JPH08223971A - Control method for brushless motor - Google Patents

Abstract

PURPOSE: To detect the rotor position of a brushless motor from the start of operation thereof. CONSTITUTION: An inverter section 4 for driving a brushless motor 3 turns a plurality of switching elements at the inverter section 4 ON/OFF and chops the ON interval thereof variably thus varying the r.p.m. of the brushless motor 3. In such a method for controlling the brushless motor 3, a microcomputer 10a for driving the inverter section 4 decides whether the brushless motor 3 is starting or not. When the brushless motor 3 is starting, the chopping frequency is set lower than that during the operation and a driving signal for the switching element is delivered, along with a chopping signal of set frequency, to a driver circuit 6b.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a rotation control technology for a sensorless DC brushless motor (hereinafter referred to as a brushless motor), and more specifically, it reliably detects the position of a rotor when the brushless motor is started and starts the brushless motor. The present invention relates to a control method for a brushless motor that enables a mode transition from a to position detection operation in the shortest time.

[0002]

2. Description of the Related Art In a brushless motor control method of this kind, generally, when the brushless motor is started up, it is accelerated by a synchronous operation, and when it is accelerated enough for a position detection operation, a position detection operation mode is entered.

When controlling the rotation speed of a brushless motor, the duty cycle of a chopping signal for chopping the voltage applied to the armature winding is changed to a target rotation speed, for example. Specifically, for example, in operation, the frequency of the chopping signal is set to 3 kHz, the on-time of the duty cycle of this chopping signal is lengthened to increase the rotation speed of the brushless motor, and the on-time is shortened to decrease the rotation speed of the brushless motor. To lower.

By the way, as a position detecting circuit for detecting the position of the rotor of the brushless motor, an analog type or a digital type is currently proposed. In the former case, the terminal voltage (induced voltage) of each phase is integrated, the integrated signal is compared with the reference voltage, and the energization switching timing of the brushless motor is obtained based on the comparison result.

However, in the former analog system, it takes time until the output of the integrator stabilizes, that is, even if the position can be detected by the induced voltage, unless the output of the integrator stabilizes, the start The mode cannot be switched from the synchronous operation to the position detection operation, and the synchronous operation time at startup becomes long.

Therefore, the latter digital control device, as shown in FIG. 4, for example, has an AC / DC converter 2 for converting a commercial power source 1 into a DC power source, and a brushless motor 3 for switching the converted DC power source. To the position of the rotor 3a by comparing the armature winding voltage (induced voltage) of the brushless motor 3 with a reference voltage (for example, 1/2 of the applied voltage of the pigless motor 3). In order to control the rotation of the brushless motor 3, the position detection circuit 5 for detecting the position of the switching element of the inverter unit 4 is turned on and off based on at least the position detection, and the armature winding of the brushless motor 3 is energized. And a control circuit 6 for switching.

The position detection circuit 5 divides the applied voltage of the brushless motor 3 into halves, and the terminal voltage (induced voltage) of the armature winding U with the divided voltage as a reference voltage. It comprises a comparison circuit 5b for comparison. The control circuit 6 comprises a microcomputer 6a and a drive circuit 6b.

In the digital control device, the comparison result of the position comparison circuit 5 (the intersection of the induced voltage and the reference voltage) is input to the microcomputer 6a. The microcomputer 6a detects the position detection timing of the rotor 3a. Then, the time between the position detections is measured, and the energization switching timing of the armature winding is calculated based on this measured time.

By the way, in the known control method, the synchronous operation is performed at the time of start-up, and the mode shifts to the position detection operation after a lapse of a predetermined time. However, in the control method adopting the digital method, the position detection is started from the start of the brushless motor 3. It is possible to change the mode to operation in the shortest time.

That is, in the control method adopting the above digital system, the rotor 3a is positioned (locked) when the brushless motor 3 is started, and then the energization is switched to rotate the rotor 3a, thereby winding the armature. An induced voltage is generated on the line U. This is because the induced voltage can be compared with the reference voltage to detect the position, and the energization switching timing of the armature winding can be calculated based on the position detection as described above.

In this way, when the digital system is adopted, the drawbacks of the analog system can be solved, and moreover, the mode transition from the start-up to the position detection operation can be completed in the shortest time, and the efficient operation can be realized. .

