JPH07184394A - Control circuit for brushless motor - Google Patents

Abstract

PURPOSE:To provide a control circuit for a brushless motor capable of variably controlling a braking force by using a low function microcomputer. CONSTITUTION:Switching means 3 for individually setting each coil of a motor 1 to short-circuit conditions and also control means 4 for ON/OFF controlling the switching means 3 for each coil are provided, and the control means 4 selectively controls the number of coils set to short-circuit conditions. Therefore, each coil is continuously set to a short-circuit state based on an electrical angle of the motor, so that a braking current as a generating source of a braking force can be obtained and therefore the braking force can be secured; and this braking force becomes variable according to the number of coils selected because the number of coils is selectively set to short-circuit conditions by the control means. Thus, a stable braking force can be secured even though the control is very simple.

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 variably controlling the braking force of a motor by selectively bringing a plurality of coils of the motor into a conductive state.

[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, the high-side FETs 15, 17, 19 are all turned off, and the low-side FETs 16, 18, 20 are turned on to short-circuit the coil, which is generated by electromagnetic action. A braking force is secured by controlling the braking current with a chopper. That is, 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), a positive braking current flows in the coil 6, for example. The FET 16 is cut off during the operation, and the counter electromotive voltage generated by the cutoff of the current is regenerated to the power source to secure the braking force and charge the battery.

There are various drawbacks in the above-mentioned motor braking control by the PWM control, and in order to eliminate the drawback that the characteristic of the braking force changes for each rotation speed as a representative thereof.
The present inventor has proposed a technique for variably controlling the short circuit time of the coil based on the electrical angle of the motor. According to this technology, PW
Although it is possible to eliminate the drawbacks of M control, it is difficult to apply it to a microcomputer without a timer because it uses a high-performance microcomputer with multiple timers / counters 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 the braking force by using a low-performance microcomputer. It is in.

[0008]

According to the present invention, there is provided a control circuit for controlling braking by setting a plurality of coils of a brushless motor in a short-circuited state based on the electrical angle of the motor. It has a switching means for individually setting the coils into a short-circuited state, and a control means for performing on / off control of the switching means for each of the coils, and the control means sets the respective coils in the short-circuited state. This is achieved by providing a control circuit for a brushless motor which is characterized by selectively controlling the number.

[0009]

With this configuration, the braking force can be generated by putting the coils in the short-circuited state, and the number of the coils is selectively made into the short-circuited state. Therefore, the braking force is controlled according to the number of the selected coils. Power can be changed.

[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, a motor is rotated from the outside to create a pseudo braking state, and the FETs 15 to 20 in the drive circuit 9 are
All the FETs 15, 17, and 19 located on the high side are turned off, and the FETs 16, 18, and 20 located on the low side are turned off.
In (a), when all are turned on, in (b) when FETs 16 and 18 are turned on and FET 20 is turned off, in (c), only FET 16 is turned on and other FETs are turned on. FIG. 3 is a diagram showing the waveforms of the braking currents flowing through the coils of each phase when they are all turned off at the output terminals 10 to 12, and showing the rotor position in each case together with a signal IHu that electrically indicates the rotor position. .

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.
And a permanent magnet (not shown). In this embodiment, a rotating field type brushless motor including a permanent magnet in the rotor and a three-phase field winding star-connected to the stator is provided. Therefore, when all the phases are short-circuited, the alternating braking currents Iu, Iv, and Iw flowing with a phase difference of (2/3) π from each other are output as shown in FIG. 4A. It can be observed at terminals 10-12. It is well known that the braking current thus generated has a short cycle when the rotation speed is high, and has a long cycle when the rotation speed is low. Also, since the braking force uses regenerative braking, when regenerating electric power to the DC power supply,
The braking force is obtained by regenerating the counter electromotive voltage generated by cutting off the positive braking current (current flowing in the direction of arrow A in FIG. 2) to the power supply. In addition, the electric angle of the motor in this case represents one cycle of the braking current as an angle, and an electric angle of 360 degrees is one cycle of the braking current. This electrical angle can be detected by a Hall element which is a magnetic field sensor.

Next, let us consider the relationship between the braking current and the short-circuited state of each coil 6-8. As shown in FIG. 4A, all the FETs 15, 17, 19 located on the high side are turned off, and the FETs 16, 18, located on the low side are turned off.
When all 20 are turned on, alternating braking currents Iu, Iv, and Iw that flow with a phase difference of (2/3) π flow to the output terminals 10 to 12. 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, a negative current is generated, so that power is not regenerated. Next, in the case shown in FIG. 4B, since the FETs 15 and 17 are turned on and the FET 19 is turned off, a negative braking current is obtained in the section B. 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, since only the FET 15 is turned on and all the other FETs are turned off, the braking current is 0 in the section C.
Becomes This is because the FETs 18 and 20 are off and no current flows in the negative direction. 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, 20 during braking
Since the OFF state is verified by the above-described 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 turned on in this section C and turned off in a predetermined phase section, electric power is regenerated to the power supply. The same applies to the other FETs 18 and 20. Since the coils 6 to 8 are star-connected, in the case of the FET 18, it may be turned on with a delay of (2/3) π from the off point of the FET 16. In the case of the FET 20, if it is turned on with a delay of (2/3) π, power regeneration is performed.

