JPH08223977A - Control method for brushless motor - Google Patents

Abstract

PURPOSE: To prevent overcurrent of a motor without requiring a special hardware circuit. CONSTITUTION: In the method for controlling the r.p.m. of a brushless motor 4 by detecting the rotor position and switching the conduction to very the applying voltage, the position detection signal of a rotor 4a is fed to a microcomputer 20 where the applying voltage is calculated, as well as the r.p.m., based on the ON time of the position detection signal having a duty ratio determined by PWM system and an input current is detected through an input current detection circuit 10. A microcomputer 20 estimates the current of the armature winding of the brushless motor 4 based at least on the two of the r.p.m., applying voltage and input current thereof, and lowers the applying voltage, sustains the applying voltage, as it is, for a predetermined time or stops operation of the brushless motor 4 depending on the current thus estimated.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a control technology for a sensorless DC brushless motor (hereinafter referred to as a brushless motor), and more particularly to a control method for a brushless motor which prevents an overcurrent of the motor.

[0002]

2. Description of the Related Art In a brushless motor control method of this type, the energization of the armature winding of the brushless motor is switched based on the position detection of the rotor of the brushless motor, while the rotational speed of the brushless motor is controlled. In order to achieve this, the energization voltage (applied voltage) of the armature winding is chopped and varied.

Therefore, in a control device to which the control method is applied, as shown in FIG. 9, for example, a commercial power source 1 is converted into a direct current by a converter section 2, and this converted direct current power source is switched by an inverter section 3 to generate three DC currents. It is supplied to the brushless motor 4 as phase alternating current.

Further, the terminal voltage (induced voltage) of the armature winding of the brushless motor 4 is input to the position detection circuit 5, which detects the induced voltage and the reference voltage (for example, the applied voltage of the brushless motor 4). 1/2) of
The signal of the comparison result (position detection signal) is output to the microcomputer 6.

The microcomputer 6 drives the switching elements (transistors U, V, W, X, Y, Z) of the inverter unit 3 based on the position detection signals for controlling the rotation of the brushless motor 4 (drive signals ( An energization switching signal of the brushless motor 4) and a chopping signal (PWM signal of PWM method) for chopping the driving period thereof are output to the chopping circuit 7. The chopping circuit 7 chops a predetermined drive signal and outputs it to the drive circuit 8,
The drive circuit 8 drives the predetermined transistors U, V, W, X, Y, Z of the inverter unit 3.

The position detection circuit 5 includes, for example, a resistance circuit for dividing the applied voltage of the brushless motor 4 into 1/2.
This divided voltage is used as a reference voltage for comparison with the terminal voltage (induced voltage) of the armature winding.

Further, the control device outputs an input current detection signal to the microcomputer 6 based on the current sensor 9 for detecting the input current (primary side current) in order to limit the input current and the detected current. Input current detection circuit 10
And secondary current (motor current) for overcurrent protection function
And a current sensor 11 that detects the current and an overcurrent detection circuit 12 that outputs an overcurrent detection signal (for example, L or H level) to the microcomputer 6 based on the detected current.

For example, when the brushless motor 4 is used as a compressor motor for an air conditioner or the like, the load fluctuates, and when this load becomes very heavy, the microcomputer 6 causes the rotation speed of the compressor motor to be commanded due to the overload. Increase the voltage applied to the compressor mode so that it does not fall below the rotational speed.

When the state of high applied voltage continues for a long time, the current (motor current) flowing through the armature winding (compressor motor) of the brushless motor 4 increases, and the transistors U, V, W of the inverter section 3 increase. , X, Y, Z may be damaged.

In this case, the overcurrent detection circuit 12 outputs an overcurrent detection signal when the motor current (secondary side current) reaches a limit value, integrates the secondary side current, and outputs the integration result. Also outputs a different kind of overcurrent detection signal when reaches a predetermined value. The microcomputer 6 stops the compressor motor when the secondary side current reaches the limit value, and the secondary side current gradually increases, and when this state has passed for a predetermined time, the compressor motor Lower the number of revolutions.

Further, in response to the input current detection signal from the input current detection circuit 10, the microcomputer 6 stops the compressor motor or lowers the rotation speed so that the input current of the device does not exceed the allowable value for use.

As described above, since the input current (primary side current) does not exceed the allowable value for use and the motor current (secondary side current) does not become an overcurrent, the control device, for example, The safety and reliability of the air conditioner can be improved.

