of the low-pass filter is set so as to remove at least the eleventh harmonic, ripples (high-order harmonics), which are pulsating components of the reluctance torque, are removed by the low-pass filter. Because it is possible to remove the ripple included in the induced voltage and prevent the erroneous position detection,
There is an effect that the motor rotation control can be smoothed and step-out and the like can be prevented.

According to the present invention, an active filter circuit is used as the low-pass filter, an attenuator for varying the input resistance of the active filter circuit is used, and the cut-off frequency of the active filter circuit is optimized according to the rotation speed of the brushless motor. Value, or using a switched capacitor filter IC, and changing the clock frequency of the switched capacitor filter IC to an optimal value according to the rotation speed of the brushless motor. Ripple (higher harmonics) included in the voltage can be removed, and there is an effect that erroneous position detection is always prevented.

[Brief description of the drawings]

FIG. 1 is a schematic block diagram of a control device according to a first embodiment of the present invention, to which a control method of a brushless motor is applied.

FIG. 2 is a schematic filter characteristic graph for explaining the operation of the control device shown in FIG. 1;

FIG. 3 is a schematic block diagram of a control device according to a second embodiment of the present invention, to which a brushless motor control method is applied;

FIG. 4 is a schematic block diagram of a control device according to a third embodiment of the present invention, to which a brushless motor control method is applied;

FIG. 5 is a schematic block diagram of a conventional brushless motor control device.

FIG. 6 is a schematic induced voltage waveform and a ripple waveform chart based on reluctance torque for explaining the problem of the control device shown in FIG. 5;

[Explanation of symbols]

Reference Signs List 4 brushless motor (sensorless DC brushless motor) 5, 10, 20, 30 position detection circuit 5a synthesis circuit 5b voltage generation circuit 5c comparison circuit 6, 21, 31 control circuit (microcomputer) 10a low-pass filter 20a active filter circuit 20b variable resistance Means (Attenuator) 20c Operational amplifier circuit 30a Switched capacitor IC

Claims (8)

[Claims] 1. A position detection signal is obtained by comparing a reference voltage with an induced voltage generated in a non-energized phase of a brushless motor that generates at least a reluctance torque, and a position of a rotor is detected by the position detection signal. A brushless motor control method for switching the energization of the armature winding of the brushless motor, wherein a low-pass filter is provided in a stage preceding the comparing means in order to remove a ripple which is a pulsating component of the reluctance torque. A method for controlling a brushless motor, wherein a ripple included in a voltage is removed. 2. A position detection signal is obtained by comparing a reference voltage with an induced voltage generated in a non-energized phase of a three-phase four-pole brushless motor that generates at least reluctance torque, and a position detection signal is obtained. A brushless motor control method for switching the energization of the armature winding of the brushless motor by detecting the position of the brushless motor, in order to remove high-order harmonics that are pulsating components of the reluctance torque,
A method for controlling a brushless motor, characterized in that a low-pass filter is provided before the comparing means, and a cut-off frequency of the low-pass filter is set so as to remove at least an eleventh harmonic. 3. The brushless motor control method according to claim 1, wherein a cutoff frequency of the low-pass filter is varied according to a rotation speed of the brushless motor. 4. A position detection signal is obtained by comparing a reference voltage with an induced voltage generated in a non-energized phase of at least a brushless motor that generates reluctance torque, and a position of the rotor is detected by the position detection signal. A brushless motor control method for switching the energization of the armature winding of the brushless motor, wherein a low-pass active filter circuit is used in a preceding stage of the comparing means in order to remove a ripple which is a pulsating component of the reluctance torque. A variable resistance means for varying the input resistance of the active filter circuit is used, the resistance value of the variable resistance means is switched according to the rotation speed of the brushless motor, and the cutoff frequency of the active filter circuit is varied. Characterized by removing ripples contained in the induced voltage. How to control a motor. 5. A method for empirically obtaining information for varying a cutoff frequency in accordance with the rotational speed, storing the information in a storage means, and detecting a position of the rotor by the position detection signal for a predetermined time. 5. The control method for a brushless motor according to claim 3, wherein when the position detection is masked, the cutoff frequency is switched in a region of the mask. 6. A position detection signal is obtained by comparing an induced voltage generated at least in a non-energized phase of a brushless motor generating reluctance torque with a reference voltage, and a position of the rotor is detected based on the position detection signal. A brushless motor control method for switching the energization of the armature winding of the brushless motor, wherein a low-pass switched capacitor IC is used in a stage preceding the comparing means to remove a ripple which is a pulsating component of the reluctance torque. A method of controlling the brushless motor, wherein the cut-off frequency of the switched capacitor IC is varied according to the number of revolutions of the brushless motor to remove a ripple included in the induced voltage. 7. A clock frequency is empirically obtained in advance to vary the cut-off frequency of the switched capacitor IC and stored in a storage means in a table form, and the switched capacity is referred to in accordance with the rotation speed by referring to the table. 7. The method for controlling a brushless motor according to claim 6, wherein the cutoff frequency of the filter IC is changed. 8. When the brushless motor is started, the low-pass filter, the active filter circuit, or the switched-capacitor IC is controlled so that the cut-off frequency is empirically obtained in advance and stored in the storage means.
7. The control method for a brushless motor according to claim 1, wherein the brushless motor is controlled.