JP2018057170A - Controller for alternating electric motor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a stable current control with a torque as a priority when a voltage is saturated.SOLUTION: The controller includes: a q-axis current command limiter which limits a q-axis current command to be a specific value in a current control of a dq-axis by a regular proportional integral amplification; a d-axis current command regulator which regulates a d-axis current deviation to be smaller than the specific value; a limited q-axis integrator for integrating the current error between both the axes when the voltage is saturated; and a d-axis integrator for integrating the current error of the q-axis alone when the voltage is saturated.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 converted component. The d-axis is generally defined in the direction of the secondary linkage magnetic flux vector of the AC motor 1 when the AC motor 1 is an induction motor, and generally rotates 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 gain amplifier 11 to become a d-axis proportional component. The ider is amplified by the d-axis integral gain amplifier 13 and then time-integrated by the limited d-axis integrator 25 to become a d-axis integral component. The deviation iqr between iqr and iq obtained by the q-axis deviation calculator 8 is amplified by a predetermined factor by the q-axis proportional gain amplifier 10 to become a q-axis proportional component. Further, iqer is amplified by the q-axis integral gain amplifier 12 and then time-integrated with restriction by the restricted q-axis integrator 17 to become a q-axis integral component.

  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.

The q-axis interference calculator 19 calculates and outputs the third and fourth terms on the right side of the equation (2) or (4). In this case, in the case of FIG. 2, a d-axis current command idr is used instead of the d-axis current id. The d-axis interference calculator 20 calculates and outputs the third term on the right side of the equation (1) and the fourth term on the right side of the equation (4) or (3). At that time, in the case of FIG. 2, the q-axis current command iqr is used instead of the q-axis current iq.

  The adder 21 calculates the sum of the q-axis proportional gain amplifier 10 output, the restricted q-axis integrator 17 output, and the q-axis interference calculator 19 output, and outputs a q-axis voltage command vqr. The adder 22 calculates the sum of the output of the d-axis proportional gain amplifier 11, the output of the limited d-axis integrator 25, and the output of the d-axis interference calculator 20, 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 in accordance with 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 from the power converter 3, the maximum voltage is applied to the AC motor 1. Apply to.

  In the current control shown in FIG. 2, if 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.

  A signal obtained by amplifying the d-axis current deviation ider by the d-axis speed proportional amplifier 14 by the adder 23 is added to the input of the limited q-axis integrator 17. 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 velocity 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 an unrestricted d-axis integrator 18 instead of the limited d-axis integrator 25. A switch 16 is inserted at the input of the d-axis integral gain amplifier 13, and the switch 16 is used when the magnitude of the input voltage command of the power converter 3 is sufficiently smaller than the maximum output possible voltage of the power converter 3. Shaft current deviation ider, otherwise 0 is output. Further, the q-axis interference calculator 19 and the d-axis interference calculator 20 are not provided.

  Even when the switch 16 is off, the d-axis current deviation is reduced to 0 by correcting the q-axis voltage command by the restricted 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 reaches a voltage saturation state that exceeds the maximum output voltage of the power converter 3, the output of the limited q-axis integrator 17 is 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 orthogonal to the magnetic flux axis, the torque of one of the AC motor can be controlled by controlling the q-axis current, so that the torque control can be maintained even if 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 of the axes cannot be performed, and a desired output torque of the AC motor cannot be obtained. In the prior art shown in FIG. 3, the q-axis priority control can be performed even when the voltage is saturated, and a desired output torque can be obtained. Therefore, the above problem can be solved, but there are the following problems.

  FIG. 4 shows voltage command vectors vr and vr1 at the time of voltage saturation and voltage vectors v and v1 applied to the AC motor 1 in the prior art of FIG. The voltage vectors v and v1 are limited within a voltage output limit circle, which 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 voltage saturation and the q-axis integrator 17 is limited. The limit value is 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 is 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.