[0013]

However, in the above brushless motor control method, a special circuit (current sensor and overcurrent detection circuit) is required for overcurrent protection for preventing overcurrent of the motor. For example, when it is applied to an air conditioner, it not only increases the cost but also hinders downsizing.

The present invention has been made in view of the above problems, and an object thereof is to provide a control method of a brushless motor capable of preventing an overcurrent of a motor without using a special hardware circuit. Especially.

[0015]

In order to achieve the above-mentioned object, the present invention switches the position of the rotor of the brushless motor when switching the DC power supply and supplying the brushless motor to control the rotation of the brushless motor. While switching the energization of the brushless motor to detect the, while controlling the rotation speed by varying the applied voltage of the brushless motor, at least based on the rotation speed and the applied voltage of the brushless motor. The current of the armature winding of the brushless motor is estimated, and the applied voltage of the brushless motor is reduced by the estimated current, or the applied voltage of the brushless motor is maintained for a predetermined time, or the operation of the brushless motor is stopped. The point is to do so.

Further, according to the present invention, a DC power supply obtained by converting an AC power supply into a DC power is switched to be supplied to a brushless motor, and when the brushless motor is rotationally controlled by a PWM system, the rotor of the brushless motor is controlled. While detecting the position and switching the energization of the brushless motor, in the method of controlling the brushless motor in which the applied voltage of the brushless motor is varied to control the rotational speed, the rotational speed of the brushless motor is detected by detecting the position of the rotor. Then, the applied voltage is calculated based on the ON time of the duty ratio of the chopping signal according to the PWM method, the input current from the AC power supply is detected, and the rotation speed, the applied voltage, and the input are detected. The brushless motor is based on current, or on the basis of two of the rotation speed, applied voltage and input current. Of the current of the armature winding, and the applied voltage of the brushless motor is lowered by the estimated current, or the applied voltage of the brushless motor is maintained for a predetermined time, or the operation of the brushless motor is stopped. It is a thing.

Further, according to the present invention, when the estimated current has reached a predetermined value and the state has not continued for a predetermined time, the applied voltage of the brushless motor is lowered or the applied voltage of the brushless motor is left as it is for a predetermined time. ,
When the estimated current reaches a predetermined value and the state continues for a predetermined time, the operation of the brushless motor is stopped.

[0018]

According to the above means, even if the number of rotations of the brushless motor is the same, the applied voltage is changed according to the weight of the load, and accordingly, the input of the circuit for supplying power to the brushless motor is input. The current (primary side current) changes. That is, if the applied voltage is not increased as the load becomes heavier,
This is because the rotation speed will decrease.

Therefore, when controlling the rotation of the brushless motor, the rotation speed and applied voltage of the brushless motor are detected, and the input current of the circuit is detected, and based on these rotation speed, applied voltage and input current. The armature winding current (motor current) is estimated. For example, even at the same rotation speed, the heavier the load, the larger the applied voltage and the input current, that is, the larger the motor current.

The applied voltage of the brushless motor is lowered based on the estimated current, or the applied voltage is maintained for a predetermined time, or the operation of the brushless motor is stopped.

For example, the estimated current has reached a predetermined value (a value slightly lower than the limit value in the conventional overcurrent protection function), but when this state does not continue for a predetermined time, the motor current does not become so large. Therefore, the applied voltage of the brushless motor is lowered, or the applied voltage is maintained as it is. Further, when the estimated current reaches a predetermined value, and when this state continues for a predetermined time, it is highly possible that the motor current becomes abnormally large,
The operation of the brushless motor is stopped.

As described above, overcurrent of the brushless motor can be prevented without using a current sensor or an overcurrent detection circuit.

[0023]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS In the present invention, the current flowing in the armature winding of a brushless motor can be estimated at least by the applied voltage and the number of revolutions of the brushless motor. This is because it can be assumed that a considerable amount of current will flow in the armature winding when it is necessary to raise it to zero.

Therefore, the control device to which the brushless motor control method of the present invention is applied has the configuration shown in FIG. In the figure, the same parts as those in FIG. 9 are designated by the same reference numerals, and the duplicated description will be omitted.

