JPH05227787A - Driver for brushless motor - Google Patents

Abstract

PURPOSE:To provide a driver for brushless motor employing a starting system for making a switch from synchronous operation to position detecting operation in which ultra low speed operation can be realized by making a switch again to the synchronous operation if ultra low speed operation takes place during position detecting operation. CONSTITUTION:At the time of starting a motor, synchronous operation is performed until a voltage induced in an armature winding 4 exceeds a predetermined level and a position detecting operation is performed based on a position detection signal of a rotor 5 when the voltage induced in the armature winding 4 exceeds the predetermined level. If ultra low speed operation takes place during the position detecting operation, switching is made again to synchronous operation. If the phase of voltage to be applied on the motor immediately after switching is lagged, stability can be enhanced at the time of switching.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a brushless motor using an inverter circuit, which is used in a variable capacity air conditioner and the like, and more particularly to an armature winding of a brushless motor having a magnet rotor. The present invention relates to a brushless motor drive device that detects a relative voltage position between a rotor and an armature winding by detecting a voltage signal that is generated, and drives and controls the motor based on the detected relative position.

[0002]

2. Description of the Related Art In a brushless motor drive device,
Detects the counter electromotive force induced in the armature winding without using a position detection element such as a Hall element to detect the relative position between the stator armature winding and the permanent magnet rotor. A method is known (see, for example, Japanese Patent Laid-Open No. 2-197291). In this method, since the back electromotive force is induced in the armature winding only when the rotor is rotating, magnetic pole position information cannot be obtained when the rotor is stopped.
Therefore, at the time of startup, a synchronous startup method is used in which the motor is started as a synchronous machine. That is, at the time of start-up, regardless of the magnetic pole position of the rotor, a drive signal that causes a rotating magnetic field is applied to the armature winding, the frequency is gradually increased, and then the counter electromotive force is applied to the armature winding. Switch to the position detection operation when is sufficiently generated.

[0003]

By the way, even during the position detecting operation as described above, the motor is operated according to the speed command from the outside, but when the extremely low speed command is given, the armature winding is performed. The magnitude of the back electromotive force induced in the line is proportional to the speed, which makes position detection operation at extremely low speeds difficult. Such an extremely low speed command is issued, for example, when the air conditioner has a small load and can be operated with a small capacity. Conventionally, since it is difficult to operate at such an extremely low speed, there is a limit to the minimum (minimum) capacity in continuous operation, and operation has to be turned on and off. Will be hunting.

The present invention is intended to solve the above-mentioned problems, and an object of the present invention is to provide a brushless motor drive device adopting a start-up system for switching from synchronous operation to position detection operation, and to perform pole detection during position detection operation. When the speed becomes low, the mode is switched to the synchronous operation again to enable extremely low speed operation and the minimum ability is lowered, which contributes to improvement of comfort of the air conditioner, for example.

[0005]

In order to achieve the above object, the invention of claim 1 detects the voltage induced in the armature winding of a brushless motor having a magnet rotor to determine the position of the rotor. A position detection circuit for detecting, an inverter circuit having a switching element for converting a DC voltage into an AC voltage to supply a voltage to the brushless motor, and a switching element of the inverter circuit for a signal from the position detection circuit and an external speed. In a brushless motor drive device including a control circuit that controls drive according to a command, the control circuit performs synchronous operation at the time of starting the motor until the voltage induced in the armature winding reaches a predetermined value or more, After the voltage induced in the armature winding reaches a predetermined value or more, the position detection operation based on the signal from the position detection circuit is performed. Controls inverter circuit, further, in which to perform the re-switching to the synchronous operation becomes a very low speed operation in the position detection operation. According to a second aspect of the present invention, in the above, when the control circuit becomes extremely low speed operation during the position detection operation, the operation is switched again to the synchronous operation, and the phase of the voltage applied to the motor is delayed immediately after this switching.

