JP3164748B2 - Induction motor control device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a control device for an induction motor, and more particularly, to a control device for an induction motor which detects a primary current of the induction motor and feeds back a current detection value to control the induction motor.

[0002]

2. Description of the Related Art Conventionally, various control devices have been proposed for controlling an induction motor, particularly a three-phase induction motor. In particular, in recent years, inverter technology has made it possible to easily create alternating current of any amplitude and frequency as a motor drive power supply, and a processor capable of high-speed digital operation has also been developed. Has been

[0003] Among them, the instantaneous value of the primary current flowing through the induction motor is detected, the next control value is calculated from various values such as the current value, and the control signal is output to the inverter. A method of controlling the induction motor every time has been proposed. For example, there is a proposal of an "instantaneous space magnetic flux vector control method" proposed in Nagaoka University of Technology Research Report, No. 8, 1986, pp. 43-50, by Isao Takahashi.

This control method is based on a magnetic flux calculation type in which the primary magnetic flux of the induction motor is calculated from the detected value of the primary current of the induction motor and the like, and the torque is calculated from the primary magnetic flux and the primary current. This control method is characterized in that torque control can be performed at high speed. In the three-phase induction motor, when the primary magnetic flux vector is represented by φ1 and the torque is also represented by T, then φ1 = ∫ (V1−R1 × i1) dt (1) T = φ1 × i1 (2) Where V1: primary voltage vector i1: primary current vector R1: primary winding resistance. For this reason, it can be said that this is a control method suitable for an application in which the torque response needs to be digitally controlled at high speed. less than,
The principle of the instantaneous space magnetic flux vector control method will be schematically described.

FIG. 7 is a diagram showing a conventional induction motor control device. In this figure, a three-phase inverter 7, a three-phase induction motor 8 controlled by the three-phase inverter 7,
Means 9a for detecting the secondary current and one
Means 9b for detecting a secondary voltage, means for processing the instantaneous primary current from the current detecting means 9a and the voltage detecting means 9b, and an instantaneous space magnetic flux vector forming means 100 for controlling the three-phase inverter 7 by processing the primary voltage. Is shown. Current detection means 9a
Is a three-phase / two-phase conversion means, which inputs each phase current i1 to the three-phase induction motor 8 and converts it into i1d and i1q. The voltage detecting means 9b is a three-phase / two-phase converting means, which inputs each phase voltage V1 to the three-phase induction motor 8 and converts it into V1d and V1q. Means for realizing the instantaneous space magnetic flux vector forming means 100 may be hardware, or a digital processor such as a DSP (digital signal processor) may be used.

FIG. 8 is a diagram showing a switching state of the three-phase inverter of FIG. The three-phase inverter shown in the figure
Positive bus 17a, negative bus 17b, 18a and 18b, 1
Three sets of U, V, and W phase changeover switches each including a pair of semiconductor switching elements 9a and 19b and 20a and 20b, and positive buses 17a,
A DC power supply 21 is connected through the negative bus 17b, and each switch is switched to apply a voltage on the positive bus 17a side or the negative bus 17b side to the three-phase induction motor. Each pair of changeover switches does not conduct simultaneously.

Here, the changeover switches 18a, 19
a, 20a conduct when "1", 18b, 19b,
When the conduction state of the switch 20b is set to “0” and the conduction state is expressed in the order of the U, V, and W phases, the state of the changeover switch illustrated in FIG. 7 is (010). FIG. 9 is a diagram illustrating a voltage vector applied to the three-phase induction motor from the three-phase inverter of FIG. As shown in the figure, voltage vectors having the same magnitude and different directions are applied to the three-phase induction motor depending on the conduction state of each changeover switch. (0
In the case of (00), the voltage on the negative bus side 17b is applied to the three-phase induction motor, and in the case of (111), the voltage on the positive bus side 17a is applied, resulting in a voltage vector having no magnitude and direction.

The voltage drop calculators 10a and 10b provided in the instantaneous space magnetic flux vector forming means 100 calculate the voltage drop at the primary winding resistance using the converted current of the three-phase / two-phase converter 9b. The integrating means 11a and 11b have three phases /
The primary magnetic fluxes φ1d and φ1q of equation (1) are obtained by subtracting the voltage drop obtained by the voltage drop calculators 10a and 10b from the voltage converted by the two-phase converter 9a and performing time integration.

