JP2008043058A - Synchronous motor control unit and control method thereof - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a synchronous motor control unit for enabling precise positioning and the suppression of vibration in stop even if noise is mixed into a current detection section and voltage output resolution is low, and to provide a method of controlling the synchronous motor control unit. <P>SOLUTION: The synchronous motor control unit comprises: a position detection section 11 for detecting a rotation position; a current detection section 1 for detecting current; a coordinates conversion section 2 for converting the current to a d-axis current in a magnetic flux direction and a q-axis current orthogonally crossing magnetic flux by an electric angle phase with a magnetic pole position obtained from the rotation position as a reference; a dq-axis current control section for controlling the d- and q-axis currents based on a torque command given to a synchronous motor; and a rotational speed detection section 12 for detecting the rotational speed of the synchronous motor. In the synchronous motor control unit, there are an offset angle addition section 15 for adding an offset angle to the electric angle phase and an offset angle adjustment section 14 for adjusting the offset angle according to the rotational speed, the torque command, or the rotation position. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a synchronous motor control device and a control method thereof capable of precise control by suppressing torque fluctuation due to noise or the like even when current detection accuracy or voltage output resolution is low at low torque / low speed and when stopped.

A conventional synchronous motor control device will be described with reference to the drawings. FIG. 2 shows a dq coordinate system based on the magnetic pole position of the synchronous motor. On the dq coordinate system, the torque T can be expressed as shown in Equation (1) by the q-axis current Iq and the torque constant Kt.
T = Kt × Iq (1)
FIG. 3 shows a conventional control block diagram. The current of the synchronous motor is detected by the current detector 1 and read through the A / D converter. The read current detection value is converted by the coordinate converter 2 into a current in the dq coordinate system, that is, a d-axis current Id and a q-axis current Iq. The q-axis current command Iq * is obtained from T * / Kt from the torque command T * obtained by the speed controller 3, and the difference from the q-axis current Iq is taken to determine the q-axis control command by the PI controller 4a. The d-axis current command is set to 0, the difference from the d-axis current Id is taken, and the d-axis control command is obtained by the PI controller 4b similarly to the q-axis. The feedforward compensator 5 obtains the induced voltage and the voltage for compensating the impedance of the synchronous motor separately for the d-axis and the q-axis and adds them to the respective d-axis control command and q-axis control command to obtain the dq-axis voltage command. The dq axis voltage command is converted into a phase voltage command by the two-phase / three-phase converter 6, and the inverter circuit 8 is controlled by the PWM controller 7 to output the voltage to the synchronous motor. In the case of a synchronous motor with a built-in permanent magnet, the d-axis current command is determined according to the torque command and the motor characteristics in order to effectively use the reluctance torque.
When driving precision equipment using such synchronous motor control, it is necessary to increase the control gain to ensure responsiveness. If the control gain is high, the discretization error of the encoder, current detection resolution, voltage Small vibrations occur when stopping due to the command resolution. In order to suppress this vibration, conventionally, the gain of position control and speed control has been adjusted so as to decrease only at the time of stopping.

In FIG. 4, the phase current of the motor is taken into a current amplifier 125 having a plurality of amplifying means, and a plurality of amplified current vectors 125a and 125b are selected on the basis of the external select signal X by the current switch 126 and one current is selected. By selecting a vector and converting the current command based on the external select signal, the required current accuracy can be selected by the external select signal.
In addition, in order to reduce torque pulsation due to current detection resolution and increase the precision of torque control, there are some which have a plurality of current amplifiers with different amplification factors and switch the amplifiers according to the required current detection resolution (for example, , See Patent Document 1). In addition, there is a type in which equivalently precise torque control is performed by changing the phase and amplitude of flowing current according to a torque command based on the equation of the synchronous motor (for example, see Patent Document 2).