  In Patent Document 2, in order to solve the above problem, an M axis that coincides with the primary linkage magnetic flux vector of an AC motor and a T axis that is orthogonal to the M axis are introduced, and the MT axis is replaced with the MT axis in the same manner as in FIG. The configuration has the following problems. T-axis current priority control can be used, but when the MT-axis current command is obtained from the dq-axis current command by rotating coordinate conversion, the q-axis current does not match the command due to voltage saturation, and the 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 change suddenly, current control may become unstable if the phase of the MT axis 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, even if the q-axis current is increased, the torque may not be increased, resulting in a divergence state and the control becomes impossible. In the case of a permanent magnet synchronous motor, the voltage vector may be too close to the d-axis, which makes control 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 gain amplifier 11 becomes large, and it is corrected. In addition, 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 converts the stator current of an AC motor into a d-axis current and a q-axis current of each component on the dq axis, which is an orthogonal coordinate for rotating, in the current control of the AC motor. If 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. If the magnitude is larger than the maximum voltage that can be output, a power converter that applies a voltage of the magnitude of the maximum voltage to the AC motor, and a d-axis current command and a q-axis current command on the dq coordinate are generated. A current command generator for output, 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, and q of the current command generator output Axis current command and q-axis power of the current detector A q-axis deviation calculator for obtaining a difference between the output, a d-axis proportional gain amplifier for multiplying the output of the d-axis deviation calculator by a proportional gain, a q-axis proportional gain amplifier for multiplying the output of the q-axis deviation calculator by a proportional gain, When the voltage command is smaller than a predetermined value, the d-axis deviation calculator output is selected. When the voltage command is larger than the predetermined value, a switch is selected and output, and the switch output is multiplied by an integral gain. A d-axis integral gain amplifier, a q-axis integral gain amplifier that multiplies the q-axis deviation calculator output by an integral gain, and amplifies the d-axis deviation calculator output with a gain proportional to the rotational angular frequency of the dq axis. An axial velocity proportional amplifier, a q-axis velocity proportional amplifier that amplifies the q-axis deviation calculator output with a gain proportional to the rotational angular frequency of the dq-axis, the q-axis integral gain amplifier output, and the d-axis velocity proportional amplifier A limited q-axis integrator that integrates the sum of forces with a limit, a d-axis integrator that integrates the sum of the d-axis integral gain amplifier output and the q-axis speed proportional amplifier output, and the q-axis of the AC motor A term relating to the d-axis current in the voltage characteristic equation of q is a q-axis interference computing unit that calculates the d-axis current command and a term relating to the q-axis current in the voltage characteristic equation on the d-axis of the AC motor. A d-axis interference calculator that calculates using an axis current command, a q-axis voltage command that is the sum of the q-axis proportional gain amplifier output, the q-axis integrator output, and the q-axis interference calculator output, and the d-axis A voltage coordinate converter that obtains a voltage command in the stationary coordinate system from a d-axis voltage command that is the sum of a proportional gain amplifier output, the d-axis integrator output, and the d-axis interference calculator output;

  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 output from the current command generator, and the larger one in the negative direction is selected. The d-axis current command adjuster is output, and the output of the d-axis current command adjuster is used as an input to the d-axis deviation calculator and the q-axis interference calculator instead of the d-axis current command.

  Further, the limit value of the q-axis current command 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. And a q-axis current command limiter that limits the q-axis current command to the limit value and outputs it to the q-axis deviation calculator and the d-axis interference calculator.

  The limit value of the limited q-axis integrator can be reduced by combining the d-axis interference calculator and the q-axis interference calculator with the prior art shown in FIG. Even when the direction of the voltage vector is far away from the q-axis, the change Δvdr in the d-axis voltage command necessary for changing the voltage vector phase can be reduced.

  In addition, 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.

  The q-axis current command limiter can limit the voltage command vector from approaching the d-axis 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 to output 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 to an appropriate value with the q-axis current command limiter.

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 in FIG. 3 will be omitted, and the q-axis current command limiter 6, d-axis current command adjuster 7, q-axis interference calculator 19 and d-axis interference calculator 20 will be described.

  The q-axis interference computing unit 19 obtains and outputs the third and fourth terms on the right side of the equations (2) and (4) as in the case of FIG. At this time, in the case of FIG. 1, the d-axis current command idrr is used instead of the d-axis current id, but the d-axis current id may be used. The d-axis interference calculator 20 calculates and outputs the third and fourth terms on the right side of equation (1) or the third term on the right side of equation (3). In this case, in the case of FIG. 1, the q-axis current command iqrr is used instead of the q-axis current iq, but the q-axis current iq may be used. With the q-axis interference calculator 19 and the d-axis interference calculator 20, the restricted q-axis integrator 17 and the d-axis integrator 18 need only compensate for the voltage drop due to the winding resistance value R1. Since the value is relatively small, the limit value of the limited q-axis integrator 17 can be set as small as vqlmt in FIG. Then, 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 the 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. When the AC motor 1 is a permanent magnet synchronous motor, the q-axis current limit value is used to limit the phase difference between the d-axis and the voltage command vector to θvx.

