JP2008099444A - Synchronous motor controller and control method therefor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a synchronous motor controller which can perform high-accuracy positioning and suppress vibrations at halt, even if noise is mixed into a current-detecting section or the resolution of the voltage output is low, and to provide a control method for the controller. <P>SOLUTION: The synchronous motor controller is equipped with a current-detecting section (1) for detecting the current flowing into a synchronous motor, a current control unit (14) for controlling the current, by decomposing the current into a d-axis current in the magnetic flux direction and a q-axis current orthogonal to the magnetic flux direction, a position detecting section (9) for detecting the rotational position of the synchronous motor, and a rotation speed detecting section (12) for detecting the rotational speed of the synchronous motor. The synchronous motor controller, further includes a d-axis current adjusting section (15) for adjusting the magnitude of the d-axis current, corresponding to the rotating speed and a torque command. <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.

4, the motor phase current is taken into a current amplifier 125 having a plurality of amplifying means, and a plurality of amplified current vectors 125a, 125b... Are selected by a current switch 126 based on an external select signal X. By selecting the current 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 current control unit for controlling a current by decomposing the current into a d-axis current in a magnetic flux direction and a q-axis current orthogonal to the magnetic flux, and detecting a current flowing in the synchronous motor. In the synchronous motor control device comprising: a position detecting unit that detects a rotational position of the synchronous motor; and a rotational speed detecting unit that detects the rotational speed of the synchronous motor, the d-axis is controlled according to the rotational speed and the torque command. A d-axis current adjusting unit that adjusts the magnitude of the current is provided.

  According to a second aspect of the present invention, in the synchronous motor control device according to the first aspect, the d-axis current adjusting unit is higher than a stop level set by the rotation speed or a torque switching level set by the torque command. The d-axis current is adjusted to 0, and the d-axis current is adjusted to increase when the rotational speed is lower than the stop level and the torque command is lower than the torque switching level. Is.

  According to a third aspect of the present invention, in the synchronous motor control device according to the first aspect, the d-axis current adjusting unit adjusts the d-axis current to be increased when positioning is completed when performing position control of the synchronous motor. It is characterized by this.

  According to a fourth aspect of the present invention, in the synchronous motor control apparatus according to the first to third aspects, the d-axis current adjusting unit is proportional to the torque command while the torque command is smaller than the torque switching level. The d-axis current is adjusted.

  According to a fifth aspect of the present invention, in the synchronous motor control device according to the first to third aspects, the torque switching level is determined by a current detection resolution.

  According to a sixth aspect of the present invention, in the synchronous motor control device according to the first to third aspects, the torque switching level is determined by a voltage output resolution.

  According to a seventh aspect of the present invention, in the synchronous motor control device according to the first to third aspects, the d-axis current adjustment unit is configured so that a combined current of the d-axis current and the q-axis current is smaller than a rated current. The d-axis current is adjusted to be proportional to the torque command, and the d-axis current is adjusted to be smaller than the rated current when the combined current is larger than the rated current.

According to an eighth aspect of the present invention, there is provided a current control unit that controls a current by decomposing the current into a d-axis current in a magnetic flux direction and a q-axis current orthogonal to the magnetic flux. In the synchronous motor control method, the d-axis current adjustment is performed based on the rotation speed and the torque command. The synchronous motor control method includes: a rotation speed detection section that detects a rotation speed of the synchronization motor; A step of generating a value; and a step of adding the d-axis current adjustment value to the d-axis current command.

