JP2002247873A - Electric motor controlling method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress the change of a rotational speed during one rotation by restraining load torque, and to expand an operating range in a low-revolution region in an electric motor. SOLUTION: This electric motor controlling method is provided for suppressing the change of load torque during one rotation in an electric motor for a compressor and the like. While the driving torque of the electric motor is generated in accordance with the change of the load torque, the rate of change of the driving torque during one rotation is made variable in accordance with the result of a comparison of target revolutions with current ones (Fig. 1 (a) or Fig. 1 (b)). In this case, when the driving torque shown in the Fig. (a) is generated, the power-on time of switching elements at the position of the smallest driving torque during one rotation is a minimum value, and when the target revolutions of the electric motor is fewer than the current ones, the rate of change of the driving torque is made smaller (Fig. 1(b)), and the power-on time is shortened of the switching elements of an inverter that drives the electric motor at the position of larger driving torque.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a control technique for an electric motor used for a compressor of an air conditioner, and more particularly to a control method for an electric motor for reducing a variation in load torque during one rotation.

[0002]

2. Description of the Related Art As shown in FIG. 5 (a), for example, when the rotation of a motor is controlled, if the load torque of the motor does not fluctuate during one rotation, even if the energization time of the motor is kept constant, it will be 1
The rotation speed during rotation does not fluctuate. However, when the load torque fluctuates during one rotation, the rotation speed during one rotation greatly fluctuates while the energization time of the motor remains constant. For example, in a compressor or the like of an air conditioner, load torque fluctuation occurs during one rotation due to refrigerant suction, compression and discharge cycles, so that the rotation speed fluctuation of the electric motor increases, causing noise and vibration. .

In the case of controlling the rotation of a motor having a load torque fluctuation during one rotation, for example, as shown in FIG. 5B, the energization time of the motor is changed according to the load torque fluctuation. By adjusting the torque to the fluctuation of the load torque, the rotation speed of the electric motor is suppressed to reduce noise and vibration.

As a control device for controlling the rotation of the electric motor, there is, for example, a control device shown in FIG. This control device converts an AC power supply 1 into a predetermined DC voltage by an AC / DC conversion circuit 2, and switches this DC voltage by switching elements Ua, Va, Wa, X, Y, and Z of an inverter circuit 3. A rectangular wave voltage of a phase is applied to the armature windings U, V, W of the electric motor (for example, a brushless motor) 4.

The position detection circuit 5 compares an induced voltage waveform (induced voltage waveform generated in a non-energized phase) included in the terminal voltages of the armature windings U, V, and W of the brushless motor 4 with a reference value. To detect a half point of the induced voltage waveform.
A position detection signal including the / 2 point is output to a control circuit (mainly composed of a microcomputer) 6.

The control circuit 6 determines the energization switching timing of the armature windings U, V, W on the basis of the input position detection signal, and outputs a drive signal of the energization switching timing via the driving circuit 7 to the inverter circuit. Output to 3. When the PWM control method is used to control the brushless motor 4, the control circuit 6 generates a PWM waveform (predetermined on / off ratio) for setting the rotation speed of the brushless motor 4 to the target rotation speed. The PWM waveform is superimposed on the drive signal.

The operating time of the switching element of the inverter circuit 3 corresponds to the above-mentioned energizing time of the electric motor (see FIG. 5). This energizing time is determined by the on-time of the switching element in each energizing section of the energizing pattern. Of total time. Accordingly, the energization time is changed by changing the ON ratio of the PWM waveform, so that the applied voltage (output voltage) of the brushless motor 4 can be changed.

As described above, when the switching elements Ua, Va, Wa, X, Y, and Z of the inverter circuit 3 are turned on and off in a predetermined manner and the energization of the armature windings U, V, and W is switched, the brushless motor 4 generates a rotational torque. In this case, the current rotation speed is calculated based on the detection interval of the position detection signal, and the calculated current rotation speed is compared with the target rotation speed.
By feeding back the difference to the on / off ratio of the PWM waveform, the rotation speed of the brushless motor 4 can be controlled to the target rotation speed.

