JP2016167946A - Current controller for ac motor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To achieve stable current control, giving a priority to torque even when a voltage is saturated.SOLUTION: The current controller for AC motor includes a switcher for switching between a normal mode in which a d-axis voltage command is taken as a sum of a proportional amplification and an integration amplifier of a d-axis current deviation and a q-axis voltage command is taken as a sum of a proportional amplification and an integration amplifier of a q-axis current deviation, and an other-axis integration mode in which a d-axis voltage command is taken as a sum of a proportional amplification of a d-axis current deviation and an integration amplification of a q-axis current deviation and a q-axis voltage command is taken as a sum of a proportional amplification of a q-axis current deviation and an integration amplification of a d-axis current deviation.SELECTED DRAWING: Figure 1

Description

  The present invention relates to current control of an AC motor.

  A conventional current control technique for an AC motor will be described below with reference to FIG. The current detector 2 converts the stator current of the AC motor 1 into a d-axis current id and a q-axis current iq of each component on the dq axis, which are orthogonal coordinates for rotation, and outputs the result. The d-axis is generally defined in the direction of the secondary linkage magnetic flux vector of the motor when the AC motor 1 is an induction motor, and the rotation of the motor is generally performed when the AC motor 1 is a permanent magnet synchronous motor. Defined in the north pole direction of the permanent magnet of the child. The current command generator 5 generates and outputs a d-axis current command idr and a q-axis current command iqr on the dq coordinate. The deviation ider between idr and id obtained by the d-axis deviation calculator 9 is amplified by a predetermined factor by the d-axis proportional amplifier 11 and becomes a d-axis proportional component. The ider is amplified by the d-axis integral gain amplifier 13 and then time-integrated by the d-axis integrator 18 to become a d-axis integral component. A deviation iqer between iqr and iq obtained by the q-axis deviation calculator 8 is amplified by a predetermined factor by the q-axis proportional amplifier 10 to become a q-axis proportional component. The iqer is amplified by the q-axis integral gain amplifier 12 and then time-integrated by the q-axis integrator 17 to become a q-axis integral component.

  The adder 21 calculates the sum of the q-axis proportional amplifier 10 output and the q-axis integrator 17 output, and outputs a q-axis voltage command vqr. The adder 22 calculates the sum of the output of the d-axis proportional amplifier 11 and the output of the d-axis integrator 18 and outputs a d-axis voltage command vdr. The voltage coordinate converter 4 converts vdr and vqr, which are axis voltage commands on the rotating dq axis coordinates, into component voltage commands var and vbr on a stationary ab coordinate and outputs them to the power converter 3. . The power converter 3 applies a voltage according to the input voltage command to the AC motor 1. If the magnitude of the voltage command is larger than the maximum voltage that can be output by the power converter 3, the magnitude is the maximum voltage. A voltage whose phase is as commanded is applied to the AC motor 1.

  In the current control shown in FIG. 2, when the magnitude of the voltage command vector having the a-axis component var and the b-axis component vbr or the d-axis component vdr and the q-axis component vqr exceeds the maximum output voltage of the power converter 3. Since the commanded voltage cannot be applied to the AC motor 1, current control of one or both of the dq axes cannot be performed. In order to solve this problem, the current control described in Patent Document 1 shown in FIG. 3 is proposed. 3 will be described below, but the description of the same parts as those in FIG. 2 will be omitted, and only different parts will be described.

  When the AC motor 1 is an induction motor, the voltage equation on the primary side is expressed by equations (1) and (2). Here, vd is a d-axis voltage, vq is a q-axis voltage, R1 is a winding resistance value, Lσ = L1-M · M / L2, ω is an output angular frequency, M is a mutual inductance, and L1 and L2 are primary. And secondary self-inductance, φ2 is the magnitude of the secondary flux linkage, and p is the time derivative. The voltage equation when the AC motor 1 is a permanent magnet synchronous motor is expressed by the equations (3) and (4). Here, Ld and Lq are the d-axis and q-axis inductances, respectively, and φ is the magnitude of the permanent magnet magnetic flux.

