JPS63305790A - Control method of induction motor - Google Patents

Abstract

PURPOSE:To reduce the deviation of an actual value to the target value of torque by variably controlling magnetizing currents together with torque currents. CONSTITUTION:A torque target value T is divided by a flux arithmetic value psi2 from a flux computing element 10 in a divider 1, and changed into the target value iT of torque currents. The target value iT of torque currents is divided by the flux arithmetic value psi2 in a divider 2, turned into the phase theta1 of a flux vector through a multiplier 3, and integrator 4 and an adder 5, and input to a vector rotating equipment 7. The target value iT of torque currents is input to the vector rotating equipment 7 while being input to a nonlinear function generator 8. The nonlinear function generator 8 generates the original target value of magnetizing currents. A value generated at an output end for a limiter 9 is input to the vector rotating equipment 7 as the actual target value iM of magnetizing currents.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention separates the primary current of an induction motor into a component parallel to the magnetic flux vector (magnetizing current) and a component perpendicular to this (torque current). , relates to a control method for variable speed drive of an induction motor, in which the torque of the motor is controlled by vector control in which both components are controlled independently of each other.

[Conventional technology]

FIG. 3 shows an example of a conventional vector control configuration for an induction motor. What is the target value for W1 bundle? is constant below the base rotation speed of the motor, and in a constant output range above the base rotation speed, is given so as to decrease in inverse proportion to the rotation speed of the motor in order to suppress a rise in the primary voltage. The torque target value T' is divided by the magnetic flux target value vt'' in the divider 1 and converted into the torque current target value i?'. This division result is divided by the next (1
After being multiplied by the function f given by Equation 1, the signal is input to the integrator 4.

12+11 However, r2 : Secondary resistance 12 ; Secondary leakage inductance Il, : Mutual inductance The output of the integrator 4 is the position of the magnetic flux vector with respect to the secondary conductor, and the position signal θ2 of the secondary conductor is added to this by the adder 5. By adding them, the position θ of the magnetic flux vector is determined. On the other hand, 'P! By inputting ' into the magnetizing current calculator 6, which has a differential element and nonlinear characteristics, the target value ir of the magnetizing current can be obtained from the output of the magnetizing current calculator 6*
IM”+iT” is input to the vector rotator 7,
The coordinate axes are rotated by an angle θ1 and converted into three-phase quantities. As a result, the vector rotator 7 outputs current target values i m''+i b''+ i c'' for each phase of the motor to obtain the desired torque current and magnetizing current.

The current target value 1 m''+1 b''+lC* is input to a power conversion device (not shown), and a desired current is supplied to the electric motor. In addition, when controlling the speed of the induction motor, it is obtained from the output of a speed regulator (not shown).

The above configuration is a method of calculating a magnetic flux vector from a current command value or detected value, and is called a magnetic flux current model method (see Fuji Jiho, Vol. 53, No. 9, pp. 640-648).

In the current model method, as shown in Equation 11, the calculated value of the magnetic flux vector is a function of the secondary resistance r2, and the value changes depending on the conductor temperature, so there is a calculation error that depends on the conductor temperature. A magnetic flux voltage model method is also known in which the magnetic flux vector is calculated from the primary voltage of the motor, but at low speeds the voltage is low (and it is difficult to accurately detect the voltage), so it is not possible to accurately calculate the magnetic flux vector.

[Problem that the invention seeks to solve]

Due to incorrect magnetic flux vector calculation, 1 m”1 1 b
"+ic" is different from the current required to obtain the desired 'H+'T, so the desired 'Nol?' cannot be obtained, and therefore the desired torque cannot be obtained.

In view of the above-mentioned problems of the conventional technology, it is an object of the present invention to solve the problem in vector control of an induction motor even when there is an error in the calculation of the magnetic flux vector and therefore the desired magnetizing current or torque current cannot be obtained. The object of the present invention is to control an induction motor so that an error with respect to a desired value of torque is reduced.

[Means for solving problems]

According to the present invention, the above object is to separate the primary current of an induction motor into a component parallel to the magnetic flux vector (magnetizing current) and a component perpendicular to this (torque current), and control both components independently of each other. In a control method for variable speed drive of an induction motor that controls the torque of an electric motor by vector control, the torque is controlled by increasing and decreasing both magnetizing current and torque current in accordance with increases and decreases in a variable target value of torque. achieved by.

