JPS59113784A - Controlling method for induction motor - Google Patents

Abstract

PURPOSE:To maintain a loop gain of a speed control system constantly irrespective of a magnetic flux by regulating the gain of a speed control circuit in response to the actual value of the magnetic flux. CONSTITUTION:An output of a magnetic flux calculator is inputted to a magnetic flux control circuit 13 and dividers 15, 16. The divider 15 divides the output of a speed control circuit 11 by the output of a magnetic flux calculator 14, and the output, i.e., the command signal of the torque current of the primary current is inputted to a vector calculator 19. Since the output of the circuit 11 is divided by the magnetic flux phi in this manner, the characteristics of the speed control system is determined irrespective of the magnetic flux. Therefore, high responding speed control can be always performed irrespective of the amplitude of the magnetic flux, the variation in a loop gain of a speed control system based on the magnetic flux phi can be eliminated, thereby performing the stable operation.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a method for controlling an induction motor in which the primary current of the induction motor is controlled by dividing it into a torque component and an excitation component.

[Prior art]

Vector control is a high-response variable-speed drive system for induction machines. According to vector control, the primary current is controlled by dividing it into a torque component and an excitation component, so any torque characteristic can be selected, such as series winding characteristic or shunt winding characteristic, in which the torque generated by the motor is controlled by a DC machine. is possible. Therefore, it is possible to perform field weakening control to perform constant output control, and to perform field control according to torque to achieve high efficiency operation. I can do it.

However, the following problem occurs when speed control is performed. That is, the torque generated by the induction motor is τ, and the torque component of the primary current (hereinafter abbreviated as torque current) is Ii)
If the frequency is fl and the magnetic flux is Φ, then rCrCΦl, ocΦ” f, −(
There is the relationship 1). Since the gain from the output of the speed control circuit to the motor generated torque is determined depending on the magnetic speed Φ, as mentioned above, when a large field control is performed for constant output control or high efficiency operation, the loop gain of the speed control system increases. changes significantly. As a result, not only the response of the speed control system changes significantly, but also the speed control system may become unstable, which has the disadvantage that the high-performance control inherent to vector control cannot be fully demonstrated. .

In order to solve this drawback, a method has been proposed in which the output of the speed control circuit is divided by the magnetic flux command value to stabilize the output.

However, since the actual value of the magnetic flux and the command value do not necessarily match when considering the transient state, the speed control system may become cine-stable in the transient state. Especially when the magnetic flux command value changes drastically instantaneously (
(This can be done with high-efficiency control, etc.), the discrepancy between the actual value of the magnetic flux and the command value cannot be ignored, and instability of the speed control system becomes a problem.

[Purpose of the invention]

The present invention has been made to address the above-mentioned drawbacks, and its purpose is to provide a method for controlling an induction motor that can be operated stably at all times with little change in speed response regardless of the field value. .

[Summary of the invention]

The feature of the present invention is that the gain of the speed control system is adjusted in accordance with the actual value of the magnetic flux in order to keep the loop gain of the speed control system substantially constant.

[Embodiments of the invention]

FIG. 1 shows an embodiment of the invention.

In FIG. 1, 1 is an AC power source that supplies power to a power converter 2 that outputs a variable voltage, variable frequency tributary. As the power converter 2, a PWM inverter, a cycloconverter, or the like is used. The power converter 2 is connected to the induction motor 3 and causes the induction motor 3 to operate at variable speed. The rotational speed of the induction motor 3 is determined by a speed detector 4 connected to the induction motor 3.
detected by. A signal proportional to the rotational speed detected by the speed detector 4 is input to a speed control circuit 11 with a deviation from the output signal of the speed command circuit 10. Speed control circuit 1
1 operates according to the output signal deviation of the speed detector 4 and the speed command circuit 10, and its output becomes a signal for commanding the torque of the induction motor. The output of the speed command circuit 10 is input to a divider 15.

