JP6347639B2 - Servo motor control system and servo motor control method - Google Patents

Description

  The present invention relates to a servo motor control system and a servo motor control method for controlling the current of an AC servo motor used as a drive source for machine devices such as machine tools and industrial machines and robots.

In an AC (AC) servo motor control system, a position deviation is obtained by subtracting a position feedback value detected by an encoder or the like from a position command, and a position command is performed by multiplying the position deviation by a position gain to obtain a speed command. Then, the speed feedback value is subtracted from the speed command to obtain a speed deviation, speed loop processing such as proportional / integral control is performed, and a torque command (current command) is obtained.
Further, the current feedback value is subtracted from the torque command, current loop processing is performed to obtain a voltage command for each phase (each axis), PWM control is performed, and the AC servo motor is controlled.

In such a control system, an AC current control method is known in which a three-phase AC servomotor separately controls a three-phase current (U, V, W).
In this AC current control method, the torque command (current command) obtained by the speed loop process is shifted by 2π / 3 in electrical angle with respect to the U, V, and W phases from the rotor position of the servo motor detected by the encoder or the like. The current command for each phase is obtained, and current control is performed in accordance with the current command.

  However, in the AC current control method, when the motor rotation speed increases, the frequency of the current command also increases, and the current phase gradually delays. As a result, there are many ineffective components of the current, making it impossible to generate torque efficiently. There is.

A DQ control method is known as a method for improving the problem of such an alternating current control method.
The DQ control method is a method in which a three-phase current is subjected to DQ conversion (converted to rotor reference coordinates) and controlled by a DC component of d-phase and q-phase two-phase d-axis current and q-axis current.
In the DQ control method, the q-axis component of the current command corresponds to the torque component, and the d-axis component corresponds to the reactive current in the alternating current control, and the reactive current is suppressed by setting the d-axis current command to 0 (zero). be able to.

However, in the current control method for suppressing the reactive current, there is a problem that the current control system becomes unstable due to the counter electromotive force and the control performance is deteriorated.
This decrease in control performance is due to the fact that the voltage that can be used to drive the motor decreases due to the back electromotive force proportional to the rotation speed, and it becomes impossible to perform stable rotation up to a high speed range. It cannot be rotated at the speed (number of rotations).

As a measure for solving this problem, a method is known in which a current phase is shifted in the d-axis direction by flowing a current proportional to the motor speed to the d-axis component. Control by this method is called field weakening control.
However, the d-axis component current is a reactive current, and there is a problem that the motor easily generates heat.

  Therefore, a current control method for a servo motor that enables stable rotation up to a high speed range has been proposed (see Patent Document 1).

In this method, in the current control by DQ conversion of the servo motor, the terminal voltage of the motor is lowered by flowing an invalid current to the d phase only during high speed rotation.
The supply of reactive current starts from the vicinity of the speed at which voltage saturation occurs, increases by a linear increase function in accordance with the speed, and is fixed to a constant value at or above the set speed.
This eliminates the instability of the current control system due to the counter electromotive force during high-speed rotation, and suppresses heat generation by reducing the reactive current in a region where voltage saturation does not occur.

JP-A-9-84400

  However, the above-described method of linearly increasing the reactive current supply according to the linear increase function according to the speed can suppress the heat generation due to the reactive current, but the maximum torque obtained in the desired rotational speed range. There are limits. As a result, there is a limit in expanding the rotation speed control region, and there is a disadvantage that it is difficult to sufficiently exhibit the effect of field weakening control.

  It is an object of the present invention to reduce the reactive current in a region where voltage saturation does not occur, to suppress heat generation due to the reactive current, and to increase the maximum torque obtained in a desired rotational state region. It is an object of the present invention to provide a servo motor control system and a servo motor control method capable of expanding the area and performing stable rotation up to a high speed range.

A servo motor control system according to a first aspect of the present invention includes a multi-phase AC servo motor, a DC d-axis command voltage and a q-axis command voltage converted into multi-phase AC power, and the servo motor A power supply unit that supplies AC power; a DQ conversion unit that generates a d-axis current and a q-axis current by performing dq conversion on the current of each phase of the servo motor based on a rotation phase of the servo motor; and the servo A command generation unit that generates a command according to the rotation state of the motor, a d-axis current command generated by the DQ conversion unit, and a q-axis current command as a torque command, and a direct current according to the d-axis current and the d-axis current A d-axis command voltage is generated and supplied to the power supply unit, and a q-axis command voltage is generated in accordance with the q-axis current command and the q-axis current generated by the DQ conversion unit. And A d-axis current commanded by the d-axis current command is set to zero until the first rotation state, and exceeds the first rotation state to the second rotation. The d-axis current increases in such a manner as to gradually approach a linear function from the rotation speed of zero to the second rotation state, and starts flowing current from the first rotation state. In the region, the arc increases toward the linear function side of the asymptotic target while increasing in a curved shape.

