JP5418961B2 - Induction motor control device - Google Patents

Description

  The present invention relates to a control device for controlling an induction motor with high accuracy by vector control.

Vector control is widely known as a high-performance and high-accuracy control method for induction motors. In vector control, detects the current flowing through the electric motor, and calculates the excitation current i _d and a torque current i _q is the current components of the two orthogonal axes. Excitation current i _d is proportional to the secondary magnetic flux phi ₂ of the motor, since the torque current i _q proportional to the output torque T of the electric motor, the secondary magnetic flux of the motor by controlling the excitation current i _d and a torque current i _q And the output torque can be controlled independently.

In vector control, control is generally performed so that the secondary magnetic flux φ ₂ is constant. In this case, the output torque T is given by Equation 1.
[Equation 1]
T = φ ₂ × i _q
Therefore, the output torque T can be controlled linearly by the torque current _iq .

FIG. 6 shows an equivalent circuit of the induction motor converted to the primary side, where R ₁ is the primary resistance, L _σ is the primary leakage reactance, R ₂ is the primary converted value of the secondary resistance, and s is the slip It is. In the figure, the exciting inductance L current flowing to _m correspond to the exciting current, since ideally the secondary magnetic flux phi ₂ in proportion to the magnitude of the exciting current is changed, the excitation current to be proportional to the magnetic flux command Adjust.
However, in practice due to the influence of magnetic saturation of the excitation inductance L _m, it becomes non-linear relationship between the exciting current and the secondary magnetic flux phi _2. From Equation 1, in order to control the output torque T with high accuracy, it is important to control the secondary magnetic flux φ ₂ as instructed, and means to compensate for the above-described magnetic saturation of the excitation inductance L _m is important. Become.

  Here, Patent Document 1 discloses a technique for compensating for the influence of magnetic saturation of excitation inductance. FIG. 7 shows a control device for an induction motor described in Patent Document 1. Description of the same part as that of a conventional vector control device is omitted, and in the following, a part for compensating for the influence of magnetic saturation of excitation inductance is shown. Will be explained with emphasis.

In FIG. 7, reference numeral 101 denotes a power supply device such as an inverter that supplies AC power to the induction motor 200, and the output currents i _u and i _w are detected by the current detector 102, and the biaxial component is detected by the coordinate converter 103. The excitation current i _d and the torque current i _q are converted.
The function unit 104 estimates the secondary magnetic flux φ _d based on the detected excitation current i _d and torque current i _q . In other words, a table representing the relationship between the secondary magnetic flux φ _d and the excitation inductance M _t is prepared inside the function unit 104, and using the excitation inductance M _t corresponding to the magnetic flux command, to estimate the next magnetic flux φ _d.
[Equation 2]
φ _d = M _t · _id

Figure 8 is an example of a characteristic diagram of the excitation inductance M _t, which corresponds to the characteristic of the function 104 in FIG. Although M _t is constant in the region where the secondary magnetic flux φ _d is small, magnetic saturation occurs as the secondary magnetic flux φ _d increases, and M _t gradually decreases.
In the magnetic flux regulator 105 shown in FIG. 7, the excitation current command value i _d ^* is calculated so as to eliminate the deviation between the secondary magnetic flux command value φ _d ^* and the estimated value φ _d and to make them coincide. Reference numeral 107 denotes a direct-axis current regulator that operates so as to make the excitation current i _d coincide with the excitation current command value i _d ^* , and 106 operates so that the torque current i _q matches the torque current command value i _q ^*. It is a horizontal axis current regulator.
With the above configuration, even if a magnetic saturation phenomenon occurs in the excitation inductance M _t , the secondary magnetic flux φ _d can be controlled according to the command value φ _d ^* to improve the torque control accuracy.

Next, FIG. 9 shows another example of a characteristic diagram of the excitation inductance M _t. The characteristic diagram, in flux-weakening region weakened than the rated value the flux command, and has a characteristic with reduced excitation inductance M _t in accordance with the value of the torque current i _q. This eddy current as the secondary magnetic flux phi ₂ are canceled is generated by the torque current i _q, in particular for the effect as the flux command is decreased is increased.
By the above principle, it is possible to control as commanded secondary magnetic flux phi ₂ of the induction motor in any case, it is possible to improve the torque control accuracy.