FIG. 10 shows an instantaneous space magnetic flux vector forming means 1.
FIG. 9 is a diagram illustrating a state of a primary magnetic flux vector of 00. Here, when the voltage drop at the primary winding resistance is omitted, the primary magnetic flux can be represented by a vector sum of voltage vectors as shown in FIG. Absolute value means 12 is integrated means 1
From the primary magnetic fluxes φ1d and φ1q obtained in 1a and 11b, (φ1d ² + φ1q ² ) ^1/2 is obtained. The magnetic flux determination means 14 determines the excess or deficiency by taking the difference between this and the φ1 command value. When the primary magnetic flux is to be increased, the voltage vector in the outer circumferential direction is output every moment, and when the primary magnetic flux is to be decreased, the voltage vector in the inner circumferential direction is output every moment, so that the primary magnetic flux has a fixed hysteresis width. Control can be performed by approximating a circle.

FIG. 11 is a diagram for explaining the quadrant of the primary magnetic flux vector. As shown in the figure, the dq coordinates are equally divided into six. The magnetic flux quadrant judging means 15 includes integrating means 11a, 11
The rotation angle θ is obtained from the primary magnetic fluxes φ1d and φ1q obtained in b, and it is determined in which divided region the primary magnetic flux exists, and this determination is output to the switching table 16.

As shown in (2), the torque determination means 13 calculates the torque of the induction motor 8 calculated by the cross product of the primary magnetic fluxes φ1d, φ1q and the currents i1d, i1q after the three-phase / two-phase conversion. Since it is proportional to the slip, the difference between the calculated torque and the T command value is determined to determine whether there is excess or deficiency. If the torque is to be increased, the primary magnetic flux is taken as a voltage vector in the rotation direction. If the torque is to be decreased, the voltage vector in the reverse rotation direction is combined with the determination result of the magnetic flux quadrant determination means 15 to control the torque. be able to. FIG. 12 is a diagram showing a voltage vector table determined by the switching table 16 of FIG. As shown in the figure, a voltage vector in the magnetic flux quadrant is set in advance in the switching table 16 for the magnetic flux determination and the torque determination. It is selected by the magnetic flux quadrant determining means 15 and the torque determining means 13 and output to the three-phase inverter 7.

[0012]

The conventional instantaneous space magnetic flux vector forming means 100 has a substantially constant control cycle from the detection of the primary current to the output of the voltage vector. A considerable delay occurs. Therefore, when the control system outputs the voltage vector to the induction motor, the state of the induction motor may be different from the time when the current is detected. That is, since the control is performed with a time delay, the optimal control is not performed.

Specifically, the ripple of the primary current is large,
The locus of the primary magnetic flux is likely to be a locus deviating from the hysteresis. As a result, torque ripple is also increased.
In an extreme case, the control falls into an unstable state. This tendency tends to be remarkable in a motor having a large output, that is, a motor having a low impedance, since the amount of change in current is large.

On the other hand, a current value at the time of outputting a voltage vector is predicted from a circuit equation in which a detected value of a current, an applied voltage of an induction motor, an induction motor constant and the like are taken into consideration, and the predicted current value is used for control. A prediction method has been proposed.
However, in such a prediction method, there is a problem that an error occurs in the current prediction value due to the influence of the variation of the induction motor constant, the induction motor driving state, and the like, and as a result, optimal control is not performed.

Accordingly, the present invention has been made in view of the above-described problems, and performs optimal control without causing a time delay in control. An object of the present invention is to provide a motor current control method.

[0016]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention provides a control apparatus for an induction motor for applying voltage vectors having the same magnitude and different directions to each other.
Means for detecting the primary current of the induction motor; means for detecting the primary voltage of the induction motor; and processing of the detected primary current and the detected primary voltage to periodically rotate the primary magnetic flux. An instantaneous space magnetic flux vector forming means for forming the voltage vector based on the determination of the excess or deficiency of the primary magnetic flux and the excess or deficiency of the torque. The current prediction means stores the voltage vector output in the past and the amount of change in the detected primary current of the induction motor during the period in which the voltage vector was output as a current deviation, and stores the same as the current voltage vector. The current deviation of the past voltage vector is read and added to the detected primary current to form a current predicted value, and the instantaneous section magnetic flux vector forming means is used as the detected primary current to be processed by the instantaneous section magnetic flux vector forming means. To use the predicted current value.

