JPH04312382A - Control method for induction motor - Google Patents

Abstract

PURPOSE:To facilitate speed control in a high revolution region by a method wherein vector control with a speed sensor is performed if a speed is smaller than a speed at which a revolution detector can detect an accurate revolution and vector control without a speed sensor is performed if the speed is larger than that speed. CONSTITUTION:If the speed of an induction motor 1 exceeds a speed at which a revolution detector 2 can detect an accurate revolution, vector control with a speed sensor can not be performed. Therefore, a switch 12 is so turned as to have a speed signal omegar on the output side of a torque current controller 8 to perform vector control without a speed sensor. That is, the torque current controller 8 estimates the motor speed omegar so that a torque current instruction value IT' agrees with a torque current estimated value IT. With this constitution, the speed control of the induction motor can be performed even if the speed is larger than the speed at which the revolution detector can detect accurate revolution.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a control method using vector control of an induction motor, and more particularly to a control method applied to a high-speed spindle drive of a machine tool.

0002

2. Description of the Related Art FIG. 2 shows the configuration of a system. This system includes an induction motor a, a rotation speed detector b attached to the induction motor a, and an inverter c that detects the rotation speed and drives the induction motor a.

[0003] In the prior art, during low speed rotation, an inverter device c performs vector control with a speed sensor based on a detection signal ωr from a rotation speed detector b to drive an induction motor. However, if servo performance is required during low-speed operation or a high-resolution rotational speed detector b is required for positioning control, the detection signal ωr of the rotational speed detector b is high-frequency during high-speed rotation. , and the detection signal ω
The speed sensor vector control becomes impossible. Conventionally, the induction motor was driven under constant V/f control that did not require the detection signal ωr of the rotational speed detector b during high-speed rotation.

0004

However, in the prior art, there is a problem in that in a high-speed rotation region where constant V/f control is performed, speed control that is possible with vector control with a speed sensor cannot be achieved. Therefore, an object of the present invention is to enable speed control even in the high-speed rotation range.

[0005]

[Means for Solving the Problems] In order to solve the above problems, the present invention includes an induction motor, a rotation speed detector attached to the induction motor, and an inverter device that detects the rotation speed and drives the induction motor. In the method for controlling an induction motor, if the speed of the induction motor is smaller than the speed at which the rotation speed detector can accurately detect the rotation speed, vector control with a speed sensor is performed, and if it is larger, speed sensorless vector control is performed. It is characterized by doing.

[0006]

[Operation] In the present invention, speed sensorless vector control is applied, which is inferior in control performance to speed sensor-equipped vector control at high speed rotations, but allows speed control that cannot be achieved with constant V/f control. This allows speed control even in the high-speed rotation region.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A specific embodiment of the present invention will be described below with reference to the control block diagram of FIG. This system consists of an induction motor 1
It consists of a rotation speed detector 2 attached thereto, and an inverter device 3 that detects the rotation speed and drives the induction motor 1. The inverter device 3 includes a speed control section 4, a magnetic flux control section 5, a current control section 6, a magnetic flux/torque current estimator 7, a torque current controller 8, a slip frequency calculator 9 including a motor circuit constant 10, and a motor constant correction It is composed of a function 11, a switch 12 for switching between a detected speed value and an estimated speed value, a primary current command generator 13, an excitation inductance function 14, a multiplier 15, a power converter 16, and an integrator 17.

[0008] Vector control generally involves finding the torque generation mechanism of a motor using a mathematical solution, inversely developing it, and controlling the voltage, frequency, and phase applied to the motor so that it generates torque faithfully to the torque command. It is something. If this mathematical solution is simplified and expressed, it will be as shown in equations (1) to (7). Torque T=kφ2
IT
(1) Excitation current amplitude IM = (1
/M)φ2 (2)
Primary current amplitude I1 =√(IM2
+IT2) (3)
Primary current delay angle θT = tan-1(IT
/IM ) (4) Primary frequency ω1 = ωr + ωs
(5) 1
Next current vector I1 =I1 ∠θ1
(6) Slip frequency ωs = Ks (IT /φ2)
(7) Therefore, in the inverter,
Vector control is performed based on equations (1) to (7). The magnetic flux control unit 5 controls the command magnetic flux φ2* and the estimated magnetic flux value φ2 so that they match, and the output thereof is converted into the exciting current command IM* via the exciting inductance function 14 as shown in equation (2). . The output of the speed control section 4 is the torque current command I
T*, the primary current command generator 13 is (3), (
4) Output I1* and θT* based on the formula. On the other hand, 1
The next frequency calculation is performed by the slip frequency calculator 9 based on equation (7), and outputs a slip frequency signal ωs*. Based on equation (5), the speed signal ωr and the slip frequency signal ωs* are added to create the primary frequency signal ω1, and the value integrated by the integrator 17 and the primary current delay angle θT* are added, A primary current phase angle θ1* is generated. Multiplier 15
are the primary current command amplitude I1* and θ1* based on equation (6).
The primary current command vector I1* is generated by multiplying the The current command unit 6 generates a primary current command vector V1* so that the same current as the primary current command vector flows,
The power converter 17 generates the necessary voltage, frequency, and phase and supplies it to the induction motor 1. In the magnetic flux/torque current estimator 7, the primary current vector I1 and the primary voltage command vector V
1*, the estimated torque current value IT and the estimated magnetic flux value φ2 are obtained. Inverter output voltage V1 may be used instead of primary voltage command vector V1*.