The magnetic flux command circuit 12 is a circuit that issues a magnetic flux command to perform field control for constant output control or high efficiency control. For example, in constant output control, the magnetic flux command is given in inverse proportion to speed, and in high efficiency control, the magnetic flux command is given in accordance with torque.

The output signal of the magnetic flux command circuit 12 is input to the magnetic flux control circuit 13 after the deviation from the output signal of the magnetic flux calculation circuit 14 is determined. The magnetic flux control circuit 13 operates according to the output signal deviation of the magnetic flux command circuit 12 and the magnetic flux calculation circuit 14, and its output signal becomes a command for the excitation current of the primary current. The output of the magnetic flux control circuit 13 is input to a magnetic flux calculation circuit 14 and a vector calculation circuit 19. The magnetic flux calculation circuit 14 calculates magnetic flux based on the output of the magnetic flux control circuit 13. The output of the magnetic flux calculation circuit 14 is input to the magnetic flux control circuit 13 and dividers 15 and 16. Divider 15
divides the output of the speed control circuit 11 by the output of the magnetic flux calculation circuit 14, and inputs the output, that is, a command signal corresponding to the torque current of the primary current, to the vector calculation circuit 19. Divider 1
6 divides the output of the divider 15 by the output of the magnetic flux calculation circuit 14, and inputs the output to the adder 17. The output of the divider 16 is a command for the overall frequency of the induction motor 3. Adder 17 adds the outputs of divider 16 and speed detector 4, calculates a command for the primary frequency of induction motor 3, and sends the signal to oscillator 18. The oscillator 18 outputs a sine wave signal based on the primary frequency command of the adder 17, and outputs a sine wave signal based on the primary frequency command of the adder 17.
Enter it in 9.

The vector calculation circuit 19 performs vector addition of the outputs of the divider 15 and the magnetic flux control circuit 13 using the sine wave signal of the oscillator 18, and calculates a primary current command for the induction motor 3. The current detector 2o detects the primary current flowing through the induction motor 3. The signal detected by the current detector 2o and proportional to the 7'C primary current is the output of the vector calculation circuit 19. The primary current command and the deviation are input to the stain flow control circuit 21. The current control circuit 21 includes a vector calculation circuit 19 and a current detector 20
The power converter 2 outputs a signal according to the deviation of the output signal of
make it work.

Next, the operation will be explained.

The output of the speed control circuit 11 is the output of the induction motor 3.The output of the magnetic flux control circuit 13 is the command signal I for the excitation current of the primary current.
The magnetic flux calculation circuit 14 calculates the magnetic flux Φ of the induction electric machine 3 by the following calculation.

Here, M is the excitation inductance of the induction motor 3, T2
is a quadratic time constant. The divider 15 performs the following operation,
Find the torque current component of the primary current.

Here, kl is a constant. Further, the divider 16 calculates 1'...(4) f8*-Φ to obtain the total multi-frequency command f- of the induction motor 3. Then, in the adder 17, f1*=J N+f
81, the one missing frequency command f1* is calculated.

Here, , k are constants, and N is the rotational speed detected by the speed detector 4. The oscillator 18 outputs a sine wave signal based on one missing frequency command f. As a result, in the vector calculation circuit 19, F = I - "a + I t" b = 11" sin (2ff ft * t + θ *) ・
The vector calculation in (6) is performed and a primary current command is output. Here it is. The current control circuit 21 operates so that the primary current signal 1 detected by the current detector 20 matches the primary current command 1*, and operates the power converter 2.

As described above, if the speed of an induction motor is controlled using vector control, high-response control similar to that of a DC motor can be achieved.

At this time, the block diagram of the transfer function of the speed control system is as shown in FIG. In Fig. 2, 101 is the gain of As, 102 is the divider 15, 103 is the closed loop transfer characteristic of the torque current control system, 104 is the torque coefficient, 105 is the characteristic of the mechanical system, and 106 is the gain of the speed detector 4. represents. The torque coefficient can be expressed as ζΦ because the torque τ is expressed as τ=ζΦIt...(8)
This is because it can be expressed as the product of Φ and I.

