JPH02285991A - Vector controller for induction motor - Google Patents

Abstract

PURPOSE:To obtain a desired control signal without using the circuit constant of a motor by calculating the phase value of an exciting current from a primary current and the absolute value of the exciting current in a vector controller for an induction motor to be calculated based on a vector control system. CONSTITUTION:A primary current I1 and a command value B of a phase angle difference from an exciting current are added by an adder 32 to obtain the phase angle command value of the primary current as an input signal of a current command value calculator 7. The value 11 of the primary current absolute value is calculated by a root-mean-square calculator 8 similarly as an input signal of the calculator 7. The primary current command values of three phases are compared with primary current momentary values (iU, iV, iW) output from a current detector 2 in which they are input to a current control circuit 6, and a PWM inverter 3 is so controlled that the momentary value becomes the primary current command value.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a vector control device that is often used for high-speed variable speed control of induction motors.

[Conventional technology]

The vector control method converts the primary current, which is the drive current of the induction motor, into orthogonal coordinates (generally called dq coordinates) on the stator, and converts the current vector II into an exciting current i and a torque current izv. It is characterized by controlling the absolute value and phase of the primary current under the condition that the absolute value of the exciting current 10 is constant, and is used in AC motors in general, including not only induction motors but also synchronous motors. This is a control method characterized by high-speed response characteristics.

Since the vector control method can control the instantaneous value of torque, it has become possible to perform high-speed control, which was not possible with conventional AC motor control methods, and has replaced DC motors with AC motors and inverters. This was the driving force behind the widespread use of control systems in combination with

As mentioned above, vector control is a method of controlling the torque and rotational speed of a motor by controlling the absolute value and phase of the primary current, which is the drive current of the motor, under the condition that the absolute value of the excitation current is constant. However, since the excitation current cannot be directly measured, calculations are performed in the following order.

Excitation current component 1. Under the condition that the absolute value of is constant,
The following formula holds between the various quantities. These equations hold true not only in the steady state but also in the transient state (
Transactions of the Institute of Electrical Engineers of Japan, Vol. 108, No. 8, 1983 r A C
(Vector control of motors).

r-Ml. lha 1tt=-(Ll/M)lt 1, -no1st'+i.

0m -(Rt/x-z) t□ β-ta, n-' (itt/I m)θ,-
(ω, 10pω,)dt θ1−θ. +β Here, τ; Torque Lt; Self-induction coefficient M of the secondary winding; Mutual induction coefficient ll between the primary and secondary windings; Absolute value θ1 of the primary current in vector representation on the dq ridge ; Phase angle of primary current i (rotating on tiq pedestal with angular velocity ω1) tx i Primary side conversion value of absolute value in vector representation on dq pedestal of secondary current 1, secondary current II Excitation current component (absolute value is always constant) 1 F? i Torque current component in primary current 11 (i.

) θ, ;1. (rotating on dq coordinates with angular velocity ω) p; pole logarithm β il+ and 1. FIG. 2 is a vector diagram showing the relationship between the aforementioned quantities and their command values. In this figure and the following description, various quantities of the actual instantaneous values of the primary current of the induction motor are shown in lowercase letters with the necessary index attached, and command values are displayed in uppercase letters with the necessary index attached. All of the above equations express relationships between instantaneous values, but by using uppercase letters instead of lowercase letters, they can also express relationships between command values or between instantaneous values and command values.

Although the direction of the d-axis is arbitrary, it is usually set at the center of the U-phase winding of the primary winding, and the q-axis, also called the horizontal axis, is usually set in the direction electrically perpendicular to this.

Since the excitation current i changes other command values under the condition that its absolute value is always constant, the length of i in the diagram is constant, and it rotates on the diagram with an angular velocity ω. and the phase angle θ
. represents the phase angle at a certain moment. Primary current i
The angular velocity of t is ω.

In steady state, it is ω, -ω·, which matches the angular frequency of the power supply. The primary current 11 is an exciting current 1. which is two components orthogonal to each other on the d9 zadan. and torque current + 11
The torque current i sr is also the vector sum of (2
), there is a proportional relationship with the secondary current 18, and their directions are also balanced with each other.

Primary dynamic current 11 and f11 magnetic current 1. The phase difference β with the torque current it? is constant in steady state, which also means that the torque current it?
is constant, and torque τ is also constant as is clear from equation (1).

When controlling the rotation speed of a three-phase induction motor to increase the rotation speed, such as when the load increases and the rotation speed decreases and then returns to the original speed, or when increasing the rotation speed, the new rotation speed The angular velocity Ω, determined from ω, is given as a command value that is different from the instantaneous angular velocity ω. From this, the torque 1i flow command value tut and the phase angle difference command value B are calculated, and as a result, the command value ■ of the primary current absolute value and its phase angle θ1 are calculated, and based on these two command values, the induction motor The three-phase primary currents C1,+, Ima, and [ga] are determined.

The command value of the slip frequency type vector control method is calculated by calculating the torque command (l [T as an input signal, the primary current is dq
Absolute value 11 when converted to coordinates and its phase angle command value θ
1 is the basic calculation in the vector control system. The calculation procedure is as follows.