In FIG. 5, the current calculation unit changes the amplitude and phase when generating a three-phase current command by changing the phase and amplitude for commanding the current based on the phase θA detected by the encoder and the torque command. Is necessary, the phase is shifted from the optimum value and the amplitude is increased to increase the current, thereby giving a characteristic equivalent to increasing the current resolution.
Japanese Patent Laid-Open No. 10-17222 (FIG. 1) Japanese Patent Laid-Open No. 4-161085 (pages 2 to 4, FIG. 1)

Conventional motor control devices have fixed current detection and voltage output resolutions, and control accuracy depends on these resolutions, so expensive high-resolution sensors and high-resolution outputs are required for high-precision control. I was trying. Further, the method of switching the control gain reduces the vibration at the time of stopping by suppressing the response, but there is a problem that the vibration cannot be suppressed when disturbance such as an error or noise included in the sensor information or the like enters.
In the method of switching a plurality of amplifiers disclosed in Patent Document 1, an amplifier and a switching unit are required, which increases the cost.
In the method of adjusting the phase and amplitude of the current command in Patent Document 2, the current detection resolution can be increased equivalently, but it is not intended for vibration at the time of stop, and disturbance is introduced into the current detection signal and phase information. And vibration cannot be suppressed. In addition, there is a problem in that the calculation becomes complicated in order to operate the current command.
The present invention has been made in view of such a problem, and even if noise is mixed in the current detection unit or the voltage output resolution is low, the synchronization can be performed with high accuracy and the vibration at the time of stopping can be suppressed. It is an object to provide a motor control device and a control method thereof.

In order to solve the above problem, the present invention is configured as follows.
According to the first aspect of the present invention, there is provided a position detector that detects a rotational position of the synchronous motor, a current detector that detects a current flowing through the synchronous motor, and an electrical angle based on a magnetic pole position obtained from the rotational position. A coordinate conversion unit that converts the current into a d-axis current in the direction of magnetic flux and a q-axis current orthogonal to the magnetic flux according to the phase, and controls the d-axis current and the q-axis current based on a torque command given to the synchronous motor. In a synchronous motor control device comprising: a dq axis current control unit; and a rotation speed detection unit that detects a rotation speed of the synchronous motor, an offset angle addition unit that adds an offset angle to the electrical angle phase; and the rotation speed Alternatively, an offset angle adjusting unit that adjusts the offset angle according to the torque command or the rotational position is provided.

  According to a second aspect of the present invention, there is provided the synchronous motor control device according to the first aspect, wherein the offset angle adjustment unit is configured such that the rotation speed is higher than a set stop level or a torque switching set by the torque command. The offset angle is set to 0 when larger than a level, and is adjusted so that the offset angle becomes larger when the rotational speed is lower than the stop level and the torque command is smaller than the torque switching level. It is what.

  According to a third aspect of the present invention, in the synchronous motor control device according to the first aspect, when the position control of the synchronous motor is performed in the offset angle adjustment unit, the position command and the rotation are eliminated. The offset angle is adjusted to be increased when the deviation from the position becomes smaller than a set deviation level.

According to a fourth aspect of the present invention, in the synchronous motor control device according to the first to third aspects, the torque command is multiplied by a torque correction value obtained from the offset angle.
According to a fifth aspect of the present invention, in the synchronous motor control device according to the fourth aspect, the torque correction value is calculated by 1 / cos Δθ where the offset angle is Δθ.

According to a sixth aspect of the present invention, there is provided a position detection unit that detects a rotational position of the synchronous motor, a current detection unit that detects a current flowing through the synchronous motor, and an electrical angle based on a magnetic pole position obtained from the rotational position. A coordinate conversion unit that converts the current into a d-axis current in the direction of magnetic flux and a q-axis current orthogonal to the magnetic flux according to the phase, and controls the d-axis current and the q-axis current based on a torque command given to the synchronous motor. In a synchronous motor control method comprising a dq-axis current controller and a rotational speed detector for detecting a rotational speed of the synchronous motor, a step of obtaining an electrical angle phase from the rotational position, and an offset to the electrical angle phase Adding an angle; adjusting the offset angle according to the rotational speed; obtaining a torque correction value according to the offset angle; A step of multiplying the serial torque correction value to the torque command, is characterized in that comprises a.
According to a seventh aspect of the present invention, in the synchronous motor control method according to the sixth aspect of the invention, instead of the step of adjusting the offset angle according to the rotational speed, the offset according to the torque command or the rotational position. A step of adjusting the angle is provided.

