JP2006238536A - Single-phase brushless dc motor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fan motor having low noise by eliminating the rotational torque ripples of a single-phase brushless DC motor, thus suppressing the generation of vibration noise. <P>SOLUTION: A rotor magnet is formed by applying an appropriate magnetic-field orientation of polar anisotropy during formation out of an injection-moldable magnet member. A current that passes through a motor coil is detected, and an energizing command signal for gradually lowering the trailing of current waveform is developed for energization. Moreover, a feedback circuit is provided so as to keep the output voltage of a Hall element constant. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a single-phase brushless DC motor (hereinafter referred to as a motor) that is a DC motor for driving a fan.

  Conventional motors reduce costs by simplifying the structure. In other words, the number of poles of the rotor magnet and the number of teeth of the stator core are set to about 4, one Hall element is used as a magnetic sensor for detecting the magnetic pole position of the rotor magnet, and a single-phase motor coil is energized in an alternating direction by a semiconductor. The rotor is rotating. Since this configuration has a single phase, there is a point where no rotational torque is generated.

  If the gap between the salient poles of the rotor magnet and the teeth is constant in the circumferential direction, the point where the cogging torque generated between the salient pole and the rotor magnet becomes zero and the point where the rotational torque does not occur are at the same position. Because of this, there is a so-called dead point where the motor cannot be started.

Fig. 4 shows the relationship between the back electromotive force generated in the coil and the gogging torque during motor rotation when the magnetic flux distribution of the rotor magnet is sinusoidal. 4-1 is a uniform gap between the stator core salient pole and the rotor magnet. When the counter electromotive force waveform is sin θ, the cogging torque can be expressed by −sin 2θ and the cycle is doubled, and it can be seen that the dead point P exists.
4-2 is a device in which a non-uniform portion is appropriately provided in the gap between the salient pole and the rotor magnet, and the magnetization of the magnet is devised. Value). Generally, a method of avoiding the above-described dead point by shifting the position of the cogging torque 0 point is generally adopted.

JP 2004-140897 A IEEJ Industrial Application Division April 2002 Paper “Reducing Cogging Torque of Permanent Magnet Brushless Motor” FIG. 5 is a diagram showing the structure of the conventional motor, wherein 1 is a rotor core, 2 is an annular rotor magnet, The arrow indicates the magnetic field orientation direction of the rotor magnet and is magnetized to 4 poles. A counter electromotive force is generated in the motor coils 7 and 8 by the rotation of the motor. Reference numeral 3 denotes a hall element that detects the magnetic pole of the magnet 2 and is attached to a printed circuit board (not shown). Reference numeral 4 denotes a stator core formed by punching and stacking silicon steel plates, and has four teeth 5 and salient poles 6. The gap between the salient poles 6 and the rotor magnet 2 is not constant but uneven as shown in FIG. It has become. 7 and 8 are motor coils.

  For example, the salient pole 6 has a 6A portion having a narrow gap with the rotor magnet 2 and a 6B portion having a wide gap, and when the motor coils 7 and 8 are not energized, the magnetic pole center portion 2A of the opposing rotor magnet 2 is The magnetic pole 6 is attracted to a portion 6A having a narrower gap than the center portion 6C of the salient pole 6, and the positional relationship between the pole of the rotor magnet 2 and the salient pole 6 of the tooth 5 is stopped in the state shown in FIG. At this position, due to the positional relationship between the Hall element 3 and the rotor magnet 2, the motor coils 7 and 8 are energized through the IC dedicated to the DC fan by the output voltage of the Hall element 3, and the salient pole 6 of the tooth 5 and the rotor magnet. Rotational torque is generated in 2 and the rotor core 1 rotates.

  In recent years, there has been a strong demand for reducing vibration and noise of fan motors mounted on devices used in homes and offices, and the present inventors have disclosed in Japanese Patent Application Laid-Open No. 2004-140897 the sum of energized torque and gogging torque generated by energizing a motor coil. A method for reducing torque ripple of rotational torque is disclosed.

  In Japanese Patent Laid-Open No. 2004-140897, in order to achieve the above-described object, the output voltage of the Hall element is extracted in a sine wave shape (sin θ), amplified, and a sine wave current is applied to the motor coil. In addition, the back electromotive force of the motor coil is also extracted in a sine wave shape (sin θ), and the air gap between the stator core salient pole and the magnet is made non-uniform so that the cogging torque waveform has a cosine of approximately twice the rotation period of the sine wave It is disclosed that it is possible to eliminate the torque ripple by taking out in a wave shape (cos 2θ) and setting the energization torque to be almost twice the cogging torque.