Accordingly, since the back electromotive force can be suppressed by the d-axis current in a high speed region where the back electromotive force is generated, stable rotation can be performed up to the high speed region.
Further, by increasing the d-axis current asymptotically to a linear function from a lower rotational state than the first rotational state, the torque in the predetermined rotational state can be increased rather than increasing linearly. As a result, the controllable region of the rotation state, for example, the rotation speed and the rotation speed can be expanded.

Preferably, the d-axis current is supplied so as to increase from the first rotation state to the second rotation state, and is fixed to a constant value in the rotation state equal to or higher than the second rotation state.
Accordingly, since the d-axis current is fixed in the second rotation state or more, an increase in heat generation due to the d-axis current (reactive current) can be suppressed.

Preferably, the first rotational state is a rotational speed different from the rated rotational speed.
When the d-axis current starts to flow from the rated speed, the linearity on the speed vs. torque characteristics (NT characteristics) is lost, for example, in a state below the rated speed and above the rated speed. A torque change occurs.
On the other hand, it is possible to prevent the loss of linearity at least in the vicinity of the rated rotational speed that is in the use range by starting to flow the d-axis current from the rotational speed different from the rated rotational speed.

Preferably, the first rotational state is a rotational speed at which a torque limit is applied and the torque is constant regardless of the rotational speed.
As a result, since the d-axis current starts to flow from the rotational speed at which the torque limit is applied, the linearity is not lost on, for example, the rotational speed versus torque characteristic (NT characteristic). That is, since there is no linearity already in the region where the torque limit is applied, linearity outside the torque limit region can be ensured.

Preferably, the increasing form of the d-axis current increases so as to be asymptotic to a linear function from the rotational speed of zero to the second rotational state.
Thus, by increasing the d-axis current asymptotically from a rotational speed of zero, the torque in a predetermined rotational state can be increased rather than increasing linearly, and as a result Thus, the controllable region of the rotation state, for example, the rotation speed and the rotation speed can be expanded.

A servo motor control method according to a second aspect of the present invention includes a command generation step for generating a d-axis current command and a q-axis current command as a torque command according to the rotation state of the servo motor, a direct current d-axis command voltage, A q-axis command voltage is converted into multi-phase AC power, and a power supply step of supplying multi-phase AC power to the servo motor, and currents of respective phases supplied to the servo motor are rotated by the servo motor. A DQ conversion step of performing dq conversion based on the phase to generate a d-axis current and a q-axis current, and the DC d-axis command according to the d-axis current command and the d-axis current generated in the DQ conversion step A d-axis control step for generating a voltage and supplying the voltage to the power supply step; and the direct current according to the q-axis current command and the q-axis current generated in the DQ conversion step. a q-axis control step for generating a q-axis command voltage and supplying the q-axis command voltage to the power supply step, wherein the d-axis current commanded by the d-axis current command is zero until the first rotation state, The d-axis current increases in such a manner as to gradually approach a linear function from zero to the second rotation state. In the vicinity region where current starts to flow from the first rotation state, the arc increases toward the linear function side of the asymptotic target and increases in a curved line.

Accordingly, since the back electromotive force can be suppressed by the d-axis current in a high speed region where the back electromotive force is generated, stable rotation can be performed up to the high speed region.
Further, by increasing the d-axis current asymptotically to a linear function from a lower rotational state than the first rotational state, the torque in the predetermined rotational state can be increased rather than increasing linearly. As a result, the controllable region of the rotation state, for example, the rotation speed and the rotation speed can be expanded.

  According to the present invention, it is possible to reduce the reactive current in a region where voltage saturation does not occur, suppress the heat generation due to the reactive current, and increase the maximum torque obtained in a desired rotational state region. The area can be expanded, and stable rotation can be performed up to the high speed range.

It is a block diagram which shows the structural example of the servomotor control system which concerns on embodiment of this invention. It is a figure for demonstrating the control form of the d-axis current by the d-axis current command of the command generation part of this embodiment. It is a figure which shows an example which formed the increase form which increases in a curve shape, forming an arc toward the linear function straight line side of the asymptotic object by the SQRT function. It is a block diagram which shows the d-axis controller which concerns on this embodiment, a q-axis controller, and the function structural example on the motor side. It is a figure for demonstrating this embodiment, Comprising: It is a figure which shows the voltage state of the d-axis during acceleration when a d-axis current command CId is set to zero and the q-axis. It is a figure which shows the voltage state of d phase and q phase when the d-axis current command CId is zero and the back electromotive force and the DC link voltage coincide with each other as a comparative example. It is a figure for demonstrating this embodiment, Comprising: It is a figure which shows the voltage state of d-axis and q-axis at the time of inputting d-axis current command CId and q-axis current command CIq in a high speed area | region. It is a flowchart for demonstrating operation | movement of the servomotor control system which concerns on this embodiment centering on the process of the speed loop of an instruction | command production | generation part, and a current loop. It is a figure which shows the outline | summary about the rotation speed versus torque characteristic at the time of applying the control method of this embodiment, Comprising: It is a figure for demonstrating compared with a comparative example. It is a figure which shows the experimental result about the rotation speed versus torque characteristic at the time of applying the control method of this embodiment, Comprising: It is a figure for demonstrating compared with a comparative example.