According to the first aspect of the present invention, when the current detection value is subjected to coordinate conversion, the generated torque is suppressed by adding the offset angle with respect to the coordinate conversion phase of the current, and as a result, the same torque is generated. It is possible to increase the current and increase the S / N ratio with respect to the control command.
According to the second aspect of the present invention, the offset angle can be added only when the rotational speed of the motor is at the stop level and the torque command is low, and the efficiency during normal operation is maximized while being low. High-precision torque and speed can be controlled during rotation.
According to the third aspect of the present invention, the offset angle can be added only during the positioning operation during the position control, and the high-precision positioning and the vibration during the stop are performed while maximizing the efficiency when the motor rotates. Can be suppressed.
According to the fourth and fifth aspects of the present invention, the torque control can be made highly accurate by adding a function for correcting the torque command.
According to the inventions described in claims 6 and 7, a method for controlling a synchronous motor capable of high-accuracy positioning and suppressing vibration at the time of stopping even if noise is mixed in the current detection unit or the voltage output resolution is low. Can provide.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 is a control block diagram of the synchronous motor control device of the present invention. FIG. 1 shows an embodiment in which position control is performed. In the figure, the position controller 11 compares the position fetched from the encoder 10 with a position command to obtain a speed command. The speed control unit 3 inputs the rotational speed obtained from the position through the differentiating unit 12 and the speed command, and calculates a torque command T *. The current command calculation unit 13 calculates a q-axis current command Iq * and a d-axis current command Id * from the torque command. Here, the current command calculation unit 13 obtains the q-axis current command Iq * and the d-axis current command Id * as follows. The relationship between torque and current is given by equation (2) where φ is the magnetic flux, pn is the number of pole pairs, and Ld is the inductance converted to the dq axis.

In the case of a surface magnet type synchronous motor (SPMM), since Ld = Lq, equation (2) becomes equation (3).

That is, the current command may be obtained as follows.

Iq * = T * / (pn · φ) (4)
Id * = 0
In the embedded magnet type synchronous motor (IPMM), since the reluctance torque is used for high efficiency, the d-axis current does not become zero. The d-axis current Id * for obtaining the maximum efficiency is as shown in Expression (5).

The Id * and Iq * are obtained by solving the simultaneous equations of the equations (2) and (5). In actual calculations, in order to reduce the amount of calculation, there are cases where the formulas (2) and (5) are simplified or previously calculated and tabulated. In addition, in the high-speed rotation region, the d-axis current command may be further manipulated by applying field weakening control or the like so that the voltage is not saturated.
The current control unit detects the current of the synchronous motor by the current detection unit 1, reads it through the A / D conversion unit, and converts it into the current in the dq coordinate system, that is, the d-axis current Id and the q-axis current Iq by the coordinate conversion unit 2. The The d-axis current command Id * and the q-axis current command Iq * take the difference from the d-axis current Id and the q-axis current Iq, respectively, and input them to the PI control units 4a and 4b, respectively, Determine the axis control command. The feedforward compensation unit 5 obtains voltages for compensating the induced voltage and the impedance of the synchronous motor separately for the d-axis and the q-axis according to the motor equation shown in the equation (6), and the respective d-axis control command and q-axis control command. To obtain dq axis voltage commands Vd and Vq.

Here, vd and vq are a d-axis voltage and a q-axis voltage, R is a winding resistance, ω is an electrical angular frequency, and p is a differential operator. The electrical angular frequency is obtained by multiplying the rotational speed by the number of poles of the motor. The obtained dq-axis voltage command is converted into a phase voltage command by the two-phase / three-phase converter 6, and the inverter 8 is driven by the PWM controller 7 to output the voltage to the synchronous motor. The offset angle adjustment unit 14 calculates an offset angle based on a torque command, a rotation speed, or a position command. The position detector 9 calculates the magnetic pole position of the motor from the position fetched from the encoder 10. The offset angle is added to the magnetic pole position by the adder 15 and input to the coordinate converter 2.

  The present invention is different from the prior art in that it includes an offset angle calculation unit that calculates an offset angle according to the state of the motor and an offset angle addition unit that adds the offset angle to the phase detected from the encoder. . By adding the offset angle, the torque and current are as follows. That is, assuming that the offset angle is Δθ, the relationship between the d-axis current Idm and q-axis current Iqm actually flowing through the synchronous motor and the d-axis current Id and q-axis current Iq after the coordinate conversion is expressed by the equation (7). It becomes like this.

