JPH06292384A - Vector control method for induction motor having no speed sensor - Google Patents

Abstract

PURPOSE:To reduce the influence of the error of an identification speed upon a generated torque and facilitate stable vector control of an induction motor having no speed sensor by a method wherein a flux level can be varied in accordance with the magnitude of a torque instruction. CONSTITUTION:A flux instruction phi2d* is made variable in accordance with the magnitude of a torque instruction tau* by a flux instruction generator 12. A torque current instruction is calculated from the values of the torque instruction tau* and the flux instruction phi2d* by a torque current instruction device 16. Taking the magnetic saturation characteristics of an induction motor 1, for instance, into account, when the torque instruction exceeds a rated torque, a certain value is given to the flux instruction. When the torque instruction is zero, a value smaller than the rated flux is given to the flux instruction. With this constitution, in the case of the torque control, the control error can be suppressed to a small value for the small torque instruction value and, in the case of the speed control of a low inertia system or a low load system, a disturbance torque which can be produced when the torque instruction is small can be suppressed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a vector control method for an induction motor, and more particularly to a vector control method without a speed sensor.

[0002]

2. Description of the Related Art Generally, when controlling an induction motor by a vector control method, information on the speed of the induction motor is indispensable. Therefore, in order to perform vector control without using a speed sensor, it is necessary to identify the speed by some method. Therefore, IEEJ Technical Report (Part II) No. 416: Sensorless technology; pp37-49, 1992 Sugimoto, et al .: Speed sensorless vector control of induction motors applying model reference adaptation system;
3, pp306, 1988 Okuyama, et al .: Speed / voltage sensorless vector control method for induction motors; Denki D107, pp 191, 1987 Okuyama, et al .: Influence of control constant setting error in speed / voltage sensorless vector control and its guarantee; Denki D11
0, pp 477, 1990 Miyasita, etc: speed senso.
rless highspeed torque an
d speed control based i
nstaneous spatial vector
theory; proc. IPEC-Tokyo, 11
40, 1990 Kubota et al .: Full-order secondary magnetic flux observer with speed adaptation mechanism for induction motors;
26-519, 1991 and the like have been devised. FIG. 8 shows an example of a conventional slip angle frequency control type vector control method for an induction motor that does not use a speed sensor. In FIG. 8, 1 is an induction motor,
2 is a 3 phase / 2 phase converter, 3 is a 2 phase / 3 phase converter, 4 is a rotary / fixed axis converter, 5 is a fixed / rotary axis converter, 6 is a torque current controller, 7 is an exciting current control , 8 is a magnetic flux controller,
9 is a speed identifier, 10 is a power source angular frequency calculator, 11 is an integrator, 12 is a slip angular frequency calculator, 13 is a magnetic flux observer, 14 is a magnetic flux command, 15 is a torque current command device, 16
Is the torque command τ ^* . Next, the operation of this example will be described. The speed identifier 9 receives the received two-phase voltage ν
_The rotation speed ω _2e is calculated from the information of the _{1a ′} ν _{1b ′} two-phase current i _{1a ′} i _1b . The slip angular frequency calculator 12 calculates the slip angular frequency ω _s from the dq axis current i _{1d ′} i _{1q of} the rotating coordinate system that rotates at the power supply angular frequency ω _1e , and notifies the power supply angular frequency calculator 10 of this. The power source angular frequency calculator 10 adds the information from the velocity identifier 9 and the slip angular frequency calculator 15 to calculate the power source angular frequency command ω _1e , and notifies the integrator 11 of this. The magnetic flux observer 13 calculates the d-axis magnetic flux φ _2d from the exciting current i _1d and notifies the magnetic flux controller 8 of this. The magnetic flux controller 8 uses φ of the magnetic flux command 14.
_2d ^* and d-axis magnetic flux value φ obtained from the magnetic flux observer 13.
_2d, and the magnetic flux φ _2d is controlled so as to match the command value φ _2d ^* . The torque current command device 15 is the torque command 1
6 is multiplied by a constant to calculate a torque current command, and this is notified to the torque current controller 6. The torque current controller 6 receives the received torque current command i _1q ^* and the actual torque current i