[0006]

According to the above construction, when the motor is started, the synchronous operation is performed until the voltage induced in the armature winding reaches a predetermined value or more, and the voltage induced in the armature winding obtains a predetermined value or more. After that, the position detection operation based on the position detection signal of the rotor by the voltage induced in the armature winding is performed. Further, if the extremely low speed operation is performed during the position detection operation, the operation is switched to the synchronous operation again. If the phase of the voltage applied to the motor is delayed immediately after this switching, the stability at the time of switching is improved.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 shows a main configuration of a brushless motor driving device. In FIG. 1, an inverter circuit 2 for converting a DC voltage into an AC voltage is connected to a DC power supply 1, and an armature winding of a brushless motor 3 is connected to an AC output terminal of this inverter circuit 2. The inverter circuit 2 connects the transistors, which are six switching elements, in a three-phase bridge connection,
A diode is connected in parallel with each transistor. The brushless motor 3 comprises a three-phase armature winding 4 star-connected to the stator and a permanent magnet rotor 5. The position detection circuit 6 detects the magnetic pole position of the magnet rotor 5 by detecting the voltage due to the back electromotive force induced in the armature winding 4 of the brushless motor 3. This position detection signal Sa, S
b and Sc are input to the microcomputer 7 as a control circuit for driving and controlling the brushless motor 3.

The microcomputer 7 conducts the conduction of U, V, W and the six transistors of each phase of U-bar, V-bar, W-bar of the inverter circuit 2 in a predetermined procedure based on a predetermined start signal. Control. Microcomputer 7
A pulse width modulation circuit 8 is interposed on the output lines from the U ', V'and W'terminals. This pulse width modulation circuit 8
Is supplied with a chop signal output from the microcomputer 7, and the chop signal causes U, V, W
The duty of the voltage for conducting the phase transistors is changed. The outputs from the U-bar, V-bar and W-bar terminals of the microcomputer 7 control the conduction of the U-bar, V-bar and W-bar phase transistors.

Next, the operation of the apparatus of this embodiment will be described with reference to FIGS.
This will be described with reference to the flowchart in FIG. In FIG.
Since the back electromotive force is not generated in the armature winding 4 when the motor is started, the position detection operation cannot be performed, and the microcomputer 7 starts the motor as a synchronous machine (# 1). After that, when the back electromotive force becomes sufficient (YES in # 2), the operation is switched to the position detection operation based on the position detection signal from the position detection circuit 6 (# 3, # 4). If the motor rotation speed becomes extremely low during the position detection operation, the counter electromotive voltage is proportional to the speed, so that the counter electromotive voltage required for the position detection operation cannot be obtained. At that time, the microcomputer 7 outputs a switching request signal from the position detection operation to the synchronous operation (YE in # 5).
S), # 7 and the following synchronous operations are performed. If the motor rotation speed does not become extremely low during the position detection operation, the signal for requesting switching to the synchronous operation is not output and the position detection interrupt waiting process is performed (# 6).

FIG. 3 shows the position detection interrupt processing. When the predetermined interruption time is reached, this processing is started, and first, the actual frequency f'is calculated from the position detection signal (# 12) and the mode to be set is calculated (# 13). Here, mode 0
1 is sequentially incremented from 1 to 5, and mode 0 is set after mode 5. Then, the duty of the voltage determined by the operation command for speed control is calculated (# 14), and the signal for driving the motor in the mode obtained above is output (# 15). At this time, the voltage applied to the motor is controlled by chopping the voltage of the DC power supply 1 so that the duty obtained by the calculation is obtained. Then, the process returns.

Next, the processing when there is a request for switching from the position detection operation to the synchronous operation will be described. Start the timer for synchronous operation (# 7), then calculate the interrupt time T ′ immediately after switching (# 8), then wait for the timer interrupt (# 9), and calculate the next interrupt time T. Then (# 10), the process returns to # 9. The interrupt time T ′ immediately after the switching is made longer than the interrupt time T after that. As a result, immediately after switching, the phase of the voltage applied to the motor is forcibly delayed. Here, when the rotation frequency is f, for example, T'is (1 / 2πf)
Calculated by (1/6) × 1.5, T is (1 / 2πf)
Calculate by (1/6).