Japanese Patent No. 3537586 ([0015] to [0026], FIGS. 1 to 3 etc.)

In Patent Document 1, an increase in the influence of magnetic saturation with the excitation current i _d, and by compensating the degradation of the secondary magnetic flux phi ₂ due to eddy currents caused by the torque current i _q in flux weakening region, the torque control precision Has improved. However, the magnetic flux command is in the region near the rated value, does not take into account the effect of changes in the torque current i _q has on the secondary magnetic flux phi _2.

Generally, an induction motor is designed such that a region where magnetic saturation of excitation inductance has already occurred becomes a rated value of magnetic flux. Therefore, changes due to magnetic saturation of the magnetizing inductance is a dominant influence by the excitation current i _d, generated no small influence of magnetic saturation of the excitation inductance the torque current i _q. In particular, when it is desired to control the induction motor with higher accuracy, it is necessary to compensate for the influence of magnetic saturation caused by the torque current _iq .
Accordingly, a problem to be solved by the present invention is to provide a control device for an induction motor that can compensate for not only the exciting current i _d but also the magnetic saturation of the exciting inductance caused by the torque current i _q and enables highly accurate torque control. There is.

In order to solve the above-mentioned problem, a control device according to claim 1 is a coordinate system for decomposing the current of an induction motor driven by a power converter into an excitation current parallel to the magnetic flux of the motor and a torque current orthogonal to the excitation current. A conversion means; a means for calculating an excitation current command value from the magnetic flux command value; a means for calculating a torque current command value from the torque command value; and a d-axis voltage command for matching the detected excitation current value with the excitation current command value. Excitation current adjusting means for outputting a value, and torque current adjusting means for outputting a q-axis voltage command value for making the torque current detection value coincide with the torque current command value, wherein the d-axis voltage command value and the q-axis In the induction motor control apparatus that controls the power converter using a voltage command value,
It is a correction value according to the torque current command value or the magnitude of the torque command value, and the torque control accuracy satisfies the target when a trial operation is performed with the torque current command value or the torque command value being 100%. a correction value calculating means for outputting a Do correction value, the correction value has, an adding means for adding the torque current command value, the torque current command value after correction outputted from said adding means torque current This is input to the adjusting means.

  The correction value calculated by the correction value calculation means is a value proportional to the torque current command value or the square value of the torque command value, as described in claim 2, or described in claim 3. Thus, it is desirable to set the torque current command value or a value proportional to the torque command value.

  According to the present invention, high-accuracy torque control can be realized by compensating not only the excitation current but also the influence of magnetic saturation of the excitation inductance caused by the torque current.

It is a block diagram which shows the structure of embodiment of this invention. It is a block diagram of the torque current command calculating means in FIG. It is a T type equivalent circuit diagram of an induction motor. It is a figure explaining the effect | action of a torque electric current command correction value calculating means. It is a figure explaining the effect | action of a torque electric current command correction value calculating means. It is an equivalent circuit diagram of an induction motor. It is a block diagram which shows the control apparatus of the induction motor described in patent document 1. It is a characteristic view of the excitation inductance of an induction motor. It is a characteristic view of the excitation inductance of an induction motor.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 shows a configuration of a control device according to an embodiment of the present invention. The present embodiment is characterized in that the calculation content of the torque current command value is improved in a general vector control device. In the following embodiment, a case where a speed sensor is installed in the induction motor will be described. However, the present invention does not have a speed sensor, and the speed sensorless that estimates the rotation speed from the applied voltage / current to the induction motor. It can also be applied to control.

  In FIG. 1, the rotational speed detection means 1 calculates the rotational speed from the output signal of a pulse generator as a speed sensor installed in the induction motor 200. The slip frequency calculating means 2 outputs a slip frequency proportional to the torque current command value in order to output torque according to the command value. By adding the rotation speed and the slip frequency calculated as described above by the adding means 3, the primary frequency command value is calculated.

  The phase angle is calculated by integrating the primary frequency command value by the coordinate conversion means 5, and the three-phase output current of the power converter 12 detected by the current detection means 4 is coordinate-converted based on the phase angle. Breaks down into biaxial component excitation current and torque current.