Find the required torque T from the difference between ■■ and V, and calculate the torque current component ■□ required to produce this torque T.

is calculated from equation (1).

(2) Calculate the primary current absolute value I as a command value from equation (3).

■Calculate the slip angle frequency ω from equation (4).

■Primary current as command value (absolute value is Il) and exciting current 1
．． The phase angle difference β is calculated from equation (5).

■Since the angular velocity ω of the rotation of the induction motor is detected by the angular velocity detector 5 provided in the motor, Ω1 and this ω
, into equation (6) to obtain θ. Calculate.

(2) Calculate the phase angle θ of the primary current as a command value from equation (7).

Primary current absolute value ■1 and phase Ω1 determined by the above calculations
Determine the primary current of the motor using as an input signal. The actual control circuit will be explained below.

Figure 3 shows PWM (pulse width variation al) by vector control.
1) A block configuration diagram showing a conventional system for driving an induction motor using an inverter. In this figure, an induction motor 4 is driven by a three-phase alternating current*100 consisting of a rectifier I and a PWM inverter 3 that converts the direct current output from the rectifier 1 into the required three-phase alternating current. It is controlled by a control circuit 200 consisting of a current command value calculation circuit 7 and a current control circuit 6.

The output current of PWM inverter 3 is 111 at current detector 2.
% Ivz 1w is measured and fed back to the current control circuit 6 to generate a command signal 1. The PWM inverter 3 is controlled so that the difference between S + and 1 becomes zero.

The primary current (2) as the aforementioned control signal and its phase angle command value θ1 serve as input signals to the current command calculation circuit 7.

To calculate each of the above terms, first, the angular velocity ω, which is the rotational speed of the induction motor detected by the angular velocity detector 5, is subtracted by the subtractor 31.
The difference signal subtracted from the control angular velocity Ω1 is input to the speed controller 9, and the speed controller 9 outputs a torque current component itt that produces the desired torque T. This current component ■. and excitation current component 1 set to a constant value. From this, the sum of squares square root calculator 8 calculates the primary current absolute value command value ■1
is calculated and becomes the input signal of the current command value calculation circuit 7,
The torque current component ■ is determined by the phase angle calculator 18. and excitation current component 1. The phase angle difference B is calculated from the arctangent of the ratio.

Furthermore, the slip angle frequency ω is calculated by the slip angle frequency calculator 19 based on the above-mentioned equation (4). On the other hand, ω as the output signal of the angular velocity detector 5 is multiplied by the number of pole pairs P by the multiplier 20, and the aforementioned slip angular frequency ω and Pω as the output signal of the multiplier 20 are added to the adder 33. By integrating this added value in the integrator 22, the excitation current component 1. The phase θ of is determined and input to the current command value calculation circuit 7.

Since the various quantities used in the process of these calculations are all instantaneous values, the primary current of the three-phase induction motor 4 can also be controlled with respect to instantaneous values. Therefore, since the response speed of the H control is fast, this vector control method is particularly suitable as a control method for controlling load characteristics that fluctuate widely.

[Problem to be solved by the invention]

In the process of calculating the phase angle command value θ1 of the primary current ■, which is one of the input signals of the current command value calculation circuit 7, equation (4) is used to calculate the slip angle frequency ω. 4
) The secondary winding resistance RX and the self-induction conductivity L8 included in the equation are values that vary depending on conditions. That is, the secondary winding resistance R8 is a function of temperature, and the resistance temperature coefficient of copper or aluminum used as the conductor of the secondary winding is approximately 0.
4%/, so a temperature rise of nearly 100 degrees during operation will cause a change in resistance R2 of several tens of percent, resulting in a large error in the value of ω as calculated by equation (4). There is a problem. Also, the self-induction coefficient L of the secondary winding! includes the nonlinear characteristics of the iron core, so the self-induction coefficient L1 depends on the value of the am current component set.
As a result, an error occurs in the value of ω, similar to the change in resistance R3.

An object of the present invention is to solve the above-mentioned problems and provide a vector control device that can obtain a desired control signal without using the circuit constants of the motor.

Means for Solving Problem C] According to the present invention, in order to solve the above problems, there is provided a three-phase AC power source that can control the peak value, frequency, and phase of the output current, and a three-phase AC power source that is driven by the three-phase AC power source. induction motor,
A control circuit that controls the output current of the three-phase AC power supply based on two command values of the peak value and phase of the primary current of the induction motor, which is the drive current, and two commands of the peak value and phase of the primary current. a command value calculation means for calculating a value from the angular velocity of the induction motor and a command value of the angular velocity, and the command value calculation means maintains a constant peak value of an excitation current component included in the primary current; A vector control device for an induction motor in which the phase command value is calculated based on a vector control method in which the phase command value is the sum of the phase value of the excitation flow and the command value of a phase difference between the primary current and the excitation current, The phase value of the excitation current is calculated from the primary current and the absolute value of the excitation rIf11.