  If the magnitude of the voltage vector is the maximum voltage Em that can be output from the power converter 3 and the phase is θvx, the voltage is expressed by equation (5). If the current limit value is Im, it can be expressed by equation (6) in the limited state. By substituting Eqs. (5) and (6) into Eqs. (3) and (4) with p = 0 in a steady state and ignoring R1, the relational expression of Eq. (7) can be obtained. This expression indicates that the magnitude of the current vector should be limited to Im in order to set the voltage phase to θvx. Therefore, the current vector magnitude limit value Im is obtained from the maximum output voltage Em of the power converter 3 and the phase difference limit value θvx by the equation (7), and the q-axis current limit value iqlmt is obtained by the equation (8). If the q-axis current command is limited at, the phase difference of the voltage command vector from the d-axis can be limited between θvx and π−θvx, and the voltage command vector can be prevented from approaching the d-axis, It can be prevented that the current control is disabled.

  When AC motor 1 is an induction motor, p = 0 is set in a steady state, R1 is ignored, (5) is substituted into Eqs. (1) and (2), and φ2 = M · id. Substituting and deriving the condition for obtaining the maximum torque yields θvx = π / 4 or θvx = 3 · π / 4. Therefore, if θvx = π / 4 and the q-axis current limit value iqlmt is obtained by the equation (9) 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. In consideration of ignoring R1 and other constant errors, it is desirable to set θvx to a value larger than π / 4.

  Next, the operation of the d-axis current command adjuster 7 will be described. The d-axis current command adjuster 7 selects a new d-axis current by selecting a value obtained by removing a high-frequency component of the d-axis current id and adding a predetermined value Δid 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 AC motor control devices, current control with priority on torque control can be continued stably even when voltage saturation occurs, and voltage saturation is further increased due to an increase in motor speed and a decrease in power supply voltage of the power converter. Even if it is improved, it is possible to avoid the 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 gain amplifier 11 d-axis proportional gain 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 restricted q-axis integrator 18 d-axis integrator 19 q-axis Interference calculator 20 d-axis interference calculator 21, 22, 23, 24 Adder 25 Limited d-axis integrator

Claims (3)

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 the maximum voltage magnitude to the AC motor if greater than a 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 a q-axis current command of the current command generator output and a q-axis current of the current detector;
A d-axis proportional gain amplifier for multiplying the d-axis deviation calculator output by a proportional gain;
A q-axis proportional gain amplifier for multiplying the q-axis deviation calculator output by a proportional gain;
A switch that selects and outputs the d-axis deviation calculator output when the voltage command is smaller than a predetermined value, and selects and outputs 0 when the voltage command is larger than the predetermined value;
A d-axis integral gain amplifier for multiplying the switch output by an integral gain;
A q-axis integral gain amplifier for multiplying the q-axis deviation calculator output by an integral gain;
A d-axis velocity proportional amplifier that amplifies the d-axis deviation calculator output with a gain proportional to the rotational angular frequency of the dq axis;
A q-axis velocity proportional amplifier that amplifies the q-axis deviation calculator output with a gain proportional to the rotational angular frequency of the dq axis;
A restricted q-axis integrator that integrates the sum of the q-axis integral gain amplifier output and the d-axis velocity proportional amplifier output with restriction;
A d-axis integrator for integrating the sum of the d-axis integral gain amplifier output and the q-axis velocity proportional amplifier output;
A q-axis interference calculator for calculating a term related to the d-axis current in the voltage characteristic equation on the q-axis of the AC motor by the d-axis current command;
A d-axis interference computing unit that computes a term related to the q-axis current of the voltage characteristic equation on the d-axis of the AC motor using the q-axis current command;
The q-axis voltage command of the sum of the q-axis proportional gain amplifier output, the q-axis integrator output, and the q-axis interference calculator output, the d-axis proportional gain amplifier output, the d-axis integrator output, and the d-axis A control apparatus for an AC motor, comprising: a voltage coordinate converter that obtains a voltage command in the stationary coordinate system from a d-axis voltage command that is the sum of the interference calculator output.
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 output from the current command generator, and the larger one in the negative direction is selected. Output d-axis current command adjuster, and the output of the d-axis current command regulator is used as an input to the d-axis deviation calculator or the q-axis interference calculator instead of the d-axis current command. The control device for an AC motor according to claim 1. 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. And a q-axis current command limiter that limits the q-axis current command to the limit value and outputs the command to the q-axis deviation calculator and the d-axis interference calculator. 2. The control apparatus for an AC motor according to 2.

Images