(数２)

(数３)

(数４)

(Equation 1)

(Equation 2)

(Equation 3)

(Equation 4)

  The input of the q-axis integrator 17 is added with the d-axis current deviation ider amplified by the d-axis speed proportional amplifier 14 by the adder 23. The d-axis speed proportional amplifier 14 is based on the third term on the right side of the equation (2) if the AC motor 1 is an induction motor, and if it is a permanent magnet synchronous motor, the amplification gain is proportional to the angular frequency ω. Will be. Similarly, the adder 24 adds the q-axis current deviation iqer amplified by the q-axis speed proportional amplifier 15. The q-axis speed proportional amplifier 15 is based on the third term on the right side of the equation (1) if the AC motor 1 is an induction motor, and if it is a permanent magnet synchronous motor, the amplification gain is proportional to the angular frequency ω. Will be. The output of the adder 24 is input to the d-axis integrator 18. A switch 16 is inserted at the input of the d-axis integral gain amplifier 13, and the switch 16 has a d-axis current when the magnitude of the input voltage command of the power converter 3 is smaller than the maximum output voltage of the power converter 3. Deviation ider, 0 otherwise.

  Even when the switch 16 is off, the d-axis current deviation can be reduced to 0 by correcting the q-axis voltage command by the q-axis integrator 17 via the d-axis speed proportional amplifier 14 and the adder 23. D-axis current control can be realized. However, when the magnitude of the input voltage command of the power converter 3 exceeds the maximum output possible voltage of the power converter 3, the output of the q-axis integrator 17 becomes a fixed value limited to the limit value. Therefore, d-axis current control cannot be performed. On the other hand, the q-axis current deviation of the output of the q-axis deviation calculator 8 is maintained by correcting the d-axis voltage command via the q-axis velocity proportional amplifier 15, the adder 24, and the d-axis integrator 18. Will remain. That is, in the voltage saturation state, the d-axis current control can be abandoned and the control giving priority to the q-axis current control can be performed. Since the q-axis is an axis perpendicular to the magnetic flux axis, the torque of the AC motor 1 can be controlled by controlling the q-axis current, so that the torque control can be maintained even when the voltage is saturated.

JP 2003-88193 A JP 2003-209997 A JP 2012-151931 A

  The problem to be solved is that, in the prior art of FIG. 2, when the voltage is saturated, control of both axes or one axis cannot be performed, and a desired output torque of the AC motor cannot be obtained. In the prior art of FIG. 3, even when the voltage is saturated, the q-axis priority control can be performed and a desired output torque can be obtained, so that the above problem can be solved, but there are the following problems.

  FIG. 4 illustrates voltage command vectors vr and vr1 and voltage vectors v and v1 applied to the AC motor 1 when the voltage is saturated in the prior art of FIG. The voltage vectors v and v1 are limited within a voltage output limit circle that is the maximum output voltage of the power converter 3, and the q-axis component of the voltage command vectors vr and vr1 is limited by the q-axis integrator 17 due to voltage saturation. Limited to the value vqrlmt. This vqrlmt needs to be equal to or higher than the maximum output voltage of the power converter 3. As shown in the figure, since the q-axis voltage command is limited to the limit value vqrlmt in the voltage saturation state, the d-axis voltage command is adjusted to change the phase of the voltage vector to control the q-axis current. It will be. For example, in order to change the voltage vector phase by Δθ, it is necessary to change the d-axis voltage command of Δvdr. In the case of an induction motor, as shown in the figure, since the voltage vector is oriented in the direction close to the q-axis, the amount of change in the d-axis voltage command required to change the voltage vector phase is small. However, in the case of a permanent magnet synchronous motor, the direction of the voltage vector may be far away from the q axis. The change Δvdr in the d-axis voltage command necessary to change the voltage vector phase must be increased. Therefore, it is necessary to make the output range of the d-axis integrator 18 very large, and it becomes difficult to adjust the gain of the q-axis velocity proportional amplifier 15 and the d-axis integral gain amplifier 13 that become the integral gain.

  Further, when the direction of the voltage vector is close to the d-axis, the voltage vector phase cannot be controlled by the d-axis voltage command control, and the control becomes impossible. This is the same when the voltage vector is in the first quadrant of FIG. 4 in the regenerative operation.