The current predicting means periodically forms a current predicted value using the latest current deviation. If the current deviation does not change significantly, the current predicting means does not periodically read the latest value and replaces the current deviation before the latest value. It may be used to form a current prediction value. Further, the current prediction means periodically forms a current prediction value using the latest current deviation, but if the change in the current deviation is small, the current deviation is not updated periodically but updated intermittently. The predicted current value may be formed using the updated current deviation.

The current predicting means may form a current predicted value on behalf of any of the output voltage vectors even when the voltage vector is switched a plurality of times during a control cycle.

[0019]

According to the current control device for an induction motor of the present invention,
The voltage vector output in the past and the amount of change in the detected primary current of the induction motor during the period when the voltage vector was output are stored as a current deviation, and the same voltage vector as the current voltage vector is stored in the past. The current deviation is read, added to the detected primary current to form a current predicted value, and the instantaneous section magnetic flux vector forming means is provided with the current predicted value as the detected primary current to be processed by the instantaneous section magnetic flux vector forming means. By using, it is possible to output the optimal voltage vector every moment,
The ripple of the primary current and the torque is small, and the induction motor can be controlled stably. Further, the efficiency is improved because the ripple of the primary current and the torque is reduced. Further, since the average switching frequency is improved, a secondary effect such as a reduction in noise is derived. If the current deviation does not greatly change, the processing amount can be reduced by forming the predicted current value using the current deviation before the latest value without periodically reading the latest value. If the change in current deviation is small,
The current amount is not updated periodically, but is updated intermittently, and the updated current deviation is used to form a predicted current value, thereby reducing the processing amount. Even in the case where the voltage vector is switched a plurality of times during the control cycle, by representing any of the output voltage vectors and forming the current prediction value,
Be adaptive.

[0020]

FIG. 1 is a diagram showing an embodiment of a relationship between a voltage vector and a change in a primary current. As shown in the figure, in the relationship between the voltage vector and the primary current change when the control cycle is 60 μS, the current deviation is the difference between the primary current detection value in the immediately preceding control cycle, ie, the primary current. Represents the inclination of. Using the table in the figure, when the magnetic flux is in the five quadrants, as described above, the primary magnetic flux and the torque
The voltage vector (00) determined from the quadrant where the next magnetic flux exists
In (0), the current deviation is −50 A, in the voltage vector (100), the current deviation is +60 A, and in the voltage vector (101), the current deviation is 0 A. If the magnetic flux is in the quadrant, the voltage vector (000) is
The current deviation is −50 A, the current deviation is +60 A in the voltage vector (100), and the current deviation is 0 A in the voltage vector (110).

Although not uniquely determined by the specifications of the induction motor, the conditions such as the induction motor constant, the induction motor rotation speed, and the load torque do not significantly change within a short period of several to several tens of control cycles. Focusing on
The current deviation within the above-mentioned short time is substantially constant for each same voltage vector output period. Therefore, the amount of change in the primary current during the period in which the same voltage vector was output in the past, that is, the current deviation, is added to the detected value of the primary current to obtain a current prediction value, thereby preventing a delay corresponding to the control cycle from occurring. It becomes possible to do.

FIG. 2 is a diagram showing an induction motor control device according to an embodiment of the present invention. In this figure, the configuration different from that of FIG. 7 is the current prediction means 30a, 30b of the induction motor provided at the subsequent stage of the three-phase / two-phase conversion means 9b. Based on the output current value of the three-phase / two-phase conversion means 9b, the current prediction means 30a, 30b calculates a difference from the primary current detection value in the immediately preceding control cycle, that is, a current deviation (the gradient of the primary current). ΔI
m (d), ΔIm (q)), the current deviation is stored using the voltage vector from the switching table 16 as a parameter, and this is sequentially updated. Then, the current prediction means 30
a and 30b read the current deviation using the voltage vector from the switching table 16 as a parameter, and perform the following processing in addition to the output current of the three-phase / two-phase conversion means 9b.

FIG. 3 shows the current predicting means 3 of the induction motor shown in FIG.
It is a figure explaining the current prediction algorithm of 0a, 30b. As a current deviation used for current prediction in the present embodiment,
The latest value of the current deviation during the period when the same voltage vector is output in the past is applied. That is, as shown in the figure, in section 3 such as section 1, 2, 3, 4, 5, etc., such as a fixed control cycle, the current prediction means 30a, 30b of the induction motor.
Stores the current deviation ΔIm (B) from the beginning and end of the period during which the voltage vector B was output. Thereafter, in a section 5 in which the same voltage vector B as in section 3 is output, the primary current value Im (n) detected at the beginning of this section almost simultaneously with the output of the voltage vector B, and the current deviation ΔIm in section 3
The sum with (B) is set as the current predicted value at the end of section 5. Then, a voltage vector to be output to the next inverter 7 is calculated and determined using the predicted current value.

