JP7291104B2 - Three-phase brushless motor and method for detecting rotational position of three-phase brushless motor - Google Patents

Description

The present invention relates to a three-phase brushless motor and a rotational position detection method for the three-phase brushless motor.

As conventional three-phase brushless motors and rotational position detection methods for three-phase brushless motors, there are, for example, Patent Documents 1 and 2.

Patent Document 1 relates to a magnetic pole position detection device and a drive device for a brushless DC motor, and in particular, a magnetic pole position detection device that detects the magnetic pole position using a Hall element, and a sine wave PWM drive for the magnetic pole position detection device and the brushless DC motor. The present invention relates to a driving device for a brushless DC motor using a 180-degree conduction type inverter.

Patent Document 1 describes a magnetic pole position detection element unit that detects the magnetic pole position of a rotating body using three magnetic pole position detection elements using magnetic changes, and a detection signal generator that generates a magnetic pole position detection signal based on the magnetic pole position. and a controller for controlling the magnetic pole position detection based on the magnetic pole position detection signal. In this magnetic pole position detection device, the control section includes conversion correction means for converting and correcting the three magnetic pole position detection signals with a phase difference of 120 degrees generated and output by the detection signal generation section; signal selection means for selecting a predetermined one magnetic pole position detection signal from the magnetic pole position detection signals; relative magnetic pole position detection means for detecting a relative magnetic pole position from the value of the selected magnetic pole position detection signal; It is characterized by comprising absolute magnetic pole position detection means for detecting a continuous absolute magnetic pole position from the section of the magnetic pole position detection signal and the relative magnetic pole position.

According to Patent Document 1, it is determined whether or not the motor is rotating at low speed immediately after starting the motor, and the offset correction amount and amplitude correction amount are detected only at low speed. I do. These detections and corrections are performed for each of the three phases. The amplitude and offset amount of the output signal waveform of each hall element are detected using the maximum and minimum values of the digital detection value, and the amount of correction for the digital detection value is determined and corrected, thereby making circuit components such as hall elements. It is said that high-precision magnetic pole position detection can be performed by removing the influence of variations in . Here, the permissible range is a value obtained in advance through experiments and stored in the ROM of the microcomputer.

Patent Document 2 describes an encoder that also serves as a rotor position detection sensor for drive control of a three-phase brushless motor. According to the document, three magnetic sensors are arranged at intervals of 120° or 60° in the circumferential direction, and two of the three magnetic sensors are further positioned to face each other at 180°. Sensors are arranged, and the outputs of the magnetic sensors arranged at positions facing each other by 180° are combined to detect the rotational position of the rotor. In this document, for the purpose of suppressing output voltage level fluctuations, in order to cancel errors due to rotor eccentricity, magnetic flux unevenness, etc., two Hall elements are arranged facing each other, outputs are combined and averaged to suppress level fluctuations. is described.

JP-A-9-121584 JP 2012-194086 A

In Patent Document 1, it is necessary to determine whether or not the motor is rotating at a low speed immediately after starting the motor, detect the amount of offset correction and the amount of amplitude correction only when the speed is low, and furthermore, perform the calculation of the offset amount and the amplitude error. be. Furthermore, it is necessary to store in the ROM of the microcomputer whether each calculation is within the permissible range, which is determined in advance by experiments.

In Patent Document 2, a magnetic sensor is further arranged at a position opposed to each of the two magnetic sensors at 180°, and the outputs of the magnetic sensors arranged at positions opposed to each other at 180° are combined to produce a rotor is detected. Then, a 90° phase conversion is performed from a 120° phase, and rotor angle conversion is performed as a relationship between a sine wave and a cosine wave. However, if the magnetic poles of the motor are magnetized in a trapezoidal wave, or even if they are magnetized in a sine wave, if they are detected as a trapezoidal wave due to the placement of the magnetic sensor, etc., the sine wave and cosine wave In relation, the plateaus of the two trapezoidal waves may partially overlap. In this overlap, since the ratio of the sine wave and the cosine wave does not change, although the rotor is rotating, the detected position does not change, making accurate position detection difficult.

In view of the prior art, it is an object of the present invention to efficiently detect the rotational position of a three-phase brushless motor using a magnetic sensor that detects the magnetic field from a rotor magnet without using an expensive encoder. .