According to the first aspect of the present invention, the d-axis current adjustment value can be generated by the rotation speed and the torque command, the d-axis current command can be increased, the generated torque is not changed, the detected current is increased, and the control is performed. The S / N ratio for the command can be increased. Further, by increasing the d-axis current command, the d-axis voltage command and the q-axis voltage command can be increased, and a minute torque can be output even if the voltage output resolution is low.
According to the second aspect of the present invention, the d-axis current adjustment can be performed when the rotation speed of the motor is lower than the set stop level or when the torque command is lower than the set torque switching level. While maximizing the efficiency, it becomes possible to control the torque and speed with high accuracy when the rotational speed of the motor is lower than the set stop level or when the torque command is lower than the set torque switching level.
According to the third aspect of the invention, the d-axis current adjustment value can be added only during the positioning operation during the position control, and the high-precision positioning and stopping can be performed while maximizing the efficiency when the motor rotates. The vibration at the time can be suppressed.
According to the fourth aspect of the present invention, the d-axis current is easily adjusted by adjusting the d-axis current so that it is proportional to the torque command while the torque command is smaller than the torque switching level. The generated torque remains the same, the detected current can be increased, and the S / N ratio for the control command can be increased. Further, by increasing the d-axis current command, the d-axis voltage command and the q-axis voltage command can be increased, and a minute torque can be output even if the voltage output resolution is low.
According to the invention described in claim 5, by determining the torque switching level based on the current detection resolution, it is possible to flow a current that can be detected when the torque command is smaller than the set torque switching level. S / N ratio can be increased.
According to the sixth aspect of the present invention, by determining the torque switching level based on the voltage output resolution, it is possible to output a constant voltage when the torque command is smaller than the set torque switching level. Can be output.
According to the invention described in claim 7, by adjusting the d-axis current while comparing the combined current and the rated current, the combined current does not exceed the rated current and can be prevented from becoming an overcurrent. .
According to the eighth aspect of the present invention, the d-axis current adjustment value can be generated by the rotation speed and the torque command, the d-axis current command can be increased, the generated torque is not changed, the detected current is increased, and the control is performed. The S / N ratio for the command can be increased. Further, by increasing the d-axis current command, the d-axis voltage command and the q-axis voltage command can be increased, and a minute torque can be output even if the voltage output resolution is low.

  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 by the rotational speed detection unit 16 that generates the rotational speed from the position through the differentiation unit 12 and the speed command, and calculates the 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
The current control unit 14 detects the current of the synchronous motor by the current detection unit 1, reads it through the A / D conversion unit, and converts the current in the dq coordinate system by the coordinate conversion unit 2, that is, the d-axis current Id and the q-axis current Iq. Is done. At this time, the magnetic pole position for coordinate conversion is obtained by converting the position taken in from the encoder 10 into the magnetic pole position of the motor by the position detector 9.
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 (5), 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 d-axis current adjustment unit 15 calculates a d-axis current adjustment value based on the torque command and the rotation speed. Control is performed by adding the d-axis adjustment value to the d-axis control command.

  The present invention is different from the prior art in that it includes a d-axis current adjusting unit that adjusts the magnitude of the d-axis current in accordance with the rotational speed and the torque command. By adjusting the d-axis current command, the current and voltage output are as follows. That is, when the d-axis current command increases, the d-axis voltage command and the q-axis voltage command increase from Equation (5). When the d-axis voltage command and the q-axis voltage command increase, the U-phase voltage command and the V-phase voltage command applied to the motor increase from Equation (6).

As a result, the current flowing through the motor increases, and the U-phase detection current and the V-phase detection current also increase. At this time, in the case of a surface magnet type synchronous motor (SPMM), the torque generated in the motor is the same as that in the case of no d-axis current adjustment according to the equation (3). That is, the torque generated in the motor does not change, and the current flowing through the motor can be 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 (7), since the magnitude is stored, if there is an error in current detection, it becomes the 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, the generated torque does not change by adjusting the d-axis current, and the current flowing through the motor increases.
When the d-axis current adjustment value is given and the detected current value is kept at 2%, the error is half that of 0.5% compared to when the torque current command is 1%. 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 d-axis current 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 d-axis current adjustment value is obtained by multiplying the coefficient KS and the KT, and a d-axis current adjustment value is obtained by multiplying the set d-axis current setting value. In this way, the d-axis current adjustment value 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. As described in 1, the response to the disturbance can be lowered to suppress the vibration.

FIG. 7 is a diagram illustrating Example 3 of the d-axis current 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 d-axis current set value is set to the position command stop determination switch 71 and the positioning determination switch 72. When d is closed, the d-axis current adjustment value is output.
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 d-axis current adjustment value is output after the positioning is stabilized. Can also be planned.

FIG. 8 is a block diagram showing Example 4 of the d-axis current 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 such that 0 is obtained when the stop determination value obtained by subtracting the absolute value of the rotational speed from the stop level is negative, and 1 is obtained when the stop determination value is positive. That is, KS is used for d-axis current adjustment use determination. 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 d-axis current adjustment value is obtained by multiplying the coefficient KS and the KT, and a d-axis current adjustment value is obtained by multiplying the set d-axis current setting value. In this way, the d-axis current adjustment value 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. As described in 1, the response to the disturbance can be lowered to suppress the vibration.