Comparing the _1q, controls so _{that i 1q} matches the _{i 1q.} If the speed ω _2e calculated by the speed identifier 9 matches the actual speed of the induction motor, the power supply angular frequency calculator 10 can give an accurate power supply angular frequency ω _1e . At this time, it is known that the q-axis magnetic flux φ _2q becomes zero. However, the mathematical model of the induction motor used for speed identification is a simplified model, and it is difficult to obtain accurate induction motor parameters due to the nonlinearity of the characteristics of the induction motor and temperature dependence. Therefore, there is an error between the actual speed and the identified speed in any of the conventional methods. The magnitude of this error depends on the identification method or changes in the environment, and in some cases, it can be quite large. As described above, when the speed identification value ω _2e has an error, it becomes an error of the power source angular frequency ω _1e , and this eventually appears as an error between the slip command value ω _s and the actual slip. If the slip command value ω _s is correct, q
- the actual value of the axial magnetic flux phi _2q is becomes zero, the actual value of ω may have errors in the _s q- axis magnetic flux phi _2q is no longer zero. FIG. 9 is an example of a magnetic flux orientation type vector control method for an induction motor that does not use a conventional speed sensor. In FIG. 9, 1 is an induction motor, 2 is a 3 phase / 2 phase converter, 3 is a 2 phase / 3 phase converter, 4 is a rotary / fixed shaft converter, 5 is a fixed / rotary shaft converter, and 6 is Torque current controller,
Reference numeral 7 is an exciting current controller, 8 is a magnetic flux controller, 9 is a speed identifier, 10 is a magnetic flux observer, 11 is a magnetic flux command, 12 is a torque current command device, and 13 is a torque command. Next, the operation of this example will be described. The velocity identifier 9 receives the received two-phase voltage ν _{1a ′} ν _{1b ′} two-phase current i _{1a ′} i _{1b ′.}
The rotation speed ω _2e is calculated from the information of 1) and is notified to the magnetic flux observer 10. The magnetic flux observer 10 calculates the magnetic flux from the received two-phase voltage ν _{1a ′} ν _{1b ′} two-phase current i _{1a ′} i _{1b ′} and the identification speed information ω _2e , and notifies the magnetic flux controller 8. Also, based on this, the rotation angle θ is calculated, and this is notified to the rotation / fixed axis converter 4 and the fixed / rotation axis converter 5. The magnetic flux controller 8 uses the magnetic flux command 11 φ
_2d ^* and d-axis magnetic flux value φ obtained from the magnetic flux observer 10.
_2d, and the magnetic flux φ _2d is controlled so as to match the command value φ _2d ^* . The torque current command unit 12 multiplies the received torque command 13 by a constant to calculate a torque current command.
Torque current controller 6 compares the actual torque current _{i 1q} and the torque current command _{i 1q ^*,} controls so _{that i 1q} matches the _{i 1q} ^*. If the speed ω _2e calculated by the speed identifier 9 and the actual speed of the induction motor match,
An accurate magnetic flux can be obtained by the magnetic flux observer 10. However,
When there is an error in the velocity identification value ω _2e due to the same cause as in the conventional example of FIG. 8, accurate magnetic flux information cannot be obtained, that is,
The actual value of the q-axis magnetic flux φ _2q is not zero. In the above two examples, it was found that the actual value of the q-axis magnetic flux φ _2q was not zero when the velocity identification was incorrect. In the above two examples, the torque τ generated by the induction motor is obtained by _{comparing the} primary currents i _1d, i _1q on the dq axes of the rotating coordinate system with 2
It is known that τ = φ _2d ^* i _1q −φ _2q ^* i _1d (1) can be expressed by using the secondary magnetic flux φ _{2d ′} φ _2q . When the vector control method holds, the q-axis magnetic flux φ _2q becomes zero. In the conventional vector control method, if the d-axis magnetic flux φ _2d is controlled to be constant,
A linear relationship is maintained between the generated torque τ and i _1q , i
_The torque can be controlled by controlling _1q . Usually φ
_2d is called magnetic flux, i _1d is called exciting current, and i _1q torque current is called. However, as described above, when the actual magnetic flux φ _2q is not zero due to an error such as speed identification, the second term of the equation (1) becomes an error term for torque generation. In the conventional vector control method, since the value of the exciting current i _1d is usually large,
The error term of the term cannot be ignored even if φ _2q is small.
Especially when the command torque is small, the torque current i
_{Since 1q} is controlled to be small, the value of the error term may become larger than the first term. Although only the torque control system has been described above, when configuring a speed control system that does not use a speed sensor, the torque control system is usually included as shown in FIG. It is clear that the torque generation error of the torque control system still exists than the error of speed identification. As shown in the same example, in the case of speed control, the output of the speed controller is generally the torque command.

