Induction motor speed control device

Abstract

To provide a speed controller for an induction motor that can achieve a high-speed high-accuracy secondary magnetic flux response even to a sudden change in secondary magnetic flux command value.SOLUTION: A speed controller 1 for an induction motor using slip frequency type vector control includes a d-axis current generation unit 2 for calculating a d-axis current command value ids*. The d-axis current generation unit 2 calculates a secondary magnetic flux detection value from a d-axis current detection value ids, calculates a magnetization-component current feed-forward output ids1* from a d-axis secondary magnetic flux command value (Φdr / M)*, calculates a difference between the secondary magnetic flux detection value and the d-axis secondary magnetic flux command value (Φ dr / M)* as a secondary magnetic flux deviation φe, calculates a secondary magnetic flux feedback loop output ids2* from the secondary magnetic flux deviation φe, and weight and synthesize the magnetization-component current feed-forward output ids1* and the secondary magnetic flux feedback loop output ids2* at a proportion according to the secondary magnetic flux deviation φe to calculate the d-axis current command value ids*.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] This specification discloses a speed control device that mainly controls the speed of an induction motor used in a spindle in axis control of an NC machine tool or the like. [Background technology]

[0002] Generally, squirrel-cage induction motors (hereafter simply referred to as "induction motors") that can secure a wide constant output range are often used as drive motors for the spindles of NC machine tools. Induction motors have a robust structure, but since they cannot directly control the current on the secondary (rotor) side or the magnetic flux generated by the current, they generally have inferior controllability of motor torque compared to magnet-type synchronous motors, which do not generate secondary current.

[0003] In the control of induction motors, in the constant output region where the speed exceeds the base speed, in order to suppress the primary (stator) voltage, the higher the speed, the more control is required to reduce the secondary magnetic flux (hereafter referred to as "field weakening control"). Also, when the main shaft (induction motor) is not used, control that maintains the secondary magnetic flux in a greatly reduced state (hereafter referred to as "low noise field weakening control") is applied for the purpose of saving power and reducing noise.

[0004] Fig. 6 is a block diagram showing an example of a conventional speed control device using slip frequency type vector control for an induction motor (hereinafter, sometimes simply referred to as a "motor"). Since this specification deals with technology that controls induction motors, a controlled plant driven by an induction motor 50 is not shown, and a position / speed detector 60 that detects the rotational speed ωm of the motor is connected to the motor.

[0005] Next, the operation of the conventional speed control device 70 will be described. A higher-level device (not shown) issues a speed command value ωm * is input. Speed ​​command value ωm *The motor rotation speed ωm is subtracted from the subtractor 20. The speed deviation output from the subtractor 20 is proportionally and integrally amplified by the speed loop gain Gv(s) in the speed deviation amplifier 21 to obtain the motor torque command value τc * Here, s is the Laplace transform operator, and Gv(s) represents a transfer function expressed using the Laplace operator.

[0006] Here, the d-axis and q-axis voltage equations used in the known vector control of induction motors are shown in Equation (1) and Equation (1.1). Note that the d-axis may be described as the magnetization component and the q-axis as the torque component, but hereafter the terms d-axis and q-axis will be mainly used.

[0007]

number

[0008] where P (=d / dt): differential operator, Vds: d-axis primary voltage, Vqs: q-axis primary voltage, ids: d-axis primary current, iqs: q-axis primary current, M: mutual inductance, Ls: primary inductance, Lr: secondary inductance, ls: primary leakage inductance, lr: secondary leakage inductance, ω: current angular velocity, ωre: motor electrical angular velocity, ωse: slip angular velocity, Rs: primary resistance, Rr: secondary resistance, Φdr / M: d-axis secondary magnetic flux (current), φqr / M: q-axis secondary magnetic flux (current).

[0009] Rr is the secondary resistance in the three-phase voltage equation of a known induction motor. 2 is the secondary resistance after 3-phase to 2-phase (d, q) transformation, and the relationship between the two is generally shown in the third line of equation (1.1).