In the current control, the command and the detected value are controlled to coincide with each other. Taking a surface magnet type synchronous motor as an example, control is performed so that Id becomes 0 according to Equation (4). Therefore, when the current command and the current detection value match, the following is obtained from Equation (7).

In this case, the torque T generated in the synchronous motor by the q-axis current command Iq * is calculated from the equation (3):

Thus, the actually generated torque is smaller than the command by the amount of cos Δθ. At this time, the speed control unit 3 operates to compensate for the insufficient torque, and the torque command T * is greatly corrected. This means that the current required to generate the same torque is increased.

  Here, the effect when the current is increased will be described. When controlling a three-phase motor, since three phases are short-circuited inside the motor, it is common to detect two of the three phases. When the U-phase current iu and the V-phase current iu are detected, the coordinate conversion unit is as follows.

In Expression (10), since the magnitude is stored, if there is an error in current detection, it becomes an error of Id and Iq as it is. If the current detection value has an error of 1%, Id and Iq also include an error of 1%. When current control is performed at the time of stop, torque due to current detection error is generated and the motor rotates. As the motor rotates, a torque command is generated by the position control unit 11 and the speed control unit 3. This applies not only to current detection, but also when the voltage output resolution is low. In such a situation, by operating the offset angle, the generated torque becomes smaller than the torque command, so the torque command increases and the current value also increases. When the offset angle Δθ is 60 degrees, the torque command for generating the same torque is doubled, and the current flows twice as much. At this time, assuming that the current error component is 1%, the current error has a relatively half effect of 0.5% because twice the current flows. That is, the influence of the current detection error is halved. Further, the gain is equivalently halved and the response to the disturbance is lowered, so that vibration can be suppressed.

  FIG. 6 is a block diagram showing Example 2 of the offset adjusting unit. In the figure, a rotational speed and a torque command are input and compared with a stop level and a torque switching level set value, respectively. A coefficient KS is obtained that is 0 when the stop determination value obtained by subtracting the absolute value of the rotational speed from the stop level is negative, and increases in proportion to the stop determination value when the stop determination value becomes positive. Further, a coefficient KT is set such that 0 is obtained when the torque judgment value obtained by subtracting the absolute value of the torque command from the torque switching level is negative, and is increased in proportion to the torque judgment value when the torque judgment value is positive. Ask. A coefficient for the offset angle is obtained by multiplying the coefficient KS and the KT, and an offset angle is obtained by multiplying the set offset angle reference value. As a result, the offset angle is added only while the speed is low and the torque command is low, so that when the torque command is large or the rotational speed is large, the operation is performed with high efficiency. In the low speed / low torque region, the first embodiment will be described. As described above, the response to the disturbance can be lowered to suppress the vibration.

FIG. 7 is a diagram showing a third embodiment of the offset adjusting unit . In the figure, a position command and a rotational position are input, and a position command stop determination switch 71 that operates when the difference between the previous value of the position command becomes 0 and a difference value between the position command and the rotational position are calculated. And a positioning determination switch 72 that operates when the difference value becomes lower than a set positioning level. The position command stop determination switch 71 and the positioning determination switch 72 indicate the offset angle setting value. The offset angle is output when closed. In FIG. 6, a first-order lag filter 73 is added to prevent the offset angle from changing suddenly. Thereby, when performing position control, highly accurate torque control is possible only during positioning, and high-efficiency operation is possible while the position is changing.
If there is an overshoot at the time of positioning, a delay circuit that operates the switch after a lapse of a certain time is provided to stabilize the positioning so that the offset angle is output after the positioning is stabilized. You can also.

  FIG. 8 is a control block diagram showing the fourth embodiment. In the first to third embodiments, an error occurs between the torque command and the generated torque of the motor. For this reason, the command and the actual torque cannot be matched during torque control. In order to prevent this, a torque command correction unit 81 is added that multiplies the torque command by a gain that changes according to the offset angle when calculating the current command from the torque command. Since the torque change due to the offset angle is cos Δθ times as shown in equation (9), the torque command and the actual torque can be matched by multiplying by (1 / cos Δθ) as a coefficient. By using this together with the first to third embodiments, the rotation speed is low and low, or the torque is controlled with high accuracy when stopped, and highly efficient operation is possible in other regions.

FIG. 9 is a flowchart of the synchronous motor control method of the present invention. In FIG. 9, the electrical angle phase is obtained from the rotational position at step ST1, the offset angle is added to the electrical angle phase at step ST2, the offset angle is adjusted according to the rotational speed at step ST3, and the offset angle is determined at step ST4. In step ST5, the torque correction value is multiplied by the torque command.

  As described above, even when the current detection accuracy and voltage output accuracy are poor, it is possible to improve the current control at the time of stopping, low speed and low torque, so only for applications that require high accuracy. In addition, low-cost current detection means and voltage output means can be used in general applications, and the cost of the control device can be reduced.

1 is a control block diagram of a motor control device showing a first embodiment of the present invention. Diagram showing coordinate system of synchronous motor Conventional synchronous motor control block diagram The figure which shows the structure of the conventional patent document 1 The figure which shows the structure of the conventional patent document 2 The block diagram of the offset adjustment means which shows Example 2 of this invention The block diagram of the offset adjustment means which shows Example 3 of this invention Control block diagram showing Embodiment 4 of the present invention Flowchart of synchronous motor control method of the present invention

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Current detection part 2 Coordinate conversion part 3 Speed control part 4a PI control part (q axis)
4b PI controller (d-axis)
5 Feedforward Compensation Unit 6 Two-phase Three-phase Conversion Unit 7 PWM Control Unit 8 Inverter Circuit 9 Position Detection Unit 10 Encoder 11 Position Control Unit 12 Differentiation Unit 13 Current Command Calculation Unit 14 Offset Angle Adjustment Unit 15 Offset Angle Adder Unit 25 Current amplifiers 25a and 25b Current vector 26 Current switching unit 71 Position command stop determination switch 72 Positioning determination switch 73 Primary delay filter 81 Torque command correction unit

Claims (7)

A position detection unit for detecting the rotational position of the synchronous motor, a current detection unit for detecting a current flowing through the synchronous motor, and an electric angle phase based on a magnetic pole position obtained from the rotational position, the current in the direction of magnetic flux. A coordinate conversion unit that converts an axial current and a q-axis current orthogonal to the magnetic flux; a dq-axis current control unit that controls the d-axis current and the q-axis current based on a torque command applied to the synchronous motor; In a synchronous motor control device comprising a rotation speed detection unit for detecting the rotation speed of the motor,
An offset angle addition unit that adds an offset angle to the electrical angle phase, and an offset angle adjustment unit that adjusts the offset angle in accordance with the rotation speed, the torque command, or the rotation position. Synchronous motor control device.   The offset angle adjustment unit sets the offset angle to 0 when the rotation speed is higher than the set stop level or greater than the torque switching level set by the torque command, and the rotation speed is lower than the stop level. 2. The synchronous motor control device according to claim 1, wherein the offset angle is adjusted to be larger when the torque command is lower than the torque switching level.   The offset angle adjustment unit adjusts the offset angle when the position command does not change when the position control of the synchronous motor is performed and the deviation between the position command and the rotational position becomes smaller than a set deviation level. 2. The synchronous motor control device according to claim 1, wherein the synchronous motor control device is adjusted so as to increase.   4. The synchronous motor control device according to claim 1, wherein the torque command is multiplied by a torque correction value obtained from the offset angle. The torque correction value is 1 / cos Δθ where the offset angle is Δθ.
5. The synchronous motor control device according to claim 4, wherein the calculation is performed by the following equation. A position detection unit for detecting the rotational position of the synchronous motor, a current detection unit for detecting a current flowing through the synchronous motor, and an electric angle phase based on a magnetic pole position obtained from the rotational position, the current in the direction of magnetic flux. A coordinate conversion unit that converts an axial current and a q-axis current orthogonal to the magnetic flux; a dq-axis current control unit that controls the d-axis current and the q-axis current based on a torque command applied to the synchronous motor; In a synchronous motor control method comprising a rotation speed detection unit that detects a rotation speed of a motor,
Obtaining an electrical angle phase from the rotational position;
Adding an offset angle to the electrical angle phase;
Adjusting the offset angle according to the rotational speed;
Obtaining a torque correction value according to the offset angle;
Multiplying the torque command by the torque correction value;
A synchronous motor control method characterized by comprising:   The synchronous motor control method according to claim 6, further comprising a step of adjusting the offset angle according to the torque command or the rotational position instead of the step of adjusting the offset angle according to the rotational speed. .