In addition, the generated driving torque is large at a position where the load torque is large (a conduction section), and the generated driving torque is small at a position where the load torque is small, so that the driving torque of the brushless motor 4 is adjusted to the fluctuation of the load torque. That is,
As shown in FIG. 5B, the energization time is changed for each energization section interval in the energization pattern. As a result, the load torque fluctuation is suppressed by the driving torque.

[0010]

However, in the above-described electric motor control method, the rotational speed of the brushless motor 4 is not lower than a certain value when the torque control for suppressing the fluctuation of the load torque is performed. Therefore, the minimum number of revolutions (minimum number of revolutions) is large to some extent, and there is a disadvantage that it is difficult to operate in a low rotation speed region.

That is, when the torque control is performed, the inverter circuit 3 is generally used due to the problem of position detection.
In some cases, the minimum value of the energization ON time of the switching element is limited, and the driving torque during one rotation must secure the minimum value of the energization ON time at the minimum position. This is because the power-on time cannot be reduced to the minimum value at the position.

In other words, when the rate of change of the driving torque during one rotation is large (that is, when the difference between the maximum driving torque and the minimum driving torque is large), at the position where the driving torque is large, the energization ON time of the switching element is reduced. The drive torque does not decrease by more than the difference, and if the energization ON time at the position where the drive torque is the smallest is the minimum value, it does not reach the minimum value.

For the above reasons, for example, when the brushless motor 4 is used for a compressor of an air conditioner, the minimum number of revolutions of the brushless motor 4 cannot be reduced. Difficult to do, too cold or too warm,
This leads to a decrease in the comfort of the indoor environment.

SUMMARY OF THE INVENTION The present invention has been made in consideration of the above problems, and has as its object to reduce load torque fluctuations during one rotation and lower the minimum rotation speed to widen the operating range at low rotation speeds. In particular, it is an object of the present invention to provide a method for controlling an electric motor that can improve the comfort of an indoor environment when applied to a compressor of an air conditioner.

[0015]

In order to achieve the above object, the present invention converts an AC power supply into a DC voltage and supplies the DC voltage to an inverter circuit. While controlling the inverter circuit based on the position of the rotor of the motor, and controlling the rotation of the motor by switching the energization of the armature windings of the motor during one rotation of the motor. A method for controlling a motor that suppresses fluctuations in the load torque of the motor, wherein the driving torque of the motor is generated in accordance with the fluctuations of the load torque, and the rate of change of the driving torque during one rotation is at least the target rotation speed. It is characterized in that it can be varied according to the result of comparison with the current rotational speed.

According to the motor control method of the present invention, while the drive torque of the motor is generated in accordance with the fluctuation of the load torque, the rate of change of the drive torque during one rotation is variable at least according to the current rotation speed. Possible and the above 1
When the energization ON time of the switching element at the position where the driving torque during rotation is the minimum is the minimum value, and the target rotation speed of the electric motor is lower than the current rotation speed, the change rate of the driving torque is reduced. Thus, the power-on time of the switching element at the position where the drive torque is large is shortened.

When the target rotation speed of the electric motor becomes higher than the current rotation speed, the change rate of the drive torque may be increased. Thereby, even if the rotation speed of the motor increases and the load torque fluctuation changes, the driving torque of the motor can be adjusted to the load torque fluctuation.

When the rate of change of the driving torque becomes equal to or more than a predetermined value, the driving torque of the electric motor may be generated in accordance with the fluctuation of the load torque, and the control may be returned to the normal feedback control. As a result, the change rate of the drive torque does not become unnecessarily large, and the load torque fluctuation is suppressed without increasing the load torque fluctuation.

[0019]

FIG. 1 is a block diagram showing an embodiment of the present invention.
This will be described in detail with reference to FIG. In FIG. 2,
The same parts as those in FIG. 6 are denoted by the same reference numerals, and redundant description will be omitted.