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

In this embodiment, basically, in a servo motor control system that controls current by DQ conversion, a reactive current is supplied to the d-axis only during high-speed rotation, and the terminal voltage of the servo motor is lowered by the reactive current (d-axis current). .
In this case, in this embodiment, as will be described in detail later, the d-axis current is zero until the first rotational speed [A] during acceleration, and the first rotational speed [A], which is a high speed region, is set. It flows so as to gradually increase to the second rotation speed [B].
The increasing form of the d-axis current increases so as to be asymptotic to a linear function up to the second rotational speed, and in the vicinity of starting the current flow from the first rotational speed [A], an arc is formed toward the asymptotic target primary function side. It is configured to increase in a curved shape while forming.
In the present embodiment, the rotation speed of the servo motor 20 is adopted as a parameter representing the rotation state.

  Hereinafter, after describing the overall configuration and functions of the servo motor control system according to the present embodiment, the characteristic flow of the d-axis current and the effects thereof will be specifically described.

[Configuration of main part of servo motor control system]
FIG. 1 is a block diagram illustrating a configuration example of a servo motor control system according to an embodiment of the present invention.

  The servo motor control system 10 includes a multi-phase (three-phase in this embodiment) servo motor 20, a power supply unit 30, a current detection unit 40, a phase detection unit 50, a DQ conversion unit 60, and a rotation speed as a rotation state detection unit. The detection unit 70, the command generation unit 80, and the d-axis controller 90d and the q-axis controller 90q are configured.

  The power supply unit 30 converts the two-phase DC d-axis command voltage Vd and the q-axis command voltage Vq supplied by the d-axis controller 90d and the q-axis controller 90q into three-phase AC power, and this three-phase AC power Electric power is supplied to the servo motor 20.

The power supply unit 30 in FIG. 1 includes a voltage conversion unit 31 and a power amplifier 32.
The voltage conversion unit 31 converts the two-phase DC d-axis command voltage Vd and the q-axis command voltage Vq supplied by the d-axis controller 90d and the q-axis controller 90q into three-phase (U, V, W phase) AC voltages Vu, The voltage is converted into Vv, Vw, and the converted voltage is supplied to the power amplifier 32 as command voltages Vu, Vv, Vw.

  The power amplifier 32 receives the command voltages Vu, Vv, and Vw from the voltage conversion unit 31 and supplies currents Iu, Iv, and Iw to each phase of the servomotor 20 with an inverter or the like to supply power to the servomotor 20. Do.

The current detection unit 40 detects the currents Iu, Iv, and Iw of each phase supplied from the power supply unit 30 to the servo motor 20.
The current detection unit 40 supplies the detected currents Iu, Iv, and Iw to the DQ conversion unit 60.

The phase detector 50 detects the rotational phase θ (rotational position) of the servo motor 20 and supplies the detected rotational phase θ to the DQ converter 60.
The phase detector 50 calculates the rotational phase θ based on, for example, a rotation detection signal from an encoder (not shown).

The DQ conversion unit 60 performs dq conversion on the currents Iu, Iv, and Iw detected by the current detection unit 40 based on the rotational phase θ detected by the phase detection unit 50, and the d-axis current Id and the q-axis current Iq. Is generated.
The DQ conversion unit 60 supplies the d-axis current Idf generated by the dq conversion to the d-axis controller 90d, and supplies the q-axis current Iqf generated by the dq conversion to the q-axis controller 90q.

  The rotation speed detector 70 detects the actual rotation speed (actual rotation speed) of the servomotor 20 and supplies the detected rotation speed to the command generator 80.

The command generator 80 generates a d-axis current command CId corresponding to the rotation speed N of the servo motor 20 and a q-axis current command CIq as a torque command.
The command generation unit 80 supplies the generated d-axis current command CId to the d-axis controller 90d. On the other hand, the command generation unit 80 supplies a q-axis current command CIq as a generated torque command to the q-axis controller 90q.

The command generator 80 calculates a torque command in a speed loop in a speed control block (not shown), and sets the torque command as a q-axis current command CIq in a current loop in a current control block (not shown).
The q-axis current Iq commanded by the q-axis current command CIq becomes zero depending on the rotation speed during servo motor drive control, flows during a high-speed rotation period, or reaches a fixed value when reaching a certain rotation speed. Such control as the d-axis current is not performed, and a current corresponding to the q-axis current command CIq is supplied throughout the motor driving period.