In order to achieve the above object, a three-phase brushless motor according to the present invention comprises a permanent-magnet rotor in which N and S poles are alternately magnetized along the circumferential direction, and an electrical phase difference between the three phases. is 120 degrees and the number of slots is a multiple of 6; and a second set of magnetic sensors consisting of three magnetic sensors arranged radially opposite the three magnetic sensors in the first set to detect the magnetic field of the rotor. I have. Outputs of two magnetic sensors arranged so as to face each other in a radial direction are synthesized to obtain three synthesized outputs , the three synthesized outputs obtained by the synthesis are converted into two phases, and after the conversion, The rotational position of the rotor is detected from the output of .

According to the present invention, in a three-phase brushless motor, the rotational position can be efficiently detected using a magnetic sensor that detects the magnetic field from the rotor magnet without using an expensive encoder.

1 is a cross-sectional view of a three-phase brushless motor; FIG. FIG. 4 is an explanatory diagram showing the arrangement of magnetic sensors in a three-phase brushless motor; 4 is a waveform diagram of an output signal of a magnetic sensor; FIG. FIG. 10 is a waveform diagram showing output waveforms after the combined U-phase and V-phase output waveforms are converted from 120-degree phase to 90-degree phase; FIG. 4 is a waveform diagram of U-phase, V-phase, and W-phase after synthesis; 6 is a waveform diagram showing an output waveform after converting the waveform of FIG. 5 into two phases; FIG. FIG. 4 is an output waveform diagram of 90-degree phases from two magnetic sensors;

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described below based on the illustrated embodiments. However, the present invention is not limited by the embodiments described below.

In a three-phase brushless motor, drive control is performed to rotate the rotor by changing the direction of the current flowing through the coils of the stator according to the rotation angle of the rotor. That is, a magnetic sensor for checking the rotor position of the three-phase brushless motor detects changes in magnetic flux due to the rotation of the rotor magnet, and changes the direction of the current flowing through the stator coils according to the detection result.

A three-phase brushless motor is driven by a sinusoidal wave drive system in which a sine wave synchronized with the rotation of the rotor is used, and a rectangular wave drive system in which a rectangular wave is used to drive the motor. The sinusoidal wave drive system has better drive efficiency than the square wave drive system, and has less torque fluctuation, so that it produces less vibration and less noise. In such drive control, a magnetic pole position sensor is used to generate a drive voltage in synchronization with rotor rotation.

In detecting the magnetic poles of a three-phase brushless motor, an alternating type magnetic sensor (NS switch type) such as an inexpensive Hall IC may be used as a magnetic sensor. The magnetic pole position is estimated by interpolation based on the elapsed time from the timing detected by these sensors. However, if the rotation speed of the motor is extremely low, or if the rotation of the motor is irregular or intermittent, the interpolation may not be performed well.

When driven at extremely low speed, a high-speed resolver, encoder, or the like can be used that can detect the rotational position with high accuracy. However, since the structure is complicated and a dedicated drive circuit is required, the drive system including the motor is large and expensive.

The inventor has invented a 3-phase brushless motor and a rotational position detection method for the 3-phase brushless motor using an inexpensive magnetic sensor capable of analog magnetic pole detection.

FIG. 1 is a cross-sectional view of a three-phase brushless motor 100 according to one embodiment. A three-phase brushless motor 100 includes a stator 200, a rotating shaft 350, and a rotor 300 attached to the rotating shaft. A plurality of slots are formed in the stator 200, and windings such as the U-phase winding portion 210 are wound around the slots. The rotor 300 has a rotor core 310 and rotor magnets 320 provided on the peripheral surface of the rotor core. This rotor magnet is alternately magnetized with N poles and S poles along the rotor circumferential direction. That is, the rotor 300 is a permanent magnet type rotor.

The 3-phase brushless motor 100 further includes a magnetic sensor mounting board 450 . The magnetic sensor mounting substrate 450 is arranged to face the rotor 300 in the rotation axis direction, and has six magnetic sensors mounted thereon. These six magnetic sensors detect changes in magnetic flux due to the rotation of the rotor 300 as will be described later, and detect the rotational position of the rotor 300 . Rotor 300 and rotating shaft 350 rotate at a predetermined speed by changing the direction of the current flowing through the windings of stator 200 according to the detection result.

FIG. 2 shows the three-phase brushless motor 100 as viewed in the rotation axis direction.

The stator 200 has a total of 12 slots from the first slot S1 to the twelfth slot S12. The first slot S1 to the twelfth slot S12 are provided in order at equal intervals in the circumferential direction.

