JP3286054B2 - Control circuit for brushless motor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a control circuit for a brushless motor, and more particularly to a control circuit for a brushless motor that controls a braking force based on an electric angle of the motor.

[0002]

2. Description of the Related Art Generally, a brushless motor is supplied with electric power by a drive circuit composed of a plurality of switching elements, and speed control is generally performed by PWM control in which a signal for controlling on / off of these switching elements is chopper-controlled. It is.

FIG. 2 is an electric circuit diagram schematically showing a drive circuit for supplying a current to each phase coil of a three-phase brushless motor. Star-connected U-phase coil 6, V
The phase 7 and the W phase 8 are connected via output terminals 10 to 12 to a plurality of field effect transistors (hereinafter, referred to as FETs), which are switching elements in the drive circuit 9 surrounded by broken lines in the figure. . The drain D-source S of the FET 15 and the FET 16 are connected between the power terminal 13 to which both terminals of the power source (not shown) are connected and the ground terminal 14.
Are connected in this order. The node between the source S of the FET 15 and the drain D of the FET 16 is connected to one terminal of the U-phase coil 6 via the output terminal 10. Further, between the terminals 13 and 14, the drain D-source S of the FET 17 and the FET 1
Eight drains D-sources S are connected in this order.
The source S of the FET 17 and the drain D of the FET 18
Are connected to one terminal of the V-phase coil 7 via the output terminal 11. Similarly, terminals 13 and 14
Between the drain D-source S of FET 19 and FE
The drain D-source S of T20 is connected in this order. The node between the source S of the FET 19 and the drain D of the FET 20 is connected to one terminal of the W-phase coil 7 via the output terminal 12. And each FET1
A diode 2 is connected between the drain D and the source S of 5 to 20.
1 to 26 are connected in parallel in opposite directions.

Each of the FETs 15 to 20 in the driving circuit 9 configured as described above is turned on / off, and each phase coil 6 is controlled.
The rotation of the motor is controlled by commutating the current flowing through. For example, when driving this motor,
As shown in FIG. 3, the rotor position detection signals IHu,
Gate G of each FET 15 to 20 for IHv and IHw
Are connected to each terminal U +, U-, V +, V-, W +, W
A drive signal is supplied from control means (not shown) in accordance with the respective modes (a) to (e), and the drive signal is subjected to PWM control to control the current supplied to each phase coil 6 to 8 to control the motor speed. It has been like that.

When the motor is braked by the PWM control, the high-side FETs 15, 17, and 19 are all turned off, and the low-side FETs 16, 18, and 20 are turned on to short-circuit the coil, which is generated by electromagnetic action. The braking force is ensured by chopper control of the braking current. That is, as shown in FIG. 4, when the braking currents Iu, Iv, Iw flowing for each coil are positive components (currents flowing in the direction of arrow A in FIG. 2), for example, a positive braking current flows through the coil 6. In this case, the FET 16 is cut off, and the back electromotive voltage generated by the cutoff of the current is regenerated to the power supply, thereby ensuring and charging the braking force.

There are various disadvantages in the motor braking control by the PWM control described above, and in order to eliminate the disadvantage that the characteristic of the braking force changes at each rotation speed as a typical example,
The present inventor has proposed a technique for variably controlling the short-circuit time of the coil based on the electric angle of the motor. According to this technology, PW
It can eliminate the disadvantages of M control, but it is difficult to apply to microcomputers that have no spare timer because a high-performance microcomputer with multiple timers / counters is used to convert the electric angle of the motor into time. Met.

[0007]

SUMMARY OF THE INVENTION In view of the above problems of the prior art, a main object of the present invention is to provide a control circuit for a brushless motor capable of variably controlling a braking force using a low-function microcomputer. It is in.

[0008]

SUMMARY OF THE INVENTION According to the present invention, there is provided a motor for braking a motor by setting a plurality of coils of a brushless motor in a short-circuit state over a phase section based on an electric angle of the motor. A control circuit for controlling, comprising: a switching unit for causing each of the coils to be in a short-circuit state; and a control unit for performing on / off control of the switching unit in accordance with the phase interval. By providing a control circuit for a brushless motor, the braking force is variably controlled by selectively thinning out m (≦ n−1) of n consecutive n phase sections. Achieved.

