JPH0759386A - Starting up of brushless dc motor - Google Patents

Abstract

PURPOSE:To start up a motor exactly without stopping it for protection by preventing overcurrent from flowing because motor output torque is too large for a motor load. CONSTITUTION:This equipment is provided with a brushless DC motor 2 constituted of a permanent magnet-built-in rotor and a field magnetic winding built-in stator, an inverter circuit to drive this motor 2, a position detecting circuit 3 which detects the position of the rotor with the induced voltage of the field magnetic winding, a current detector 5 to detect secondary-side current of the inverter circuit 1, and a controlling circuit 5 to control the inverter circuit 1. When a current value detected by the current detector 5 becomes larger than the preliminarily set value during the synchronous operation wherein a commutation timing is forcibly changed at the time of start-up when the position detection of the rotor by the position detecting circuit 3 is difficult, the controlling circuit 4 drops the voltage by a specified level below that of a pattern determined for a frequency and then starts up the motor.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for starting a brushless DC motor.

[0002]

2. Description of the Related Art A brushless DC motor comprises a rotor incorporating a permanent magnet and a stator incorporating a field winding, and detects the rotor position by calculation from a voltage waveform induced in the field winding. The energization phase to the stator is controlled.

In a brushless DC motor, it is difficult to detect the rotor position from the voltage waveform induced in the field winding at the time of starting when the rotation speed is very low. Therefore, the commutation timing is forced by the inverter circuit. "Synchronous operation" to control the energization phase to the stator to rotate / accelerate the rotor, and then reach the speed at which the rotor position can be detected. A start-up method of switching to "phase detection rotation" for controlling the phase is used.

Since a signal from the motor cannot be obtained during the "synchronous operation", the frequency and voltage output from the inverter circuit are preset to have appropriate values according to the load.

When a brushless DC motor is used by incorporating it into an air conditioner compressor, the torque to be output from the motor is the required torque of the compressor. This value is the pressure condition of the compressor and the friction torque of the compressor. It varies greatly depending on variations such as. In addition, it is necessary to assume that the power supply voltage of the inverter circuit normally has a variation value of about ± 10%, and the voltage applied to the motor changes due to this voltage, which changes the output torque.

[0006]

When a brushless DC motor is used by incorporating it into, for example, a compressor for an air conditioner, when the load of the compressor is large at startup or the power supply voltage is low, the torque of the brushless DC motor is It becomes smaller than the required torque and may get out of synchronization during "synchronous operation". In this case, the compressor vibrates greatly in the rotation direction, and therefore excessive stress is generated in the pipes connected to the compressor, which may break the pipes or generate abnormal noise. Has become.

Further, when the load of the compressor is small at the time of start-up or the power supply voltage is high, the current flowing during the "synchronous operation" becomes excessive, and the motor stops due to overcurrent in order to protect the inverter circuit.

The present invention has been made in view of the above circumstances, and provides a method for starting a brushless DC motor, which can prevent out-of-synchronization due to insufficient torque and can reliably start the motor without causing vibration or noise. The purpose is to do.

[0009]

(First Invention) A method for starting a brushless DC motor according to the present invention comprises a rotor incorporating a permanent magnet and a stator incorporating a field winding. Position detection of the rotor in a brushless DC motor that detects the position of the rotor from the induced voltage of the magnetic winding and controls the energization phase from the inverter circuit to the stator based on the position detection signal of the rotor. It is difficult to start the motor, and the inverter circuit forcibly determines the commutation timing for synchronous operation, and at the same time the current flowing through the motor is detected during this synchronous operation, and the current detection value is a preset value. It is characterized in that the drive voltage is started by lowering the drive voltage by a predetermined value from the voltage of the pattern determined with respect to the drive frequency when the drive voltage becomes higher.

(Second Invention) Brushless D according to the present invention
The starting method of the C motor consists of a rotor incorporating a permanent magnet and a stator incorporating a field winding. The position of the rotor is detected from the induced voltage in the field winding, and the rotor In a brushless DC motor that controls the energization phase from the inverter circuit to the stator based on the position detection signal, the inverter circuit forcibly determines the commutation timing and synchronizes the motor when the rotor position is difficult to detect. In addition to the operation, at the time of this synchronous operation, it has two or more patterns that show the relationship between the motor rotation speed and the drive voltage. First, use the pattern with the high drive voltage setting for the motor rotation speed to start and stop overcurrent. When this is done, a restart is performed using a pattern of a lower voltage.