1 (a) and 1 (b), the motor control method of the present invention enables the change rate of the drive torque (output torque) of a motor (eg, a brushless motor) to be variable, and Small position (current section)
When the energization ON time to the drive element of the brushless motor (the switching element of the inverter circuit) is the minimum value and the target rotation speed of the brushless motor is lower than the current rotation speed, the change rate of the drive torque is reduced. (Fig. (B)
), The minimum rotation speed of the brushless motor at low rotation can be reduced as much as possible during torque control for suppressing load torque fluctuation during one rotation of the brushless motor.

The drive torque change rate means the change rate of the drive torque during one rotation, and as shown in FIG. 1A, the change of the drive torque during one rotation (the maximum drive torque and the minimum drive torque Is greater, the rate of change in drive torque is greater. Also, as shown in FIG. 1B, if the change in the driving torque during one rotation is small,
It is said that the driving torque change rate is small.

Explaining the change of the drive torque change rate, when the change rate is decreased, the drive torque during one rotation is relatively reduced, and is reduced by a predetermined ratio (percentage). It should be noted that the drive torque is reduced according to the magnitude of each drive torque. In other words, the rate of descent may be increased at locations where the drive torque is high, and the rate of descent may be reduced at locations where the drive torque is low. When the drive torque change rate is increased, the drive torque change rate is opposite to the decrease in the change rate. That is, the drive torque during one rotation is relatively increased, or is increased in accordance with the magnitude of each drive torque.

Therefore, as shown in FIG. 2, the control device to which the motor control method of the present invention is applied, at the time of torque control, determines at least the driving torque based on the magnitude relationship between the rotation speed of the brushless motor 4 and the target rotation speed. A control circuit (microcomputer) 10 for increasing the rate of change or decreasing the rate of change is provided, the applied voltage (minimum output voltage) of the brushless motor 4 is made as small as possible, and the range of low-speed operation is widened. Become. The control circuit 10 also has the function of the control circuit 6 shown in FIG.

Next, the operation of the control device having the above configuration will be described with reference to the flowchart of FIG. 3 and the graph of FIG. First, the control circuit 10 calculates the position detection interval based on the position detection signal, and outputs a drive signal based on the energization switching timing of the brushless motor 4 on the basis of the position detection interval in the same manner as in the related art. It drives and switches the energization of the brushless motor 4 to perform rotation control.

In the case where the PWM control method is adopted for the brushless motor 4, as in the conventional case, the rotation speed of the brushless motor 4 is set to the target rotation speed.
A PWM waveform having an OFF ratio is generated and superimposed on the drive signal.

At this time, a driving torque is generated in accordance with the rotation speed fluctuation of the brushless motor 4. The drive torque is determined, for example, based on the length of the energizing section (or the position detection interval). When the position interval time is long, the energization time is increased. The time is shorter than the energization time.

By performing such feedback control, when the target rotation speed of the brushless motor 4 changes,
Since the rotation speed fluctuation also changes, the driving torque changes in accordance with the changed rotation speed fluctuation, thereby suppressing the rotation speed fluctuation during one rotation.

Here, if the target rotation speed of the brushless motor 4 becomes lower than the current rotation speed due to, for example, a change in the setting of a remote controller in the air conditioner, the process proceeds from step ST1 to step ST2 to step ST3, and the driving torque change rate is set to a predetermined value. It is determined whether the value is equal to or greater than the value. The predetermined value may be set to a value smaller than the value of the driving torque change rate which does not cause the disadvantage of the conventional example.

In this case, the target rotation speed is a low rotation speed,
When the driving torque change rate is large, as described in the conventional example, the rotation speed of the brushless motor 4 cannot be reduced to a certain value or less due to the large driving torque change rate, and the minimum rotation speed becomes somewhat large. In some cases, the rotation speed of the brushless motor 4 cannot be set to the target rotation speed.