[0009]

In this way, the electric angle of the motor is determined based on the electric angle .
Since m (≦ n−1) phase sections are thinned out of n consecutive phase sections, the braking force due to the short-circuit state of the coil is obtained.
Can be made variable according to the number of thinning-out operations.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described below in detail with reference to the accompanying drawings.

FIG. 1 is a block diagram schematically showing a control circuit of a brushless motor to which the present invention is applied, and a switching means 3 for supplying electric power of a power supply 2 to a motor 1.
And a control means 4 for controlling on / off of the switching means, and a rotor position detecting means 5 for detecting a position of a rotor (not shown) of the motor 1.

When the switching means 3 is applied to, for example, a three-phase brushless motor, the switching means 3 is configured as shown by a drive circuit 9 in FIG. 2, and the description is as described above. A case where the motor is braked using the drive circuit 9 will be described with reference to FIGS. FIG. 4 shows that the motor is rotated from the outside to create a pseudo braking state, and the FETs 15 to 20 in the drive circuit 9 are
The FETs 15, 17, and 19 located on the high side are all turned off, and the FETs 16, 18, and 20 located on the low side are turned off.
When (a) is turned on all, in (b), FETs 16 and 18 are turned on and FET 20 is turned off, and in (c) only FET 16 is turned on and other FETs are turned on. FIG. 3 is a diagram showing waveforms of braking current flowing through each phase coil when they are all turned off, observed at output terminals 10 to 12, respectively, and showing a rotor position in each case together with a signal IHu which is electrically shown. .

Here, the relationship between the braking current, the braking force, and the electrical angle will be described. First, the braking current is applied to each coil 6-8.
In the present embodiment, a rotating field type brushless motor having a three-phase field winding star-connected to a stator is used as a rotating field type brushless motor. When all the phases are short-circuited, AC braking currents Iu, Iv, Iw flowing with a phase difference of (2/3) π as shown in FIG. Observable at terminals 10-12. It is well known that the period of the braking current generated in this way becomes shorter when the rotation speed is high, and becomes longer when the rotation speed is low. In addition, since regenerative braking is adopted for the braking force, when regenerating power to the DC power supply,
The braking force is obtained by regenerating the back electromotive voltage generated by interrupting the positive braking current (current flowing in the direction of arrow A in FIG. 2) to the power supply. In this case, the electric angle of the motor represents one cycle of the braking current as an angle, and 360 degrees of the electrical angle is one cycle of the braking current. This electrical angle can be detected by a Hall element which is a magnetic field sensor.

Next, the relationship between the braking current and the short-circuit state of each of the coils 6 to 8 will be considered. As shown in FIG. 4A, all of the FETs 15, 17, and 19 located on the high side are turned off, and the FETs 16, 18, and 18 located on the low side are turned off.
When all the switches 20 are turned on, alternating current braking currents Iu, Iv, and Iw flowing through the respective output terminals 10 to 12 with a phase difference of (2/3) π are flowing. Now, output terminal 1
Attention is paid to the braking current Iu flowing through 0. In the section A shown in the figure, the braking current is negative. In this section A, even if the FET 16 is turned off, the back electromotive voltage generated is connected in series to the power supply, so that power regeneration is not performed. Next, in the case shown in FIG.
Section 17 because FET 17 is on and FET 19 is off
, Resulting in a negative braking current. The section B is shorter than the section A and has a smaller amplitude. In this case, similarly, if the FET 16 is turned off in the section B, power regeneration is not performed. Further, in the case shown in FIG.
Since only 5 is on and all the other FETs are off, the braking current becomes 0 in section C. This is FET
This is because currents do not flow in the negative direction because the switches 18 and 20 are off. Therefore, in section C, the FET
When 16 is turned off, no back electromotive voltage is generated, and thus no power regeneration is performed.

When the FETs 16, 18, and 20 are turned on during braking,
Since the off state is verified by the three patterns described above, it can be seen from the results that section C is included in section A and section B. Therefore, if the FET 16 is controlled to be turned on in this section C and turned off in a predetermined phase section, power regeneration to the power supply is performed. The same can be said for the other FETs 18 and 20. Since the coils 6 to 8 are star-connected, in the case of the FET 18, it is only necessary to turn on with a delay of (２) π from the off point of the FET 16. In the case of the FET 20, if it is turned on further with a delay of (2/3) π, power regeneration is performed.