  In Patent Document 2, in order to solve the above problem, an M axis that coincides with the primary linkage magnetic flux vector of the AC motor and a T axis that is orthogonal to the M axis are introduced, and the MT axis is the same as that of FIG. 3 instead of the dq axis. The configuration has the following problems. Although the T-axis current priority control can be performed, when the MT-axis current command is obtained from the dq-axis current command by rotational coordinate conversion, the q-axis current does not match the command due to voltage saturation, and a desired torque can be obtained. Disappear. Also, the M-axis phase viewed from the d-axis may change suddenly due to a sudden change in current. At that time, it is necessary to suddenly change the voltage command of each axis to a value corresponding to the phase. However, since the output of the integrator cannot be changed suddenly, current control may become unstable if the MT axis phase changes suddenly.

  In the prior art shown in FIG. 3, for example, when the AC motor is an induction motor, the d-axis current automatically decreases as the rotational speed increases, but the q-axis current command is increased to keep outputting the desired torque. There must be. However, since the induction motor has a stationary torque under the applied voltage limit, the torque may not be increased even if the q-axis current is increased. In the case of a permanent magnet synchronous motor, the voltage vector may be too close to the d-axis, and as a result, control becomes impossible as described above.

  In the state where the d-axis current control is abandoned due to voltage saturation in the prior art shown in FIG. 3, the output of the d-axis deviation calculator 9 becomes a large value, the output of the d-axis proportional amplifier 11 becomes large, and it is corrected. The d-axis integrator 18 operates. Therefore, a sudden change in the d-axis current command becomes a large disturbance in the q-axis current control and the control becomes unstable.

In order to solve the above problems, the present invention
A current detector that converts and outputs a d-axis current and a q-axis current of each component on the dq axis, which are orthogonal coordinates for rotating the stator current of the AC motor,
When a voltage command in a stationary coordinate system is input and the voltage command is smaller than the maximum voltage that can be output, a voltage according to the voltage command is applied to the AC motor, and the magnitude of the voltage command is the maximum that can be output. A power converter that applies a voltage substantially in phase with the voltage command at the magnitude of the maximum voltage, if greater than the voltage, to the AC motor;
A current command generator for generating and outputting a d-axis current command and a q-axis current command on the dq coordinate;
A d-axis deviation calculator for obtaining a difference between the d-axis current command of the current command generator output and the d-axis current of the current detector;
A q-axis deviation calculator for obtaining a difference between the q-axis current command of the current command generator output and the q-axis current of the current detector;
A d-axis proportional amplifier for multiplying the d-axis deviation calculator output by a proportional gain;
A q-axis proportional amplifier that multiplies the q-axis deviation calculator output by a proportional gain;
A d-axis integrator that integrates the input over time and outputs it after being limited by a predetermined limit value VdLt;
A q-axis integrator that integrates the input over time and limits and outputs a predetermined limit value VqLt;
From the q-axis voltage command that is the sum of the q-axis proportional amplifier output and the q-axis integrator output and the d-axis voltage command that is the sum of the d-axis proportional amplifier output and the d-axis integrator output, In an AC motor current control device comprising a voltage coordinate converter for obtaining a voltage command of
Normal mode in which at least the output of the d-axis deviation calculator is multiplied by a predetermined gain to the input of the d-axis integrator, and the input of the q-axis integrator is only the one obtained by multiplying the output of the q-axis deviation calculator by a predetermined gain. And the input of the d-axis integrator is only the q-axis deviation calculator output multiplied by a predetermined gain, and at least the d-axis deviation calculator output is multiplied by a predetermined gain to the input of the q-axis integrator. A switch for switching between the different axis integration modes is provided.

  In the switch, the other-axis integration mode is selected when the voltage modulation rate of the power converter is greater than a predetermined value and the absolute value of the q-axis integrator output is greater than or equal to the d-axis integrator output.

  The VdLt is obtained by adding the d-axis error correction value Vdx to the absolute value of the d-axis voltage value obtained by removing the current differential term from the d-axis characteristic formula of the AC motor, and the VqLt is the q of the AC motor. Assume that the q-axis error correction value Vqx is added to the absolute value of the q-axis voltage value obtained by excluding the current differential term from the axis characteristic equation.