The U-phase first winding portion 210 includes a first winding portion 210a provided in the first slot S1 and a second winding portion 210b provided in the second slot S2. The first winding portion 210a and the second winding portion 210b have opposite winding directions (winding directions).
The V-phase first winding portion 220 includes a first winding portion 220a provided in the fourth slot S4 and a second winding portion 220b provided in the third slot S3. The winding directions of the first winding portion 220a and the second winding portion 220b are opposite.
The W-phase first winding portion 230 includes a first winding portion 230a provided in the fifth slot S5 and a second winding portion 230b provided in the sixth slot S6. The winding directions of the first winding portion 230a and the second winding portion 230b are opposite.

In the seventh slot S7 to the twelfth slot S12, winding portions for each phase are similarly provided.
That is, the U-phase second winding portion includes a first winding portion provided in the eighth slot S8 and a second winding portion provided in the seventh slot S7. The winding directions of both winding sections are opposite.
The V-phase second winding portion includes a first winding portion provided in the ninth slot S9 and a second winding portion provided in the tenth slot S10. The winding directions of both winding sections are opposite.
The W-phase second winding portion includes a first winding portion provided in the 12th slot S12 and a second winding portion provided in the 11th slot S11. The winding directions of both winding sections are opposite.

The rotor magnet 320 of the rotor 300 has 10 poles, and the N poles and S poles are alternately magnetized along the circumferential direction. That is, the rotor 300 is a 10-pole permanent magnet rotor.

A first set of magnetic sensors consisting of magnetic sensors 410 , 420 and 430 and a second set of magnetic sensors consisting of magnetic sensors 411 , 421 and 431 are mounted on the magnetic sensor mounting board 450 . All six magnetic sensors in total are for detecting the rotational position of the rotor 300 .

In the first set, the magnetic sensors 410, 420 and 430 are arranged with an electrical angle shift of 120 degrees. Specifically, the magnetic sensor 410 includes a first winding portion 210a (first slot S1) of the U-phase first winding portion 210 and a second winding portion 210b (second slot S2) of the U-phase first winding portion 210 as viewed in the rotation axis direction. ) are placed between The magnetic sensor 420 is arranged between the first winding portion (the ninth slot S9) and the second winding portion (the tenth slot S10) of the V-phase second winding portion when viewed in the rotation axis direction. there is The magnetic sensor 430 is positioned between the first winding portion 230a (fifth slot S5) and the second winding portion 230b (sixth slot S6) of the W-phase first winding portion 230 when viewed in the rotation axis direction. are placed.

Each of the magnetic sensors 410, 420, and 430 is a Hall element capable of analog magnetic pole detection, or a linear Hall IC having a Hall element with an amplification function.

By arranging the magnetic sensors 410, 420 and 430, respectively, between two adjacent slots that constitute the U-phase, V-phase and W-phase when viewed in the direction of the rotation axis, the excitation of each phase winding, the magnetic The influence on sensor detection can be suppressed.

Furthermore, magnetic sensors 411, 421 and 431 are arranged at positions facing the magnetic sensors 410, 420 and 430 in the radial direction, respectively. That is, the magnetic sensor 411 is arranged between the seventh slot S7 and the eighth slot S8, the magnetic sensor 421 is arranged between the third slot S3 and the fourth slot S4, and the magnetic sensor 431 is arranged between the eleventh slot S11. and the 12th slot S12.

Similarly, the magnetic sensors 411, 421, and 431 are Hall elements capable of analog magnetic pole detection, or linear Hall ICs having a Hall element with an amplifying function.

The magnetic sensors 411, 421, and 431 are also arranged between two adjacent slots constituting the U-phase, V-phase, and W-phase, respectively, when viewed in the direction of the rotation axis. The influence on sensor detection can be suppressed.

Next, the waveform of the detection signal of the magnetic sensor will be described. First, the magnetic sensor 410 and the magnetic sensor 411 arranged to face the magnetic sensor 410 in the radial direction will be described.

Looking at the output waveform A of the magnetic sensor 410 shown in FIG. 3, it can be seen that the amplitude deviates greatly within one rotation (360°). This is presumed to be due to mechanical errors such as rotor eccentricity.

Since the rotor 300 is a 10-pole permanent magnet rotor magnetized alternately with N and S poles as described above, five cycles of output waveforms are obtained in one rotation (360°).