[0010] In the following, for convenience, we will refer to 2is called the "secondary resistance", Φdr / M is called the "d-axis secondary magnetic flux", and Φqr / M is called the "q-axis secondary magnetic flux". Generally, in vector control of an induction motor, the q-axis secondary magnetic flux is controlled to be identically Φqr / M = 0. To achieve this, from equation (1), it is necessary to control the d-axis secondary magnetic flux Φdr / M and slip angular velocity ωse as shown in the following equations (2.1) and (2.2).

[0011]

number

[0012] As a result, the output torque τ of the induction motor is expressed by the formula (3), and high torque control performance can be realized. Note that p is the number of pole pairs.

[0013]

number

[0014] The torque current converter 22 converts the q-axis current command value iqs, which is the torque current, from the torque expression of the induction motor according to equation (3). * The q-axis current control unit 24 calculates the q-axis current command value iqs * A subtractor 23 subtracts the q-axis current (detected value) iqs from the d-axis current command value ids to calculate the q-axis current deviation, which is then amplified. * Furthermore, the q-axis current control unit 24 adds the amplified value of the q-axis current deviation and the q-axis feedforward voltage, and outputs a q-axis voltage command value Vqs.

[0015] The secondary magnetic flux generating unit 25 normally generates a d-axis secondary magnetic flux command value (Φdr / M) in accordance with the motor rotation speed ωm. * In general, the magnitude of the motor rotation speed ωm is determined by the base speed ω B In the following cases, the rated excitation current I 0 max is selected ((Φdr / M) * =I 0 max), base velocity ωB At the motor rotation speed ωm, in order to keep the output constant, (Φdr / M) * =(ω B / ωm)I 0 It is determined to be max.

[0016] The noise reduction field weakening command Fwnz is a binary command value sent from a higher-level device (not shown) to the secondary magnetic flux generating unit 25 depending on whether the spindle is moving or not. When Fwnz:OFF, the secondary magnetic flux generating unit 25 generates the d-axis secondary magnetic flux command value (Φdr / M) depending on the motor rotation speed ωm as described above. * On the other hand, when Fwnz is ON, the d-axis secondary magnetic flux command value (Φdr / M) is set to execute low noise field weakening. * Greatly reduces output.

[0017] The d-axis current generating unit 26 generates a d-axis secondary magnetic flux command value (Φdr / M) * From the d-axis current command value ids * 7 is a block diagram showing the internal configuration of the d-axis current generating unit 26. * The low noise field weakening command Fwnz: OFF → ON is required to rapidly reduce the noise. On the other hand, even when Fwnz: ON → OFF, the reduced d-axis secondary magnetic flux command value (Φdr / M) * The d-axis secondary magnetic flux command value (Φdr / M) according to the motor rotation speed ωm * It is required that the system be restored as quickly as possible and return to a steady state.

[0018] For this reason, the d-axis current generating unit 26 configures a secondary magnetic flux loop in order to speed up the command response of the d-axis secondary magnetic flux (Φdr / M). * The d-axis secondary magnetic flux (Φdr / M) is subtracted from the d-axis current command value ids to obtain the secondary magnetic flux deviation φe. The secondary magnetic flux deviation amplifier 101 performs operational amplification (for example, proportional integral compensation) to obtain the d-axis current command value ids * The d-axis secondary magnetic flux (Φdr / M) used for the secondary magnetic flux feedback is calculated by multiplying the d-axis current (detected value) ids by a transfer function block 102, which is the transfer characteristic of equation (2.1).

[0019] The d-axis current control unit 28 outputs the d-axis current command value ids * The d-axis current (detected value) ids is subtracted by a subtractor 27, and the deviation is amplified by the output of the d-axis current deviation amplifier, and the current angular velocity ω, q-axis current command value iqs * The d-axis voltage command value Vds is output by adding the d-axis feedforward voltage generated from

[0020] The divider 29 divides the q-axis current command value iqs * is divided by the d-axis secondary magnetic flux (Φdr / M) output from the d-axis current generating unit 26, and the output is input to the amplifier 30 as a time constant parameter: R 2 / M 0 The motor rotation speed ωm is amplified by an amplifier 31 to become a motor electrical angular velocity ωre, multiplied by the number p of pole pairs. An adder 32 adds the motor electrical angular velocity ωre and the slip angular velocity ωse to output a current angular velocity ω. An integrator 33 receives the current angular velocity ω as an input and outputs a current phase angle θ.