  The second d-axis current command obtained by adding a predetermined value to the d-axis current from which the high frequency component is removed is compared with the d-axis current command of the current command generator output, and the larger one in the negative direction is selected. The d-axis current command regulator is output, and the output of the d-axis current command regulator is used as the input of the d-axis deviation calculator instead of the d-axis current command.

The limit value of the q-axis current command is obtained from the voltage vector phase limit value, which is a limit value of the phase from the d-axis of the voltage command vector having the d-axis voltage command and the q-axis voltage command as components, and the maximum voltage. A q-axis current command limiter is provided for limiting the q-axis current command to the limit value and outputting the limit value to the q-axis deviation calculator.

  When the voltage is not saturated or during regenerative operation, the switch is equivalent to the same control configuration as in FIG. During regenerative operation, there is a voltage vector in the first quadrant of FIG. 4, and increasing the regenerative torque will increase the q-axis current command in the negative direction, and the voltage vector will approach the d-axis. Even in the voltage saturation state, the q-axis current control can be maintained even in the configuration of FIG. 2 during the regenerative operation. On the other hand, since the d-axis integrator 18 is limited to the limit value, the d-axis current control cannot be maintained. From the above, according to the present invention, at least on the regeneration side, q-axis priority control can be performed even when the voltage vector direction is very close to the d-axis.

  The switch selects another axis integration mode corresponding to FIG. 3 when the voltage modulation rate of the power converter is equal to or greater than a predetermined value and the absolute value of the q-axis integrator output is equal to or greater than the d-axis integrator output. In this case, if the normal mode corresponding to FIG. 2 is selected, the voltage command jump does not occur at the time of switching, so that smooth switching can be performed.

  The limit value VdLt of the d-axis integrator is obtained by adding the d-axis error correction value Vdx to the absolute value of the value obtained by removing the differential term on the right side of the equation (1) or (3), and the limit value VqLt of the q-axis integrator. When the q-axis error correction value Vqx is added to the absolute value of the expression excluding the differential term on the right side of the expression (2) or (4), the q-axis integrator output is limited to the limit value. Thus, vqr is not increased unnecessarily, and as a result, the change Δvdr in the d-axis voltage command necessary to change the voltage vector phase even when the direction of the voltage vector is far away from the q-axis as in a permanent magnet synchronous motor. Can be reduced.

  Moreover, the d-axis current command adjuster can reduce the deviation between the d-axis current command and the d-axis current to a predetermined value or less, and even if the d-axis current command output from the current command generator changes suddenly, the q-axis current control is performed. The influence of can be reduced.

  Also, the q-axis current command limiter can limit the voltage command vector from approaching the d-axis during powering in the case of a permanent magnet synchronous motor, and the voltage vector phase cannot be adjusted by adjusting the d-axis voltage command. Can be prevented. In the case of an induction motor, the d-axis current automatically decreases as the rotational speed increases, and the q-axis current command must be increased in order to continue outputting the desired torque. Even if the q-axis current is increased by torque, torque may not be generated and the control may be disabled. However, it is possible to prevent an uncontrollable state by limiting the q-axis current command limiter to an appropriate value.

It is explanatory drawing which showed the Example of this invention of current control. Example 1 It is explanatory drawing of the prior art example 1 of electric current control. It is explanatory drawing of the prior art example 2 of electric current control. The relationship between the voltage vector of a prior art and each voltage command is shown in figure. The relationship between the voltage vector of this invention and each voltage command is shown in figure.

  An embodiment of the current control technique for an AC motor of the present invention is shown in FIG. 1, and the embodiment of the present invention will be described based on this figure. The description of the same parts as those in FIG. 3 is omitted, and only the q-axis current command limiter 6, the d-axis current command adjuster 7, and the switch 19 will be described.

