JPH07184391A - Control circuit for brushless motor - Google Patents

Abstract

PURPOSE:To prevent power regeneration during braking and make braking force variable by selectively setting respective coils to short-circuit conditions, determining the end point of a phase interval as a point where no power regeneration is performed and releasing the short-circuit conditions at that point. CONSTITUTION:Power of a power supply 2 is supplied to a motor 1 by switching means 3. This switching means 3 is ON/OFF controlled by control means 4. Also, the position of a rotor of a motor 1 is detected by rotor position detecting means 5. By doing the above, the short-circuit conditions of coils can be released in a state where no braking current is flowing or a negative component current is flowing, so that braking can be performed without performing power regeneration. Moreover, by making the start point of the short-circuit conditions variable, the braking force can be adjusted by varying conducting conditions of coils. Therefore, the braking force can be controlled under changing conditions without charging.

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 which can prevent power regeneration to a power source during braking and can control the braking force variably.

[0002]

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

Here, FIG. 2 is an electric circuit diagram showing an outline of 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 respectively 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 provided between the power supply terminal 13 to which both terminals of the power supply (not shown) are connected and the ground terminal 14.
Drain D-source S of are connected in this order. The nodes of the source S of the FET 15 and the drain D of the FET 16 are connected to one terminal of the U-phase coil 6 via the output terminal 10. Further, the drain D-source S of the FET 17 and the FET 1 are provided between the terminals 13 and 14.
8 drains D-sources S are connected in this order.
And the source S of FET17 and the drain D of FET18
The nodes of and 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 and FE of the FET 19
The drain D-source S of T20 is connected in this order. The nodes of the source S of the FET 19 and the drain D of the FET 20 are connected to one terminal of the W-phase coil 7 via the output terminal 12. And each FET1
The diode 2 is provided between the drain D and the source S of 5 to 20.
1 to 26 are connected in parallel in opposite directions.

The FETs 15 to 20 in the drive circuit 9 thus constructed are controlled to be turned on and off, and the phase coils 6
The rotation of the motor is controlled by diverting the current flowing through 8 to 8. For example, when driving this motor,
As shown in FIG. 3, the rotor position detection signal IHu,
Gate G of each FET 15 to 20 for IHv and IHw
Connected to each terminal U +, U-, V +, V-, W +, W
A drive signal is supplied from a control means (not shown) according to each of the modes a to f, and the PWM signal is used to control the current supplied to the phase coils 6 to 8 to control the motor rotation speed. Is being done.

When the motor is braked by the PWM control, all the high side FETs 15, 17, 19 are turned off, and the low side FETs 16, 18, 20 are turned on so that a braking current flows through the coil, thereby short-circuiting the coil. And 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, and Iw flowing in each coil are positive components (currents flowing in the direction of arrow A in FIG. 2), for example, the braking current having a positive component in the coil 6 is FET16 while flowing
If the power is cut off, a large counter electromotive voltage is generated in parallel with the power supply due to the cutoff of the current, and by doing so, the power is regenerated to charge the power supply.

However, in the above-mentioned control, when the braking and the charging are separately controlled, for example, when there is a fear of overcharging, it is not necessary to secure only the braking force and perform the charging. FET with positive braking current flowing
It is necessary to control with a duty cycle of 100% so as not to turn off. Since the braking force is proportional to the time during which the braking current flows, that is, it changes according to the electrical energy stored in each coil, controlling with a 100% duty cycle makes the braking force constant. Therefore, the speed control becomes inconvenient.

[0007]

In view of the above problems of the prior art, a main object of the present invention is to provide a brushless motor control circuit capable of preventing electric power regeneration during braking and varying braking force. To provide.

[0008]

According to the present invention, there is provided a control circuit for controlling the braking of a motor by setting a plurality of coils of a brushless motor into a short circuit state over a selected phase section. , Switching means for selectively short-circuiting each of the coils, and defining the end point of the phase section at a point where power regeneration is not generally performed, and at this point the short-circuited state of each coil is released. It is achieved by providing a control circuit for a brushless motor, characterized in that it has a control means for controlling the switching means. Then, the control means releases the short-circuited state of the coil when the braking current generated by putting the respective coils into the short-circuited state flows in the reverse direction or becomes substantially zero, or short-circuits the coil. It is even better if the switching means is controlled so as to change the starting point of the state.

[0009]

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

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT A preferred embodiment of the present invention will now be described in detail with reference to the accompanying drawings.

FIG. 1 is a block diagram showing an outline of 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 source 2 to the motor 1.
And a rotor position detecting means 5 for detecting the position of a rotor (not shown) of the motor 1 and a control means 4 for ON / OFF controlling the switching means.

When the switching means 3 is applied to, for example, a three-phase brushless motor, the switching means 3 is constructed as shown by the drive circuit 9 in FIG. 2, and its description has been given above. A case where the motor is braked by using the drive circuit 9 will be described with reference to FIGS. 4 and 5. In FIG. 4, the drive circuit 9 is driven by rotating the motor from the outside.
FETs 15 to 20 in the FE located on the high side
When T15, 17, 19 are all turned off, and FETs 16, 18, 20 located on the low side are all turned on in (a), FETs 16, 18 are turned on and FET20 is turned off in (b). In (c), when only the FET 16 is turned on and all the other FETs are turned off in (c), the waveform of the braking current flowing in each phase coil is observed at the output terminals 10 to 12, respectively, and It is a figure which shows the rotor position in a case with the signal IHu which showed electrically.