The output waveform -A of the magnetic sensor 411, also shown in FIG. I know there is. Furthermore, the output waveform -A has the opposite magnitude of amplitude deviation compared to the output waveform A of the magnetic sensor 410 . For example, at a rotational position where the deviation of the amplitude of the output waveform A of the magnetic sensor 410 is large, the deviation of the amplitude of the output waveform -A of the magnetic sensor 411 is small. Further, at a rotational position where the deviation of the amplitude of the output waveform A of the magnetic sensor 410 is small, the deviation of the amplitude of the output waveform -A of the magnetic sensor 411 is large.

Therefore, as shown in the following equation, the output waveform A of the magnetic sensor 410 and the output waveform -A of the magnetic sensor 411 are subtracted and divided by 2 to eliminate mechanical errors due to rotor eccentricity. is canceled, the output waveform of the opposing cancellation shown in FIG. 3 can be obtained.
(A-(-A))/2=average A (1)

Similarly, the output waveform B of the magnetic sensor 420 and the output waveform −B of the magnetic sensor 421 arranged so as to face the magnetic sensor 420 in the radial direction are also subjected to the following calculations to determine the eccentricity of the rotor, etc. It is possible to obtain an output waveform in which mechanical errors due to are canceled.
(B-(-B))/2=average B (2)
This output waveform is 120 degrees out of phase with the combined output waveforms of the magnetic sensors 410 and 411 .

In principle, the rotational position of the rotor 300 can be detected by converting these two output waveforms from three phases with a phase of 120 degrees to two phases with a phase of 90 degrees.

However, in some cases, the rotor magnet 320 is magnetized so that the detection signal of the magnetic sensor becomes a trapezoidal wave. Alternatively, even if the rotor magnet 320 is magnetized so that the detection signal of the magnetic sensor becomes a sine wave, the detection signal may become a trapezoidal wave depending on the arrangement of the magnetic sensor.

As described above, from the output waveform obtained by synthesizing the waveforms of the magnetic sensors 410 and 411 and the output waveform obtained by synthesizing the waveforms of the magnetic sensors 420 and 421, mechanical errors are canceled, and the phase is changed from 120° to 90°. FIG. 4 shows the output waveform converted to two phases. Symbols A1 and B1 denote waveforms obtained by converting the 120° phase of the waveform obtained by combining the signal outputs A and -A and the waveform obtained by combining the signal outputs B and -B into 90° phase. As indicated by symbol Z1, the flat portions of the trapezoidal waves partially overlap in the two phases (relationship between sine wave and cosine wave). Since the ratio of each phase does not change while the flat portions partially overlap, the detected position does not change even though the rotor is rotating, making it difficult to perform accurate position detection.

Therefore, the output waveform C of the magnetic sensor 430 and the output waveform -C of the magnetic sensor 431 are also subjected to the following calculations to obtain output waveforms in which the mechanical error due to the eccentricity of the rotor is canceled. be able to.
(C-(-C))/2=average C (3)
This output waveform is 120 degrees out of phase with both the synthesized output waveform of the magnetic sensors 410 and 411 and the synthesized output waveform of the magnetic sensors 420 and 421 .

FIG. 5 shows three-phase output waveforms in which mechanical errors due to rotor eccentricity and the like are cancelled. Due to the influence of the magnetic poles of the rotor magnet 320, the arrangement of the magnetic sensor, and the like, this output waveform is not a sine wave but a trapezoidal wave, which is the output waveform of the magnetic sensor.

ただし、Ｈ_Ａ、Ｈ_Ｂ、Ｈ_Ｃはそれぞれ３相各出力波形値である。また、Ｈ_α、Ｈ_βはそれぞれ２相の出力波形値である。 By converting the three-phase output waveform shown in FIG. 5 from three-phase to two-phase as shown in the following equation, the output waveform of sine wave and cosine wave with a phase difference of 90 degrees as shown in FIG. 6 is obtained. be able to.

However, H _A , H _B , and H _C are three-phase output waveform values, respectively. H _α and H _β are two-phase output waveform values, respectively.

Even with a trapezoidal three-phase output waveform with a phase difference of 120°, by converting from three phases to two phases, a sine wave and a cosine wave with a phase difference of 90° can be obtained as shown in FIG. An output waveform is obtained. The rotational position of the rotor 300 can be detected from this output waveform.