  The switch 19 switches to B when the voltage modulation rate of the power converter 3 is equal to or greater than a predetermined value immediately before voltage saturation and the absolute value of the q-axis integrator 17 output is equal to or greater than the d-axis integrator 18 output. Switches to A. In the normal mode in which the switch 19 is switched to A, the input of the q-axis speed proportional amplifier 15 is q-axis deviation in the case of FIG. 1, but may be 0 similarly to the input of the d-axis speed proportional amplifier 14. . Then, it becomes the same as the configuration of FIG. 2, and current control of both axes can be realized in a voltage unsaturated state. When the absolute value of the q-axis integrator 17 output is less than the d-axis integrator 18 output, the phase difference from the d-axis of the voltage vector is within ± 45 degrees in FIG. It has become. Then, when the voltage is saturated, the d-axis integrator 18 is limited to the limit value VdLt, but the output of the q-axis integrator 17 is not limited and the phase of the voltage vector can be controlled, so that the q-axis current control can be maintained.

  In the other axis integration mode in which the switch 19 is switched to B, the state is the same as the state in which the switch 16 in FIG. 3 is off. Therefore, when the voltage is saturated, the q-axis integrator 17 is limited to the limit value VqLt, and the d-axis deviation that is the input remains. On the other hand, by setting d-axis error correction value Vdx >> q-axis error correction value Vqx, d-axis integrator 18 is less likely to be restricted, and vdr can be controlled, thereby adjusting the voltage phase and adjusting the q-axis current. Control can be maintained. At that time, the limit value VqLt of the q-axis integrator 17 is set to a value obtained by adding the q-axis error correction value Vqx to the absolute value of the value excluding the differential term on the right side of the equations (2) and (4). Therefore, it is not necessary to unnecessarily increase the output of the q-axis integrator 17, and the value of the q-axis error correction value Vqx only needs to be large enough to correct the calculation error in the equations (2) and (4). As shown in FIG. 5, even if the voltage vector v is away from the q axis, the change Δvdr of the d-axis voltage command for changing the voltage vector phase can be reduced. Therefore, the output range of the d-axis integrator 18 can be reduced, and the gain adjustment of the q-axis speed proportional amplifier 15 and the d-axis integral gain amplifier 13 serving as the integral gain is simplified.

  Next, the operation of the q-axis current command limiter 6 will be described. The q-axis current command limiter 6 obtains a q-axis current limit value by inputting the voltage vector phase limit value θvx and the maximum voltage Em that the power converter 3 can output, and limits the q-axis current command to that value. Is output as a new q-axis current command iqrr.

(数６)

(数７)

(Equation 5)

(Equation 6)

(Equation 7)

  When the AC motor 1 is a permanent magnet synchronous motor, the q-axis current command limiter 6 uses the q-axis current limit value to limit the phase difference between the d-axis and the voltage command vector to θvx. By substituting equation (5) into equation (3) and ignoring the term of winding resistance and the current differential term, equation (6) is obtained as an absolute value. By limiting the q-axis current command with this equation, the phase difference between the d-axis and the voltage command vector can be limited within the range of θvx to 180−θvx when ω> 0, for example.

  When AC motor 1 is an induction motor, θvx = π / 4 or θvx = 3 · π / 4 is obtained as a condition for obtaining the maximum torque. Therefore, if θvx = π / 4 and the q-axis current limit value iqlmt is obtained by the equation (7) and the q-axis current command is limited by iqlmt, the current control cannot be prevented from exceeding due to exceeding the stall torque. Can do.

  Next, the operation of the d-axis current command adjuster 7 will be described. The d-axis current command regulator 7 selects a new d-axis current by selecting a value obtained by adding a predetermined value Δid to a value obtained by removing the high-frequency component of the d-axis current id and a d-axis current command idr that is larger in the negative direction. Output as command idrr. As a result, the deviation ider between idrr and id obtained by the d-axis deviation calculator 9 does not become larger than Δid. Then, even if the d-axis current command idr output from the current command generator 5 suddenly changes in a voltage saturation state in a range larger than id, the current control is not affected at all.

  In an AC motor control device, current control with priority on torque control can be stably continued even when voltage saturation occurs, and voltage saturation is further increased due to an increase in motor speed or a decrease in power supply voltage of the power converter. Even if it is improved, it is possible to avoid an uncontrollable state by accurately limiting the q-axis current command. Therefore, the present invention can be applied to all drive systems using induction motors or permanent magnet synchronous motors, and operation of speed and power supply voltage can be performed. The allowable range can be expanded.