  When a current capable of current detection is passed when the torque switching level in FIGS. 6 and 8 is smaller than the torque switching level set by the torque command, the minimum current value that can be detected by the current detector is obtained from the current detection resolution. The torque switching level is set to a value larger than the detected minimum current value. Further, the d-axis current adjustment value is set so as to flow a current larger than the minimum detection current value. At this time, it is preferable to set the torque switching level sufficiently higher than the minimum detection current in consideration of the case where disturbance such as noise occurs.

  When the torque switching level shown in FIGS. 6 and 8 can be output when the torque command is smaller than the torque switching level set by the torque command, the minimum voltage that can be output by the voltage output device is determined by the voltage output resolution. The torque that can be generated with the voltage of is determined. The torque switching level is set to a value larger than the torque that can be generated with the minimum voltage. The d-axis current adjustment value is set to a value that generates a voltage command that is greater than the minimum voltage that can be output by the voltage output device.

FIG. 9 is a block diagram showing Example 7 of the d-axis current adjusting unit. In the figure, a torque command is input and compared with a torque switching level set value.
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. Here, the combined current is obtained from the d-axis current and the q-axis current, and compared with the rated current. As a result of comparison, if the combined current is smaller than the rated current, the coefficient for the d-axis current adjustment value is obtained by multiplying the coefficient KS and the KT, and the d-axis current adjustment value is obtained by multiplying the set d-axis current setting value. Ask for. When the combined current is larger than the rated current, the d-axis current processing unit 91 performs a process for reducing the d-axis current so that the combined current becomes smaller than the rated current. Thus, the combined current does not become larger than the rated current, and overcurrent can be prevented. Further, by adding the d-axis current adjustment value only when the speed is low and the torque command is low, the operation is performed with high efficiency when the torque command is large or when the rotation speed is large. As described above, the response to the disturbance can be lowered and the vibration can be suppressed.

  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 d-axis current adjustment part which shows Example 2 of this invention The block diagram of the d-axis current adjustment part which shows Example 3 of this invention The block diagram of the d-axis current adjustment part which shows Example 4 of this invention. The block diagram of the d-axis current adjustment part which shows Example 7 of this 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 to 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 Current Control Unit 15 d-axis Current Adjustment Unit 16 Rotation Speed detector 71 Position command stop judgment switch 72 Positioning judgment switch 125 Current amplifier 125a, 125b Current vector 126 Current switch

Claims (8)

A current detection unit for detecting a current flowing through the synchronous motor; a current control unit for controlling the current by decomposing the current into a d-axis current in a magnetic flux direction and a q-axis current orthogonal to the magnetic flux; and a rotational position of the synchronous motor In a synchronous motor control device including a position detection unit to detect and a rotation speed detection unit to detect the rotation speed of the synchronous motor,
A synchronous motor control device comprising a d-axis current adjusting unit that adjusts the magnitude of the d-axis current in accordance with the rotation speed and a torque command.   The d-axis current adjustment unit sets the d-axis current 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. The synchronous motor control device according to claim 1, wherein the d-axis current is adjusted to be increased when the torque command is low and smaller than the torque switching level.   The synchronous motor control device according to claim 1, wherein the d-axis current adjustment unit adjusts the d-axis current to be increased when positioning is completed when performing position control of the synchronous motor.   4. The synchronization according to claim 1, wherein the d-axis current adjustment unit adjusts the d-axis current so as to be proportional to the torque command while the torque command is smaller than the torque switching level. Motor control device.   The synchronous motor control device according to claim 1, wherein the torque switching level is determined by current detection resolution.   The synchronous motor control device according to claim 1, wherein the torque switching level is determined by a voltage output resolution. The d-axis current adjustment unit adjusts the d-axis current to be proportional to the torque command while the combined current of the d-axis current and the q-axis current is smaller than the rated current, and the combined current is larger than the rated current. 4. The synchronous motor control device according to claim 1, wherein the d-axis current is adjusted so as to be smaller than the rated current when it is large. A current detection unit for detecting a current flowing through the synchronous motor; a current control unit for controlling the current by decomposing the current into a d-axis current in a magnetic flux direction and a q-axis current orthogonal to the magnetic flux; and a rotational position of the synchronous motor In a synchronous motor control method including a position detection unit to detect and a rotation speed detection unit to detect the rotation speed of the synchronous motor,
From the rotational speed and torque command, generating a d-axis current adjustment value;
Adding the d-axis current adjustment value to a d-axis current command;
A synchronous motor control method characterized by comprising: