JPH053695A - Rotor position detector for brushless motor - Google Patents

Abstract

PURPOSE:To obtain a brushless motor driver having no practical pole sensor by detecting the rotor position of motor from the phase difference between an exciting signal and a rotational angle signal or a rotational. angular speed signal produced according to generated torque or microvibration. CONSTITUTION:When a controller 4 detects pole position, a commanding section 46 commands a rotary angular speed omega corresponding with a torque current command value i'rand exciting frequency under a state where switches 48, 49 are turned as shown on the drawing, and an integrator 41B determines a rotational angle phi' from the rotary angular speed omega'. When the rotational angle phi' and the torque current command value i'r are fed to a vector rotator 44 in order to drive a motor 1 through a power amplifier 3, microvibration occurs. Pulses generated from an encoder 2 are processed through a pulse processor 5 and fed to a speed detecting section 40 and a rotational angle operating section 41 thence to a detecting section 47 where a pole position signal phio, representing the phase difference between a rotational angle theta or a detected value (n) of rotational speed and the rotational angle command phi' is produced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a rotor position detecting device suitable for use in a case where a three-phase brushless motor having a permanent magnet as a rotor is driven without a magnetic pole sensor.

[0002]

2. Description of the Related Art A brushless motor is driven by a DC motor that performs commutation mechanically, while an electric switch is used to perform commutation. The commutation needs to be performed so that it can be operated with the highest power factor, but in the permanent magnet type brushless motor, the timing is uniquely determined by the position of the magnetic pole by the permanent magnet incorporated in the rotor. Therefore, a sensor for detecting the magnetic pole position is indispensable for driving the brushless motor. Therefore, the brushless motor requires not only a sensor but also a signal line for transmitting a signal from the sensor to the control device, which causes problems in cost, size and weight, and reliability. Therefore, brushless motors that do not use such a sensor have been proposed, for example, in Japanese Patent Laid-Open Nos. 63-57983 and 2-241388 (hereinafter, also referred to as a conventional system). The ones described above detect the magnetic pole position (rotor position) by exciting the brushless motor with direct current at an arbitrary angle before performing normal control and detecting the direction and magnitude of the torque generated at that time. To do.

[0003]

In the above conventional method, the direct current is passed through at a preset angle, and the magnitude of the generated torque is detected from the change in the rotation angle of the rotor during that period. There are the following problems. In order to accurately detect the change in the rotation angle, it is necessary to set the speed and acceleration at the start of flow to exactly zero, so you must take sufficient time to switch the set angle next time. However, the detection time becomes long. When the load inertia and friction torque are unknown, it is difficult to determine the optimum DC current amplitude. Therefore, an object of the present invention is to minimize the angle of rotation by rotor position detection, prevent the motor from rotating significantly due to a transient phenomenon at the start of excitation, and perform rotor position detection stably and in a short time. Another object of the present invention is to provide a brushless motor drive device without a magnetic pole sensor.

[0004]

In order to solve such a problem, in the first invention, a three-phase brushless motor comprising a stator winding and a rotor having a permanent magnet, and a rotor shaft mounted on the same Encoder, counting means for counting the pulses emitted from the encoder, a controller for giving a voltage command or a current command and a frequency command to the motor, and the three-phase brushless motor for amplifying these commands. At least a power amplifier for driving a three-phase AC excitation is given through the control device and the power amplifier to give a predetermined frequency command so that a rotating magnetic field having a predetermined rotation angle is generated in a stator winding of the motor. , The resulting microvibration of the same frequency is detected through the encoder and the counting means, and the excitation signal and the generated torque or microvibration From the phase difference between the angle signals or rotational angular velocity signal is characterized by detecting the rotor position of the motor. A second aspect of the invention is characterized in that the phase difference in the first aspect of the invention is detected at the time when the rotational angular velocity signal has a positive or negative maximum value.

According to a third aspect of the invention, the frequency command for exciting the three-phase AC in the first or second aspect of the invention is gradually reduced from a sufficiently high frequency with the lapse of time at first, and the frequency command is set to a predetermined value. It is characterized in that the reduction of the frequency command is stopped when the fluctuation of the rotation angle based on the frequency or the minute vibration due to the excitation or the rotation angle reaches a predetermined amplitude, and the detection of the rotor position is started from this time. Further, in the fourth invention, the voltage command or the current command for exciting the three-phase AC in the first or second invention is gradually increased from zero or a sufficiently small value equal thereto at first with the passage of time. It is characterized by stopping the increase of the voltage command or the current command when the fluctuation of the rotation angle based on the minute vibration due to the excitation or when the rotation angle reaches a predetermined amplitude, and starting the detection of the rotor position from this time. There is.