In particular, it is preferable that the absolute value of the target value of the torque current and the target value of the magnetizing current are approximately equal to each other. Furthermore, preferably, when the target value of the magnetizing current is smaller than a predetermined value, the absolute value of the target value of the torque current and the target value of the magnetizing current are approximately equal;
When the target value of the magnetizing current is larger than the predetermined value, the absolute value of the target value of the torque current is preferably larger than the target value of the magnetizing current. In this case, at least the magnetic flux is larger than the first predetermined value and the second The target value of the magnetizing current may be limited on the condition that it is smaller than a predetermined value.

[Effect]

Before explaining the present invention in detail, the principle of the present invention will first be explained.

The magnitude 'Pa of the magnetic flux interlinking with the secondary conductor of the induction motor is given by the first-order lag of the magnetizing current i, 4 parallel to the magnetic flux vector, and in a steady state is expressed by the following equation.

A, = IllIi −・−・・−・・−・−・
-1----・ (2) The generated torque T is proportional to the product of the torque current iy perpendicular to the magnetic flux vector and the magnitude of the magnetic flux A2, and if the proportional constant is , then T=KI Az it - −−−−・−・−・
−・ (3) T=に１ １＠ 's it --
−−−・−・−−−−1・(4) becomes.

The purpose of controlling the electric motor is to control the torque that the electric motor should generate or the rotational speed thereof. If there is an error in the calculation of the magnetic flux vector, the desired tM+
f? - cannot be obtained (although the torque is proportional to the product of iH and 1. as shown in equation (4).The present invention is able to calculate the difference between iH and T7 even when there is a magnetic flux vector calculation error. Target values are given for io and iy so that the error with respect to the desired value of the product, ie, torque, is small.

Next, a description will be given of how to give a target value of 1M+i, which is desirable for improving torque control accuracy, for a given torque target value.

FIGS. 4(a), (b), and (C) show the -order current vector I and the magnetizing current vector T. , is a vector diagram showing the relationship between seven torque current vectors. Each vector of the target current is shown by a broken line, and is expressed as 50, ``n'' + T. Moreover, the solid line represents each vector that actually occurs because the magnetic flux model has not identified it.

In Figure 4, (a) is i, 4 $ > I T*, (b) is i, "-i," (7), and (C) is iH"<iT" (7). However, i engineering +
Let fT+iM"+t7m represent the size of the vectors "TN+L,", and 7.", respectively. Since the actual primary current vector is easy to detect, feedback control of the current is possible so that the knee becomes zero. Therefore, if the penalty is 1r, the target primary current vector engineering 9 is as shown in these figures.
overlaps with the actual primary current vector ball.

The torque is given by equation (4), and when the effective mutual inductance E is constant, the ratio (T/T”) of the actual torque value T to the target value T* is, in the case of (a), T/
In the case of T"< 1 false), T/T"-1 In the case of (C), it can be seen that T/T"> 1. In this way, i, 4$=i?
In the case of 1) 1/fH" and 11711" have a reciprocal relationship, and the above ratio (T/T'") is small.

Figure 5 shows the estimated value r of the secondary resistance in the current model method.
Actual value r for 2! Taking the ratio of i on the horizontal axis, i
, 11 as parameters and shows the transition of the calculated value of T/T'''. From this figure, it can also be seen that ige/iM''=1
It can be seen that T/T''#1 occurs when .

Next, iM increases and 1. Let us now discuss the case where magnetic saturation occurs. In this case, the target value of magnetic flux is f? Then, when (i M/ i M”) > 1, A!”
“1IIiN” iM” (However,
l□ is the effective mutual inductance when the magnetizing current is i,'', 11 is the effective mutual inductance when the magnetizing current is 19). That is, in the case of C1, iN/iM
``> 1, but as the proportion of T14 increased with respect to iI4'', 'P2 becomes 'P? T of T
The increase over 1 is 1. If 1 is smaller than when there is no magnetic saturation, and the change in torque with respect to the target value is smallest when there is no magnetic saturation at In other words, when T14 increases and magnetic saturation occurs, the condition under which the change in torque with respect to the target value of torque becomes the smallest is i t''/i
The principle of the present invention is 0 or more such that pi''>1.

As can be seen from the above principle, according to the method of the present invention that controls torque by increasing or decreasing both the magnetizing current and the torque current in accordance with the increase or decrease in the variable target value of torque, regardless of the increase or decrease in the variable target value of torque, Compared to the conventional method in which the magnetizing current is not changed in order to keep the magnetic flux constant, the error in the actual torque with respect to the variable target torque is reduced when there is an error in the calculation of the magnetic flux vector. In particular, such an error is minimized when the absolute value of the target value of the torque current and the target value of the magnetizing current are made almost equal to each other. When the target value of the magnetizing current is smaller than the predetermined value (that is, when it is not in the magnetic saturation region), the absolute value of the target value of the torque current and the target value of the magnetizing current are approximately equal, and the target value of the magnetizing current is set to the predetermined value. By making the absolute value of the target value of the torque current larger than the target value of the magnetizing current (that is, in the magnetic saturation region), even in the magnetic saturation region, the actual torque with respect to the variable target torque can be adjusted. The error is reduced.