[0021] A two-phase to three-phase converter 34 performs well-known two-phase to three-phase conversion at a current phase angle θ to d, q-axis voltage command values ​​Vds, Vqs, performs power conversion using PWM or the like, and outputs three-phase input voltages Vus, Vvs, Vws that drive an induction motor. On the other hand, a three-phase to two-phase converter 35 performs well-known three-phase to two-phase conversion at a current phase angle θ to three-phase currents ius, ivs, iws detected by a current detector (not shown), and outputs d, q-axis currents ids, iqs.

[0022] The above is the block configuration and operation of the conventional induction motor speed control device 70. The d-axis secondary magnetic flux command value (Φdr / M) * In response to a sudden change in , a jump occurs in the response of the d-axis secondary magnetic flux (Φdr / M), and high-speed and high-precision secondary magnetic flux control cannot be realized by adjusting the amplification factor of the secondary magnetic flux error amplifier 101. Summary of the Invention [Problem to be solved by the invention]

[0023] 8 to 10 are graphs showing an example of the time response of a conventional speed control device 70. The horizontal axis is the time axis represented by the number of calculations k (calculation period 0.2 ms). In this example, the upper device issues a low noise field weakening command Fwnz:ON during the period k<0, the command is released (Fwnz:OFF) at k=0, and a step speed command value ωm for the maximum speed (top speed) at k=1000. * is entered.

[0024] For such a time series input, the upper diagram of Fig. 8 shows the speed command value ωm * and the motor rotation speed ωm, and the lower diagram shows the torque command value τc * The response of the output torque τ to the torque command value τc * is limited by a limit value corresponding to the current limit of the control device. * and d-axis secondary magnetic flux (Φdr / M), and the lower diagram shows the d-axis current command value ids * Furthermore, Fig. 10 shows an enlarged view of the secondary magnetic flux deviation φe.

[0025] As described above, in the conventional speed control device 70 for an induction motor having a d-axis current generating unit 26, a sudden d-axis secondary magnetic flux command value (Φdr / M) * The noise reduction field weakening command Fwnz is switched ON and OFF with the change of the maximum speed (top speed) step speed command value ωm * However, a jump occurred in the response of the d-axis secondary magnetic flux (Φdr / M), resulting in an extended settling time.

[0026] Furthermore, the jump in the response of the d-axis secondary magnetic flux (Φdr / M) during acceleration causes excessive flux weakening, which reduces the output torque τ too much in the high-speed range, resulting in a problem of longer acceleration time. Therefore, in this specification, the d-axis secondary magnetic flux command value (Φdr / M) *This invention discloses a speed control device for an induction motor equipped with a d-axis current generator that can realize high-speed and high-precision d-axis secondary magnetic flux (Φdr / M) response even to abrupt changes in current. [Means for solving the problem]

[0027] The speed control device for an induction motor disclosed in this specification is a d-axis secondary magnetic flux command value (Φdr / M) * The d-axis current command value ids1 calculated from * (i.e., magnetization component current feedforward output) and the d-axis current command value ids2, which is the secondary flux loop output. * (i.e., secondary magnetic flux feedback loop output) and are synthesized according to the magnitude of the secondary magnetic flux deviation φe to obtain the final d-axis current command value ids * Generate. Effect of the Invention

[0028] In the speed control device for an induction motor disclosed in this specification, when switching the field weakening command, a d-axis current command value is generated that mainly utilizes the secondary magnetic flux feedback loop output, and when the magnetic flux transitions in the constant output region, a d-axis current command value is generated that mainly utilizes the magnetization component current feedforward output that uses the transfer characteristics between the secondary magnetic flux and the d-axis current. As a result, the d-axis secondary magnetic flux command value (Φdr / M) * Even with a sudden change in the d-axis secondary magnetic flux (Φdr / M), a high-speed and high-precision response can be achieved, and the acceleration time in response to the step speed command value at the maximum speed (top speed) can be shortened. [Brief description of the drawings]

