JP2902477B2 - Starting method of sensorless motor and sensorless motor - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a DC brushless motor, and more particularly to a method of starting a sensorless DC brushless motor and a sensorless DC.
It relates to a brushless motor.

[Prior Art] A DC brushless motor has no brush, so it has high reliability and long life, and generates low noise. In addition, there are few defects at the time of manufacture, and the defect rate of maintenance is also low.

For example, electronic devices and control devices are vulnerable to heat and need to be cooled when they generate heat. If the cooling power is insufficient with natural cooling, a method of forcibly cooling with a fan such as an axial fan, a transverse fan, a centrifugal fan, or the like is effective for ensuring normal operation of the device. The characteristics of the DC brushless motor are very suitable, for example, for driving such a device cooling fan.

FIG. 2 shows an example of a conventional brushless two-phase DC motor circuit.

The rotor 1 coupled to the impeller is driven by the current flowing through the coils 2a, 2b, and rotates in the direction indicated by the arrow. The currents flowing through the coils 2a and 2b are controlled by the transistors Tr1 and Tr2 and alternately flow through the backflow prevention diodes D2 and D3. The rotation of the rotor 1 is detected by the Hall element 18, and a detection signal is supplied to the logic circuit 16. The logic circuit 16 calculates how to control the current flowing through the coils 2a and 2b based on the detection signal, and supplies a control signal to the bases of the transistors Tr1 and Tr2 via the resistors R2 and R3. The capacitors C1 and C2 connected to the bases of the transistors Tr1 and Tr2 are used for voltage stabilization and high-frequency short-circuit. In the figure, D1 is a backflow prevention diode, R1 is a protection resistor, and C3 and C4 are voltage stabilizing high frequency short-circuit capacitors.

At the time of startup, the rotation position of the rotor 1 is detected by the Hall element 18 and the rotation of the rotor 1 is started by supplying a drive current to the drive coils 2a and 2b. In applications such as a cooling fan, there is no problem even if the rotor 1 rotates to a certain extent as long as the rotor 1 starts to rotate forward. However, the rotation needs to be stable as normal rotation, and therefore, at the time of manufacturing the motor, it is necessary to control the mounting position of the circuit member so that the Hall element 18 can be mounted at an appropriate position with respect to the rotor 1. . For this reason, restrictions are imposed on the automatic assembly, which hinders mass production.

[Problem to be Solved by the Invention] According to the above-described conventional technology, InSbGa
A Hall element made of As or the like is used. Such a Hall element has a finite life and has a limited temperature characteristic.
In addition, individual element characteristics vary, and a means for correcting the characteristics is required. Further, a single chip cannot be integrated with a silicon integrated circuit.

In addition, since the Hall element is used in the control circuit, it is necessary to individually and strictly adjust the mounting position of the Hall element individually with respect to variations in the location of the rotor of the motor or the like during manufacturing.

An object of the present invention is to provide a reliable start-up method of a sensorless motor that does not use a Hall element.

It is another object of the present invention to provide a sensorless motor that does not require strict positioning, can be started reliably, and can be manufactured automatically.

[Means for Solving the Problems] A method for starting a sensorless motor according to the present invention includes a rotor having a permanent magnet and a stator having a driving core coil, and a sensor capable of detecting a rotor position when the rotor is stopped. A method of starting a sensorless motor that does not have
After supplying a predetermined starting current to the driving coil, when detecting a back electromotive voltage generated in the driving coil by rotation of the rotor, a predetermined bias magnetic field is supplied to a core of the detection coil. .

Further, the sensorless motor according to the present invention is a sensorless motor having a rotor having a permanent magnet and a stator having a coil having a driving core, and having no sensor capable of detecting the rotor position when the rotor stops. Has a means for supplying a predetermined magnetic field to the core in addition to the driving coil.

[Operation] When the position of the rotor is detected by the induced back electromotive force of the coil, the position of the rotor is not known at the time of startup. When a current is applied to the first drive coil, the rotor starts to rotate forward or reverse depending on how many poles of the rotor are in the vicinity and the position of the rotor.

Once the rotor starts rotating, an induced electromotive force is generated in the driving coil.

The stator core has hysteresis. Therefore, when a bias magnetic field is present, a change in magnetic flux caused by a change in the external magnetic field changes depending on the polarity of the external magnetic field.

By knowing the polarity and magnitude of this induced back electromotive voltage,
The position of the rotor can be known.

Therefore, it is possible to determine whether the rotor is the north pole or the south pole, and the rotor position can be detected.

By sequentially supplying a drive current to the drive coil based on the detected rotor position, the rotation of the rotor can be started normally.

Embodiment FIG. 1 shows a stator portion of a sensorless motor according to an embodiment of the present invention. The case of two-phase four-pole is exemplified.

FIG. 1A shows the configuration of the stator. Stator 10
Are the driving coils 2a, 2b, 2c, 2d are the cores 3a, 3b, 3c, 3d
And a bias magnet 4 that can apply a bias magnetic field to each of the cores 3a, 3b, 3c, 3d at the center thereof.

FIG. 1B shows the bias magnet 4 in an enlarged manner.
In the illustrated configuration, since the stator has a four-pole configuration, the biasing magnet has a four-pole configuration. Each core 3a, 3b,
According to 3c and 3d, the bias magnet 4 is magnetized so as to have four poles in the circumferential direction. A predetermined bias magnetic field is applied to the core by these magnets.

FIG. 1 (C) shows a BH curve of each core. As shown, the material of each core has hysteresis. The bias magnet 4 applies a magnetic flux for bias to each core, and an external magnetic field is applied so as to overlap the magnetic flux for bias. This bias magnetic flux density is shown by + B1 and -B1 in FIG. 1 (C).

