JPH06253575A - Vector control inverter for induction motor - Google Patents

Abstract

PURPOSE:To prevent the voltage induced in a motor from approaching the input side voltage of an inverter in high speed region thus allowing the torque component current of the motor to follow up a command value. CONSTITUTION:The vector control inverter for induction motor individually controlling the torque component current and field component current of primary current comprises an inverter input voltage detecting circuit 14 for determining the relationship of magnitude between inverter input voltage Vi and rated voltage Vr of the motor. Furthermore, a field weakening circuit 15 is constituted such that the starting r.p.m. of field weakening control for decreasing the field component current and suppressing the voltage to be induced in the motor is lowered as the Vi decreases.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention controls an inverter main circuit such that a primary current of an induction motor is divided into a torque component current and a field component current, and the field component current is controlled in a high speed region. The present invention relates to a vector control inverter device for an induction motor having field weakening means for performing control to make the torque inversely proportional to the rotation speed.

[0002]

2. Description of the Related Art As is well known, a vector control inverter device has been provided for the purpose of controlling an induction motor with a high-speed response and high precision like a synchronous motor or a DC motor. This is a configuration in which the primary current of the induction motor is vector-divided into a torque component current and a field component current (secondary magnetic flux current component), and each of them is independently controlled. An example thereof is shown in FIG. . In FIG. 3, 1 is a three-phase induction motor to which a primary voltage is applied from the inverter main circuit 2, and 3 is a rotation speed detector that detects the rotation speed of the induction motor 1 and outputs a rotation speed signal Na in the form of a pulse. The output rotation speed signal Na is converted into a phase signal, that is, a position signal Pa by an integrator 4 such as a counter.

The first coordinate conversion section 5 vectorizes the primary current (phase current) detected by the current detector 6 provided in the output line of the inverter main circuit 2 so as to detect the primary current of the induction motor. Is divided into a torque component current i _q and a field component current i _d . Of these, the torque component current i
_q is the deviation between the torque command signal I _q by the first mixer 7 is taken for the purpose of feedback control, likewise field component current id is through the field weakening circuit 8 by the second mixer 9 From the magnetic flux command signal Id given by the second coordinate conversion unit 1 that has received these deviation values.
0 is converted into a phase voltage command Va for obtaining a primary current obtained by vector-synthesizing the torque component current and the field component current. Upon receiving the phase voltage command Va, the PWM control unit 11 changes the mixer 7
The switching elements of the inverter main circuit 2 are controlled to be turned on and off in the direction in which the feedback control in which the deviation value of the torque component current and the deviation value of the field component current output from 9 and 9 respectively become zero is completed.

Usually, in this type of vector control inverter device, the secondary induced voltage proportional to the product of the magnetic flux and the rotational speed rises as the motor speed increases, and the internal induced voltage seen from the primary side (hereinafter simply referred to as the motor induced voltage). Is increased in a direction approaching the input voltage V _i to the inverter main circuit 2 which is the external power supply voltage for the electric motor, and when the voltage difference becomes a certain value or less, the actual primary current increases the current command value. The current control limit is reached, at which the current control limit cannot be increased in accordance with, and the limit of the torque or speed control range is reached.

In other words, the vector control collapses and the rotational speed becomes an uncontrolled state that depends only on the inverter output voltage. In order to prevent this, conventionally, a field weakening circuit 8 is provided,
In a region where the rotation speed is equal to or higher than a predetermined set value, the magnetic flux command signal I _d is corrected so that the field component current decreases in inverse proportion to the increase in the rotation speed, and thus the motor induced voltage in the high speed region is reduced. I was trying to slow down the rate of increase.

[0006]

By the way, in order to expand the vector control range, even when the maximum current command value is the maximum output, the electric motor with respect to the external power supply voltage for the electric motor which is the input voltage Vi of the inverter main circuit 2 is increased. The motor may be designed so that the induced voltage is sufficiently low and the rated voltage has an ideal relationship. However, in that case, the load current increases due to the decrease in the rated voltage, leading to an increase in loss and the switching element of the inverter main circuit must have a large capacity.
For this reason, in the past, in order to meet the conflicting requirements, the minimum value of the variable rated voltage of the inverter main circuit should match the rated motor voltage in order to increase the external power supply voltage without lowering the rated motor voltage. I was doing. Since this is a mode of use that gives a large margin to the external power supply voltage, it can be said that it is an economically uneconomical power supply system due to apparently low efficiency use.

An object of the present invention is to provide a vector control inverter for an induction motor capable of ensuring a wide current control range by vector control without expanding the power supply voltage margin, which is the difference between the magnitude of the external power supply voltage for the motor and the rated voltage of the motor. The purpose is to provide a device.

[0008]

A vector control inverter device for an induction motor according to the present invention is a vector control means for separately controlling a primary current of an induction motor into a torque component current and a field component current and an electric motor. Field weakening means for decreasing the field component current as the number of revolutions increases when the number of revolutions exceeds the set number of revolutions, and correction means for making the set number of revolutions lower as the external power supply voltage for the motor is lower. Become.

More specifically, the vector control inverter device includes an inverter main circuit for supplying a primary voltage to the induction motor, and a primary current supplied from the inverter main circuit to the induction motor as a torque component current. A field component current is divided into control means for controlling each by a torque command signal and a magnetic flux command signal, a rotation speed detection means for detecting the rotation speed of the electric motor, and a rotation speed signal given from the rotation speed detection means is a set rotation speed. Field weakening means for decreasing the field component current as the number of revolutions increases, a voltage detecting means for detecting the input voltage to the inverter main circuit, and the lower the detected voltage, the more the set rotation Correction means for lowering the number.