In the present invention, when the speed of the induction motor 1 is smaller than the speed at which the rotational speed detector 2 can accurately detect the rotational speed, the switch 12 changes the signal of the rotational speed detector 2 to the speed signal ωr. Then, perform vector control with a speed sensor. At the same time, the torque current command IT*
and torque current estimated value IT are input to the torque current controller 8. Here, the estimated torque current value can be expressed as follows from equation (7). IT = (ωsφ2)/Ks
(8
) Also, since the estimated magnetic flux value φ2 is controlled by the magnetic flux controller 5 to match the command magnetic flux φ2*, φ2*
is considered to be equal to φ2. Moreover, rotation speed detector 2
Since the output of is used in the calculation formula (5) of the primary frequency,
The actual slip frequency ωs is equal to the slip frequency signal ωs*. Therefore, the torque current command IT* can be expressed as the following equation. IT*=(ωsφ2)/Ks
* (9
) Here, Ks* is a motor circuit constant output by the motor constant correction function 11. Therefore, the difference between the torque current command IT* and the estimated torque current value IT occurs because the motor circuit constant Ks* does not match the true motor circuit constant Ks. Therefore, the torque current controller 8 outputs a torque current command IT* during vector control with a speed sensor.
It has a function of correcting the motor circuit constant Ks* so that the estimated torque current value IT coincides with the motor circuit constant Ks*, thereby bringing the motor circuit constant Ks* closer to the true motor circuit constant Ks.

In the present invention, when the speed of the induction motor 1 becomes higher than the speed at which the rotational speed detector 2 can accurately detect the rotational speed, vector control with a speed sensor cannot be performed as described in the section of the prior art. Therefore, the switch 12 is set to a state where the output side of the torque current controller 8 is set as the speed signal ωr, and speed sensorless vector control is performed. Here, the motor constant correction function 11 holds the value of Ks* used in vector control with speed sensor. Assuming that the motor constant Ks* is equal to the true motor constant Ks,
Equation (9) can be expressed as the following equation. IT*=(ωs*φ2)/K
s (
9)' Therefore, from equations (8) and (9)', it is considered that the difference between the torque current command IT* and the estimated torque current value IT is caused by the difference between the slip frequency signal ωS* and the true slip frequency ωs. It will be done. Therefore, the torque current controller 8 has a function of estimating the motor speed ωr so that the torque current command IT* matches the estimated torque current value IT. If the motor constant Ks* is equal to the true motor constant Ks, the motor speed will perfectly match the motor speed estimate ωr. In this way, even with speed sensorless vector control, since the estimated motor speed value ωr is available, the speed of the induction motor 1 can be controlled.

[0011]

[Effects of the Invention] As described above, according to the present invention,
It is now possible to control the speed of an induction motor even when the rotation speed is higher than the rotation speed can accurately detect.

[Brief explanation of drawings]

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

FIG. 2 is a system configuration diagram of an induction motor control device.

[Explanation of symbols]

1 induction motor, 2 rotation speed detector, 3 inverter device, 4 speed control unit 5 magnetic flux control unit, 6 current control unit, 7 magnetic flux/torque current estimator 8 torque current controller, 9 slip frequency calculator,
10 Motor circuit constant 11 Motor constant correction function, 12 Switch, 13
Primary current command generator 14 Excitation inductance function, 15 Multiplier, 1
6 Power converter 17 Integrator, 18 Current detector, 19 Voltage detector ωr* Speed command ωr Speed detection signal IT* Torque current command IT Torque current estimated value φ2* Command magnetic flux φ2 Magnetic flux estimated value IM* Exciting current command I1* Primary current command I1* Primary current command vector I1 Primary current vector V1* Primary voltage command vector V1 Inverter output voltage ω1 Primary frequency θT* Primary current delay angle θ1* Primary current phase angle ωs* Slip frequency command

Claims (2)

[Claims] 1. A method for controlling an induction motor, comprising: an induction motor; a rotation speed detector attached to the induction motor; and an inverter device that detects the rotation speed and drives the induction motor. A method for controlling an induction motor, characterized in that when the speed is smaller than the speed at which a speed detector can accurately detect the rotation speed, vector control with a speed sensor is performed, and when the speed is larger, vector control without a speed sensor is performed. 2. A speed control section that receives as input the speed detection signal of the rotation speed detector according to claim 1 and a speed command given to the inverter device and controls the actual speed to match the command speed; a magnetic flux/torque current estimator that receives an output detection voltage or a control signal equivalent thereto and an output detection current of the inverter or a control signal equivalent thereto, and outputs an estimated torque current value and an estimated magnetic flux value; It has a torque current control section that compares and controls the output torque current command and the estimated torque current value, and during vector control with a speed sensor, the torque current control section operates as a motor circuit constant correction function to obtain the slip frequency command. and during speed sensorless vector control, control is performed based on motor circuit constants that were corrected during vector control with speed sensor, and the torque current control section is operated as a speed estimator. Item 1. A method for controlling an induction motor according to item 1.