[0012]

However, in the brushless motor control method adopting the above digital method, the frequency of the chopping signal for driving the brushless motor 3 is constant at, for example, 3 kHz.
When the brushless motor 3 is started, the on-time of the duty cycle becomes short (because the pulse width becomes thin),
There is a problem that the peak value of the armature winding voltage waveform of the brushless motor 3 decreases and the position cannot be detected.

Explaining with reference to the time chart of FIG. 5, the control circuit 6 positions the rotor 3a of the brushless motor 3 at a predetermined position (after locking the rotor 3a) and then switches the switching element of the inverter unit 4 (for example, a lock element). The transistors Wa and Y are driven (see FIGS. 7C and 7D), and the transistor Wa is chopping-driven.

In this case, when the brushless motor 3 is started, the frequency of the chopping signal is high (cycle t1).
Is small), and the on-time of the duty cycle is short, that is, the width of the drive pulse is extremely narrow as shown in FIG. Then, the drive pulse is blunted by the drive circuit 6b, and the peak value of the induced voltage waveform generated in the armature winding U becomes low as shown in FIG.

As a result, the position detection circuit 5 cannot detect the position (see FIG. 2B), and the control method adopting the above digital system cannot be realized, that is, the mode transition from the start to the position detection operation. It cannot be done in the shortest time.

The present invention has been made in view of the above problems, and an object thereof is to be able to reliably detect the position of the rotor from the time of starting the brushless motor, and thus to shorten the mode transition from the start to the position detection operation. It is an object of the present invention to provide a brushless motor control method that can be reliably performed in time.

[0017]

In order to achieve the above object, the present invention has inverter means for driving a brushless motor, and turns on and off a plurality of switching elements of the inverter means, and at the same time, the switching elements. Is a method for controlling a brushless motor that chops the ON period of, and makes it possible to vary the rotation speed of the brushless motor by varying the ON time of the chopping, and determines whether or not the brushless motor is in operation. The gist is that the chopping frequency is lowered when it is being started.

Further, according to the present invention, when the brushless motor is started, the rotor of the brushless motor is positioned at a predetermined position, the energization of the armature winding of the brushless motor is switched, and then the armature winding of the brushless motor is switched. The position of the rotor is detected by comparing the induced voltage generated in the wire with the reference voltage, the time is measured at each position detection, and the energization of the armature winding is switched based on the measured time. On the other hand, during the start-up, the chopping frequency is set lower than the chopping frequency during operation, and when the brushless motor is accelerated to a position where the position detection operation can be performed by switching the energization, the chopping frequency is switched to the position detection operation. It was done like this.

[0019]

According to the above means, when the brushless motor is started, the rotor of the brushless motor is first positioned at a predetermined position, and the energization of the armature winding is switched after the positioning is completed. After this energization switching, the induced voltage generated in the one-phase armature winding is compared with the reference voltage,
The position of the rotor is detected based on this comparison result, and the energization switching timing of the armature winding of the brushless motor is obtained based on this position detection timing. On the other hand, it is determined whether or not the brushless motor is starting,
The chopping frequency is lowered when the engine is starting.

As a result, the width of the drive pulse for driving the inverter means for switching the energization is increased, and the drive pulse of the switching element is rounded when the switching element of the inverter means is driven through the driver circuit. Not at all. Therefore, an appropriate voltage is applied to the armature winding of the brushless motor, and the peak value of the induced voltage generated in the armature winding of the position detection coil becomes the original level, that is, the peak value of the induced voltage decreases. The position of the rotor can be reliably detected during the start of the brushless motor.

[0021]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention reduces the chopping frequency for driving the inverter section at the time of starting a sensorless DC brushless motor (hereinafter referred to as a brushless motor), and keeps an appropriate voltage applied to the armature winding. The focus is on the ability to generate an appropriate induced voltage in the armature winding of the position detection coil.

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.

In FIG. 1, the control circuit 1 of this control device is shown.
In addition to the function of the control circuit 6 shown in FIG. 4, 0 indicates that the brushless motor 3 is being started, and if it is being started, the chopping frequency is made lower than the chopping frequency during operation, and at least from start to position detection operation. It has a microcomputer 10a for returning the chopping frequency to its original value after the mode transition.

Next, the operation of the control device will be described in detail with reference to the flow chart of FIG. 2 and the time chart of FIG. The brushless motor 3 has a rotor 3a.
Is positioned at a predetermined position and is in a locked state.

