JP3286052B2 - 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 capable of preventing power regeneration to a power supply during braking and variably controlling the braking force.

[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 so that a braking current flows through the coil, thereby short-circuiting the coil. In this state, the braking force is secured by the braking current generated by the electromagnetic action. Further, 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, the braking current of the positive component flows through the coil 6. FET 16 when flowing
Is cut off, a large back electromotive voltage is generated in parallel with the power supply due to the interruption of the current, thereby charging the power supply by regenerating the power to the power supply.

However, in the above-described control, when the braking and the charging are individually controlled, for example, when there is a risk of overcharging, it is not necessary to secure only the braking force and perform the charging. FET with positive braking current flowing
Must be controlled with a 100% duty cycle so as not to turn off. Since the braking force is proportional to the time during which the braking current is flowing, that is, it changes in accordance with the electric energy stored in each coil, controlling with a 100% duty cycle requires a constant braking force. This causes inconvenience in speed control.

[0007]

SUMMARY OF THE INVENTION In view of the above-mentioned problems of the prior art, a main object of the present invention is to provide a brushless motor control circuit which can prevent power regeneration during braking and can vary the braking force. To provide.

[0008]

SUMMARY OF THE INVENTION In accordance with the present invention, there is provided a control circuit for controlling the braking of a motor by shorting a plurality of coils of a brushless motor over a selected phase interval. A switching means for selectively bringing each coil into a short-circuit state, and an end point of the phase section being substantially set to a point where power regeneration is not performed, and at this point, the short-circuit state of each coil is released. have a control means for controlling said switching means, said control hand
The step is caused by short-circuiting each of the coils.
The braking current flowing for each coil becomes a negative component or almost zero.
The present invention is attained by providing a control circuit for a brushless motor, characterized in that the short-circuit state of the coil is released when the control circuit is operated. Then, the control means, even better by controlling the switching means so as to change the starting point of the short circuit state before Symbol coil.

[0009]

In this way, if the short-circuit state of the coil is released when the braking current flowing through the coil is approximately 0, no back electromotive voltage is generated and power regeneration is not required, and depending on the state of the braking current, Generates a negative current to the power supply,
Also in this case, it is not necessary to perform power regeneration. Further, if the time during which the braking current is flowing is variably controlled by varying the starting point of the short-circuit state, the braking force can be variably controlled.

[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 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 low-side FETs 16, 18, and 20 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 the coils of the respective phases 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.

First, as shown in FIG. 4A, alternating current braking currents Iu, Iv, Iw flowing through the respective output terminals 10 to 12 with a phase difference of (2/3) π from each other.
Since the principle of generation is clear, the description is omitted. Attention is now directed to the braking current Iu flowing through the output terminal 10. 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, since a negative current is generated with respect to the power supply, power regeneration is not performed. Next, in the case shown in FIG.
, 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. 4C, the braking current is 0 in the section C. This is FET18,
This is because no current flows in the negative direction because 20 is off. Therefore, if the FET 16 is turned off in the section C, no back electromotive voltage is generated, and no power regeneration is performed.

When the FETs 16, 18, and 20 are turned on during braking,
Since the OFF state has been 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 off in this section C, power regeneration to the power supply will not be performed. Other FETs 18,
The same can be said for 20. Since the coils 6 to 8 are wound with a phase angle of (2/3) π from each other, in the case of the FET 18, (2/3) from the off point of the FET 16 It may be turned off with a delay of π.
In this case, if the power is further turned off with a delay of (2/3) π, power regeneration is not performed.

Now, in the concrete control, the braking current is generated by the electromagnetic action of the coils 6 to 8 and the permanent magnets (not shown).
The point at which the switches 8 and 20 are turned off is determined by the rotor position, which is fixed at the motor design stage although there is some deviation depending on the rotational speed. Therefore, the rotor position detecting means 5 capable of detecting the position of the rotor and outputting the detection result as an electric signal is provided.
This can be realized by providing corresponding Hall elements for outputting edge signals at the points where the switches 16, 18, and 20 are turned off. In this embodiment, a rotating field type brushless motor having a permanent magnet for the rotor and a field winding for the stator is employed. And three Hall elements are provided.

FIG. 5 shows a waveform diagram of a signal output from the rotor position detecting means 5. The Hall element, which is a rotor position detecting means, has an edge signal I having a phase difference of (2/3) π different from each other corresponding to a braking current flowing through each of the terminals 10 to 12.
Hu, IHv, and IHw are output to the control means 4. The control means 4 receiving the signal from the rotor position detecting means 5 controls the gates of the FETs 16, 18, and 20 so that the off-point of each of the FETs 16, 18, and 20 at the time of braking is determined by the rising edge signal from each Hall element. U-, V-, W
To supply a signal to the negative side. At this time, the position signals IHu, IHv, IHw and the FETs 16, 18, 20
The supply signal to the gate is different from the driving state in FIG.

By turning on / off each FET located on the low side by the control means 4 in synchronization with the position signal, the motor can be braked without regenerating power to the power supply. 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 on, the FET 1 is turned on when the position signal IHv rises.
6 is turned off, and the position signal IHw is
The control 20 is turned off when the corresponding position signal rises, such as a position signal IHu. Therefore, each of the low-side FETs 16, 18, 2
When turning off 0, each of the corresponding terminals 10-1
Since no current flows or a current of a negative component flows in 2, a back electromotive voltage does not occur or a negative current is generated with respect to the power supply even if it occurs. There is no need to perform power regeneration.

The braking force changes electrically according to the electric energy stored in each coil except for mechanical elements, that is, the braking force changes according to the time during which the braking current flows. It is. Therefore, by changing the starting point of turning on each FET as shown in section D in FIG. 6, the braking force can be increased by, for example, increasing the time from ON to OFF, and conversely, by shortening the time. A small braking force can be obtained.
When the switches 6, 18, and 20 are turned off, the current is not flowing or the current of the negative component is flowing, so that the braking force can be variably controlled without performing power regeneration.

[0019]

As described above, according to the present invention, the short-circuit state of the coil can be released in the state where the braking current is not flowing or the current of the negative component is flowing, so that power regeneration is not performed. By changing the starting point of the short-circuit state to be variable, it is possible to adjust the braking force by changing the energization state to the coil. Therefore, the effect is great because the braking force can be controlled variably without charging.

[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.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Motor 2 Power supply 3 Switching element 4 Control means 5 Rotor position detecting means 6 U-phase coil 7 V-phase coil 8 W-phase coil 9 Drive circuit 10-12 Output terminal 13 Power supply terminal 14 Ground terminal 15, 17, 19 High side FET 16 , 18, 20 Low-side 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) , A) JP-A-1-190286 (JP, A) JP-A-3-36987 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H02P 6/24 H02P 6/08

Claims (2)

(57) [Claims] 1. A control circuit for controlling braking of a motor by setting a plurality of coils of a brushless motor to a short-circuit state over a selected phase section, and a switching means for selectively setting each of the coils to a short-circuit state. And control means for controlling the switching means so that the end point of the phase section is substantially set to a point where power regeneration is not performed, and at this point, the short-circuit state of each coil is released.
The control means may set each of the coils in a short-circuit state.
The braking current generated for each coil generated by the
Is a control circuit for a brushless motor , wherein the short-circuit state of the coil is released when the voltage becomes substantially zero . 2. The control circuit for a brushless motor according to claim 1, wherein said control means controls said switching means so as to change a starting point of a short-circuit state of said coil.