First, as shown in FIG. 4 (a), alternating braking currents Iu, Iv, and Iw that flow with a phase difference of (2/3) π flow from the output terminals 10 to 12, respectively,
Since the principle of its occurrence is clear, its explanation is omitted. Attention is now paid to the braking current Iu flowing through the output terminal 10. In the section A shown in the figure, the braking current is negative. Even if the FET 16 is turned off in this section A, since a negative current is generated with respect to the power source, power regeneration is not performed. Next, in the case shown in FIG.
It becomes a negative braking current at. This section B is shorter than the section A and its amplitude is also smaller. Also in this case, if the FET 16 is turned off in the section B, the power is not regenerated. 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, the counter electromotive voltage is not generated, and thus the power regeneration is not performed.

Turning on the FETs 16, 18 and 20 during braking
Since the OFF state has been verified by the above-mentioned three patterns, it is understood that the section C is included in both the section A and the section B by examining the result. Therefore, if the FET 16 is controlled to be turned off in this section C, power regeneration to the power source will not be performed. Other FET 18,
The same can be said for 20. Since the coils 6 to 8 are wound with a phase angle of (2/3) π with respect to each other, in the case of the FET 18, from the off point of the FET 16 (2/3). It may be turned off after a delay of π, and FET20
In this case, if the power is turned off with a delay of (2/3) π, power regeneration will not be performed.

In the concrete control, the braking current is generated by the electromagnetic action of the coils 6 to 8 and the permanent magnet (not shown).
The point at which 8 and 20 are turned off is determined by the rotor position, which is fixed at the motor designing stage, although some deviation occurs depending on the rotation speed. Therefore, the rotor position detecting means 5 capable of detecting the rotor position and outputting the detection result as an electric signal is provided, that is, the FET.
This can be realized by providing corresponding Hall elements that output edge signals at the points where 16, 18, 20 are turned off. In this embodiment, since a rotor is a permanent magnet and a stator is a rotating field type brushless motor having field windings, although not shown in the drawing, an interval of 120 degrees is provided at appropriate positions of the stator. Is provided with three Hall elements.

FIG. 5 shows a waveform diagram of a signal output from the rotor position detecting means 5. The Hall element, which is the rotor position detecting means, has an edge signal I having a phase difference of (2/3) π from each other corresponding to the braking currents flowing through the terminals 10 to 12.
Hu, IHv, IHw are output to the control means 4. The control means 4 which receives the signal from the rotor position detecting means 5 performs the gate of each FET 16, 18, 20 so that the off point of each FET 16, 18, 20 at the time of braking is performed by the rising edge signal from each hall element. U-, V-, W
The signal is supplied to −. Position signals IHu, IHv, IHw at this time and respective FETs 16, 18, 20
The signal supplied to the gate of is different from the driving state of FIG.

By controlling on / off of each FET located on the low side in synchronization with the position signal by the control means 4, the motor can be braked without regenerating electric power to the power source. Specifically, as shown in FIG. 6, when the high side FETs 15, 17, and 19 are turned off, and the low side FET, for example, the FET 16 is on, when the position signal IHv rises, the FET1
6 is turned off and the position signal IHw is fed to the FET 18
The position control signal 20 is controlled to turn off when the corresponding position signal, such as the position signal IHu, rises. Therefore, the low side FETs 16, 18, 2
When turning off 0, the corresponding terminals 10 to 1
Since no current is flowing in 2 or a current of a negative component is flowing, a counter electromotive voltage is not generated or a negative current is generated with respect to the power source even if it is generated. Eliminates the need for power regeneration.

The braking force, except for mechanical elements, changes electrically according to the electric energy stored in each coil, that is, in this case, it changes according to the time during which the braking current flows. Is. Therefore, by changing the starting point for turning on each FET as shown in the section D in FIG. 6, for example, the braking force can be increased by increasing the time from on to off, and conversely by shortening the time. A small braking force can be obtained, and each FET1
When turning off 6, 18, 20, the current is not flowing or the current of the negative component is flowing, so the braking force can be variably controlled without performing power regeneration.

[0019]

As described above, according to the present invention, the short-circuited state of the coil can be released while the braking current is not flowing or the current of the negative component is flowing, so that the power regeneration is not performed. The braking force can be adjusted by changing the energization state to the coil by varying the starting point of the short-circuited state. Therefore, since the control can be performed without charge and the braking force can be changed, the effect is great.

[Brief description of drawings]

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

FIG. 2 is an electric circuit diagram showing an outline of 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 thereof showing states of signals supplied to respective switching elements when the motor of FIG. 2 is driven.

FIG. 4 is a waveform diagram showing a waveform observed at each terminal during braking of the motor of FIG.

5 is a diagram electrically showing the position of the rotor when the motor of FIG. 2 is being braked.

FIG. 6 is a waveform diagram supplied to each switching element during braking of the motor of FIG.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 motor 2 power supply 3 switching element 4 control means 5 rotor position detection 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 FETs 21-26 Diodes

Claims (3)

[Claims] 1. A control circuit for controlling braking of a motor by setting a plurality of coils of a brushless motor into a short-circuited state over a selected phase section, and switching means for selectively short-circuiting each of the coils. And an end point of the phase section is set to a point where power regeneration is not generally performed, and at this point, a control unit that controls the switching unit to release the short-circuited state of each coil is provided. Brushless motor control circuit. 2. The control means releases the short-circuited state of the coils when the braking current flowing by each coil generated by putting the respective coils into the short-circuited state is in the reverse direction or substantially zero. The brushless motor control circuit according to claim 1. 3. The control circuit for a brushless motor according to claim 1, wherein the control means controls the switching means so as to change the starting point of the short-circuited state of the coil.