First, the microcomputer 10a of the control circuit 10 outputs a drive signal for the inverter section 4 and a chopping signal to the driver circuit 6b to activate the brushless motor 3.

At this time, the microcomputer 10a executes the routine shown in FIG.
It is determined whether or not is being activated (step ST1).
In this case, since the brushless motor 3 is activated, the process proceeds to step ST2, and the frequency of the chopping signal (chopping frequency) is made lower than the chopping frequency during operation.

For example, when the chopping frequency of 3 kHz is used in the rotation control (position detection operation) of the brushless motor 3, the chopping frequency is set to 1 kHz. As a result, the period t2 (> t1) of the chopping signal for chopping the ON period of the drive signal of the inverter unit 4 becomes longer than in the conventional case. In addition, when the brushless motor 3 is not being started, for example, in the position detection operation, steps ST1 to ST3
And set the chopping frequency to 3 kHz. Therefore, when the mode is changed from the startup to the position detection operation, the original chopping frequency is restored.

Explaining in detail with reference to FIG. 3, the one-phase armature winding U is a position detecting coil, drives the transistors Wa and Y of the inverter unit 4, and chops the ON period of the transistor Wa. (Shown in (c) and (d) of the same figure).

In this case, since the period t2 of the chopping signal is large, that is, the pulse width is large, even if an appropriate voltage is still applied to the armature windings W and Y, FIG.
As shown in (a), the position detection circuit 4 can reliably obtain the position detection signal without lowering the peak value of the induced voltage waveform generated in the armature winding U (see (b) in the figure). Shown).

In this way, the position of the rotor 3a can be reliably detected from the beginning of the brushless motor 3, and the armature winding of the brushless motor 3 is detected based on this one-phase position detection. The energization switching timing of can be calculated. Therefore, it becomes possible to realize the brushless motor control method employing the digital method described in the conventional example, and the mode transition from the start of the brushless motor 3 to the position detection operation can be performed in the shortest time.

[0031]

As described above, according to the present invention, when the brushless motor is started, the chopping frequency for driving the inverter unit is lowered, so that the peak of the induced voltage generated in the armature winding is increased. Since the value does not decrease, there is an effect that the position of the rotor can be reliably detected even after the brushless motor is started.

Further, according to the present invention, since the position can be detected from the start-up, it is possible to realize the control method of the brushless motor adopting the digital system.
It is possible to surely perform the mode transition from the startup to the position detection operation in the shortest time.

[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.

FIG. 3 is a schematic time chart diagram for explaining the operation of the control device shown in FIG.

FIG. 4 is a schematic block diagram of a conventional brushless motor control device.

5 is a schematic time chart diagram for explaining the operation of the control device shown in FIG.

[Explanation of symbols]

1 AC Power Supply 2 AC / DC Converter 3 Brushless Motor (Sensorless DC Brushless Motor) 3a Rotor 4 Inverter 5 Position Detection Circuit 5a Resistance Circuit 5b Comparison Circuit 6,10 Control Circuit 6b Driver Circuit 10a Microcomputer U, V, W Armature winding (of brushless motor 3) Ua, Va, Wa, X, Y, Z Transistor (switching element)

Claims (2)

[Claims] 1. Inverter means for driving a brushless motor is provided, a plurality of switching elements of the inverter means are turned on and off, an on period of the switching elements is chopped, and an on time of the chopping is varied. A method of controlling a brushless motor that allows the number of revolutions of the brushless motor to be varied, and determines whether or not the brushless motor is in operation,
A method for controlling a brushless motor, wherein the chopping frequency is lowered when the brushless motor is being started. 2. An inverter means for driving a brushless motor is provided, a plurality of switching elements of the inverter means are turned on and off, an on period of the switching elements is chopped, and an on time of the chopping is varied. A method for controlling a brushless motor, wherein the rotation speed of the brushless motor is variable, wherein the rotor of the brushless motor is positioned at a predetermined position when the brushless motor is started, and the armature winding of the brushless motor is energized. After switching, the position of the rotor is detected by comparing the induced voltage generated in the armature winding of the brushless motor with a reference voltage, and the time is measured at each position detection. And switching the energization of the armature winding while operating the chopping frequency during the startup. Of which was lower than the chopping frequency, the control method for a brushless motor, characterized in that to switch to the position sensing operation at the time of accelerating the brushless motor to the extent possible position sensing operation by the energization switching.