On the other hand, the command generation unit 80 determines that the d-axis current Id is zero according to the rotation speed, flows during a high-speed rotation period, or becomes a fixed value when a certain rotation speed is reached. Make a command.
Specifically, the command generation unit 80 of the present embodiment issues a command based on the d-axis current command CId so that the d-axis current Id flows as shown in FIG.

FIG. 2 is a diagram for explaining a control mode of the d-axis current by the d-axis current command of the command generation unit of the present embodiment.
In FIG. 2, the horizontal axis indicates the rotational speed N of the servomotor 20, and the vertical axis indicates the d-axis current Id. In FIG. 2, a curve indicated by a solid line SL indicates a change in the value of the d-axis current, and a virtual linear function line that gradually approximates the d-axis current in a certain period indicated by a broken line DL.

As shown in FIG. 2, the d-axis current Id commanded by the d-axis current command CId is zero in the first period (acceleration region) T1 where the rotational speed N is from zero to the first rotational speed [A]. In the second period (high-speed region) T2 from the first rotation speed [A] to the second rotation speed [B], control is performed so as to gradually increase.
The increase mode of the d-axis current Id is a rotational speed (first rotational speed) lower than the first rotational speed [A] in the period T2 from the first rotational speed [A] to the second rotational speed [B]. (The number of rotations in the first period T1 that does not include) and the second number of rotations [B] so as to approach the linear function line DL asymptotically.
In the present embodiment, the d-axis current Id is increased in the period T2 from the first rotation speed [A] to the second rotation speed [B], as shown in FIG. It increases so as to be asymptotic to a linear function line DL up to a rotational speed [B] of 2.
The d-axis current Id increases in the form of an arc ARC toward the asymptotic target linear function line DL in the current flow start period T21 that is a neighboring region, starting from the first rotational speed [A]. However, it is configured to increase in a curved line.

Accordingly, since the back electromotive force can be suppressed by the d-axis current in a high speed region where the back electromotive force is generated, stable rotation can be performed up to the high speed region.
Further, by increasing the d-axis current to a rotational speed lower than the first rotational speed [A], in the example of FIG. The torque at the rotational speed can be increased, and as a result, the rotational speed controllable region can be expanded.

In the current flow start period T21, increasing in a curved line while forming an arc toward the asymptotic target linear function line DL side means, for example, a part of a curved line part that gradually increases from the top of the parabola, An arc-shaped curve of the part or a part of a curve part that gradually increases from the top of the SQRT (SQUARE ROOT) function is adopted.
In the present embodiment, in the current flow start period T21, the curve gradually increases asymptotically from the rising to the linear function line DSL so as to increase in a quadratic function to the asymptotic start position that is the start position of the period T22. A directive is generated.

FIG. 3 is a diagram illustrating an example in which an increasing form that increases in a curved shape while forming an arc toward the asymptotic target linear function line DL is formed by the SQRT function.
When an increasing form that increases in a curved shape while forming an arc toward the asymptotic target linear function line DL side is formed by the SQRT function, as shown in FIG. It is possible to shift to an asymptotic state while maintaining continuity without changing.

In the present embodiment, the d-axis current Id commanded by the d-axis current command CId flows from the first rotation speed [A] to the second rotation speed [B] as shown in FIG. In the period T3 of the rotational speed equal to or higher than the second rotational speed [B], the asymptotic state to the linear function line DL is stopped and fixed (clamped) to a constant value CV.
As described above, since the d-axis current Id is fixed at the second rotation speed [B] or more, an increase in heat generation due to the d-axis current (reactive current) can be suppressed.

The first rotational speed [A] at which the d-axis current starts to flow may be set to a rotational speed different from the rated rotational speed.
When the d-axis current starts to flow from the rated rotational speed, the linearity on the NT characteristic is lost in a state below the rated rotational speed and above the rated rotational speed, so that a torque change occurs across the rated rotational speed.
On the other hand, it is possible to prevent the loss of linearity at least in the vicinity of the rated rotational speed that is in the use range by starting to flow the d-axis current from the rotational speed different from the rated rotational speed.

Alternatively, the first rotational speed [A] may be a rotational speed at which a torque limit is applied and the torque is constant regardless of the rotational speed.
In this case, since the d-axis current starts to flow from the rotational speed at which the torque limit is applied, the linearity is not lost on the NT characteristic. That is, since there is already no linearity in the region where the torque limit is applied, linearity outside the torque limit region can be secured.

The d-axis controller 90d generates a DC d-axis command voltage Vd according to the d-axis current command CId and the d-axis current Idf generated by the DQ converter 60.
The d-axis controller 90 d supplies the generated d-axis command voltage Vd to the power supply unit 30.

The d-axis controller 90d includes a subtractor 91d and a current controller 92d.
The d-axis controller 90d obtains a current deviation by subtracting the d-axis current Idf obtained by the DQ converter 60 from the d-axis current command CId by the subtractor 91d, and the current controller 92d converts the current deviation into proportional integral control or the like. To obtain the d-axis command voltage Vd.