In FIG. 1, this control device includes a brushless motor 4 in addition to the microcomputer 6 shown in FIG.
When the applied voltage of the brushless motor 4 needs to be raised to a value equal to or higher than the specified applied voltage when is a predetermined rotation speed, it is estimated that a considerable current is flowing in the armature winding of the brushless motor 4, and The microcomputer 20 is provided with a function of not increasing the above and maintaining this state for a predetermined time or stopping the operation of the brushless motor 4. Therefore, as apparent from FIG. 1, the current sensor 11 and the overcurrent detection circuit 12 shown in FIG. 9 are omitted in this control device.

Next, the operation of the control device will be described in detail with reference to the flow chart of FIG. 2 and the graphs of FIGS. The microcomputer 20 calculates the energization switching timing of the brushless motor 4 based on the position detection signal from the position detection circuit 6, and switches energization at this calculation timing.

At this time, the microcomputer 20 detects the rotation speed f, the input current I and the applied voltage V (step ST1). The rotation speed f is calculated based on the position detection signal from the position detection circuit 5, and the input current I is calculated based on the input current detection signal from the input current detection circuit 10.
The applied voltage V is calculated based on the chopping signal (duty ratio ON time).

Then, the current flowing in the armature winding of the brushless motor 4 is estimated based on the calculated rotation speed f, the input current I and the applied voltage V (step ST).
2). In this case, the applied voltage changes depending on the weight of the load even at the same rotation speed. For example, brushless motor 4
Is the same as the rotational speed fa, but when the load is light,
As shown in Fig. 5, the applied voltage is Va, and when the load is heavy, the applied voltage is Vd (> Va) as shown in Fig. 5,
When the load is extremely heavy, the applied voltage becomes Vg (> Vd) as shown in FIG.

Further, as shown in FIGS. 3, 5 and 7, even if the brushless motor 4 has the same rotation speeds fb and fc,
The applied voltage varies depending on the load. Note that in FIGS. 3, 5, and 7, the applied voltage is Vb <Ve <Vh and Ve <
Vf <Vi.

As described above, even if the number of revolutions is the same, the applied voltage changes depending on the weight of the load. Therefore, the current flowing through the armature winding can be estimated based on the current number of revolutions and the applied voltage. You can Note that this estimation is based on information obtained empirically (for example, the change count of the applied voltage).

For example, if the applied voltage V is Va and the load is light at the same rotation speed fa (see FIG. 3), it can be inferred that the current in the armature winding is not large. If the voltage V is Vd, the load is heavy (see FIG. 5), so it can be inferred that the current in the armature winding is large, and if the applied voltage V is Vg, the load is extremely heavy (see FIG. 5). It can be inferred that the current in the armature winding is extremely large.

Further, not only the applied voltage V changes according to the weight of the load, but as shown in FIGS. 4, 6 and 8,
The input current (primary side current) changes. In addition, in FIG. 4, FIG. 6 and FIG. 8, the input current I is Ia <Id <Ig,
Ib <Ie <Ih and Ic <If <Ii.

Therefore, when estimating the current in the armature winding, the current in the armature winding can be estimated more accurately by considering not only the rotational speed f and the applied voltage V but also the input current I. it can. It should be noted that the current of the armature winding can be estimated if there are at least two of the rotational speed f, the applied voltage V, and the input current I.

Then, it is determined whether or not the estimated armature winding current has reached a predetermined value (step ST3).
The predetermined value is, for example, a value slightly smaller than the limit value described in the conventional example. When the current in the armature winding does not reach the predetermined value, it is determined that the normal operation is performed, the process returns to step ST1, and the above steps are repeated.

However, when the current in the armature winding reaches the predetermined value, the process proceeds to step ST4, and it is determined whether or not this state continues for a predetermined time. When the current in the armature winding reaches a predetermined value and this state has not continued for a predetermined time, the current does not increase so much and it is determined that there is no urgent abnormal situation, and the applied voltage V is lowered, or The applied voltage V is not increased and is kept as it is (step ST5). When the current in the armature winding reaches a predetermined value and this state continues for a predetermined time, the current is likely to increase, and it is determined that the emergency situation is an emergency, and the brushless motor 4 is operated. Is stopped (step ST6).

In this way, the current of the armature winding of the brushless motor 4 is estimated, and the applied voltage is varied according to the estimated current, or the applied voltage is left unchanged, or the operation of the brushless motor 4 is stopped. Since it was set,
Even if there is no special circuit of the current sensor 11 and the overcurrent detection circuit 12 shown in FIG. 1, the overcurrent protection function can be operated to prevent the overcurrent of the motor. , X, Y, Z can be prevented from being damaged.