Therefore, when the rate of change in drive torque is greater than the predetermined value, the process proceeds from step ST3 to step ST4 to decrease the rate of change in drive torque. For example, FIG.
(B) is changed from the drive torque change rate shown in FIG. In this case, when the rate of change in the driving torque is reduced, the applied voltage of the brushless motor 4 is correspondingly reduced, which hinders the control of the rotation speed.

Therefore, as shown in FIG. 4, the applied voltage (output voltage) of the brushless motor 4 is set to a predetermined reference voltage to a voltage necessary for torque control (the form shown in FIGS. 1A and 1B). Voltage). If the reference voltage is increased in accordance with the decreasing rate when the above-described driving torque change rate is decreased, there is no problem in controlling the rotation speed.

As described above, the on-time of the PWM waveform may be shortened by reducing the driving torque change rate. That is, the power-on time of the switching element of the inverter circuit 3 can be shortened, and the minimum rotation speed (minimum rotation speed) of the brushless motor 4 can be reduced.

This is because the difference between the maximum driving torque and the minimum driving torque during one rotation becomes small, and even at a position where the driving torque is large, the switching element is set to the minimum value of the energization ON time at the position where the driving torque is minimum. Means that you can. That is, the difference between the maximum drive torque and the minimum drive torque during one rotation is small.

Therefore, even at the time of torque control for suppressing load torque fluctuation, the minimum rotation speed as the target rotation speed of the brushless motor 4 can be reduced. That is, the voltage (minimum output) applied to the brushless motor 4 is made as low as possible, and operation in a lower region becomes possible. This allows
When the brushless motor 4 is applied to, for example, a compressor motor of an air conditioner, its performance can be controlled to be small, and it is possible to prevent overcooling or overheating, and to improve indoor environment comfort.

When the target rotation speed of the brushless motor 4 becomes higher than the current rotation speed due to the setting change of the remote controller or the like, the process proceeds from step ST1 to ST5, and it is determined whether the driving torque change rate is equal to or more than a predetermined value.

If the drive torque change rate is lower than the predetermined value, the process proceeds from step ST5 to ST6 to increase the drive torque change rate. For example, the drive torque change rate shown in FIG. Change to driving torque change rate. In this case, contrary to the case where the drive torque change rate is decreased, if the reference voltage is increased, there is no problem in controlling the rotation speed.

As described above, by increasing the driving torque change rate, the rotation speed fluctuation during one rotation of the brushless motor 4 can be further suppressed, and the rotation speed can be more quickly set to the target rotation speed.

If the change rate of the drive torque is equal to or more than a predetermined value, for example, if the difference between the minimum drive torque and the maximum drive torque during one rotation is large, the process proceeds from step ST5 to ST7, and the above-described normal feedback control is performed. As a result, a driving torque is generated as in the related art. That is, control is performed to increase the number of revolutions of the brushless motor 4, and in this case, since the driving torque change rate is large to some extent, the conventional disadvantage does not occur.

When the rotation speed of the brushless motor 4 has reached the target rotation speed, the current driving torque change rate is left as it is. That is, the current rotation speed is the target rotation speed, and it is not necessary to change the drive torque change rate. Further, even if the drive torque change rate is not reduced, the drawbacks as in the conventional example do not occur. .

Since the predetermined value is set to a value smaller than the driving torque change rate which does not cause the drawback of the conventional example, even if the target rotation speed is lower than the current rotation speed, if the driving torque change rate is not equal to or larger than the predetermined value. Keeps the current drive torque change rate as it is.

[0041]

As described above, according to the present invention,
The following effects are obtained. The motor control method of the present invention generates the drive torque of the motor in accordance with the change in the load torque during one rotation, and determines the rate of change of the drive torque at least as a result of comparison between the target rotation speed and the current rotation speed. Variable in response to a change in the load torque during one rotation, and when the target rotation speed of the motor is higher or lower than the current rotation speed, an appropriate drive torque is generated to reduce the load torque fluctuation. Can be suppressed. In addition, there is an effect that the software can be realized only at a low cost without adding a hardware circuit.