  The fact that the cogging torque can be extracted in the form of a cosine wave (cos 2θ) if the magnetic flux density in the air gap is a sine wave is explained in detail in the paper “Reduction of cogging torque of permanent magnet brushless motor” published by the Institute of Electrical Engineers in April 2002. Has been. That is, if the magnetic flux density distribution Bg in the gap between the stator core and the rotor magnet is sinusoidal (sin θ), the magnetic flux distribution slope β is 1, and the cogging torque Tc is (1) only with the fundamental wave represented by the expression (11) on page 340. Cos 2θ) is described.

  However, the output voltage of the Hall element is actually a sine wave (sin θ), the back electromotive force of the motor coil is also a sine wave (sin θ), and the cogging torque waveform is a cosine wave having a rotation period almost twice that of the sine wave ( (cos 2θ), the magnetic flux distribution from the rotor magnet needs to be a sine wave. For this reason, when magnetizing a conventional rotor magnet having anisotropy in the radial direction, an air gap is partially provided between the magnetizing yoke and the rotor magnet so that the magnet portion that does not come into contact with the magnetizing yoke A method of weakening the magnetization is implemented.

  FIG. 6 shows the surface magnetic flux distribution of such a rotor magnet. 6-1 is a surface magnetic flux waveform after magnetization of a conventional radial anisotropic magnetic field orientation magnet, which is trapezoidal, with a central portion at the center. It is low. 6-2 is a surface magnetic flux waveform after weakly magnetized with a conventional radial anisotropic magnetic field orientation rotor magnet partially provided with an air gap, which is sinusoidal, but the average value of the magnetic flux amount is It is falling. No. 6-3 is a rotor magnet with polar anisotropic magnetic field orientation, and the average magnetic flux does not decrease, and the surface magnetic flux waveform is sinusoidal.

  In this way, by orienting the magnet with a polar anisotropic magnetic field, the magnetic flux distribution becomes sinusoidal in a multi-phase brushless DC motor, and as a result, the cogging torque is reduced, which is effective in reducing vibration noise. It is known. However, in the motor (single phase) according to the present invention, the cogging torque is generated to eliminate the dead point at the start, and the cogging torque is effectively utilized during rotation to reduce the torque ripple. Different.

In the conventional fan motor configuration as described above, in order to obtain a sinusoidal magnetic flux distribution, weakening magnetization as shown in FIG. 6B is performed, which adversely affects the motor efficiency. In addition, the polar anisotropic magnetic field orientation of the rotor magnet for the outer rotor motor needs to be arranged on the inner diameter side of the rotor magnet, which makes it difficult to apply to a motor having a small rotor magnet diameter. Also, in the voltage drive method in which the magnetic pole of the magnet is detected by the Hall element and the voltage is applied to the motor coil, a phase difference occurs between the motor back electromotive force and the motor coil energization current due to the inductance present in the motor coil. The phase difference generates reverse rotational torque, which causes rotational torque ripple and reduced motor efficiency. In order to energize using the output voltage waveform of the Hall element, it is necessary to suppress changes in the output voltage of the Hall element with respect to changes in temperature, voltage, and the like.
SUMMARY OF THE INVENTION In view of the above-mentioned problems of the prior art, the present invention provides a motor that eliminates torque ripple during rotation, minimizes vibration and noise as a fan, maximizes the linkage flux of a motor coil, and has high efficiency. It is intended.

  In order to achieve the above object, a rotor magnet is molded by applying an appropriate magnetic field orientation of polar anisotropy at the time of molding with an injection moldable magnet material. The Hall element output voltage signal has a waveform in which the Hall element output voltage signal has a maximum value at a position substantially corresponding to the center of one pole of the rotor magnet. The energization command signal is generated so that the current in the approximately 50% section in the latter half of energization gradually decreases and becomes almost zero at the commutation point. Further, the current flowing through the motor coil is detected, and the current matches the energization command signal. Such a feedback circuit is provided.

Since the rotor magnet is magnetically oriented with polar anisotropy, the magnetic flux is sinusoidal and the motor interlinkage magnetic flux can be extracted greatly. Since the magnetic flux is a sine wave, the Hall element output voltage waveform, the back electromotive force waveform are converted into a sine wave, the cogging torque is converted into a cosine wave, and the ratio of the gogging torque to the energizing torque is reduced to about ½. It is theoretically possible to eliminate the torque ripple of the phase motor. By designing the motor according to the set value, the rotational torque becomes constant and vibration from the motor does not occur. The effects are listed below.
(1) It is possible to reduce torque ripple of a single phase motor.
(2) Motor excitation source due to sudden current change during commutation is eliminated, fan blade vibration and frame resonance that caused noise of conventional fan motors are not generated, and fan noise can be significantly reduced. .
(3) Even if the sine wave of the Hall element output voltage waveform / counterelectromotive force waveform and the cosine wave of the cogging torque are not perfect, by introducing the idea of the present invention, a considerable torque ripple can be reduced.
(4) Since the interlinkage magnetic flux can be taken out greatly, high efficiency of the motor can be realized.
(5) Since the rotor magnet has polar anisotropic magnetic field orientation, the rotor yoke is unnecessary and the motor can be constructed at low cost.