Based on the above, in the three-phase brushless motor 100 shown in FIGS. 1 and 2, detection of the rotational position is performed in the following three steps.
[First step]
Outputs of two magnetic sensors arranged so as to face each other in the radial direction are synthesized. That is, the outputs of the magnetic sensors 410 and 411 are combined as shown in Equation (1), the outputs of the magnetic sensors 420 and 421 are combined as shown in Equation (2), and the outputs of the magnetic sensors 430 and 431 are combined as shown in Equation (3). synthesized.
[Second step]
As shown in equation (4), the 3-phase output obtained in the first step is converted to 2-phase.
[Third step]
The rotational position of rotor 300 is detected from the output after conversion to two phases.

In the above-described embodiment, mechanical errors of the rotating body are canceled by arranging the magnetic sensors so as to face each other mechanically by 180 degrees. Also, as a countermeasure against the trapezoidal wave caused by the rotor magnet, instead of the two-phase signal shifted by 90 degrees, the three-phase signal shifted by 120 degrees is detected and converted into the two-phase signal again. Furthermore, by arranging the magnetic sensor between two adjacent slots that constitute each phase, the influence of the magnetic flux from the windings is suppressed.

This allows the rotational position of the rotor to be known more accurately. The speed stability at low speed is improved, and the positioning accuracy is also improved. Even during extremely low-speed driving, a sine wave and a cosine wave with a phase difference of 90 degrees can be obtained, and the rotational position can be detected with high accuracy. Therefore, drive control can be performed to rotate the rotor 300 by changing the direction of the current flowing through the windings of the stator 200 according to the rotation angle of the rotor 300 . A three-phase brushless motor can be stably driven even during extremely low speed driving.

According to the above embodiment, the following effects can be obtained.
・Mechanical errors caused by the eccentricity of the rotor and the mounting position of the magnetic sensor can be canceled.
・Accurate position detection is possible even if the output waveform of the magnetic sensor is trapezoidal.
・It is possible to detect the rotational position with a simple configuration at low cost and with high accuracy without making major changes to the current three-phase brushless motor structure.
・Stable drive is possible even during extremely low speed drive.
・The cost can be kept low while maintaining the same level of accuracy as encoders and resolvers.

Extremely low speed operation and positioning operation are possible using a magnetic sensor that detects the magnetic field from the rotor magnet without using an expensive encoder.

FIG. 7 shows 90-degree phase output waveforms from two magnetic sensors as a comparative example. Symbol A2 indicates the output waveform of one magnetic sensor when two magnetic sensors are arranged at a position of 90°, and symbol B2 indicates the output waveform of the other magnetic sensor. This figure shows a case where rotor angle conversion is performed as a relationship between a sine wave and a cosine wave from a magnetic sensor in a three-phase brushless motor in which the number of slots in the three-phase stator is a multiple of six. As indicated by arrows Y1 and Y2, amplitude errors occur due to mechanical error factors such as eccentricity. Also, as indicated by symbol Z2, when the flat portions of the two trapezoidal waves A and B partially overlap, accurate position detection becomes difficult.

According to the above embodiment, the amplitude error (FIG. 7) and offset can be dealt with, and even if the output waveform of the magnetic sensor is trapezoidal, the position can be accurately detected. Note that the offset means that the entire waveform deviates from the 0 point in the vertical axis direction, although not shown.

Note that conversion from three phases to two phases (equation (4)) can be performed by a calculation unit in the three-phase brushless motor 100 . Alternatively, the three-phase signals (formulas (1) to (3)) whose mechanical errors have been canceled by two radially facing magnetic sensors are transmitted from the three-phase brushless motor 100 to an external device of the three-phase brushless motor 100. It may be output to a driving device or the like, and conversion from 3-phase to 2-phase (equation (4)) may be performed in the external driving device or the like.

Furthermore, the output signals of the six magnetic sensors can be output from the 3-phase brushless motor 100 to a driving device or the like external to the 3-phase brushless motor 100 . Then, in the external driving device or the like, after generating a three-phase signal with mechanical errors canceled by two magnetic sensors facing each other in the radial direction (equation (1) to equation (3)), the three phases are converted to two A conversion to phase (equation (4)) can be performed.

[Other embodiments]
Next, another example will be shown.
The 10-pole rotor 300 may be replaced with an 8-pole permanent magnet rotor in which N and S poles are alternately magnetized in the circumferential direction. In this case, the magnetic sensors 410, 420 and 430 for detecting the rotational position are arranged at intervals of 60 degrees in the circumferential direction, and the magnetic sensors 411, 421 and 431 are arranged so as to face the magnetic sensors 410, 420 and 430 in the radial direction. can be placed.