  On the other hand, the rotational speed is input to the torque command calculation means 6. The torque command calculation means 6 calculates the torque command value so that the speed command value and the rotation speed coincide with each other, and the torque current command calculation means 7 calculates the torque current command value from the torque command value and the magnetic flux command value. The configuration and operation of the torque current command calculation means 7 will be described later.

The torque current command value is input to the torque current adjusting means 8, and a q-axis voltage command value is calculated such that the torque current output from the coordinate conversion means 5 matches the torque current command value.
Similarly, the excitation current command calculation means 9 calculates an excitation current command value corresponding to the magnetic flux command value determined from the rotation speed command value. This excitation current command value is input to the excitation current adjusting means 10, and a d-axis voltage command value is calculated so that the excitation current output from the coordinate conversion means 5 matches the excitation current command.

  By converting the d-axis and q-axis voltage command values obtained as described above into a three-phase output voltage command value by the coordinate conversion means 11, and supplying this command value to a power converter 12 such as an inverter. The three-phase AC voltage according to the voltage command value is supplied to the induction motor 200. As a result, a current that matches the excitation current command value and the torque current command value flows to the induction motor 200, and the motor 200 can be controlled with high accuracy.

FIG. 2 is a block diagram showing a configuration of the torque current command calculation means 7, and a dotted line portion in the drawing is a portion newly added by the present embodiment.
The torque current command value is proportional to the torque command value and inversely proportional to the magnetic flux command value. Here, the torque current command value is first calculated by the proportional calculation means 71 from the torque command value and the magnetic flux command value. This process is the same as general vector control.

In the present embodiment, a torque current command correction value calculation means 72 is provided inside the torque current command calculation means 7. The torque current command correction value calculation means 72 outputs a correction value having a magnitude corresponding to the torque current command value obtained by the conventional calculation. Then, a value obtained by adding the correction value to the original torque current command value in the adding means 73 is output to the torque current adjusting means 8 as a final torque current command value, and the power converter 12 is controlled.
With the above processing, even when the torque current changes, the torque can be controlled with high accuracy without being affected by the magnetic saturation of the excitation inductance.

Next, the reason why the torque control accuracy can be improved by this embodiment and the specific configuration method of the torque current command correction value calculation means 72 will be described.
FIG. 3 is a T-type equivalent circuit of the induction motor converted to the primary side, where R ₁ is the primary resistance, L ₁ is the primary leakage reactance, L ₂ is the primary converted value of the secondary leakage reactance, R ₂ Is the primary conversion value of the secondary resistance. FIG. 3 shows an equivalent circuit of the induction motor as in FIG. 6, but the physical meaning of each constant is slightly different. In FIG. 3, a current I ₀ flowing through the mutual inductance M corresponds to a current that creates a magnetic flux that can be formed in the gap between the primary side and the secondary side of the induction motor.
3 and 6, considering that the primary current I ₁ , that is, the current output from the power converter is equal, the absolute value of I ₀ is expressed by Equation 3.

From Equation 3, it can be seen that the absolute value of I ₀ changes according to the square value of the torque current I _q .
Also for the mutual inductance M, magnetic saturation occurs according to the magnitude of the flowing current. When the gap magnetic flux is reduced due to magnetic saturation, the secondary magnetic flux is also reduced by that amount, resulting in a deterioration in torque control accuracy. As is clear from Equation 3, the magnitude of the current flowing through the mutual inductance M is so changed by the torque current I _q, 2 the rotor flux phi ₂ also varies depending on the magnitude of the torque current I _q.
Therefore, in order to control the secondary magnetic flux phi ₂ constant, it is necessary to compensate for the influence of the magnetic saturation due to the torque current I _q.

Next, how to compensate for the effect of magnetic saturation due to torque current will be considered. First, the gap magnetic flux φ _G can be expressed by Equation 4.

To control the secondary magnetic flux phi ₂ constant, with an increase of the torque current i _q, it is necessary to increase the gap magnetic flux phi _G. However, in the region where the magnetic flux command is in the vicinity of the rated value, the magnetic flux command is somewhat large, so that it is easily affected by magnetic saturation. Therefore, even if the increase in the torque current i _q, it is considered that hardly increases the gap magnetic flux phi _G. As a result, error of the gap magnetic flux phi _G is as are the secondary magnetic flux phi ₂ of the error, the secondary magnetic flux phi ₂ will decrease in response to the square value of the torque current i _q.