  By molding a magnet material that can be injection-molded with an appropriate polar anisotropic magnetic field orientation at the time of molding, the magnetic flux distribution from the rotor magnet is made sinusoidal, the back electromotive force of the motor coil is made sinusoidal, and the cogging torque The waveform is extracted in the form of a cosine wave (cos 2θ) having a rotation period almost twice that of the sine wave. In addition, the air gap between the stator core salient poles and the magnets is made non-uniform to ensure starting stability. In addition, the Hall element output voltage signal has a waveform in which the Hall element output voltage signal has a maximum value at a position substantially corresponding to the center of one pole of the rotor magnet. , The current in the second half of the energization is gradually reduced, the energization command signal is generated so that it becomes almost zero at the commutation point, the current flowing in the motor coil is detected, and the current is Provide a matching feedback circuit. The current flowing in the motor coil is detected, and a current feedback loop is provided so that the rise and fall of the current waveform is similar to the rise and fall of the output voltage waveform of the Hall element, and the current drive system is energized.

  FIG. 1 is a view showing the structure of a motor of an embodiment according to claims 1 and 2 of the present invention. In the figure, reference numeral 20 denotes an annular rotor magnet showing a state in which magnetic anisotropy is set to four poles in polar anisotropy at the time of molding, and an arrow indicates an orientation direction. The counter electromotive force generated in the motor coil due to the rotation of the motor becomes sinusoidal. Reference numeral 3 denotes a hall element that detects the magnetic pole position of the magnet 20 and is attached to a printed board (not shown). Reference numeral 4 denotes a stator core formed by punching and stacking silicon steel plates, and has four teeth 5 and salient poles 6. The gap between the salient poles 6 and the rotor magnet 2 is not constant but uneven as shown in FIG. It has become. 7 and 8 are motor coils.

  The salient pole 6 has a 6A portion having a narrow gap with the rotor magnet 2 and a 6B portion having a wide gap. When the motor coils 7 and 8 are not energized, the magnetic pole center portion 2A of the opposing rotor magnet 2 has a salient pole. 6 is attracted to the 6A portion having a narrower gap than the center portion 6C, and the positional relationship between the poles of the rotor magnet 2 and the salient poles 6 of the teeth 5 is the same as that of the conventional motor. . However, as shown in FIG. 7, the motor cogging torque waveform 7-2 of the radial anisotropic magnetic field orientation includes many harmonic components, whereas the cogging torque waveform 7-1 of the polar anisotropic magnetic field orientation has a cosine wave shape. (Cos 2θ).

  In addition, when a rotor magnet is injection-molded with a ferrite-based magnetic powder containing plastic as a binder, polar anisotropic magnetic field orientation is required, and the magnet for that orientation must be placed on the inner diameter side of the rotor magnet. Some area is required on the inner diameter side. As a result of various experiments and researches, the present inventors have found that the minimum arc length of one pole necessary for polar anisotropic magnetic field orientation is about 20 mm. That is, the inner diameter of the rotor magnet that is magnetized with four poles needs to be about 25 mm or more. Similarly, the inner diameter of the rotor magnet that is magnetized with four poles is required to be about 38 mm or more.

  FIG. 2 shows an outline of the drive circuit of the embodiment according to claim 2 of the present invention, 3 is a hall element, and motor coils 7 and 8 are power transistors 26, 27, 28, connected to an H bridge. 29. Reference numeral 21 is a pre-drive IC for bipolar energizing the motor, Rf is a resistance for detecting the current of the motor coil, and 12 is a current feedback loop.