[0003]

The above-described conventional vector control method that does not use a speed sensor has a drawback in that the error in the identified speed becomes a torque generation error.
Therefore, when torque control is performed without using the speed sensor, this error is an error between the command torque and the actual generated torque. Further, when speed control is performed without using a speed sensor, this speed identification error not only affects speed control accuracy, but also causes instability and vibration of the control system. The effect is particularly significant when the load is low or the inertia is low, which causes oscillation of such a system, and is a problem that greatly affects the performance and reliability of speed sensorless vector control. An object of the present invention is to reduce the influence of the error of the identification speed on the generated torque and realize stable vector control.

[0004]

The present invention provides a vector control method for an induction motor having no speed sensor,
The magnetic flux level is variable according to the magnitude of the torque command.

[0005]

EXAMPLES Next, a method for carrying out the present invention will be described with reference to examples.

First Example (FIGS. 1, 2, 3, and 4)
(FIG.) This example is an example in which the variable magnetic flux level control method of the present invention is applied to the slip vector method. As can be seen from comparison with FIG. 8 of the conventional example, the difference from the conventional vector control method is that the magnetic flux command is made variable according to the magnitude of the torque command,
In addition, the torque current command is calculated from the values of the torque command and the magnetic flux command. FIG. 2 shows one pattern for changing the magnetic flux command according to the magnitude of the torque command. Considering the magnetic flux saturation characteristics of the induction motor, the magnetic flux command is given to a constant value for torque commands above the rated torque. When the torque command is zero, it is given smaller than the rated magnetic flux. Various types of patterns can be considered. For example, FIG. 3 shows another pattern. Although only torque control is shown in FIG. 1, when performing speed control of a system that does not have a speed sensor, a speed control system is configured as shown in FIG. 4, and the torque control part is placed inside the speed control system. If it is included, it is known that the speed control system can be easily constructed. Therefore, the method of the present invention can be applied to a speed control system having no speed sensor.

Second Example (FIG. 5) FIG. 5 shows an example in which the method of the present invention is applied to a magnetic flux orientation type vector control method. As can be seen from comparison with FIG. 9 of the conventional example, the difference from the conventional control method in which the magnetic flux command is constant is that the magnetic flux command value is changed according to the magnitude of the torque command and the torque command value is changed. The point is to calculate the torque current command from the magnetic flux command value. The generation pattern of the magnetic flux command with respect to the magnitude of the torque command and the method of configuring the speed control system are the same as in the first example.

Third Example (FIG. 6) This example is basically the same as the first example (FIG. 1), except that the torque current command device 16 is not a magnetic flux command. Foil, it is the point that contains the information of the actual magnetic flux observed from the magnetic flux observer.

Fourth Example (FIG. 7) This example is basically the same as the second example (FIG. 5), but the difference from the second example is that the torque current command device 13 is not a magnetic flux command. Foil, it is the point that contains the information of the actual magnetic flux observed from the magnetic flux observer.

[0010]

As shown in the above embodiments, in the speed sensorless vector control, a magnetic flux command is given according to the magnitude of the torque command value to control the magnetic flux, and at the same time, a torque current command is calculated based on the magnetic flux to calculate the command torque. Therefore, in the torque control, for small torque command value,
The generated error can be suppressed to a small level, and speed control of a system with low inertia or a low load system can reduce the disturbance torque that can occur when the torque command is small. The stability and control performance of the system can be improved. Furthermore, since the exciting current when the magnetic flux command is small is also small, copper loss of the induction machine is reduced, and various effects such as reduction of heat generation, suppression of resistance change, and energy saving can be achieved.

[Brief description of drawings]

FIG. 1 is a first embodiment of a magnetic flux level variable speed sensorless slip angular frequency control type vector control method proposed by the present invention.
Is.

FIG. 2 is an example of a pattern that gives a magnetic flux command according to the magnitude of a torque command.

FIG. 3 is another pattern example for giving a magnetic flux command according to the magnitude of the torque command.

FIG. 4 is an example of a configuration of a speed control system having no speed sensor.

FIG. 5 is a second embodiment of the magnetic flux level variable type velocity sensorless magnetic flux orientation type vector control method proposed by the present invention.

FIG. 6 is a third embodiment of a magnetic flux level variable speed sensorless slip angular frequency control type vector control method proposed by the present invention.
Is.

FIG. 7 is a second embodiment of the magnetic flux level variable type velocity sensorless magnetic flux orientation type vector control method proposed by the present invention.

FIG. 8 is a representative example of a conventional velocity sensorless slip angular frequency control type vector control method.

FIG. 9 is a typical example of a conventional velocity sensorless slip magnetic flux orientation type vector control method.

Claims (1)

[Claims] 1. A vector control method for an induction motor having no speed sensor, wherein the magnetic flux level is variable according to the magnitude of a torque command.