The q-axis controller 90q generates a DC q-axis command voltage Vq according to the q-axis current command CIq and the q-axis current Iqf generated by the DQ conversion unit 60.
The q-axis controller 90q supplies the generated q-axis command voltage Vq to the power supply unit 30.

The q-axis controller 90q includes a subtracter 91q and a current controller 92q.
The q-axis controller 90q obtains a current deviation by subtracting the q-axis current Iqf obtained by the DQ converter 60 from the q-axis current command CIq by the subtractor 91q, and the current controller 92q calculates the current deviation by proportional integral control or the like. To obtain the q-axis command voltage Vq.

FIG. 4 is a block diagram illustrating a functional configuration example on the d-axis controller, the q-axis controller, and the motor side according to the present embodiment.
In FIG. 4, a d-axis controller 90d and a q-axis controller 90q are control systems in which current controllers 92d and 92q have integral terms 101 and 102 (K1 is an integral gain) and proportional terms 103 and 104 (K2 is a proportional gain). It is configured.
The servo motor side has a resistance component R and an inductance component L. Each d-axis (d-phase) and q-axis (q-phase) have interference terms 105 and 106 from other phases.

In the present embodiment, as described above, the command generation unit 80 supplies the d-axis current command CId according to the rotation speed N of the servo motor 20 to the d-axis controller 90d, and the torque to the q-axis controller 90q. A q-axis current command CIq which is a command is supplied.
In the present embodiment, as the d-axis current command CId corresponding to the rotation speed (rotation state) N of the servo motor 20, a d-axis current command having the characteristics shown in the upper part of FIGS. 2 and 4 can be used.

[Voltage state of d-axis and q-axis according to d-axis current command CId and q-axis current command CIq]
Here, the voltage states of the d-axis and the q-axis according to the d-axis current command CId and the q-axis current command CIq in the present embodiment will be considered.

[Accelerating]
As described above, the d-axis current command CId sets the d-axis current Id to zero in the period (acceleration region) T1 from the rotation speed of the servo motor 20 to 0 to the first rotation speed [A].

FIG. 5 is a diagram for explaining the present embodiment, and is a diagram illustrating voltage states of the d-axis and the q-axis during acceleration when the d-axis current command CId is zero.
In FIG. 5, a circle indicated by a symbol CRL is a DC link voltage, a q-axis voltage indicated by R · Iq is an effective voltage for controlling the motor, and a q-axis voltage indicated by ωe · L · Iq is used for motor driving. It is a non-contributing reactive voltage, E represents a counter electromotive force, and a terminal voltage is the sum of the counter electromotive force E and an effective voltage (q-axis voltage) R · Iq.
Servo motor control is possible when the terminal voltage is equal to or lower than the DC link voltage. When the terminal voltage exceeds the DC link voltage, control becomes difficult.
When the terminal voltage is equal to or lower than the DC link voltage, a current for controlling the motor can be generated based on a voltage obtained by subtracting the back electromotive force E from the DC link voltage.

[Comparative example: High-speed rotation when d-axis current Id is zero]
FIG. 6 is a diagram showing, as a comparative example, voltage states of the d phase and the q phase when the d-axis current command CId is zero and the counter electromotive force and the DC link voltage match.
When acceleration is performed to a high speed, the voltage for generating the acceleration current decreases due to the increased counter electromotive force E, the acceleration current decreases, and finally the counter electromotive force and the DC link voltage coincide with each other, and the acceleration is finished. It will be.
When decelerating from this state, the voltage required to flow the deceleration current is insufficient, current control becomes difficult, and abnormal current may flow.

  Therefore, in the present embodiment, a method of shifting the current phase in the d-axis direction at the time of a large current in the high speed region is employed in order to reduce the motor terminal voltage in the high speed region.

[High-speed rotation while flowing d-axis current Id]
Next, when the rotation speed of the servo motor 20 increases and exceeds the first rotation speed [A], the back electromotive force E increases to approach the DC link voltage and voltage saturation starts. At this time, input of the d-axis current command CId to the d-axis controller is started.
In the present embodiment, when the rotation speed of the servo motor 20 increases and reaches the first rotation speed [A], the rotation is performed in a period T2 from the first rotation speed [A] to the second rotation speed [B]. The number is increased so as to be asymptotic to a linear function line DL from the number zero to the second rotational speed [B].
The d-axis current Id increases in the form of an arc ARC toward the asymptotic target linear function line DL in the current flow start period T21 that is a neighboring region, starting from the first rotational speed [A]. While increasing the curve.