  FIG. 3 is a timing chart showing the operation of the circuit of FIG. Reference numeral 3-1 denotes an output voltage waveform of the Hall element 3, which has a peak value depending on the position of the rotor magnet 20 and the Hall element 3 even if the rotor magnet 20 is oriented in a polar anisotropic magnetic field. The output voltage of the Hall element 3 is input to the pre-drive IC 21 and outputs complementary voltages 3-2 and 3-3 to the upper arm transistors 26 and 27 of the H bridge, respectively. Furthermore, the output voltage waveform 3-1 of the Hall element 3 has a maximum value in the Hall element output voltage waveform at a position substantially corresponding to the center of one pole of the rotor magnet. In the flow, the current command signal is generated so that the current in the approximately 50% section in the latter half of the current flow is gradually reduced and becomes almost zero at the commutation point. On the other hand, the current flowing through the motor coil is detected by the current detection resistor Rf, and is input to the pre-drive IC 21 by the current feedback loop 12 so as to be similar to the energization command signal, and drivability (current value control) is applied to the transistors 28 and 29. Output complementary current signals 3-4 and 3-5.

  As a result, in the energizing section of FIG. 3A, a current flowing from the motor coil 7 to the motor coil 8 flows like 3-6, and in the energizing section of B, a current flowing from the motor coil 8 to the motor coil 7 is 3- A rising and falling edge like 6 flows in a smooth shape. The reason why the current waveform after commutation is different from the energization command signal is that the rise of the current is delayed due to the inductance component of the motor coil and the back electromotive force.

  Also, the output voltage change with respect to the temperature of the Hall element made of indium antimony material is relatively large and affects the shape of the rising and falling current waveform, so that the gain of an amplifier (not shown) in the pre-drive IC is increased. Is automatically changed to suppress the change to some extent.

  In addition, the present invention can be applied as a specific measure disclosed in Japanese Patent Application Laid-Open No. 2004-140897 that suppresses the sum of the cogging torque and the energization torque, that is, the torque ripple.

  As described above, the embodiment of the present invention has been described as a single-phase bipolar energized motor, but it goes without saying that the present invention can be similarly applied to a 180-phase phase difference two-phase unipolar energized motor.

  The basic technology of each element of the present invention has been established, and by applying it to a single-phase motor, significant characteristics improvement can be expected. In addition, torque rippleless can be realized even though it is a single-phase motor. It can be said that it is an optimal drive source that combines the cost, low vibration, low noise, and high efficiency required for a fan drive motor.

The figure which shows the structure of a motor in the Example of this invention. Schematic of the drive circuit in the embodiment of the present invention Timing chart showing the operation of the circuit of the present invention Relationship diagram between back electromotive force of motor coil and gogging torque Diagram showing the structure of a conventional motor Diagram showing surface magnetic flux distribution of rotor magnet Cogging torque due to magnetic orientation of rotor magnet

Explanation of symbols

1: Rotor core 2: Rotor magnet 3: Hall element 4: Stator core 5: Teeth 6: Salient poles 7, 8: Motor coil 11: DC power supply 12: Current feedback loop 20: Rotor magnet 21: Pre-drive IC
22: Constant voltage circuit 26, 27: Upper arm transistor 28, 29: Upper arm transistor 30: Capacitor R: Resistance Rf: Current detection resistance

Claims (6)

A stator core wound with a motor coil, a multi-pole magnetized cylindrical rotor magnet that is rotatably supported with a non-uniform air gap facing the stator core, and detects the magnetic pole position of the rotor magnet In a single-phase motor having a hall element, the rotor magnet is oriented in a magnetic field with polar anisotropy so that the back electromotive force of the motor coil is sinusoidal and the cogging torque is twice that of the sine wave. A single-phase brushless DC motor characterized by a cosine wave having a rotation period. The Hall element output voltage signal has a waveform having the maximum value of the Hall element output voltage signal at a position substantially corresponding to the center of one pole of the rotor magnet. 2. An energization command signal is generated so that a current in an approximately 50% section in the latter half of energization is gradually reduced and becomes almost zero at a commutation point, and the motor coil is energized full-wave. The single-phase brushless DC motor described. The rotor magnet has an inner diameter of 25 mm or more, the rotor magnet is made of ferrite-based magnetic powder and plastic, is formed by injection molding, and the inner peripheral surface of the rotor magnet is oriented with a four-pole polar anisotropic magnetic field. The single-phase brushless DC motor according to claim 1. The rotor magnet has an inner diameter of 38 mm or more, the rotor magnet is made of ferrite-based magnetic powder and plastic, is formed by injection molding, and the inner surface of the rotor magnet is oriented with a 6-pole polar anisotropic magnetic field. The single-phase brushless DC motor according to claim 1. The current flowing in the motor coil is detected, and a current feedback loop is provided so as to gradually decrease the current in the approximately 50% section in the latter half of energization and become almost zero at the commutation point. A single-phase brushless DC motor according to 1 and 2. 6. The single-phase brushless DC motor according to claim 5, further comprising circuit means for suppressing a change in output voltage of the Hall element.