[0006]

[Operation] The torque generated in the brushless motor is
When the magnetic flux created by the magnetic poles of the rotor and the current flowing through the stator windings are captured as space vectors, the outer product is obtained. Therefore, when the three-phase AC excitation is performed with the rotor not rotating, only the current vector rotates and the amplitude of the generated torque oscillates at the excitation frequency. The phase in which the generated torque oscillates is uniquely determined by the spatial angle at which the rotor is stopped. Therefore, the rotor position can be detected by measuring the phase difference of the vibration torque with respect to a certain phase current of the motor. This will be described below using equations and figures.

First, the equation of motion of the mechanical system showing the relationship between the rotation angle θ and the torque T is assumed as in equation (1). T = J × (d ² θ / dt ² ) J: Moment of inertia [Kg · m ² ] (1) Now, when the stator winding is excited by three-phase AC at a certain angular frequency, the current vector rotates at the same angular frequency. However, if the rotor is kept stopped, the generated torque is given by equation (2). T = K | i | sin (ωt−α) (2) where K is the torque constant [Kg · m / A], | i | is the amplitude of the current vector, ω is the excitation angular frequency, and α is ωt. = 0
The angle between the current vector (i) and the magnetic flux vector at is shown. By substituting equation (1) into equation (2), the rotational angular acceleration d ² θ / dt ² and the rotational angular velocity dθ /
The dt and the rotation angle θ can be obtained by the equations (3), (4) and (5). Note that equation (4), (5)
Although the rotation angular velocity and the rotation angle of the equation have initial values depending on α, the equation becomes complicated, so the description is omitted here. d ² θ / dt ² = (K | i | / J) × sin (ωt−α) (3) dθ / dt = − (K | i | / Jω) × cos (ωt−α) (4) θ = − (K | i | / Jω ² ) × sin (ωt−α) (5)

Here, assuming that the permanent magnet 10 of the rotor is in the position as shown with respect to the three-phase stator windings 11 to 13 as shown in FIG. 6 (α = π / 2), When a current (excitation current) as shown in FIG. 7A is applied to the U-phase winding 11,
The torque generated by the motor, the rotational angular velocity and the rotational angle are shown in Figure
It becomes like (b), (c) and (d). That is, it can be seen that the phase difference between the torque that changes sinusoidally at the excitation frequency and the excitation current changes depending on the magnetic pole position that is stopped. Therefore, it is possible to detect the generated torque or the rotational angular velocity or the rotational angle of the minute vibration generated thereby, and to detect the magnetic pole position from the phase difference between this and the exciting current. In the above description, it is neglected that the position of the rotor is changed by the minute vibration and the generated torque is changed by this, but the change of the rotation angle is sufficiently small. No problems arise.

[0009]

FIG. 1 shows an embodiment of the present invention. As shown in the drawing, a brushless motor 1 whose rotor is a permanent magnet, an encoder (PE) 2 coupled to the rotor, a power amplifier 3 including a power converter that supplies a commanded current to the motor 1, From the pulse processing circuit 5 or the like which receives the pulse (two-phase pulse A, B) detected by the controller 4 and the encoder 2 which gives the current command value to the power amplifier 3 and outputs the rotation angle signal within the sampling period. Composed. The control device 4 has a built-in portion for performing normal control of the motor 1 and a portion for detecting magnetic pole position. That is, the part that performs normal control is the speed detection unit 40 that detects the speed n from the encoder pulse number Δθ within the sampling cycle, and the rotation angle calculation unit (integrator) 41A that integrates Δθ and calculates the rotation angle θ. , An adder 42 calculates an error between a speed command value and a speed detection value (actual value), and inputs the error to calculate a torque command current value i _T ^* , a speed controller (ASR) 43, a torque current command value i _T ^*
To a phase current command value for each phase of the motor 1 and an adder 45 for adding the detected magnetic pole position signal φ ₀ and the rotation angle θ to calculate an angle φ given to the vector rotator 44. To be done.

On the other hand, the control unit for detecting the magnetic pole position outputs a torque current command value i _T 'and a rotational angular velocity command ω' corresponding to the excitation frequency when the magnetic pole is detected.
6. Excitation angle φ'by integrating this rotational angular velocity command ω '
The obtained integrator 41B, detecting unit 47 for outputting a magnetic pole position signal phi ₀ detects a phase difference between the rotation angle θ or the rotation speed detection value n in the magnetic pole position detection and the rotation angle command phi ', and the magnetic pole position detection mode It is composed of switches 48, 49, etc. that can be switched in the normal operation mode. By switching these switches, either the magnetic pole position detection mode or the normal control mode is selected. However, since the normal control cannot be performed without detecting the magnetic pole position, the control device 4 is generally not powered. Immediately after being turned on, the magnetic pole position detection mode is executed, and after the magnetic pole position is detected, a starting sequence for performing normal control is prepared in advance. Further, here, when the three-phase AC excitation is performed, the current command value is given to the power amplifier 3 and the current is controlled. However, a power amplifier which gives a voltage command to control the voltage may be used. . In detecting the phase of the exciting current, there is no essential difference whether the current command value or the actual value is used.