Further, in the eight-pole permanent magnet rotor, the magnetic sensor may not be affected by the excitation of the U-phase, V-phase, and W-phase. In this case, the magnetic sensors 410, 420 and 430 for detecting the rotational position are arranged at intervals of 30 degrees in the circumferential direction, and the magnetic sensors 411, 421 and 430 are arranged so as to face the magnetic sensors 410, 420 and 430 in the radial direction. 431 can be placed.

The three magnetic sensors 410, 420 and 430 in the first set of magnetic sensors may be arranged at intervals of 120 electrical degrees. The mechanical angle of 120 electrical degrees is determined by the number of poles of the rotor. In the case of 10 poles, the mechanical angle is a multiple of 24° (however, 120° or less because 3 poles must be arranged at 360°). For 8 poles, the mechanical angles are multiples of 30°.

If the number of slots in the stator is a multiple of 12, the magnetic sensors 410, 420, and 430 are positioned between two circumferentially adjacent slots forming the U-phase, V-phase, and W-phase, respectively, when viewed from the rotation axis direction. , the effect of excitation can be eliminated. On the other hand, if the magnetic sensor is not likely to be affected by the U-phase, V-phase, and W-phase excitations, the number of slots in the stator may be a multiple of six. Furthermore, any phase winding of the stator does not necessarily have to be wound in pairs of circumferentially adjacent slots.

Although the embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments, and various modifications and changes are possible based on the technical idea of the present invention.

100 three-phase brushless motor 200 stator 210 U-phase first winding portion 220 V-phase first winding portion 230 W-phase first winding portion 300 rotor 310 rotor core 320 rotor magnet 350 rotating shaft 410, 420, 430, 411, 421 , 431 magnetic sensor 450 magnetic sensor mounting board

Claims (8)

a permanent magnet rotor in which N poles and S poles are alternately magnetized along the circumferential direction;
a stator configured such that the electrical phase difference between the three phases is 120 degrees and the number of slots is a multiple of 6;
a first set of magnetic sensors consisting of three magnetic sensors arranged at intervals of 120 electrical degrees for detecting the magnetic field of the rotor;
a second set of magnetic sensors consisting of three magnetic sensors arranged to face each of the three magnetic sensors in the first set in the radial direction and detecting the magnetic field of the rotor;
The outputs of two magnetic sensors arranged so as to face each other in the radial direction are combined to obtain three combined outputs ,
The three combined outputs obtained by the combining are converted into two phases,
a rotational position of the rotor is detected from the converted output;
3-phase brushless motor. 2. The three-phase brushless motor according to claim 1, wherein any phase winding of said stator is wound in two circumferentially adjacent slots. the number of slots of the stator is a multiple of 12;
any phase winding of the stator is wound in two circumferentially adjacent slots;
A magnetic sensor is arranged between the two slots when viewed in the direction of the rotation axis of the three-phase brushless motor,
A three-phase brushless motor according to claim 1. 4. The three-phase brushless motor of claim 3, wherein the winding directions are opposite in the two slots. The three-phase brushless motor according to any one of claims 1 to 4, wherein the magnetic sensor is a Hall element or linear Hall IC that outputs an analog signal. a permanent magnet rotor in which N poles and S poles are alternately magnetized along the circumferential direction;
a stator configured such that the electrical phase difference between the three phases is 120 degrees and the number of slots is a multiple of 6;
a first set of magnetic sensors consisting of three magnetic sensors arranged at predetermined intervals in the circumferential direction and configured to detect the magnetic field of the rotor;
a second set of magnetic sensors consisting of three magnetic sensors arranged radially opposite each of the three magnetic sensors in the first set for detecting the magnetic field of the rotor; A rotational position detection method for a brushless motor, comprising:
a synthesizing step of synthesizing the outputs of two magnetic sensors arranged so as to face each other in the radial direction to obtain three synthesized outputs ;
a converting step of converting the three synthesized outputs obtained by the synthesizing step into two phases;
and a detecting step of detecting the rotational position of the rotor from the output obtained by the converting step. 7. The rotational position detection method for a three-phase brushless motor according to claim 6, wherein the number of slots of said stator is a multiple of twelve. Control of a three-phase brushless motor, comprising the step of controlling currents in windings of the stator using the rotational position of the rotor detected by the rotational position detection method for a three-phase brushless motor according to claim 6 or 7. Method.

Images