In controlling the braking force, the braking current is generated by the electromagnetic action of the coils 6 to 8 and the permanent magnets (not shown) as described above. The turning-on point is determined by the rotor position, which is fixed at the motor design stage, although it slightly varies depending on the rotational speed. Therefore, the rotor position detecting means 5 can detect the position of the rotor and output the detection result as an electric signal.
, That is, by providing Hall ICs that output edge signals at the points where the FETs 16, 18, and 20 are turned on. In this embodiment, although not shown, a Hall IC including three Hall elements is provided at an appropriate position on the stator at an interval of 120 degrees from each other.

FIG. 5 shows a waveform diagram of a signal output from the rotor position detecting means 5. The Hall IC serving as the rotor position detecting means is provided with edge signals IHu, IHv, IHw corresponding to the points where the FETs 16, 18, and 20 are turned on.
Is output to the control means 4. The control means 4 turns off the FETs 16, 18, and 20 at the time of braking with the corresponding rising edge signals, and inputs the edges of the edge signals IHu, IHv, IHw to set the electrical angle to 60 degrees. Each is divided and used as a timing signal at the time of controlling the braking force described later. At this time, the position signals IHu, IHv, IHw and the FETs 16, 18, 2
The supply signal to the gate of 0 is different from the driving state of FIG.

Next, by turning on / off each FET located on the low side in synchronization with the position signal by the control means 4, the power can be regenerated to the power supply and the motor can be braked. Specifically, as shown in FIG. 6, the high-side FETs 15, 17, and 19 are turned off, and when the low-side FET, for example, the FET 16 is off, when the position signal IH u rises, this FET 1
6 turned on, the FET18 position signal the IH v is, FET
And so the position signal the IH w to 20, controls to turn on at the time of rise of the corresponding position signal. When turning off the FET that is on, it turns off in a predetermined phase section that has been verified in advance.
As is apparent from the braking characteristics shown in FIG.
A predetermined phase section from the electrical angle of 180 degrees to the electrical angle of 180 degrees, the FETs 16, 18, and 20 are turned on at the electrical angle of 0 degree, and the electrical angle of 1
Control is performed so as to turn off within a section up to 80 degrees. Here, FIG. 8 shows the relationship between the charging current flowing through the terminal 13 and the electrical angle, and FIG. 9 shows the relationship between the braking force and the electrical angle. From both, it can be seen that the relationship between the charging current and the braking force is proportional to the magnitude of the charging current, and the braking force is also large. Further, as shown in FIG. 9 , since the braking current has a maximum value approximately at an electrical angle of about 180 degrees, the maximum braking force can be secured by turning off at this time.

As described above, it is apparent that the braking force can be variably controlled by controlling the short-circuit state of the coil based on the electrical angle of the motor. In variably controlling the braking force, for example, using a timer, the timer is started at the rising edge, and counted up at the next rising edge, so that the electrical angle can be converted into time and variably controlled. If the means is a small-scale microcomputer having no spare timer / counter or the like, it is difficult to employ the above technique. Therefore, in the present invention, the braking force is variably controlled by selectively thinning out the phase sections based on the electrical angle. Specifically, the braking force is made variable by thinning out m (m ≦ n−1) phase sections out of n consecutive phase sections,
For example, FIG. 6 shows a pattern in which a phase section up to an electrical angle of 180 degrees at which the braking force is maximum is fixed and the phase section is thinned out.
And will be described.

As shown in FIG. 6, as the pattern A, n =
If 1, m = 0, the FET 16 is turned on when the position signal IHu rises, and the position signal IHv
Is turned on, the FET 18 is turned on, and the position signal I
When Hw rises, the FET 20 is turned on, and the coils 6 to 8 are short-circuited. Next, when the position signal IHu falls, the FET 16 is turned off, and when the position signal IHv falls, the FET 18 is turned off.
When w falls, the FET 20 is turned off, and the electrical angle 1
The coils 6 to 8 are short-circuited in a phase section up to 80 degrees. That is, when the position signals IHu, IHv, IHw rise, the corresponding FETs 16, 18, and 20 are turned on, and when the position signal falls, the respective FETs are turned off. Therefore, since the phase sections are not thinned out, each of the FETs 16, 18, 20
, The maximum braking force can be obtained.