FIG. 7 is a diagram for explaining the present embodiment, and is a diagram illustrating voltage states of the d-axis and the q-axis when the d-axis current command CId and the q-axis current command CIq are input in the high speed region.
In FIG. 7, when the d-axis current Id flows through the d-axis winding by the d-axis current command CId, a reactive voltage component R · Id is generated by the resistance component R of the d-axis winding, and the inductance component L of the d-axis winding. As a result, an effective voltage component ω · L · Id is generated (broken line in FIG. 7).
Since the effective voltage component ωe · L · Id is in the opposite direction to the counter electromotive force E, the counter electromotive force is reduced to a compensated counter electromotive force E ′ indicated by a one-dot chain line in the figure.
Therefore, when looking at the voltage in the q-axis direction, the compensated counter electromotive force E ′ falls within the DC link voltage, and a voltage sufficient to flow the control current is generated.
The voltage e in FIG. 4 is an effective voltage component ω · L · Id due to the inductance component L of the d-axis winding, and current supply to the d-axis is a voltage in the direction opposite to the counter electromotive force E (= ωe · Φ). Substantially coincident with inputting e into the q-axis controller 90q, thereby reducing the back electromotive force E at the terminal voltage.

When the rotation speed of the servo motor 20 further increases, the back electromotive force E (= ωe · Φ) increases according to the rotation speed.
At this time, by increasing the d-axis current command CId to the d-axis controller 90d in accordance with the rotational speed, the effective voltage component ωe · L · Id generated in the inductance component L of the d-axis winding is increased to increase the counter electromotive force. The voltage in the direction to cancel E is increased, and the increase of the counter electromotive force E is suppressed.

Then, the d-axis current command CId is fixed to a constant value during a period (high speed region) T3 in which the rotation speed of the servo motor 20 exceeds the second rotation speed [B].
This is to prevent troubles such as overcurrent and overheating caused by an unlimited increase in d-axis current.

As described above, the voltage states of the d-axis and the q-axis according to the d-axis current command CId and the q-axis current command CIq in the present embodiment have been considered.
Next, the operation of the servo motor control system according to the present embodiment will be described focusing on the speed loop and current loop processing of the command generator.

  FIG. 8 is a flowchart for explaining the operation of the servo motor control system according to the present embodiment, focusing on the speed loop and current loop processing of the command generator.

  First, the command generator 80 calculates a torque command in a speed loop (not shown) (step ST1), and outputs the torque command obtained in the current loop to the q-axis controller 90q as a q-axis current command CIq (step ST2).

Next, the command generator 80 compares the actual rotational speed of the servo motor 20 detected by the rotational speed detector 70 with the first rotational speed [A], and the actual rotational speed is the first rotational speed [ A] is determined (step ST3).
If it is determined in step ST3 that the rotation speed of the servo motor 20 has not reached the first rotation speed [A], the command generation unit 80 determines that the acceleration is in the period T1 and the d-axis current command CId. Is set to zero and output to the d-axis controller 90d (step ST4).
At this time, the q-axis current command CIq is the torque command set in step ST2.

On the other hand, if it is determined in step STST3 that the rotational speed of the servo motor 20 has reached the first rotational speed [A], the actual rotational speed of the servo motor 20 detected by the rotational speed detector 70 and the first rotational speed are detected. 2 is compared with the number of revolutions [B] to determine whether the actual number of revolutions has reached the second number of revolutions [B] (step ST5).
If it is determined in step ST5 that the rotation speed of the servo motor 20 has not reached the second rotation speed [B], the command generation unit 80 determines that the high-speed range is in the period T2, and the command generation unit 80 CId is not zero, and asymptotically approaches a linear function line DL from the rotation speed zero to the second rotation speed [B] in the period T2 from the first rotation speed [A] to the second rotation speed [B]. Set to increase.
In addition, the command generation unit 80 starts to flow the d-axis current command CId from the first rotational speed [A] in the current flowing start period T21 that is the vicinity region, and arcs toward the asymptotic target linear function line DL. A curve is set to increase while forming an ARC (step ST6).

If it is determined in step ST5 that the rotation speed of the servo motor 20 has reached the second rotation speed [B], a period (high speed region) T3 in which the actual rotation speed exceeds the second rotation speed [B]; As a result, the command generation unit 80 sets the d-axis current command CId to be fixed to a constant value (step ST7).
At this time, the q-axis current command CIq is the torque command set in step ST2.

Next, the d-axis controller 90d and the q-axis controller 90q take in the d-axis and q-axis current feedbacks Idf and Iqf of the servomotor 20 by current feedback.
The d-phase and q-phase current feedbacks Idf and Iqf are taken in from the actual currents Iu, Iv, and Iw in the u-phase, v-phase m, and w-phase of the servo motor, and from the output of the phase detector 50, The electrical angle θe can be obtained and DQ conversion for obtaining a two-phase direct current from the three-phase alternating current can be performed (step ST8).