[Effect]

In the configuration of this invention, by calculating the phase angle of the exciting current from the absolute values of the primary current and the exciting current, the primary current can be calculated without using circuit constants such as the resistance of the secondary winding of the induction motor or the self-induction coefficient. Since the phase command value can be calculated, it is possible to use a vector control method that is not affected by changes in resistance due to temperature, changes in self-induction coefficient due to nonlinear characteristics of the magnetic circuit, etc.

〔Example〕

The present invention will be explained below based on examples. FIG. 1 is a block diagram showing an embodiment of the present invention, and the same components as in FIG. 3 are given the same reference numerals and detailed explanations will be omitted.

In this figure, the phase converter 22 has a balanced three-phase current (iu,
fv, l@) into a two-phase current (+4, 1.), and is calculated based on the following equation.

Calculation of phase conversion based on this formula can be performed simply by four arithmetic operations, so it can be easily configured with an analog calculation circuit.

The phase angle calculator 23 calculates the two-phase current H,,i,)! I.

The phase angle θ1 as a vector of the indicated primary current 11 is calculated based on the following equation.

θ+ = jan-' (ta/ig)
(9) The phase angle difference calculator 24 calculates the phase angle difference β between the primary current 11 and the IBK magnetic current i based on the following equation.

β-5ec-' (J (14"+I@")/
L l (10) As is clear from FIG. 2, the phase angle θ of an exciting current of 1° can be obtained from the following equation.

θ. −θ1−β−・・・・
(11) This equation (11) is performed by the subtracter 34, and the command value B of the phase angle difference between the primary current 1 and the exciting current 1ψ calculated by the phase angle difference calculator 1 is added to the subtraction result by the adder 3.
2 to obtain a phase angle command value θ1 of the primary current, which is used as an input signal to the current command value calculation circuit 7. Further, a command value II of the primary current absolute value is calculated by a sum-of-squares square root calculator 8 and similarly used as an input signal of the current command value calculation circuit 7. The current command value calculation circuit 7 calculates primary current command values (Iu, It, Iw) as three-phase currents based on the following equation.

The primary current instantaneous values (io,
(v, i+s), and the PWM inverter 3 is controlled so that this instantaneous value of the primary current becomes the primary current command value.

In this way, the phase angle θ of the excitation current 11 is adjusted. can be calculated without using the resistance R2 of the secondary winding of the induction motor or the self-induction coefficient L8, so the self-induction coefficient due to the 8-fold change in resistance due to temperature changes in the secondary S wire and the nonlinear characteristics of the magnetic circuit Since this control method is not affected by changes in L3, stable speed control of the induction motor is possible.

Although the phase converter 22, phase angle calculator 23, phase angle difference calculator 24, and subtracter 34 are used to calculate the phase angle θ of the excitation current, the same result can also be obtained with a different configuration. For example, the phase converter 22 may be omitted and the two-phase current (in, l
-) instead of directly using the instantaneous values (lu, it, 1w) of each of the three-phase components of the primary current, a formula for determining the phase angle θ1 and the phase angle difference β may be used.
Furthermore, the calculation formula can be simplified by utilizing the fact that the primary current is a balanced three-phase current.

Although the command value calculation means 310 shown in FIG. 1 is shown as an analog calculation circuit, it may alternatively be configured as a digital calculation circuit. In this case, each block constituting the command value calculation means represents a software flowchart. In an actual vector control device, a command value calculation means using such digital calculation is used, and a control device with excellent controllability and reliability is put into practical use.

〔Effect of the invention〕

As mentioned above, this invention avoids using circuit constants such as the resistance of the secondary winding of the induction motor and the self-induction coefficient by calculating the phase value of the exciting current from the primary current and the absolute value of the exciting current. Since the phase command value of the primary 1f flow can be calculated, the induction motor vector can be stably controlled without being affected by changes in resistance due to temperature or changes in the self-induction coefficient due to nonlinear characteristics of the magnetic circuit. It can be a control device.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention, and FIG.
The figure is a vector diagram of IT flow in dq coordinates, and FIG. 3 is a block configuration diagram showing an example of this prior art. 100... Three-phase AC power supply, 1... Rectifier, 3...
PWM inverter, 2... Current detector, 4... Induction motor, 5... Angular velocity detector, 200... Control circuit, 6... Current control circuit, 7... Current command value operation actual circuit,

Claims (1)

[Claims] 1) A three-phase AC power supply that can control the peak value, frequency, and phase of the output current, an induction motor driven by this three-phase AC power supply, and the peak value and phase of the primary current of the induction motor that is the drive current. a control circuit that controls an output current of the three-phase AC power supply based on two command values; and a control circuit that calculates two command values of a peak value and a phase of the primary current from the angular velocity of the induction motor and the command value of this angular velocity. The command value calculating means maintains the peak value of the excitation current component contained in the primary current constant, and the command value of the phase is calculated based on the phase value of the excitation current and the primary current. In a vector control device for an induction motor that is calculated based on a vector control method in which the phase value of the excitation current is the sum of the command value of the phase difference between the primary current and the excitation current, the phase value of the excitation current is the sum of the command value of the phase difference between the primary current and the excitation current. A vector control device for an induction motor, characterized in that it performs calculations from.