The loop gain H in the block diagram of Figure 2 is υ, and the magnetic flux Φ
is unrelated to the value of . Since the output of the speed control port t@ll is divided by the magnetic flux Φ in this way, the characteristics of the speed control system are determined regardless of the magnetic flux Φ. Therefore, high response speed control is always possible regardless of the magnitude of the magnetic flux, and there is no loop gain variation in the speed control system based on the magnetic flux, allowing stable operation.

FIG. 3 shows another embodiment of the invention.

In FIG. 3, 11 and 14 are the same as those in FIG. 1, 22 is a function generator that outputs a signal that is inversely proportional to the input magnetic flux Φ, and 23 is a multiplier. The embodiment shown in FIG. 3 is characterized in that a function generator 22 and a multiplier 23 are used instead of the divider 15.

Even in this case, the calculation from the speed control circuit 11 to the torque current command is not performed in the same manner as in equation (3), and as shown in FIG. 1, the loop gain of the speed control system is determined independently of the magnetic flux Φ.

Furthermore, the idea of FIG. 3 may be advanced and the gain characteristic of the speed control circuit 11 itself may be changed depending on the magnetic flux. This method becomes easier to apply when digital control is performed using a microprocessor.

FIG. 4 shows another embodiment of the invention.

In FIG. 4, numerals 1 to 21 indicate the same parts as in FIG. 1.

24 and 26 are multipliers, and 25 is a divider. Divider 25
Then, perform the calculation to obtain the frequency command f, *.

The multiplier 26 calculates the torque current command ■1* by the following calculation.

Is"=5 ω, Φ...αυHere, k41 kB is a constant. In this way, even when calculating the Bessi frequency from the output of the speed control circuit 11, the multiplier 24 and the divider 25 By performing the calculation of equation (10), the loop gain of the speed control system can be made constant regardless of the magnetic flux Φ.

FIG. 5 shows another embodiment in which the main parts shown in FIG. 4 are changed.

In FIG. 5, 11.14 indicates the same thing as in FIG.

27 is a function generator that outputs a signal inversely proportional to the square value Φ2 of magnetic flux, and 28 is a multiplier.

A feature is that a function generator 27 and a multiplier 28 are used instead of the multiplier 24 and divider 25. The output of the multiplier 28 is subjected to the calculation of equation 11.

〔Effect of the invention〕

As explained above, according to the present invention, the gain of the speed control circuit is adjusted according to the actual value of the magnetic flux, so that the loop gain of the speed control system can be kept constant regardless of the magnetic flux. As a result, the response of the speed control system remains unchanged, allowing stable operation at all times.

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram showing one embodiment of the present invention, and FIG.
The transfer function block diagrams in the figure, FIGS. 3, 4, and 5 are configuration diagrams showing other embodiments of the present invention, respectively. 2... Power converter, 3... Induction motor, 11...
Speed control circuit, 12... Magnetic flux command circuit, 13 River magnetic flux control circuit, 14... Magnetic flux calculation circuit, 19... Vector calculation circuit. Military 2 Figure 3 Mouth + Design Figure 5 Figure 1 Page 0 continued, 7℃: Applicant Hitachi Keiyo Engineering Stock%
formula%

Claims (1)

[Claims] 1. A power converter that outputs variable voltage, variable frequency AC power, an induction motor driven by the power conversion, a speed detector that detects the rotational speed of the induction motor, and a speed command signal and the output of the speed detector. In an induction motor control device comprising a speed control circuit that controls the rotational speed of the induction motor based on a signal, the actual value of the magnetic flux is adjusted such that the gain of the open-loop transfer function of the speed control system of the induction motor is approximately constant. A method for controlling an induction motor, characterized in that the gain of the speed control circuit is adjusted according to the speed control circuit.