[0037]

As described above, according to the present invention, when controlling the rotation of the brushless motor, the position of the rotor of the brushless motor is detected and the energization of the bushless motor is switched, while the applied voltage of the brushless motor is changed. A method for controlling a brushless motor that variably controls the number of revolutions, based on at least two of the number of revolutions of the brushless motor, an applied voltage, and an input current (primary side current) of a circuit that supplies power to the brushless motor. The current of the armature winding of the brushless motor is estimated, and the applied voltage of the brushless motor is lowered by this estimated current, or the applied voltage of the brushless motor is maintained for a predetermined time, or the operation of the brushless motor is stopped. So
Without using a special hardware circuit (current sensor or overcurrent detection circuit for overcurrent protection), it is possible to prevent overcurrent of the motor, which in turn can prevent damage to the drive transistor of the motor. Further, there is an effect that the cost of the device using this motor can be reduced.

[Brief description of drawings]

FIG. 1 is a schematic block diagram of a control device to which an embodiment of the present invention is applied and to which a brushless motor control method is applied.

FIG. 2 is a schematic flowchart for explaining the operation of the control device shown in FIG.

3 is a schematic graph for explaining the operation of the control device shown in FIG.

FIG. 4 is a schematic graph for explaining the operation of the control device shown in FIG.

5 is a schematic graph for explaining the operation of the control device shown in FIG.

6 is a schematic graph for explaining the operation of the control device shown in FIG.

7 is a schematic graph for explaining the operation of the control device shown in FIG.

8 is a schematic graph for explaining the operation of the control device shown in FIG.

FIG. 9 is a schematic block diagram of a conventional brushless motor control device.

[Explanation of symbols]

1 AC power supply 2 Converter part 3 Inverter part 4 Brushless motor (sensorless DC brushless motor) 4a Rotor 5 Position detection circuit 6,20 Microcomputer 7 Chopping circuit 8 Drive circuit 9 Current sensor 10 Input current detection circuit

Claims (3)

[Claims] 1. A brushless motor is detected by detecting the position of a rotor of the brushless motor to switch the energization of the brushless motor when the brushless motor is rotated and controlled by switching a DC power supply to the brushless motor. In a method of controlling a brushless motor by varying the applied voltage to control the rotation speed, at least estimating the current of the armature winding of the brushless motor based on the rotation speed and the applied voltage of the brushless motor, A method for controlling a brushless motor, characterized in that the applied voltage of the brushless motor is lowered by an estimated current, or the applied voltage of the brushless motor is kept as it is for a predetermined time, or the operation of the brushless motor is stopped. 2. The position of the rotor of the brushless motor is detected when the DC power obtained by converting the AC power to DC is switched and supplied to the brushless motor, and the rotation of the brushless motor is controlled by the PWM method. In the control method of the brushless motor, which controls the rotation speed by changing the voltage applied to the brushless motor while switching the energization of the same bushless motor, the rotation speed of the brushless motor is calculated based on the position detection of the rotor. Then, the applied voltage is detected based on the ON time of the duty ratio of the chopping signal by the PWM method, the input current from the AC power supply is detected, and the rotation speed, the applied voltage, and the input current are detected. Estimate the current in the armature winding of the same brushless motor based on two of the rotation speed, applied voltage and input current In addition, the applied voltage of the brushless motor is reduced by the estimated current, or the applied voltage of the brushless motor is kept for a predetermined time, or the operation of the brushless motor is stopped. Method. 3. The position of the rotor of the brushless motor is detected when the DC power obtained by converting the AC power into DC is switched and supplied to the brushless motor, and the rotation of the brushless motor is controlled by the PWM method. In the control method of the brushless motor, which controls the rotation speed by changing the voltage applied to the brushless motor while switching the energization of the same bushless motor, the rotation speed of the brushless motor is calculated based on the position detection of the rotor. Then, the applied voltage is calculated based on the ON time of the duty ratio of the chopping signal according to the PWM method, and the input current from the AC power supply is detected,
While estimating the current in the armature winding of the brushless motor based on the rotational speed, the applied voltage and the input current, or based on two of the rotational speed, the applied voltage and the input current, When the estimated current reaches a predetermined value, and when the state does not continue for a predetermined time, the applied voltage of the brushless motor is lowered, or the applied voltage of the brushless motor is kept for a predetermined time, and the estimated current reaches a predetermined value, A method of controlling the brushless motor is characterized in that the operation of the brushless motor is stopped when the state continues for a predetermined time.