Next, in the d-axis controller 90d and the q-axis controller 90q, the d-axis and q-axis currents Idf and Iqf are subtracted from the phase command values of the d-axis current command CId and the q-axis current command CIq, respectively. Find the current deviation. Then, the current deviation is subjected to proportional / integral control in the current loop of the current controllers 92d and 92q to obtain the d-axis command voltage Vd and the q-axis command voltage Vq (step ST9).
Further, in the voltage conversion unit 31 for converting the biaxial voltage into the triaxial voltage, the U, V, and W phase command voltages Vu, Vv, and Vw are obtained by DQ conversion for obtaining the three-phase AC voltage from the biaxial DC voltage. (Step ST10), this command voltage is output to the power amplifier 32, and currents Iu, Iv, Iw are supplied to each phase of the servo motor by an inverter or the like to control the servo motor 20.

[Rotation speed vs. torque characteristics]
Next, with respect to the rotational speed vs. torque characteristics when the control method of the present embodiment is applied, a general system that does not employ the field weakening control method and a field weakening control method as in Patent Document 1 are employed to achieve high speed. A system that increases the d-axis current linearly according to a linear increase function in the region will be considered as a comparative example.

FIG. 9 is a diagram showing an overview of the rotational speed versus torque characteristics when the control method of the present embodiment is applied, and is a diagram for explaining in comparison with a comparative example.
FIG. 10 is a diagram illustrating an experimental result of the rotational speed versus torque characteristic when the control method of the present embodiment is applied, and is a diagram for explaining in comparison with a comparative example.
FIG. 9 schematically shows the outline.
9 and 10, the horizontal axis represents the generated torque (N · m, kg · cm), and the vertical axis represents the rotational speed N (rpm).
9 and 10, the curve indicated by X indicates the characteristic (NT characteristic) of the system according to the present embodiment, and the curve indicated by Y is a general first that does not employ the field weakening control method. The characteristic of the comparison system (N-T characteristic) is shown, the curve indicated by Z adopts the field-weakening control method, and the characteristic of the second comparison system (N-T) increases the d-axis current according to a linear increase function in the high speed range. Characteristic).

As can be seen from the figure, this system can suppress the back electromotive force with high accuracy by the d-axis current in the high speed region where the back electromotive force is generated, as compared with the first comparison system and the second comparison system. Therefore, stable rotation can be performed up to a high speed region.
In addition, this system increases the torque at a predetermined rotational speed by increasing the d-axis current asymptotically from a rotational speed of zero to a linear function as compared with the second comparative system. can do.

The effect of increasing the torque in association with the NT characteristic graph of FIG. 10 will be further described in detail.
The predetermined rotational speed is, for example, 3000 rpm on the NT characteristic graph of FIG. 10, whereas in the case of the second comparative system increased linearly, the maximum torque at 3000 arpm is 3.52 Nm. Thus, in this system, the maximum torque can be increased to 3.76 Nm when increasing asymptotically to a linear function, and the speed controllable region at 3000 rpm can be expanded.

[Effect of the embodiment]
As described above, the following effects can be obtained in the present embodiment.
In the present embodiment, basically, the d-axis current Id commanded by the d-axis current command CId has a first period (acceleration region) in which the rotational speed N is from zero to the first rotational speed [A]. It is controlled to be zero at T1, and to gradually increase in the second period (high speed region) T2 exceeding the first rotation speed [A] and reaching the second rotation speed [B].
The increasing form of the d-axis current Id is a rotational speed lower than the first rotational speed [A] in the period T2 from the first rotational speed [A] to the second rotational speed [B], in the present embodiment, the rotational speed. It increases so as to be asymptotic to a linear function line DL from zero to the second rotational speed [B].
The d-axis current Id increases in the form of an arc ARC toward the asymptotic target linear function line DL in the current flow start period T21 that is a neighboring region, starting from the first rotational speed [A]. However, it is configured to increase in a curved line.

Accordingly, since the back electromotive force can be suppressed by the d-axis current in a high speed region where the back electromotive force is generated, stable rotation can be performed up to the high speed region.
Further, by increasing the d-axis current asymptotically to a linear function from a rotational speed lower than the first rotational speed [A], for example, from the rotational speed of zero, the torque at a predetermined rotational speed is increased rather than increasing linearly. Can be increased, and as a result, the rotation speed controllable region can be expanded.

In the present embodiment, the d-axis current Id commanded by the d-axis current command CId flows from the first rotation speed [A] to the second rotation speed [B], and this second rotation speed [ B] In the period T3 of the above rotation speed, the asymptotic state to the linear function line DL is stopped and fixed (clamped) to a constant value CV.
As described above, since the d-axis current Id is fixed at the second rotation speed [B] or more, an increase in heat generation due to the d-axis current (reactive current) can be suppressed.

The first rotational speed [A] at which the d-axis current starts to flow may be set to a rotational speed different from the rated rotational speed.
When the d-axis current starts to flow from the rated rotational speed, the linearity on the NT characteristic is lost in a state below the rated rotational speed and above the rated rotational speed, so that a torque change occurs across the rated rotational speed.
On the other hand, it is possible to prevent the loss of linearity at least in the vicinity of the rated rotational speed that is in the use range by starting to flow the d-axis current from the rotational speed different from the rated rotational speed.