In this embodiment, since the latest value of the current deviation during the period in which the same voltage vector was output in the past is applied as the current deviation, the current deviation during the period when the voltage vector B was output in section 3 is , Is updated to the current deviation during the period when the voltage vector B is output, and the new current deviation is stored. Thereafter, the present invention is applied to current prediction in a section in which the same voltage vector B as in section 5 is output.

FIG. 4 is a flowchart for explaining an example of calculation of a predicted current value and updating of a current deviation. In step S1, a current value Im (n) is detected. In step S2, the current deviation ΔIm when the same voltage vector B is output
Read (B). In step S3, a predicted current value Im (n + 1) = Im (n) + ΔIm (B) is calculated.

In step S4, the current deviation updating at the time of outputting the voltage vector A is performed as follows: ΔIm (A) = Im (n) -Im (n-1) DS
When a digital processor such as P is used, a small memory for storing eight kinds of voltage vectors and a current deviation corresponding to each voltage vector is used in hardware, and a current deviation for each voltage vector is used in software. Can be realized very easily only by adding an algorithm for performing a prediction operation by storing, reading, and adding.

FIG. 5 is a diagram showing the waveforms of the primary current and torque of the induction motor before and after application of the present embodiment. Prior to the application of the current prediction algorithm of the present embodiment, the primary current and torque ripples were large as shown in FIG. 5A, whereas the application of the present embodiment was performed as shown in FIG. Later, the time delay of the control is compensated, so that both the primary current and the torque ripple are reduced.

After the application of the current prediction algorithm of the present embodiment, harmonic components that do not contribute to the rotation torque of the induction motor are reduced due to the reduction of the primary current and the ripple of the torque. The system efficiency including the inverter is improved. Furthermore, before the application of the current prediction algorithm of the present embodiment, the average switching frequency is often in the audible range, and therefore, noise and vibration generated from the induction motor are large. On the other hand, after the application of the current prediction algorithm of the present embodiment, the average switching frequency is improved in order to output the optimal voltage vector every moment by compensating for the time delay of the control, and the vibration is reduced. This has the secondary effect of making noise difficult to hear.

In this embodiment, the latest value of the current deviation during the period when the same voltage vector was output in the past is applied as the current deviation specified in the current prediction algorithm.
If the current deviation for each period during which the same voltage vector is output does not change significantly due to system specifications such as the induction motor rating, the current deviation before the latest value may be applied. Further, when the change in the current deviation for each period during which the same voltage vector is output is small, the prediction calculation of the present embodiment may be realized without updating the current deviation for each voltage vector every time.

Although the present embodiment is an example in which the same voltage vector is output during the entire period of the control cycle, even if the voltage vector is switched a plurality of times during the control cycle, any of the output voltage vectors may be output. In this embodiment, the prediction calculation may be realized. FIG. 6 is a diagram showing control of an induction motor according to another embodiment of the present invention. In this figure, the configuration different from FIG.
current predicting means 31 for an induction motor provided before
a, 31b and 31c. Current prediction means 31a, 31
Reference numerals b and 31c denote the instantaneous value of the primary current flowing through the induction motor, and based on the detected current value, the difference from the primary current detection value in the immediately preceding control cycle, that is, the gradient of the primary current. Current deviation (ΔIm (u), ΔIm (v), ΔIm
(W)), the current deviation is stored using the voltage vector from the switching table 16 as a parameter, and this is sequentially updated. Then, the current prediction means 31a, 31b, 31
As for c, the current deviation is read using the voltage vector from the switching table 16 as a parameter, added to the detected current, and output to the three-phase / two-phase conversion means 9b. As described above, even when the current prediction is performed in each of the three-phase currents iu, iv, and iw, the same operation and effect as described above can be obtained.

