JP3286053B2 - 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.

[0006] It has been clarified by actual measurement that the braking force subjected to the PWM control in this manner has characteristics as shown in FIG. In the braking control by the PWM method, since the chopper frequency is fixed, when the control is performed at the same frequency (duty cycle) even when the rotation speed is high or low, the characteristics of the braking force depend on the motor rotation speed. Variations occur. For example, a case where the rotational speed is high as shown by the broken line in the figure, one point chain
Duty cycle 60% with low case indicated by line
Comparing with the case where the control is performed, it can be understood that a braking force of about 38 kgf · cm can be secured when the control is high, but that it is only about 4 kgf · cm when the control is small.
This is because, when the rotation speed of the motor is high, the cycle of the braking current is short and the time during which the current is flowing is greatly controlled by chopper control, whereas when the rotation speed is low, the cycle of the braking current is long and the current is increased. This is because the chopper control is finely performed for the time during which the air flows. As described above, in the braking control by the PWM method, the braking characteristics tend to change depending on the rotation speed of the motor. Therefore, in order to obtain the same braking force, when the motor is rotating at a high rotation speed. Requires a large duty cycle, and conversely, if the motor is rotating at a low rotation speed, the duty cycle must be reduced, requiring complicated control such as controlling the braking force according to each rotation speed. It had been.

[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 brushless motor capable of obtaining a stable braking force without being affected by the rotation speed of the motor. It is to provide a control circuit.

[0008]

According to the present invention, there is provided a control circuit for controlling the braking of a motor by selectively short-circuiting a plurality of coils of a brushless motor. Switching means for selectively bringing each of the coils into a short-circuit state so that a braking current flows, and an electrical angle detection for detecting an electrical angle of the motor.
And means, braking by changing the basis of short-circuiting time of the coil by the switching means prior Symbol electrical angle
This is achieved by providing a motor control circuit having control means for variably controlling the force . Furthermore,
The control means may be configured to control the switching means by setting a start point for setting each of the coils in a short-circuit state to a point where power regeneration is not substantially performed, or may change an end point of the short-circuit state of each of the coils. It is even better if it controls the switching means.

[0010]

In this way, since the time during which the braking current flows is variably controlled based on the electric angle of the motor, the desired braking force can be obtained even if the period of the braking current changes according to the rotation speed of the motor. It can be easily secured. Further, the braking force can be substantially uniquely determined by the electrical angle regardless of the rotation speed.

[0011]

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 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 driving circuit 9 is driven by rotating the motor from the outside.
Each of the FETs 15 to 20 is connected to the FE located on the high side.
When T15, 17, and 19 are all turned off and the FETs 16, 18, and 20 located on the low side are all turned on in (a), the FETs 16 and 18 are turned on and the FET 20 is turned off in (b). In (c), when only the FET 16 is turned on and all the other FETs are turned off, the waveforms of the braking current flowing through each phase coil are observed at the output terminals 10 to 12, respectively. FIG. 7 is a diagram showing a rotor position in a case together with a signal IHu which is electrically indicated.

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 as electrical angle detecting means .

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 between 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, 19, 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 of the FETs 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 IHv rises, this FET 1
6 is turned on, and the position signal IHw is
20 is controlled to turn on when the corresponding position signal rises, such as a position signal IHu. Further, when turning off the ON FET, the FET is turned off in a predetermined phase section verified in advance.
As is clear 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. 7 shows the relationship between the charging current flowing through the terminal 13 and the electrical angle, and FIG. 8 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. 4, since the braking current takes the maximum value at around the electrical angle of about 180 degrees, the maximum braking force can be secured by turning off at this time. In the variable control of the braking force, as shown in FIG. 6, the point at which each FET is turned off in the section D is changed by an electrical angle of 60 degrees, so that the braking force can be variably controlled.

According to the present embodiment, as is clear from the braking characteristics shown in FIG. 9, the braking current is cut off based on the electrical angle even if the rotation speed during braking changes. In this case, since substantially the same braking force can be secured, unlike the control of the braking force by the PWM method shown in FIG. No control required.

In this embodiment, the braking control is performed for each electrical angle of 60 degrees using three Hall elements. However, the present invention is not limited to this. For example, the number of Hall elements is doubled. Then, the braking control can be performed at every 30 degrees of the electrical angle, and the braking control can be performed more finely by further increasing the electrical angle. In addition, if the time between edges is measured using a timer, the electrical angle can be considered as time, and braking control can be performed by using another timer to enable analog electrical angle control. .

[0022]

As described above, according to the present invention, since the braking force can be variably controlled without depending on the rotation speed of the motor, the rotation speed of the motor which has been regarded as a problem in the braking control by the conventional PWM is considered. Thus, it is possible to realize a braking control that can secure a stable braking force despite simple control without causing a problem such as a change in the braking characteristic according to the control.

[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 waveform chart supplied to each switching element when the motor of FIG. 2 is braked.

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.

FIG. 10 is a diagram illustrating braking control by a PWM method.

[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) JP-A-5-137377 (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 (3)

(57) [Claims] 1. A control circuit for selectively controlling a plurality of coils of a brushless motor in a short-circuit state to control braking of the motor, wherein the coils are selectively supplied to supply a braking current when braking the motor. a switching means for short circuited, have <br/> electrical angle detecting means for detecting an electrical angle of said motor, a short time of the coil by the switching means prior Symbol electrostatic <br/> vapor angle A motor control circuit comprising control means for variably controlling a braking force by changing the braking force based on the control signal. 2. The motor control according to claim 1, wherein the control means controls the switching means by setting a starting point of setting each of the coils in a short-circuit state to a point where power regeneration is not substantially performed. circuit. 3. The motor control circuit according to claim 1, wherein the control unit controls the switching unit to change an end point of the short-circuit state of each of the coils.