Alternatively, the first rotational speed [A] may be a rotational speed at which a torque limit is applied and the torque is constant regardless of the rotational speed.
In this case, since the d-axis current starts to flow from the rotational speed at which the torque limit is applied, the linearity is not lost on the NT characteristic. That is, since there is already no linearity in the region where the torque limit is applied, linearity outside the torque limit region can be secured.

  As described above, according to the present embodiment, the reactive current is reduced in the region where voltage saturation does not occur, the heat generation due to the reactive current is suppressed, and the maximum torque obtained in the desired rotational speed range can be increased. It is possible to expand the rotation speed control region, and it is possible to perform stable rotation up to a high speed region.

[Other Embodiments]
As mentioned above, although the embodiment of the invention made by the present inventor has been specifically described, the present invention is not limited to the above-described embodiment, and various modifications can be made without departing from the scope of the invention. Not too long.

  For example, in the above-described embodiment, the rotation speed is used as the control parameter for the d-axis current. However, the present invention is not limited to this, and the same effect as described above can be obtained even when the rotation speed indicating the rotation state of the servo motor is used. An effect can be obtained.

  DESCRIPTION OF SYMBOLS 10 ... Servo motor control system, 20 ... Servo motor, 30 ... Electric power supply part, 31 ... Voltage conversion part, 32 ... Power amplifier, 40 ... Current detection part, 50 ... Phase detector, 60 ... DQ converter, 70 ... rotational speed detector (rotation state detector), 80 ... command generator, 90d ... d-axis controller, 90q ... q-axis controller.

Claims (8)

A multi-phase AC servo motor,
A power supply unit that converts a DC d-axis command voltage and a q-axis command voltage into multiphase AC power and supplies the servomotor with multiphase AC power;
A DQ conversion unit that dq-converts the current of each phase of the servomotor based on the rotation phase of the servomotor and generates a d-axis current and a q-axis current;
A command generator for generating a d-axis current command and a q-axis current command as a torque command according to the rotation state of the servo motor;
A d-axis controller that generates a DC d-axis command voltage in accordance with the d-axis current command and the d-axis current generated by the DQ converter, and supplies the d-axis command voltage to the power supply unit;
A q-axis controller that generates a direct q-axis command voltage according to the q-axis current command and the q-axis current generated by the DQ conversion unit, and supplies the q-axis command voltage to the power supply unit,
The d-axis current commanded by the d-axis current command is
It is zero until the first rotation state, and flows so as to gradually increase to the second rotation state beyond the first rotation state,
The increase form of the d-axis current increases asymptotically to a linear function from the rotation speed zero to the second rotation state,
A servo motor control system that increases in a curved line while forming an arc toward a linear function side of the asymptotic object in a vicinity region where current starts to flow from the first rotation state. The d-axis current is
2. The servo motor control system according to claim 1, wherein the flow is increased from the first rotation state to the second rotation state, and is fixed to a constant value in a rotation state equal to or higher than the second rotation state. The servo motor control system according to claim 1, wherein the first rotational state is a rotational speed different from the rated rotational speed. The servo motor control system according to claim 1 or 2, wherein the first rotational state is a rotational speed at which a torque limit is applied and the torque is constant regardless of the rotational speed. A command generation step for generating a d-axis current command and a q-axis current command as a torque command according to the rotation state of the servo motor;
A power supply step of converting a DC d-axis command voltage and a q-axis command voltage into multi-phase AC power and supplying multi-phase AC power to the servo motor;
A DQ conversion step of generating a d-axis current and a q-axis current by dq-converting the current of each phase supplied to the servo motor based on the rotation phase of the servo motor;
A d-axis control step that generates the DC d-axis command voltage according to the d-axis current command and the d-axis current generated in the DQ conversion step, and supplies the DC d-axis command voltage to the power supply step;
A q-axis control step that generates the DC q-axis command voltage according to the q-axis current command and the q-axis current generated in the DQ conversion step, and supplies the DC q-axis command voltage to the power supply step.
The d-axis current commanded by the d-axis current command is
It is zero until the first rotation state, and flows so as to gradually increase to the second rotation speed beyond the first rotation state,
The increase form of the d-axis current increases asymptotically to a linear function from the rotation speed zero to the second rotation state,
A servo motor control method that increases in a curved line while forming an arc toward a linear function side of the asymptotic object in a region near the beginning of current flow from the first rotation state. The d-axis current is
The servo motor control method according to claim 5 , wherein the flow is increased from the first rotation state to the second rotation state, and the rotation number equal to or higher than the second rotation number is fixed to a constant value. The servo motor control method according to claim 5 or 6 , wherein the first rotational state is a rotational speed different from the rated rotational speed. The servo motor control method according to claim 5 or 6 , wherein the first rotational state is a rotational speed at which a torque limit is applied and the torque is constant regardless of the rotational speed.

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