When the timer interrupt of the synchronous operation is entered, the timer is restarted (# 17) and the mode calculation is performed (#
18), read the motor speed, that is, the frequency command f (# 1
9). The voltage v is read from the v / f pattern in which the motor applied voltage v is predetermined according to the frequency f (# 20), the duty of the voltage is calculated (# 21), and the motor is driven in the mode obtained above. Output signal (# 2
2), the process returns. Incidentally, in the past,
5 and the processing after # 7 are not performed, and the position detection operation of # 4 directly shifts to the processing of waiting for the position detection interrupt of # 6.

FIG. 5 is a time chart of signals before and after re-switching from the position detection operation to the synchronous operation. In FIG. 5, before the request for switching to the synchronous operation, a position detection interrupt is generated at a predetermined timing, the operation is performed in a mode obtained from the position detection signal, and a chop signal with a duty ratio determined by speed control is output. To be done. After the request for switching to the synchronous operation, the interrupt timer time T ′ of the new mode (mode 4 here) immediately after the switching is performed.
Is longer than the interrupt timer time T of the subsequent mode. As a result, the time during which the voltage is applied to the V'phase and the U-bar phase becomes longer, and the phases are forcedly delayed. The timer interrupt after switching is a forced operation mode of synchronous operation, and a chop signal having a duty ratio determined according to v / f is output.

In this way, when the motor speed becomes extremely low and the position detection operation is switched to the synchronous operation, the phase of the applied voltage is delayed immediately after that, so that the stability of the operation immediately after the switching can be improved. This prevents the motor from stepping out and stopping due to a transient phenomenon. Therefore, it becomes possible to operate at an extremely low speed, and the operating range can be widened. Therefore, for example, when the present drive device is used in a compressor of a variable capacity air conditioner, the minimum capacity in continuous operation can be reduced, so that when the air conditioning load is small and operation with a small capacity is sufficient, There is no need to intermittently drive, increasing comfort.

[0015]

As described above, according to the present invention, when the speed becomes extremely low during the position detecting operation, the mode is switched to the synchronous operation again. Therefore, a wide operating range from high speed operation to extremely low speed operation is provided. Can be secured, and the minimum capability at extremely low speed operation will be reduced. Therefore, when used for driving a compressor of an air conditioner, for example, continuous operation can be performed without turning the operation on and off as in the conventional case, and comfort can be improved. Further, by delaying the phase of the voltage applied to the motor immediately after switching, it is possible to improve stability during switching.

[Brief description of drawings]

FIG. 1 is a configuration diagram of a brushless motor driving device according to an embodiment of the present invention.

FIG. 2 is a flowchart showing an operation procedure of the device.

FIG. 3 is a flowchart showing a procedure of a position detection interrupt operation.

FIG. 4 is a flowchart showing a procedure of a timer interrupt operation of synchronous operation.

FIG. 5 is a time chart showing the operation before and after the operation switching.

[Explanation of symbols]

 2 Inverter circuit 3 Brushless motor 6 Position detection circuit 7 Microcomputer (control circuit)

Claims (2)

[Claims] 1. A position detection circuit for detecting a voltage induced in an armature winding of a brushless motor having a magnet rotor to detect the position of the rotor, and a switching element for converting a DC voltage into an AC voltage. A drive device for a brushless motor comprising an inverter circuit for converting and supplying a voltage to the brushless motor, and a control circuit for driving and controlling a switching element of the inverter circuit according to a signal from the position detection circuit and an external speed command. When the motor is started, the control circuit carries out a synchronous operation until the voltage induced in the armature winding reaches a predetermined value or more, and the voltage induced in the armature winding is obtained more than a predetermined value. After that, the inverter circuit is controlled so that the position detection operation is performed based on the signal from the position detection circuit. A drive device for a brushless motor, characterized in that it is switched to synchronous operation again when it changes. 2. The control circuit re-switches to synchronous operation when the operation becomes extremely low speed during the position detection operation, and delays the phase of the voltage applied to the motor immediately after the switching. Brushless motor drive.