[0011]

(First Invention) Since it is difficult to detect the position of the rotor when the brushless DC motor is started, the inverter circuit performs the synchronous operation for forcibly changing the commutation timing. In this case, the current flowing through the motor is detected, and it is checked whether the detected value is larger than the set value. If the detected current value is smaller than the set value, the motor drive voltage and frequency are increased according to a preset pattern. When the detected current value is larger than the set value, the motor drive voltage is made smaller than the voltage of the set pattern by a predetermined value.
After that, when the rotational speed at which the rotor position can be detected from the induced voltage of the field winding is reached, the synchronous operation ends, and the phase detection operation that controls the energization phase according to the rotor detected position is entered.

As a result, it is possible to prevent an excessive current from flowing because the motor output torque is too large with respect to the motor load.
It is possible to reliably start the DC motor without performing a protective stop.

(Second invention) At the time of starting the motor, first, the synchronous operation is performed by a pattern having a high voltage with respect to the frequency, and if there is no problem, the operation is continued as it is, and the rotation is started from the induced voltage of the field winding. When the rotational speed at which the position of the child can be detected is reached, the synchronous operation ends, and the phase detection operation that controls the energization phase according to the detected position of the rotor is entered. Further, when the overcurrent is stopped during the above-mentioned synchronous operation, the restart is performed using a pattern having a voltage lower than the initial pattern.

As a result, the motor is started with the motor output torque being larger than the required torque, so that out-of-synchronization due to insufficient torque does not occur, and vibration and noise associated therewith can be prevented.

[0015]

Embodiments of the present invention will be described below with reference to the drawings. (First Embodiment) FIG. 1 is a configuration diagram showing a starting method of a brushless DC motor according to an embodiment of the present invention. As shown in FIG. 1, the inverter circuit 1 includes a switching element TU.
, TV, TW, TX, TY, TZ and diode DU,
Brushless D consisting of DV, DW, DX, DY, DZ
The C motor 2 is driven. This brushless DC motor 2
Is composed of a rotor incorporating a permanent magnet and a stator incorporating a field winding. And brushless D
The voltage between the terminals of the field winding of the C motor 2 is determined by the position detection circuit 3
Sent to. The position detection circuit 3 calculates the induced voltage of the field winding to detect the position of the rotor, and outputs the detection signal to the control circuit 4. In addition, the inverter circuit 1
Between the brushless DC motor 2 and the brushless DC motor 2, a current detector 5 for detecting the secondary current of the inverter circuit 1 is provided, and a detection signal thereof is sent to the control circuit 4.

Based on the rotor position detection signal from the position detection circuit 3 and the secondary side current detection signal from the current detector 5, the control circuit 4 switches each switching element TU, TV, TW, TX of the inverter circuit 1. A control signal is supplied to TY and TZ to control the operation of the inverter circuit 1. The control circuit 4 is configured to
Inverter circuit 1 forcibly changes the commutation timing to perform "synchronous operation" to rotate and accelerate DC motor 2,
After that, when the speed at which the position of the rotor can be detected by the position detection circuit 3 is reached, the operation is switched to the "phase detection operation" in which the energization phase is controlled according to the position detection signal of the rotor. Further, the control circuit 4 changes the relationship between the motor drive frequency and the drive voltage output from the inverter circuit 1 in accordance with a predetermined pattern predetermined according to the load during the "synchronous operation". When the current value detected by 5 becomes larger than a preset current value, a control operation is performed such that the motor drive voltage is lowered by a predetermined value below the voltage of the pattern.

Next, the operation of the above embodiment will be described with reference to the flow chart shown in FIG. Since it is difficult for the control circuit 4 to detect the position of the rotor by the position detection circuit 3 when the DC motor 2 is started, the inverter circuit 1 forcibly performs the "synchronous operation" in which the commutation timing is changed. in this case,
First, as shown in the flow chart of FIG.
The secondary side current of the inverter circuit 1 is detected by (step A1), and it is checked whether the detected value is larger than the set value (step A2). If the detected current value is smaller than the set value, the motor drive voltage and frequency are increased in accordance with a predetermined pattern A shown in FIG. 3 (step A3
). After that, returning to step A1, the current detector 5 detects the current.

Further, in step A2, when the current detector 5 determines that the detected value is larger than the set value due to fluctuations in the power supply voltage, load conditions, etc., the motor drive voltage is changed as shown in pattern B of FIG. The voltage of the setting pattern A is reduced by a predetermined value (step A4). Then, returning to step A1, the current is detected by the current detector 5, and in step A2 it is checked whether or not the detected current value is larger than the set value. Thereafter, similar processing is repeated to increase the motor drive voltage and the frequency to accelerate the rotation of the DC motor 2.