For example, when a bias magnetic flux density of + B1 is applied to the core, the degree of saturation of the magnetic flux density B is different between a case where the magnetic poles of the rotor are close to each other and a change of + ΔB and a case of a change of −ΔB Differently, there is a difference in the resulting change in magnetic flux. Therefore, an induced voltage proportional to each magnetic flux density change width is generated, and by detecting this difference, it is possible to determine whether the adjacent magnetic pole is an N pole or an S pole.

FIG. 3 shows an example of a circuit for performing such polarity discrimination. Such a circuit can be provided instead of the Hall element circuit 18 in the sensorless motor circuit as shown in FIG. 2, for example. The back electromotive voltage generated in the driving coil 2 is applied to both ends of the capacitor C10 via the resistor R10,
Noise is removed by integration. This voltage is applied to amplifier A1
After being amplified by 0, it is applied to the comparator 6. The constant voltage Vref is also applied to the comparator 6 from the reference voltage generation circuit 7. Output voltage VD is converted to reference voltage Vref
By comparing with, it is determined whether the output is caused by the N pole or the S pole. Amplifier A1
The output VD of 0 is also derived independently and supplied to the logic circuit 16 for controlling the drive current.

When the rotor 1 rotates and the N pole and the S pole pass alternately, a back electromotive voltage as shown in FIG. 4 is generated in the coil 2. That is, there is a difference in the back electromotive voltage generated depending on whether the N pole passes or the S pole passes. In order to detect this difference, the output voltage of the reference voltage generation circuit 7 in FIG.
Vref may be selected between the voltages V1 and V2 in FIG.

Although the case where the permanent magnet for generating the bias magnetic field is attached to the stator of the sensorless motor has been described above, the means for generating the bias magnetic field is not limited to the permanent magnet.

FIG. 5 shows a stator according to another embodiment of the present invention.
In the present embodiment, a bias coil 8 for generating a bias magnetic field and having a relatively small ampere-turn is wound around each core in addition to the driving coil. At least, when detecting the back electromotive voltage, a current such as an input current or a charging current for the capacitor C3 is passed through the bias coil 8 corresponding to the detection coil 2 (therefore, the bias coil 8 is not shown in FIG. 2). , For example, diode P1
Or between the capacitors C2 and C3. In this manner, similarly to the configuration shown in FIG. 1A, the width of change in the magnetic flux density of the core 3 of the stator 10 can be modulated, and the pole through which the rotor passes can be determined.

The case of a two-phase motor has been described above as an example, but it will be obvious to those skilled in the art that the present invention is not limited to a two-phase motor.

As the means for generating the bias magnetic field, any means can be used as long as it supplies a constant bias magnetic field to the core around which the coil of the stator is wound.

After the rotation reaches a certain speed, the bias magnetic field is not always necessary.

In this manner, the sensorless motor can be reliably started with a simple configuration without using a Hall element.

Since no Hall element is used, automation and mass production in the manufacture of a sensorless motor are facilitated.

Although a sensor such as a Hall element is not used, since the polarity of the rotor at the time of startup can be detected, the reverse rotation of the rotor can be efficiently prevented.

The present invention has been described with reference to the embodiments. The present invention is not limited to these embodiments. For example, it will be apparent to those skilled in the art that various modifications, improvements, combinations, and the like can be made.

[Effects of the Invention] As described above, according to the present invention, it is possible to detect the polarity of the rotor at the time of start-up, without having a sensor such as a Hall element.

For this reason, a sensorless motor that can reliably start can be provided.

Since no sensor is used, automation and mass production in manufacturing are facilitated, and the defect rate can be reduced.

[Brief description of the drawings]

FIGS. 1A, 1B, and 1C are views for explaining a stator of a sensorless motor according to an embodiment of the present invention, and FIG. 1A is a schematic view showing a configuration of the stator. 1
FIG. 1B is an enlarged schematic view showing a bias magnet, and FIG.
FIG. (C) is a graph showing a BH curve of the stator core, FIG. 2 is a circuit diagram showing a sensorless motor circuit according to a conventional technique, and FIG. 3 is a circuit showing an example of a circuit for determining a detected voltage according to an embodiment of the present invention. FIG. 4 is a graph showing a waveform of an output voltage in the circuit of FIG. 3, and FIG. 5 is a schematic diagram showing a sensorless motor according to another embodiment of the present invention. In the figure, 1 ... rotor 2 ... drive coil 3 ... core 4 ... bias magnet 6 ... comparator 7 ... reference voltage generation circuit 8 ... bias coil 10 ... stator 18 ... hall element circuit R …… Resistance D …… Diode C …… Capacitor Tr …… Transistor

Claims (4)

(57) [Claims] 1. A method for starting a sensorless motor having a rotor having a permanent magnet and a stator having a cored coil for driving, and having no sensor capable of detecting the rotor position when the rotor stops. A sensorless sensor characterized by supplying a predetermined bias magnetic field to a core of the coil for detection when detecting a back electromotive voltage generated in the drive coil by rotation of the rotor after supplying a predetermined starting current to the coil. How to start the motor. 2. The method according to claim 1, wherein the bias magnetic field is provided by a permanent magnet attached to a stator or a bias coil for flowing a predetermined current. 3. A sensorless motor having a rotor having a permanent magnet and a stator having a driving core coil and having no sensor capable of detecting the rotor position when the rotor is stopped, wherein the stator has a driving A sensorless motor comprising: means for supplying a predetermined magnetic field to a core in addition to a coil. 4. The sensorless motor according to claim 3, wherein said magnetic field supply means includes a permanent magnet or a bias coil attached to a core.