[0010]

When the rotational speed of the induction motor reaches a region above the set rotational speed at which field weakening is started by vector control, the field weakening means reduces the field component current in an inversely proportional relationship to the rotational speed. For the increase, the degree of increase in the motor induced voltage due to the secondary induced voltage is slowed down and the margin for the external power supply voltage is retained, so that the vector controllable range is expanded. In that arrangement, where there is a change to the external power supply voltage, for example, if V _i with the change in the output voltage specification of the external power source for supplying an input voltage V _i to the inverter main circuit is changed, the change is the voltage of the V _i The control is performed by the detection means so as to correct the set rotational speed for starting the field weakening so as to decrease as the detected voltage decreases. As a result of this correction, the required power supply voltage margin is automatically maintained according to the level of the external power supply voltage.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIGS. And a voltage detecting circuit 14 to the power supply bus 13 between the input side and the external power supply (DC power supply) 12 which provides an input voltage V _i to the inverter main circuit 2 of the inverter main circuit 2 is provided. The voltage detection circuit 14 is composed of a comparison circuit 14b for comparing a voltage signal obtained by the voltage dividing resistance circuit 14a with a rated voltage _Vr which is a predetermined standard value predetermined for the induction motor 1. Is a voltage level identification signal V _d for identifying V _i = V _r , V _i <V _r , V _i > V _r .

On the other hand, the field weakening circuit 15 is provided with the field weakening characteristic shown in FIG. 2 between the motor speed N and the field component current Id given to the mixer 9. The characteristic curve L1 is selected by the voltage level identification signal Vd output from the voltage detection circuit 14 when V _i <V _r , L2 when V _i = V _r , and L3 when V _i > V _r , respectively. (The selecting means is the correcting means). In addition, as shown by the field weakening characteristic shown in FIG. 2, the correction control start rotation speed (set rotation speed), which is the start rotation speed of the field weakening operation.
Is N = N1 when V _i <V _r and N = N when V _i = V _r
2 and V _i > V _r , N = N3. Other configurations are the same as those shown in FIG. 3, and in FIG. 1, the same parts as those in FIG.

The operation of the above configuration will be described. Induction motor 1
Of the external power supply voltage V _i is determined to be lower than V _r by the voltage detection circuit 14 in the feedback control in which the number of revolutions is vector-controlled so as to match the command value based on the torque command signal I _q and the magnetic flux command signal I _d. Then, the field weakening characteristic indicated by L1 is selected by the voltage level identification signal Vd, and when the motor rotational speed N shifts to a region of N1 or more, I _d is corrected so as to change in inverse proportion to N. result, the magnetic flux is reduced rising degree of the electric induction motor voltage Ve blunted as shown in FIG. 2, therefore, with respect to V _e
The state in which _Vi is larger than the predetermined value, in other words, the voltage state in which the torque component current of the induction motor 1 can be supplied is maintained despite the increase of N, and the vector controllable range is expanded.
When it is determined that V _i = V _r , the field weakening start rotation speed is changed to N2 which is higher than N1, and when it is determined that V _i > V _r , it is changed to N3 which is higher than N2.

This is because the lower the external power supply voltage V _i , that is, the smaller the margin of the external power supply voltage with respect to the motor rated voltage, the lower the field-weakening start set rotational speed. It is avoided that the power supply voltage is reduced. This also means that the rated voltage of the induction motor can be operated in a state closer to the external power supply voltage V _i than ever before, and the load current is reduced accordingly, so that loss is expected to be reduced and the capacity of the inverter switching element is expected to be reduced. it can. Of course, in the above description, the term inversely proportional is not limited to the linear change characteristic.

[0015]

According to the present invention, the vector controllable range can be widened and the motor rated voltage can be increased without increasing the margin of the magnitude of the external power supply voltage with respect to the motor rated voltage in advance. Since the load current loss can be reduced and the capacity of the switching element for the inverter can be reduced because the voltage margin given to the external power source is reduced, high efficiency utilization can be achieved, which is economically advantageous.

[Brief description of drawings]

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

FIG. 2 is a diagram showing a field weakening characteristic and a motor induced voltage characteristic in one embodiment.

FIG. 3 is a view corresponding to FIG. 1 showing a conventional example.

[Explanation of symbols]

In the figure, 1 is an induction motor, 2 is an inverter main circuit, 3 is a rotation speed detector, 5 is a first coordinate conversion unit, 7 is a first mixer, 9 is a second mixer, and 10 is a second. Coordinate transformation part of 11
Is a PWM control unit, 12 is an external power supply, 14 is a voltage detection circuit, and 15 is a field weakening circuit.

Claims (2)

[Claims] 1. A vector control means for separately controlling a primary current of an induction motor into a torque component current and a field component current, and controlling the field component current when the rotation speed of the motor exceeds a set rotation speed. A vector control inverter device for an induction motor, comprising field weakening means for decreasing the rotational speed as it increases and correction means for making the set rotational speed a lower value as the external power supply voltage for the motor is lower. 2. An inverter main circuit for supplying a primary voltage to an induction motor, and a primary current supplied from the inverter main circuit to the induction motor is divided into a torque component current and a field component current, each of which is a torque command. Means for controlling by a signal and a magnetic flux command signal, rotation speed detection means for detecting the rotation speed of the electric motor, and rotation of the field component current when the rotation speed signal given by this rotation speed detection means exceeds a set rotation speed. Field weakening means to decrease as the number increases,
A vector control inverter device for an induction motor, comprising: a voltage detecting means for detecting an input voltage to the inverter main circuit; and a correcting means for lowering the set speed as the detected voltage is lower.