〔Example〕

FIG. 1 is a block diagram showing the main parts of an embodiment of the present invention.

In FIG. 1, T9 is the torque target value, which is
This can be provided, for example, by a speed regulator, not shown, which serves to match the rotational speed of the induction motor to the speed target value. The torque target value T0 is determined by the divider 1 as a magnetic flux calculation value 'P! from a magnetic flux calculation unit 10, which will be described later. divided by

The output terminal of this divider 1 is the target value of torque current i? *
occurs.

This torque current target value lT* is divided by the magnetic flux calculation value '1'2 by the divider 2, and the result of this division is sent to the multiplier 3.
After being multiplied by the function f given by equation (1) above,
The signal is input to an integrator 4. The output of the integrator 4 is the position of the magnetic flux vector with respect to the secondary conductor, and the position θ of the magnetic flux vector obtained by adding the position signal θ2 of the secondary conductor to this in the adder 5 is the position θ of the magnetic flux vector with respect to the secondary conductor. is input. s of the target value of torque current determined by the above divider 1
, 11 are further input to the vector rotator 7 and to the nonlinear function generator 8. Nonlinear function generator 8
generates a target value of magnetizing current i, 11m. The target value of the magnetizing current is limited by the limiter 9 so that it does not exceed the upper limit set value of the magnetic flux ``fta'' and does not fall below the lower limit set value v, ``of the magnetic flux.

The value occurring at the output of the limiter 9 is input to the vector rotator 7 as the actual desired value ir of the magnetizing current. Furthermore, this magnetizing current target value iM* is guided to the magnetic flux calculator 10. The magnetic flux calculator 10 calculates the magnetic flux calculation value type 2 to be given to the divider 1.2 from the magnetizing current target value i, 11. This magnetic flux calculator 10 has a transfer characteristic corresponding to the inverse function of the magnetizing current calculator 6 in the conventional embodiment shown in FIG. Current target value ta for each phase of the motor
l lb''+1♂ is input to a power conversion device (not shown), and a desired current is supplied to the electric motor.

FIG. 2 shows the function characteristics of the nonlinear function generator 8 in FIG. 1. In the range where i, 611 is small, is''=
There is a l iy”l te, i n”’! j big tk <
Nara i' Effective inductance 1. As the saturation characteristic is exhibited, i, *< I tv”l.

〔effect〕

As described above, according to the present invention, in the vector control of an induction motor, when the torque is variably controlled, the magnetizing current is variably controlled along with the torque current, so that when the magnetic flux model does not identify the actual value, Also, the deviation of the actual torque value from the target torque value can be reduced.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention, FIG. 2 is a function characteristic diagram of the nonlinear function generator in FIG. 1, FIG. 3 is a block diagram showing a conventional embodiment, and FIG. 4(a) , (b
l, (C1 is a vector diagram for explaining the principle of the present invention, and FIG. 5 is a characteristic diagram for explaining the principle of the present invention. 1.2 - divider, 3... multiplier, 4 - Integrator, 5.
...Adder, 7--Vector rotator, 8--Nonlinear function generator, 9--Limiter, 10--Magnetic flux calculator. Town - M Figure 2 grab - S! ! 1-

Claims (1)

[Claims] 1) A vector that separates the primary current of an induction motor into a component parallel to the magnetic flux vector (magnetizing current) and a component orthogonal to this (torque current), and controls both components independently of each other. A control method for variable speed drive of an induction motor that controls the torque of an electric motor by controlling the torque by increasing and decreasing both magnetizing current and torque current in accordance with increases and decreases in a variable target value of torque. A method for controlling an induction motor. 2) Claim 1 characterized in that the absolute value of the target value of the torque current and the target value of the magnetizing current are substantially equal to each other.
A method for controlling an induction motor as described in . 3) When the target value of magnetizing current is smaller than the predetermined value, the absolute value of the target value of torque current is almost equal to the target value of magnetizing current, and when the target value of magnetizing current is larger than the predetermined value, the target value of torque current is equal. 2. The method of controlling an induction motor according to claim 1, wherein the absolute value of the magnetizing current is larger than the target value of the magnetizing current. 4) The target value of the magnetizing current is limited on the condition that at least the magnetic flux is larger than a first predetermined value and smaller than a second predetermined value. A method for controlling an induction motor according to any one of the above.