[0031]

As described above, according to the present invention, the previously output voltage vector and the amount of change in the detected primary current of the induction motor during the period when the voltage vector was output are stored as a current deviation. , The current deviation of the past voltage vector identical to the current voltage vector, and
Since the current predicted value is formed by adding to the next current, and the instantaneous section magnetic flux vector forming means uses the current predicted value as the detected primary current to be processed by the instantaneous section magnetic flux vector forming means,
Since an optimal voltage vector can be output every moment, the induction current can be stably controlled with little ripple of the primary current and torque. Further, the efficiency is improved because the ripple of the primary current and the torque is reduced. Further, since the average switching frequency is improved, a secondary effect such as a reduction in noise is derived. If the current deviation does not change significantly, the latest value is not read periodically and the current deviation before the latest value is used to form the current prediction value. Is updated intermittently, and the predicted current value is formed using the updated current deviation, so that the processing amount can be reduced.
Even if the voltage vector is switched multiple times during the control cycle, the current predicted value is formed on behalf of any of the output voltage vectors, so that it is adaptable.

[Brief description of the drawings]

FIG. 1 is a diagram showing a relationship between a voltage vector and a change in a primary current.

FIG. 2 is a diagram illustrating an induction motor control device according to an embodiment of the present invention.

FIG. 3 shows current predicting means 30a, 30 of the induction motor of FIG.
It is a figure explaining the current prediction algorithm of b.

FIG. 4 is a flowchart illustrating an example of calculating a current prediction value and updating a current deviation.

FIG. 5 is a diagram showing waveforms of an induction motor primary current and a torque before and after application of the present embodiment.

FIG. 6 is a diagram showing a control device for an induction motor according to another embodiment of the present invention.

FIG. 7 is a diagram showing a conventional control device for an induction motor.

FIG. 8 is a diagram illustrating a switching state of the three-phase inverter of FIG. 7;

9 is a diagram illustrating a voltage vector applied to a three-phase induction motor from the three-phase inverter of FIG.

10 is a diagram illustrating a state of a primary magnetic flux vector of an instantaneous space magnetic flux vector forming means 100. FIG.

FIG. 11 is a diagram illustrating a quadrant of a primary magnetic flux vector.

FIG. 12 is a diagram showing a table of voltage vectors determined by a switching table 16 of FIG. 7;

[Explanation of symbols]

9a: Voltage detecting means 9b: Current detecting means 30a, 30b, 31a, 31b, 31c: Current predicting means 100: Instantaneous space magnetic flux vector forming means

──────────────────────────────────────────────────の Continued on the front page (72) Inventor Masaaki Tsuzuki 14 Iwatani, Shimowakaku-cho, Nishio-shi, Aichi Co., Ltd. (72) Inventor Yoshihide Arai 1st Toyota-cho, Toyota-shi, Toyota-shi, Aichi Japan Toyota Motor Vehicle Stock In-company (72) Inventor Yasushi Yasuka 1 Toyota Town, Toyota City, Aichi Prefecture Inside Toyota Motor Corporation (56) References JP-A-5-292778 (JP, A) JP-A-3-215182 (JP, A JP-A-1-270793 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H02P 5/408-5/412 H02P 7/628-7/632 H02P 21/00

Claims (4)

(57) [Claims] 1. An induction motor control device for applying voltage vectors having the same magnitude and different directions to an induction motor, comprising: means for detecting a primary current of the induction motor; and detecting a primary voltage of the induction motor. Means for processing the detected primary current and the detected primary voltage to form the voltage vector based on a periodic determination of the rotation direction of the primary magnetic flux, excess or deficiency of the primary magnetic flux, and excess or deficiency of the torque. Means for generating an instantaneous space magnetic flux vector, the voltage vector output in the past, and a change amount of the detected primary current of the induction motor during a period in which the voltage vector is output is stored as a current deviation. The current deviation of the past voltage vector that is the same as the voltage vector is read out, added to the detected primary current to form a current prediction value, and the instantaneous section magnetic flux vector forming means Current control device of an induction motor, comprising a current prediction means for the to use a current prediction value to the instantaneous interval flux vector forming means as said detected primary current to sense. 2. The current predicting means periodically forms a current predicted value using the latest current deviation. If the current deviation does not change significantly, the current predicting means does not periodically read the latest value and replaces the current deviation before the latest value. The current control device for an induction motor according to claim 1, wherein the current control value is used to form a current prediction value. 3. The current predicting means periodically forms a current predicted value using the latest current deviation. However, if the change in the current deviation is small, the current predicting means does not periodically update the current deviation but intermittently. 2. The current control device for an induction motor according to claim 1, wherein the current control device updates the current and uses the updated current deviation to form a predicted current value. 4. The current prediction unit according to claim 1, wherein even when the voltage vector is switched a plurality of times during a control cycle, the current prediction unit forms a current prediction value by representing any of the output voltage vectors. 2. The current control device for an induction motor according to claim 1.