As described above, even if controlling the excitation current i _d to be constant, so that the secondary magnetic flux phi ₂ with increasing torque current i _q decreases. Since the output torque T of the induction motor is expressed by Equation 1, the torque control accuracy deteriorates as the torque current _iq increases. One method for compensating for this phenomenon is to adjust the excitation current command value i _d ^* according to the magnitude of the torque current i _q to compensate for the decrease in the secondary magnetic flux φ ₂ .
However, since a state where magnetic saturation has already occurred, to compensate for the reduction of the secondary magnetic flux phi ₂ min needs to greatly increase the excitation current i _d, which is not preferable.

Therefore, in this embodiment, as shown in FIG. 2, by adding a correction value corresponding to the current value to the torque current command value, the output torque T is kept constant even when the secondary magnetic flux φ ₂ is reduced. Control to be. To keep the output torque T constant, only the decrease in secondary flux phi ₂ may be increased the torque current command value. Therefore, considering that the secondary magnetic flux phi ₂ decreases according to the square value of the torque current i _q, the correction value should also be proportional to the square of the torque current i _q.

FIG. 4 shows the input / output characteristics of the torque current command correction value calculation means 72 and corresponds to the invention according to claim 2.
The torque current command correction value calculation means receives the torque command value or the torque current command value and outputs a correction value proportional to the square value. For example, the correction pattern is a quadratic curve in which the correction amount is 0 when the torque current command value is 0. This is a correction pattern based on the above-described theory, and the effect of improving the torque control accuracy can be most expected.

  In this example, for the optimum correction value, for example, a trial operation is performed in a state where the torque current command value is 100%, and the correction value at that time (corresponding to A in FIG. 4) so that the torque control accuracy satisfies the target. ) Should be adjusted. Since the torque current command value is proportional to the torque command value, even if the torque command value is input instead of the torque current command value, the same effect can be obtained.

FIG. 5 shows another input / output characteristic of the torque current command correction value calculation means 72 and corresponds to the invention according to claim 3.
This torque current command correction value calculation means outputs a correction value proportional to the input value. That is, when the input value is 0, a linear correction pattern in which the correction amount is 0 is obtained. As in FIG. 4, the input may be either a torque command value or a torque current command value.

  Since the input / output characteristics shown in FIG. 5 are not strictly based on the theory, the effect of improving the torque control accuracy is low as compared with the invention of claim 2. However, since the calculation load of the CPU for calculating the correction value is lightened, it is effective when it is desired to minimize the increase in the calculation amount.

1: Rotational speed detection means 2: Slip frequency calculation means 3: Addition means 4: Current detection means 5: Coordinate conversion means 6: Torque command calculation means 7: Torque current command calculation means 71: Proportional calculation means 72: Torque current command correction Value calculation means 73: Addition means 8: Torque current adjustment means 9: Excitation current command calculation means 10: Excitation current adjustment means 11: Coordinate conversion means 12: Power converter 200: Induction motor

Claims (3)

Coordinate conversion means for decomposing the current of the induction motor driven by the power converter into an excitation current parallel to the magnetic flux of the motor and a torque current orthogonal to the excitation current, and means for calculating the excitation current command value from the magnetic flux command value A means for calculating a torque current command value from the torque command value, an excitation current adjusting means for outputting a d-axis voltage command value for making the excitation current detection value coincide with the excitation current command value, and a torque current detection value as a torque A torque current adjusting unit that outputs a q-axis voltage command value that matches the current command value, and controls the power converter using the d-axis voltage command value and the q-axis voltage command value. In the control device,
It is a correction value according to the torque current command value or the magnitude of the torque command value, and the torque control accuracy satisfies the target when a trial operation is performed with the torque current command value or the torque command value being 100%. a correction value calculating means for outputting a Do correction value, the correction value has, an adding means for adding the torque current command value, the torque current command value after correction outputted from said adding means torque current A control device for an induction motor, wherein the control device inputs the adjustment means. In the induction motor control device according to claim 1,
The control apparatus for an induction motor, wherein the correction value calculation means outputs a correction value proportional to a torque current command value or a square value of the torque command value. In the induction motor control device according to claim 1,
The control apparatus for an induction motor, wherein the correction value calculation means outputs a torque current command value or a correction value proportional to the torque command value.

Images