DESCRIPTION OF SYMBOLS 1 AC motor 2 Current detector 3 Power converter 4 Voltage coordinate converter 5 Current command generator 6 q-axis current command limiter 7 d-axis current command adjuster 8 q-axis deviation calculator 9 d-axis deviation calculator 10 q-axis Proportional amplifier 11 d-axis proportional amplifier 12 q-axis integral gain amplifier 13 d-axis integral gain amplifier 14 d-axis velocity proportional amplifier 15 q-axis velocity proportional amplifier 16 switch 17 q-axis integrator 18 d-axis integrator 19 switches 21, 22, 23, 24 Adder

Claims (5)

A current detector that converts and outputs a d-axis current and a q-axis current of each component on the dq axis, which are orthogonal coordinates for rotating the stator current of the AC motor,
When a voltage command in a stationary coordinate system is input and the voltage command is smaller than the maximum voltage that can be output, a voltage according to the voltage command is applied to the AC motor, and the magnitude of the voltage command is the maximum that can be output. A power converter that applies a voltage of approximately the same phase as the voltage command to the AC motor if the voltage is greater than the voltage,
A current command generator for generating and outputting a d-axis current command and a q-axis current command on the dq coordinate;
A d-axis deviation calculator for obtaining a difference between the d-axis current command of the current command generator output and the d-axis current of the current detector;
A q-axis deviation calculator for obtaining a difference between the q-axis current command of the current command generator output and the q-axis current of the current detector;
A d-axis proportional amplifier for multiplying the d-axis deviation calculator output by a proportional gain;
A q-axis proportional amplifier that multiplies the q-axis deviation calculator output by a proportional gain;
A d-axis integrator that integrates the input over time and outputs it after being limited by a predetermined limit value VdLt;
A q-axis integrator that integrates the input over time and limits and outputs a predetermined limit value VqLt;
From the q-axis voltage command that is the sum of the q-axis proportional amplifier output and the q-axis integrator output and the d-axis voltage command that is the sum of the d-axis proportional amplifier output and the d-axis integrator output, In an AC motor current control device comprising a voltage coordinate converter for obtaining a voltage command of
Normal mode in which at least the output of the d-axis deviation calculator is multiplied by a predetermined gain to the input of the d-axis integrator, and the input of the q-axis integrator is only the one obtained by multiplying the output of the q-axis deviation calculator by a predetermined gain. And the input of the d-axis integrator is only the q-axis deviation calculator output multiplied by a predetermined gain, and at least the d-axis deviation calculator output is multiplied by a predetermined gain to the input of the q-axis integrator. A current control device for an AC motor, comprising a switch for switching between the other-axis integration modes. In the switch, the other-axis integration mode is selected when the voltage modulation rate of the power converter is equal to or greater than a predetermined value and the absolute value of the q-axis integrator output is equal to or greater than the d-axis integrator output. The current control device for an AC motor according to claim 1. The VdLt is obtained by adding the d-axis error correction value Vdx to the absolute value of the d-axis voltage value obtained by removing the current differential term from the d-axis characteristic formula of the AC motor, and the VqLt is the q of the AC motor. 3. An AC motor current according to claim 1, wherein a q-axis error correction value Vqx is added to an absolute value of a q-axis voltage value obtained by excluding a current differential term from the shaft characteristic equation. Control device. The second d-axis current command obtained by adding a predetermined value to the d-axis current from which the high frequency component is removed is compared with the d-axis current command of the current command generator output, and the larger one in the negative direction is selected. 4. A d-axis current command adjuster for outputting the output, and the output of the d-axis current command regulator is used as an input to the d-axis deviation calculator instead of the d-axis current command. The AC motor current control device described. The limit value of the q-axis current command is obtained from the voltage vector phase limit value, which is a limit value of the phase from the d-axis of the voltage command vector having the d-axis voltage command and the q-axis voltage command as components, and the maximum voltage. 5. A current of an AC motor according to claim 1, further comprising a q-axis current command limiter that obtains and limits the q-axis current command to the limit value and outputs the limit to the q-axis deviation calculator. Control device.

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