Next, when n = 2 and m = 1 as the pattern B, the position signals IHu,
Instead of turning on / off the FETs 16, 18, and 20 for each edge of IHv, IHw, the position signals IHu, IHv,
FETs 16, 18, and 20 are turned on / off at the first rising edge / falling edge of IHw, and are not turned on / off at the second rising edge / falling edge.
Control is performed to turn on / off at the third falling edge / falling edge. That is, one of the two phase sections
That is, control is performed so as to thin out the number of phase sections.

Next, when n = 3 and m = 2 as the pattern C, control is performed so as to thin out two phase sections out of the three phase sections. Although not shown, there are a plurality of other thinning patterns. For example, one of the three phase sections is thinned, and thus m of the n phase sections are thinned out. The variable control of the braking force of the present invention becomes possible as long as the relationship of thinning out sections is not broken.

FIG. 7 shows the characteristics of the braking force obtained by controlling the FETs 16, 18, and 20 as described above. As is clear from the figure, it has been found that the braking force reaches a maximum when there is no thinning (0 times) in the phase section, and then decreases as the number of times of thinning increases. Therefore, when it is desired to obtain a high braking force, the number of times of thinning is reduced, and when it is desired to obtain a low braking force, control is performed so as to increase the number of times of thinning. From the above, since the braking force can be variably controlled without using any timer,
It can be realized even with a low-function microcomputer with no extra timer.

In the present embodiment, the braking force is variably controlled by setting the electrical angle of 180 degrees at which the maximum braking amount can be secured as a predetermined phase section.
By using each of the edge signals u, IHv, and IHw, the electrical angle can be decomposed every 60 degrees.
It goes without saying that the resolution of the braking force can be further improved by combining the thinning control at 0 degree, 120 degrees, and 180 degrees.

[0025]

As described above, according to the present invention, since the braking force of the motor can be variably controlled without using a plurality of timers, a simple microcomputer can be employed, thereby reducing the product cost and There is no problem that the braking characteristics change according to the rotation speed of the motor, which has been regarded as a problem in the braking control by the conventional PWM, and the like.
Despite simple control, it is possible to realize braking control that can secure a stable braking force.

[Brief description of the drawings]

FIG. 1 is a block diagram schematically showing a control circuit of a brushless motor to which the present invention is applied.

FIG. 2 is an electric circuit diagram schematically showing a drive circuit for supplying a current to each coil of a three-phase brushless motor.

3A and 3B are a commutation mode diagram and a waveform diagram showing a state of a signal supplied to each switching element when the motor of FIG. 2 is driven.

FIG. 4 is a waveform chart showing waveforms observed at respective terminals when the motor of FIG. 2 is braked.

FIG. 5 is a view electrically showing a position of a rotor at the time of braking of the motor of FIG. 2;

FIG. 6 is a diagram showing a state of each switching element when braking the motor of FIG. 2;

FIG. 7 is a diagram showing characteristics of a braking force obtained by the circuit of the present invention.

FIG. 8 is a diagram showing characteristics of a braking force obtained by the circuit of the present invention.

FIG. 9 is a diagram showing characteristics of a braking force obtained by the circuit of the present invention.

[Explanation of symbols]

 Reference Signs List 1 motor 2 power supply 3 switching means 4 control means 5 rotor position detecting means 6 U-phase coil 7-phase coil 8 phase coil 9 drive circuit 10-12 output terminal 13 power supply terminal 14 ground terminal 15-20 FET 21-26 diode

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-5-64304 (JP, A) JP-A-5-122982 (JP, A) JP-A-58-19180 (JP, A) 137377 (JP, A) JP-A-1-190286 (JP, A) JP-A-2-231985 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H02P 6/24 H02P 6 / 08

Claims (1)

(57) [Claims] A control circuit for controlling braking of a motor by short-circuiting a plurality of coils of a brushless motor over a phase section based on an electrical angle of the motor, wherein each of the coils is short-circuited. For controlling on / off control of the switching means in accordance with the phase interval, wherein the control means sets m
A braking force is enabled by selectively thinning out (≦ n-1) pieces.
A control circuit for a brushless motor characterized by performing variable control .