When the DC motor 2 is accelerated and reaches a speed at which the position detection circuit 3 can detect the position of the rotor, the control circuit 4 terminates the "synchronous operation", and the position detection circuit 3 starts operation. It switches to "phase detection operation" which controls the energization phase according to the detection signal of.

2 flowing to the DC motor 2 as described above
When the secondary current becomes higher than the set value, the drive voltage is reduced by a predetermined value to prevent the motor output torque from being too large for the motor load and an excessive current can be prevented from flowing, and the DC motor 2 is protected and stopped. It can be started without fail.

Further, the frequency-voltage pattern during the "synchronous operation" is set in advance so that the driving voltage becomes high in consideration of the load such as the pressure condition of the compressor, the power supply voltage of the inverter circuit 1, the variation of the compressor and the like. As a result, the motor output torque is too small for the motor load, causing loss of synchronization.
No big vibration or noise is generated and the system can be started smoothly.

(Second Embodiment) In this second embodiment, two or more frequency-voltage patterns during "synchronous operation" are set for the control circuit 4 as shown in FIG. Then, at the time of start-up, the "synchronous operation" is performed by the pattern A having a high voltage with respect to the frequency, and if there is no problem, the operation is continued as it is, and after the "synchronous operation" is finished, the "phase detection operation" is switched to.

When the overcurrent is stopped during the "synchronous operation", the pattern A is immediately or after a short time.
The pattern B having a lower voltage is used to restart. Furthermore, when the overcurrent is stopped again, the operation is started in a pattern with a lower voltage.

As described above, since there are two or more frequency-voltage patterns during "synchronous operation" and the starting is performed from a high voltage pattern, the motor output torque is larger than the required torque. Since the start-up is performed and the synchronization is not lost due to insufficient torque, the vibration and noise associated therewith can be prevented, and the commercial property can be improved.

On the other hand, the output torque of the DC motor 2 may become excessively large, and the current may increase to stop overcurrent protection. However, at this time, there is no vibration or noise, and the commerciality is not impaired. .

[0026]

As described above in detail, according to the present invention, when the secondary current flowing through the brushless DC motor during the "synchronous operation" becomes larger than the set value, the drive voltage is lowered by a predetermined value. As a result, it is possible to prevent an excessive current from flowing due to the motor output torque being too large for the motor load, and it is possible to reliably start the motor without performing a protective stop.

Further, the present invention has two or more frequency-voltage patterns during "synchronous operation" of the brushless DC motor, and starts from a high voltage pattern, and when the overcurrent is stopped, changes to a low voltage pattern. Since it is switched and restarted, the motor output torque can be started in a state where it is larger than the required torque, and there is no loss of synchronism due to insufficient torque, and vibration and noise accompanying this can be prevented. Merchandise can be enhanced.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing a method for starting a brushless DC motor according to a first embodiment of the present invention.

FIG. 2 is a flowchart showing the operation of the embodiment.

FIG. 3 is a diagram showing a frequency-voltage pattern for explaining the operation of the embodiment.

FIG. 4 is a diagram showing a frequency-voltage pattern for explaining the operation of the second embodiment of the present invention.

[Explanation of symbols]

 1 Inverter circuit 2 Brushless DC motor 3 Position detection circuit 4 Control circuit 5 Current detector

Claims (2)

[Claims] 1. A rotor comprising a permanent magnet and a stator incorporating a field winding, the position of the rotor being detected from the induced voltage of the field winding, and the position of the rotor being detected. In a brushless DC motor that controls the energization phase from the inverter circuit to the stator based on the signal, the commutation timing is forcibly determined by the inverter circuit at the time of starting the motor where it is difficult to detect the position of the rotor, and synchronous operation is performed. At the same time, the current flowing through the motor during this synchronous operation is detected, and when the detected current value becomes larger than the preset value, the drive voltage is set to the voltage of the pattern determined for the drive frequency. Is a method of starting a brushless DC motor, which is also started by lowering a predetermined value. 2. A rotor comprising a permanent magnet and a stator incorporating a field winding, the position of the rotor being detected from the induced voltage of the field winding, and the position of the rotor being detected. In a brushless DC motor that controls the energization phase from the inverter circuit to the stator based on the signal, the commutation timing is forcibly determined by the inverter circuit at the time of starting the motor where it is difficult to detect the position of the rotor, and synchronous operation is performed. When performing this synchronous operation, when there are two or more patterns that show the relationship between the motor speed and the drive voltage during the synchronous operation, and when the overcurrent is stopped by starting using the pattern with the high drive voltage setting for the motor speed first. In addition, a method of starting a brushless DC motor is characterized in that restarting is performed using a lower voltage pattern.