The magnetic pole position detecting method in FIG. 1 will be described. That is, with the switches 48 and 49 in the positions shown in the figure, the commanding unit 46 commands the torque current command value i _T ′ and the rotational angular velocity ω ′ corresponding to the excitation frequency, and the rotational angular velocity command ω ′ is used to instruct the integrator. 41B is used to obtain the rotation angle φ ′, and the torque current command value i _T ′ is given to the vector rotator 44 to drive the motor 1 via the power amplifier 3, which causes the above-described minute vibration. The generated pulse from the encoder 2 is processed by the pulse processing circuit 5 and given to the speed detecting section 40 and the rotation angle calculating section 41A, and these outputs are further detected by the detecting section 47.
By inputting into the input, the phase difference between the rotation angle θ or the rotation speed detection value n and the rotation angle command φ ′, that is, the magnetic pole position signal φ ₀ can be obtained based on the principle described with reference to FIG. 7.

By the way, each waveform shown in FIG. 7 shows an ideal state, and in reality distortion occurs due to various causes. In particular, in the case of FIG. 1, it is common to detect the zero point of the rotation angle and the rotation angular velocity and use the angle between this and the current command as the phase difference. However, for example, if the cogging torque of the motor (torque ripple caused by the shape of the motor) affects or the friction coefficient changes in the rotation direction,
The change of the rotation angle may not be a perfect sine wave.
Also, the rotational angular velocity is obtained from the change in the rotational angle per unit time, but since the rotational angle is detected from the encoder pulse that is a discrete signal of the rotational angle, it is difficult to detect near zero velocity, and near zero velocity. Will cause distortion. Therefore, the rotational angular velocity (dθ / dt) has a positive or negative maximum value within one cycle of excitation (P1 or P in FIG. 7C).
2)) and the magnetic pole position is detected from the angle with respect to the exciting current at this point, the above-mentioned inconvenience can be solved. Therefore, the detection unit 4 of FIG.
By adopting such a method in 7, it is possible to perform detection that is more realistic.

FIG. 2 is a block diagram showing a concrete example of the command unit shown in FIG. 1, and FIG. 3 is an explanatory diagram for explaining its operation. This is a setter 461 for the torque current command value i _T ′,
Setter 46 for the initial value of the excitation frequency (see ω0 in FIG. 3)
2. A setter 463 of a reduction frequency per unit time (see Δω in FIG. 3) to reduce the excitation frequency, an integrator 464 that sequentially integrates its output, and limits the frequency reduction to a certain value (stops the reduction). 3), and an adder 466 for outputting the angular velocity ω ′ for excitation by subtracting the reduced frequency from the initial value of the frequency, and the frequency for three-phase AC excitation is first shown by the solid line in FIG. Is gradually decreased from a sufficiently high frequency over time, and the frequency is reduced at a time t0 when a predetermined predetermined frequency or a change in the rotation angle based on a minute vibration due to excitation or a rotation angular velocity reaches a predetermined amplitude. Is stopped and the detection of the rotor position is started from this point.
By doing so, since the excitation frequency at the start of the magnetic pole position detection mode is high, both the rotation angular velocity and the rotation angle caused by the minute vibration are small, as is apparent from the equations (4) and (5). Also, the influence of transient phenomena at the start is small, and stable and smooth detection can be performed.

FIG. 4 is a block diagram showing another specific example of the command unit shown in FIG. 1, and FIG. 5 is an explanatory diagram for explaining its operation. That is, the exciting frequency ω'setting device 461 ',
Setter 4 for the amount of change per unit time (see Δi _T 'in FIG. 5) for gradually increasing the torque current command value i _T '
62 ', an integrator 463' for integrating its output, and a limiter 464 'for limiting the torque current command value to a constant value (stopping the increase), and the like.
As shown in FIG. 5, the voltage or current to be excited by the phase alternating current is initially zero or a sufficiently small value equal to this value and gradually increases with the lapse of time, and the fluctuation of the rotation angle due to the minute vibration or the rotation angular velocity becomes a predetermined value. The increase of the voltage or current is stopped at the time t0 when the amplitude is reached, and the detection of the rotor position is started from this time. In this case, since the exciting current at the start of the magnetic pole position detection mode is small, the rotational angular velocity and the rotational angle generated by the microvibration are also clear in this case as well as the expressions (4) and (5). Since both are small, the influence of the transient phenomenon at the start is small, and stable and smooth detection can be performed. The second
In the embodiment of FIGS. 4 and 4, an integrator is used to calculate the decrease amount ω of the excitation frequency and the excitation current i _T ′ that is gradually increased, and these are changed in proportion to time. However, the effect as described above can be obtained by decreasing the frequency or increasing the current from the start of excitation. Therefore, the frequency or current to be changed may be a function of time, and in that case, there are, for example, a square root, a square, and an exponential function.