[0029] [Figure 1] 4 is a block diagram showing a configuration example of a d-axis current generating unit. FIG. [Diagram 2] FIG. 2 is a block diagram showing an example of a schematic configuration of a speed control device. [Diagram 3] 3 is an example of the speed-torque response to a step speed command of the speed control device of FIG. 1 and FIG. 2. [Figure 4]3 is an example of a response operation of a d-axis current generating unit of the speed control device of FIG. 1 and FIG. 2 to a step speed command. [Diagram 5] 3 is another example of a response operation of the d-axis current generating unit of the speed control device of FIG. 1 and FIG. 2 to a step speed command. [Figure 6] FIG. 1 is a block diagram showing an example of a schematic configuration of a conventional speed control device. [Figure 7] FIG. 1 is a block diagram showing an example of the configuration of a conventional d-axis current generating unit. [Figure 8] 8 is an example of the speed-torque response to a step speed command of the speed control device of FIG. 6 and FIG. 7. [Figure 9] 8 is an example of a response operation of a d-axis current generating unit of the speed control device of FIG. 6 and FIG. 7 to a step speed command. [Figure 10] 8 is another example of a response operation of the d-axis current generating unit of the speed control device of FIG. 6 and FIG. 7 to a step speed command. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0030] The speed control device will be described below with reference to the drawings. Fig. 2 is a block diagram showing an example of the general configuration of the speed control device 1 for an induction motor. Since the parts other than the d-axis current generating unit 2 are similar to those of the speed control device in Fig. 6, the same reference numbers are used and the description will be omitted.

[0031] FIG. 1 is a block diagram showing an example of the configuration of the d-axis current generating unit 2 of the speed control device 1 of FIG. 2. For convenience, the output of the secondary magnetic flux error amplifier 101 is referred to as a d-axis current command value ids2. * The name has been changed to d-axis current command value ids2 * is the output of the secondary magnetic flux feedback loop, and therefore functions as the "secondary magnetic flux feedback loop output." The transfer function block 3 is the inverse transfer function of the transfer function block 102, and the d-axis secondary magnetic flux command value (Φdr / M) * The d-axis current command value ids1 corresponding to * The d-axis current command value ids1 is calculated and output as a current feedforward. *functions as the "magnetization component current feedforward output."

[0032] The synthesis calculation unit 4 synthesizes the two d-axis current command values ​​ids1 * and ids2 * From the final d-axis current command value ids * This is a block that calculates the above. The synthesis calculation unit 4 in the figure shows the relationship between "input: secondary magnetic flux deviation φe" and "output: weighting coefficient γ". The weighting coefficient γ is a rational number in the range of 0≦γ≦1, with γ=1 if |φe|≦φe_min, and γ=0 if |φe|≧φe_max. Furthermore, for φe where φe_min<|φe|<φe_max, the weighting coefficient γ is determined by linear interpolation as shown in the figure.

[0033] This (φe-γ) characteristic is because the secondary magnetic flux deviation φe increases when the low noise field weakening command Fwnz is switched ON⇔OFF. * On the other hand, when the magnetic flux transition occurs due to the speed change in the constant power region, the secondary magnetic flux deviation φe that occurs becomes small, so the d-axis current command value ids1 that constitutes the current feedforward is * This means placing weight on

[0034] Final d-axis current command value ids * ids1 * and ids2 * This d-axis current command value ids is calculated using equation (4). * is the output of the d-axis current generator 2.

[0035]

number

[0036] 3 to 5 are diagrams showing an example of the time response of the speed control device 1 of FIG. 1 and FIG. 2. The time series input is set in the same manner as in FIG. 8 to FIG. 10. The upper diagram of FIG. 4 shows the d-axis secondary magnetic flux command value (Φdr / M) *The relationship between the d-axis secondary magnetic flux (Φdr / M) and the step speed command value ωm at the maximum speed (top speed) when the noise reduction field weakening command Fwnz is switched from ON to OFF. * At the time of input, d-axis secondary magnetic flux command value (Φdr / M) * changes suddenly, but no jump occurs in the d-axis secondary magnetic flux (Φdr / M) response, and settling is achieved in a short time compared to Figure 9 of the conventional example.