According to the motor control method of the present invention, the driving torque of the motor is generated in accordance with the fluctuation of the load torque during one rotation, while the rate of change of the driving torque during one rotation is variable at least according to the current rotation speed. And the energization ON time of the switching element of the inverter circuit at the position where the driving torque during one rotation is the smallest is the minimum value, and
When the target rotation speed of the motor is lower than the current rotation speed, the rate of change of the driving torque is reduced, and the energization ON time of the switching element at the position where the driving torque is large is shortened. Therefore, it is possible to lower the minimum rotation speed by reducing the rate of change of the driving torque in terms of the number of rotations, and to widen the operating range in the low rotation speed. In particular, when applied to a compressor of an air conditioner, there is an effect that overcooling and overheating can be prevented and the comfort of the indoor environment can be improved.

[Brief description of the drawings]

FIG. 1 is a schematic drive torque change rate diagram illustrating an embodiment of the present invention and illustrating a control method of an electric motor.

FIG. 2 is a schematic block diagram for explaining a control device to which the motor control method of the present invention is applied.

FIG. 3 is a schematic flowchart for explaining the operation of the control device shown in FIG. 2;

FIG. 4 is a schematic graph for explaining the operation of the control device shown in FIG. 2;

FIG. 5 is a schematic drive torque change rate diagram for explaining the operation of a conventional motor control method.

FIG. 6 is a schematic block diagram for explaining a conventional motor control device.

[Explanation of symbols]

 Reference Signs List 1 AC power supply 2 AC / DC conversion circuit 3 Inverter circuit 4 Motor (brushless motor) 5 Position detection circuit 6, 10 Control circuit (microcomputer) Ua, Va, Wa, X, Y, Z Switching element

Claims (4)

[Claims] An AC power supply is converted into a DC voltage and supplied to an inverter means, and a switching means of the inverter means is turned on and off in a predetermined manner to obtain a voltage applied to the motor.
The inverter means is controlled based on the position of the rotor of the electric motor, and when the rotation of the electric motor is controlled by switching the energization of the armature winding of the electric motor, the fluctuation of the load torque during one rotation of the electric motor is suppressed. A method for controlling an electric motor, comprising: generating a drive torque of the electric motor in accordance with a change in the load torque; and comparing a change rate of the drive torque during one rotation with at least a comparison between the target rotation speed and a current rotation speed. A method for controlling an electric motor, wherein the method is varied according to a result. 2. An AC power source is converted into a DC voltage and supplied to an inverter means, and a switching means of the inverter means is turned on and off in a predetermined manner to obtain an applied voltage of the motor.
The inverter means is controlled based on the position of the rotor of the electric motor, and when the rotation of the electric motor is controlled by switching the energization of the armature winding of the electric motor, the fluctuation of the load torque during one rotation of the electric motor is suppressed. A method for controlling an electric motor, wherein a driving torque of the electric motor is generated in accordance with a change in the load torque, and a rate of change of the driving torque during one rotation is made variable at least according to a current rotation speed. When the energization ON time of the switching means at the position where the driving torque during one rotation is the smallest is the minimum value and the target rotation speed of the electric motor is lower than the current rotation speed, the rate of change of the driving torque is reduced. The control method of the electric motor, characterized in that the energization ON time of the switching means at the position where the driving torque is large is shortened. 3. The motor control method according to claim 2, wherein the change rate of the drive torque is increased when the target rotation speed of the motor is higher than a current rotation speed. 4. The motor according to claim 2, wherein when the rate of change of the driving torque is equal to or more than a predetermined value, the driving torque of the electric motor is generated in accordance with the fluctuation of the load torque, and returns to normal feedback control. 3. The method for controlling an electric motor according to item 3.