JPH07184392A - Control circuit for brushless motor - Google Patents

Abstract

PURPOSE:To obtain a stable braking force without being affected by the rotating speed of a motor. CONSTITUTION:Switching means 3 for selectively setting short-circuit conditions for respective phase coils of a motor in order to apply a braking current when braking a motor 1 and also control means 4 for the variable control of short- circuit time of coils by switching means based on an electrical angle are provided. By doing this, a braking force required can easily be secured even though the period of a braking current changes according to the rotating speed of the motor, and the braking force can be almost univocally established as an electrical angle independently from the rotating speed. Therefore, a stable braking force can be secured regardless of the simplicity of the control method.

Description

Detailed Description of the Invention

[0001]

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

[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.

It has been clarified by actual measurement that the braking force thus PWM-controlled has the characteristics shown in FIG. In the braking control by the PWM method, the chopper frequency is fixed. Therefore, when controlling at the same frequency (duty cycle) when the rotation speed is high or low, the characteristics of the braking force depend on the motor rotation speed. There will be variations. For example, comparing the case where the rotation speed indicated by h in the figure is high and the case where it is low indicated by l when the duty cycle is controlled at 60%, when it is high, about 38 kgf
・ It can be seen that a braking force of cm can be secured, but when it is small, it is only about 4 kgf · cm. this is,
When the rotation speed of the motor is high, the period of the braking current is short and the time during which the current is flowing is largely controlled, whereas when the rotation speed is low, the period of the braking current is long and the current flows. This is because the chopper control is finely performed during the period of time. 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, Has a large duty cycle, and conversely, the duty cycle must be small when the motor is rotating at a low rotation speed, so complex control such as controlling the braking force according to the number of rotations is required. 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 influenced 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 braking of a motor by selectively setting a plurality of coils of a brushless motor in a short-circuited state. Control means for variably controlling the short-circuiting time of the coil by the switching means based on the electrical angle of the motor, the switching means for selectively short-circuiting each of the coils in order to flow a braking current. It is achieved by providing a motor control circuit characterized by having: Further, the control means is
The starting point for putting each coil into a short-circuited state is set to a point where power regeneration is not generally performed to control the switching means, or the switching means is arranged to change the end point of the short-circuited state of each coil. It is even better if it controls.

[0010]

With this configuration, the time during which the braking current flows is variably controlled based on the electrical angle of the motor, so that the desired braking force can be obtained even if the cycle of the braking current changes according to the rotation speed of the motor. It can be easily secured. Further, the braking force can be almost uniquely determined by the electrical angle regardless of the rotation speed.

[0011]

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, it 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.

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 the present 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, the alternating braking currents Iu, Iv, and Iw that flow with a phase difference of (2/3) π from each other are output terminals 10 to 12. 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 counter electromotive voltage generated is connected in series to the power source, so that power is not regenerated. Next, in the case shown in FIG.
Section B because 17 is on and FET 19 is off
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.
Since only 5 is turned on and all the other FETs are turned off, the braking current becomes 0 in the section C. This is a FET
This is because, since 18 and 20 are off, no current flows in the negative direction. Therefore, in section C, FET
When 16 is turned off, the counter electromotive voltage is not generated, and therefore the power regeneration is not performed.

Turning on the FETs 16, 18, and 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 suffices to turn it on after (2/3) π delay 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 where the above-mentioned FETs 16, 19, 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 synchronization 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, the turned-off FET is turned off in a pre-verified predetermined phase section.
As is clear from the braking characteristics shown in FIG.
The predetermined phase section is from 180 degrees to 180 degrees electrical angle, and each FET 16, 18, 20 is turned on at an electrical angle of 0 degree, and electrical angle 1
It is controlled so as to be turned 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, 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. Further, 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 can be changed by dividing the electrical angle by 60 degrees to variably control the braking force.

According to the present embodiment, as is apparent from the braking characteristics shown in FIG. 9, even if the rotation speed during braking changes, the braking current is cut off based on the electrical angle. In this case as well, substantially the same braking force can be secured, so that unlike the braking force control by the PWM method shown in FIG. Does not require control.

In this embodiment, three Hall elements are used to perform the braking control for every 60 electrical degrees, but the present invention is not limited to this. For example, the number of Hall elements is doubled. If this is done, braking control can be performed at every 30 electrical degrees, and by further increasing it, more detailed braking control can be performed. Also, if the time between edges is measured using a timer, the electrical angle can be taken into consideration, and a timer other than the above can be used to enable analog electrical angle control and perform braking 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 conventional PWM braking control. Therefore, it is possible to realize a braking control that can secure a stable braking force in spite of simple control without causing a problem such as a change in braking characteristic according to the above.

[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 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]

 1 Motor 2 Power Supply 3 Switching Means 4 Control Means 5 Rotor Position Detecting Means 6 U Phase Coils 7 Phase Coils 8 Phase Coils 9 Drive Circuits 10-12 Output Terminals 13 Power Supply Terminals 14 Ground Terminals 15-20 FETs 21-26 Diodes

Claims (3)

[Claims] 1. A control circuit for controlling braking of a motor by selectively setting a plurality of coils of a brushless motor to a short circuit state, wherein each of the coils is selectively applied to supply a braking current when the motor is braked. A motor control circuit comprising: switching means for setting a short-circuit state, and control means for variably controlling a short-circuit time of the coil by the switching means based on an electrical angle of the motor. 2. The motor control according to claim 1, wherein the control means controls the switching means by setting a starting point at which each of the coils is in a short-circuited state to a point where power regeneration is not generally performed. circuit. 3. The motor control circuit according to claim 1, wherein the control means controls the switching means so as to change the end point of the short-circuited state of each coil.