[0015]

According to the present invention, a three-phase brushless motor is excited by three-phase alternating current at a frequency such that a rotating magnetic field is generated but the rotor does not rotate, and the vibration torque generated as a result or generated torque is generated. Since the magnetic pole position is detected by detecting the phase difference between the rotation angle or rotation angular velocity phase of the minute vibration and the voltage or current being AC-excited, it is possible to detect the magnetic pole position with one excitation. As a result, the time required for detection can be reduced, and the rotation angle of the rotor at the time of detection can be made extremely small. Further, when detecting the phase difference, if the phase difference is detected from the phase of the exciting current or voltage having the positive or negative maximum value of the rotational angular velocity due to the minute vibration, the detection accuracy of the magnetic pole position can be improved. . Further, by increasing the excitation frequency at the start of the three-phase AC excitation and gradually lowering it with the passage of time, it is possible to eliminate a large fluctuation in the rotation angle due to a transient phenomenon at the start of the AC excitation. In addition, by reducing the exciting current or voltage at the start of three-phase AC excitation and gradually increasing it over time, it is possible to eliminate large fluctuations in the rotation angle due to transient phenomena at the start of AC excitation. Becomes

[Brief description of drawings]

FIG. 1 is a configuration diagram showing an embodiment of the present invention.

FIG. 2 is a block diagram showing a specific example of a command unit shown in FIG.

FIG. 3 is an explanatory diagram for explaining the operation of FIG.

FIG. 4 is a block diagram showing another specific example of the command unit shown in FIG.

5 is an explanatory diagram for explaining the operation of FIG. 4. FIG.

FIG. 6 is an explanatory diagram for explaining a relationship between a permanent magnet and a stator winding.

FIG. 7 is a waveform diagram for explaining the principle of the present invention.

[Explanation of symbols]

1 brushless motor 2 encoder (PE) 3 power amplifier 4 control device 5 pulse processing circuit 10 permanent magnet 11 Stator winding 12 Stator winding 13 Stator winding 40 Speed detector 42 adder 43 Speed controller 44 vector rotator 45 adder 46 Command unit 47 Detector 48 switch 49 switch 41A integrator (rotation angle calculator) 41B integrator

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Tomoharu Nakayama             1-1 Tanabe Nitta, Kawasaki-ku, Kawasaki-shi, Kanagawa             Within Fuji Electric Co., Ltd. (72) Inventor Takao Yanase             1-1 Tanabe Nitta, Kawasaki-ku, Kawasaki-shi, Kanagawa             Within Fuji Electric Co., Ltd.

Claims (4)

[Claims] 1. A three-phase brushless motor comprising a stator winding and a rotor having a permanent magnet, an encoder mounted on the rotor shaft, and counting means for counting pulses emitted from the encoder, At least a control device that gives a voltage command or a current command and a frequency command to the motor, and a power amplifier that amplifies these commands to drive the three-phase brushless motor, are provided via the control device and the power amplifier. , A three-phase AC excitation is performed by giving a predetermined frequency command so that a rotating magnetic field having a predetermined rotation angle is generated in the stator winding of the motor, and the resulting microvibration of the same frequency is generated via the encoder and the counting means. The rotor of the motor is detected from the phase difference between the excitation signal and the rotation angle signal or rotation angular velocity signal generated by the generated torque or minute vibration. A rotor position detecting device for a brushless motor, which detects a position. 2. When detecting the rotor position of the motor from the phase difference between the excitation signal and the rotational angular velocity signal, the phase difference is detected at the time when the rotational angular velocity signal reaches a positive or negative maximum value. The rotor position detecting device of the brushless motor according to claim 1, which is performed. 3. The frequency command for exciting the three-phase alternating current is gradually reduced from a sufficiently high frequency at first with the passage of time, and a rotation angle based on a predetermined predetermined frequency or a minute vibration due to excitation. 3. The rotation of the brushless motor according to claim 1 or 2, wherein the reduction of the frequency command is stopped at the time when the fluctuation of the rotation speed or the rotation angular velocity reaches a predetermined amplitude, and the detection of the rotor position is started from this time. Child position detection device. 4. A rotation angle based on a minute vibration due to excitation, wherein the voltage command or the current command for exciting the three-phase AC is initially increased from zero or a sufficiently small value equal to this value with time. 3. The brushless according to claim 1 or 2, characterized in that the increase of the voltage command or the current command is stopped at the time when the fluctuation or the rotational angular velocity reaches a predetermined amplitude, and the detection of the rotor position is started from this time. Motor rotor position detector.