[0037] Furthermore, during acceleration, the d-axis secondary magnetic flux (Φdr / M) response does not jump, so appropriate magnetic flux weakening is realized and the desired output torque τ can be generated in the high speed range. Therefore, as shown in the upper diagram of Figure 3, the step speed command value ωm * The speed response to has been improved, and the acceleration time has been shortened compared to the conventional example shown in the upper graph of Fig. 8. Furthermore, comparing the lower graph of Fig. 3 with the lower graph of Fig. 8 of the conventional example, it can be confirmed that the output torque τ in the high speed range has become larger.

[0038] The upper graph in Fig. 5 shows an enlarged view of the secondary magnetic flux deviation φe, and it can be seen that the d-axis secondary magnetic flux (Φdr / M) response settles in a short time. The lower graph in Fig. 5 shows the transition of the weighting coefficient γ determined by the synthesis calculation unit 4 in response to the time series input of this example. [Explanation of symbols]

[0039] 1 speed control device, 2 d-axis current generating unit (present invention), 3 transfer function block, 4 synthesis calculation unit, 20 subtractor, 21 speed error amplifier, 22 torque current converter, 23 subtractor, 24 q-axis current control unit, 25 secondary magnetic flux generating unit, 26 d-axis current generating unit (conventional), 27 subtractor, 28 d-axis current control unit, 29 divider, 30, 31 amplifier, 32 adder, 33 integrator, 34 2-phase to 3-phase conversion unit, 35 3-phase to 2-phase conversion unit, 50 induction motor, 60 position / speed detector, 70 speed control device (conventional), 100 subtractor, 101 secondary magnetic flux error amplifier, 102 transfer function block.

Claims

1. In a speed control device for an induction motor using slip frequency type vector control, A d-axis current generating unit is provided to calculate a d-axis current command value based on a secondary magnetic flux command value and a d-axis current detection value, and the d-axis current generating unit is applying a predetermined first transfer function to the d-axis current detection value to calculate a secondary magnetic flux detection value; applying an inverse transfer function of the first transfer function to the secondary magnetic flux command value to calculate a magnetization component current feedforward output; A difference between the secondary magnetic flux detection value and the secondary magnetic flux command value is calculated as a secondary magnetic flux deviation; applying a second predetermined transfer function to the secondary magnetic flux deviation to calculate a secondary magnetic flux feedback loop output; a weighted addition of the magnetization component current feedforward output and the secondary magnetic flux feedback loop output at a ratio corresponding to the secondary magnetic flux deviation to calculate the d-axis current command value; the d-axis current generating unit performs weighted addition of the magnetization component current feedforward output and the secondary magnetic flux feedback loop output so that, as the absolute value of the secondary magnetic flux deviation becomes smaller, the ratio of the magnetization component current feedforward output becomes larger and the ratio of the secondary magnetic flux feedback loop output becomes smaller, and, as the absolute value of the secondary magnetic flux deviation becomes larger, the ratio of the magnetization component current feedforward output becomes smaller and the ratio of the secondary magnetic flux feedback loop output becomes larger.

2. A speed control device for an induction motor comprising:

2. 2. The speed control device for an induction motor according to claim 1, the d-axis current generating unit, as the weighted addition, uniquely determines a weighting coefficient γ in the range of 0 to 1 for the magnitude of the secondary magnetic flux deviation, and adds a value obtained by multiplying the magnetization component current feedforward output by the weighting coefficient γ and a value obtained by multiplying the secondary magnetic flux feedback loop output by (1-γ).

3. 3. The speed control device for an induction motor according to claim 2, a d-axis current generating unit that sets the weighting factor γ to 0 when the absolute value of the secondary magnetic flux deviation is equal to or greater than a specified upper limit, sets the weighting factor γ to 1 when the absolute value of the secondary magnetic flux deviation is equal to or less than a specified lower limit, and sets the weighting factor γ to a value that is larger in proportion to the absolute value of the secondary magnetic flux deviation when the absolute value of the secondary magnetic flux deviation exceeds the lower limit and is less than the upper limit.

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