When specifically controlling the braking force, the braking current is generated by the electromagnetic action of the coils 6 to 8 and the permanent magnet (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 is slightly deviated by the rotation 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, that is, Hall ICs that output edge signals at the points at which the FETs 16, 18, and 20 are turned on are provided correspondingly. In the present embodiment, although not shown, Hall ICs including three Hall elements are provided at appropriate positions on the stator at intervals of 120 degrees.

FIG. 5 shows a waveform diagram of a signal output from the rotor position detecting means 5. The Hall IC, which is the rotor position detecting means, has the edge signals IHu, IHv, IHw corresponding to the points at which the above-mentioned FETs 16, 18, 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, and IHw to make the electrical angle 60 degrees. It is divided for each and used as a timing signal at the time of controlling the braking force described later. Position signals IHu, IHv, IHw at this time and respective FETs 16, 18, 2
The supply signal to the gate of 0 is different from the driving state of FIG.

Next, the control means 4 turns on / off each FET located on the low side in synchronism with the position signal to regenerate electric power to the power source to brake the motor. 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, the FET 1 is turned on when the position signal IHv rises.
6 is turned on, and the position signal IHw is fed to the FET 18 by the FET
The position control signal IHu is controlled to turn on when the corresponding position signals 20 rise. Further, when turning off the turned-on FET, it turns off in a pre-verified predetermined phase section.
As is clear from the braking characteristics shown in FIG. 9, the rising point of the braking current in the section C is defined as an electrical angle of 0 degree, and the electrical phase of 0 degree to 180 degrees is defined as a predetermined phase section, Each FET16,18,2 at an electrical angle of 0 degree
It is controlled to turn on 0 and turn off within a section up to an electrical angle of 180 degrees. Here, FIG. 8 shows the relationship between the braking force and the electrical angle, and FIG. 9 shows the relationship between the charging current flowing through the terminal 13 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, the braking current takes a maximum value in the vicinity of an electrical angle of about 180 degrees, so that the maximum braking force can be secured by turning off at this point.

As described above, it is obvious that the braking force can be variably controlled by controlling the short circuit state of the coil based on the electric angle of the motor. In variably controlling the braking force, for example, a timer may be used to start the timer at the rising edge of the position signal and count up at the next rising edge to convert the electrical angle into time and perform variable control. However, if the control means is a small-scale microcomputer with no room for a timer / counter or the like, it is difficult to adopt the above technique. Therefore, the present invention variably controls the braking force by selecting the coil to be short-circuited. This will be specifically described below.

As described with reference to FIG. 4, since the braking force is obtained by regenerating the counter electromotive voltage generated by cutting off the positive component of the braking current, as shown in FIG. If the FETs 16, 18, and 20 are controlled to be turned on and off, a braking current that is a positive component can be obtained in each phase coil, and a large charging current can be obtained by cutting off the positive braking current. Therefore, a large braking force can be secured (shown by solid lines in FIGS. 8 and 9). Next, as shown in FIG. 7B, the FETs 16 and 18 are turned on.
In the case of the OFF control target, a positive braking current does not flow in the terminal 12, so that the charging current flowing in the terminal 13 decreases. Therefore, the braking force is also relatively reduced as compared with the above (indicated by a chain line in FIGS. 8 and 9). Furthermore,
As shown in FIG. 7C, if only the FET 16 is controlled to be turned on and off, a positive braking current does not flow to the terminals 11 and 12, so that the charging current further decreases and the braking force also decreases. (Shown by broken lines in FIGS. 8 and 9).

As described above, the braking force controlled for each electrical angle 60 by the edge of the position signal by selecting each phase coil to bring it into a short-circuited state has a triple resolution in this case. It is possible to control and obtain three different braking forces at the same electrical angle. Therefore, since the resolution of the braking force can be increased without using a timer / counter or the like, sufficient braking control can be realized even by using a low-performance microcomputer.

[0022]

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 / counters or the like, a simple microcomputer can be adopted, and the product cost can be reduced. A stable braking force can be achieved despite the simple control without causing the problem that the braking characteristic changes according to the rotation speed of the motor, which has been a problem in the conventional PWM-based braking control. The braking control that can generate

[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.

FIG. 7 is a diagram showing a state of each switching element when the motor of FIG. 2 is being braked.

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]

 DESCRIPTION OF SYMBOLS 1 motor 2 power supply 3 switching means 4 control means 5 rotor position detection 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

Claims (1)

[Claims] 1. A control circuit for controlling braking by setting a plurality of coils of a brushless motor into a short-circuited state based on an electrical angle of the motor, the switching circuit comprising: a switching unit for individually short-circuiting each coil; And a control unit for performing on / off control of each coil, wherein the control unit selectively controls the number of the coils in the short-circuited state. circuit.