JPH0630587A - Control apparatus for induction motor - Google Patents

Abstract

PURPOSE:To detect the temperature of an induction motor without using a special temperature detector and perform the detection or forecast of overheat. CONSTITUTION:Secondary resistance estimating means 11 receives state variables of a vector control of an induction motor 1 from a vector control part 5 and estimates a secondary resistance value of the induction motor 1 and outputs the estimated value to secondary resistance/temperature conversion means 12. The secondary resistance/temperature conversion means 12 uses a table of secondary resistance to that of temperature characteristics of the induction motor 1 previously obtained by an experiment, and obtains a corresponding motor temperature from the estimated secondary resistance value of the induction motor 1 and outputs the temperature.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an induction motor controller, and more particularly to an induction motor controller for detecting overheating of a rotating induction motor.

[0002]

2. Description of the Related Art In conventional induction motor control devices, induction motors are widely used in the FA field, such as those in which the spindle of a machine tool is rotated at a constant speed, and those in which a position loop is assembled for simple positioning. ing. In addition, induction motors have not been used in high-precision positioning devices until now because they require more complicated vector control than synchronous motors, but in recent years, due to the development of microcomputers and DSPs (digital signal processors), etc. Now that high-precision vector control can be realized, the range of applications is expanding to the fields where synchronous motors were used.

FIG. 3 is a block diagram showing an example of a conventional induction motor control device. In FIG. 3, 1 is an induction motor,
Reference numeral 2 is an encoder for detecting the rotation position of the induction motor, 3 is differentiating means for differentiating the motor position information obtained from the encoder 2, 4 is a speed control unit for controlling the motor rotation speed, and 5 is vector control for the motor torque. Vector control unit, 6 is a motor cooling means for cooling the induction motor 1,
A temperature detector 7 detects the temperature of the induction motor.

The speed controller 4 receives the motor speed command ωc from the host controller, feeds back the rotational speed ωm of the induction motor obtained from the differentiator 3, and outputs the torque current command iqc to the vector controller 5. . The vector control unit 5 controls the torque current command iqc and the exciting current command idc.
Is input, the motor rotation speed ωm and the motor three-phase AC currents (iu, iv, iw) are fed back, vector control is performed, and the three-phase AC voltage command (Vu, Vv, Vw) is applied to the induction motor 1.

The vector control process is performed as follows. First, the three-phase AC current (iu, iv, iw) flowing through the motor
Is fed back and the torque current component i is converted by coordinate transformation.
q and the exciting current component id are separated. This coordinate system is dq
It is called a coordinate system and can be expressed by the following equation (1).

[0006]

Next, the motor currents id and iq obtained by the equation (1) are used as the exciting current command idc and the torque current command iq.
A voltage command consisting of an excitation current control voltage command Vdc and a torque current control voltage command Vqc is controlled so as to match c, and this is converted into a three-phase AC voltage command (Vu, Vv, Vw) as shown in equation (5). The coordinates are converted and applied to the induction motor.

[0008]

As described above, in the vector control of the induction motor, the currents id and iq of the motor are controlled by the feedback control.
Is controlled so that the current commands idc and iqc are obtained, and the slip frequency is controlled as in Expression (3).

[0010]

In the induction motor control device described above, the induction motor constantly supplies the exciting current id for generating the magnetic flux. The cooling means 6 is provided to cool the motor. However, in the case of overload operation or failure of the motor cooling means 6, the induction motor may be abnormally heated and the motor winding may be burned. Therefore, the temperature detector 7 for detecting the overheat of the motor is used. Motor overheat is detected. Generally, many temperature detectors for detecting overheat are simple ones that open and close when an abnormal temperature is reached. For this reason, there are many cases where an alarm suddenly occurs during driving. Considering the case where an induction motor is used as the spindle of a machine tool, if an alarm like this occurs during cutting of a workpiece, the workpiece being machined may be defective and a major obstacle to unmanned operation. Becomes Therefore, measures such as observing the temperature rise of the induction motor and predicting the overheat to loosen the operating conditions can be considered, but in this case, an expensive temperature detector is required to measure the temperature of the induction motor. There is a problem that it will come.

It is an object of the present invention to provide means for detecting the temperature of an induction motor by estimation without using a special temperature detector, detecting overheat, and predicting overheat.

[0012]

SUMMARY OF THE INVENTION An induction motor control device of the present invention includes an encoder for detecting the rotational position of an induction motor and outputting it as position information, a differentiating means for differentiating the position information, and a rotational speed of the induction motor. , A vector control unit for controlling the torque of the induction motor by vector control, and a secondary resistance estimation for estimating a secondary resistance value of the induction motor by inputting a state variable of the vector control unit. And a secondary resistance / temperature conversion means for obtaining the motor temperature corresponding to the secondary resistance value estimated by the secondary resistance estimation means.

[0013]

The present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram showing an embodiment of an induction motor control device of the present invention.

In FIG. 1, 1 is an induction motor, 2 is an encoder for detecting the rotational position of the induction motor, 3 is differentiating means for differentiating the motor position information obtained from the encoder 2,
4 is a speed control unit for controlling the motor rotation speed, 5 is a vector control unit for controlling the motor torque by vector control,
Reference numeral 11 is a secondary resistance estimation means for estimating the secondary resistance value of the induction motor 1 by inputting the state variable of the vector control unit 5, 6 is a motor cooling means for cooling the induction motor 1, and 12 is a secondary resistance estimation means 11 It is a secondary resistance / temperature conversion means for obtaining the corresponding motor temperature from the secondary resistance value estimated in step S4.

Next, the operation of estimating the secondary resistance value of the induction motor 1 will be described. Induction motor secondary resistance R2
Has a tendency to increase as the motor temperature increases. The fluctuation range of R2 is about 10 to 20% / 50 [deg.] C. and has the property of monotonically increasing as shown in FIG.

When the secondary resistance value R2 of the induction motor fluctuates due to a rise in motor temperature, the control state of the vector control of the induction motor deviates from the previous state, and the secondary resistance value R2 of the induction motor is estimated in reverse from the control state. You can There are two methods of estimation: one is to give a test signal from the outside to observe the response of the control system, and the other is to make an estimation during normal operation without giving a test signal. What is estimated when driving the state is shown. In addition, there are some algorithms that take into account the estimation error such as least-squares estimation, but here we will show a simple method of directly calculating from equations.

[0018]

However, Vd, Vq: d axis, q axis motor primary voltage id, iq: d axis, q axis motor primary current Φ2d, Φ2q: motor secondary magnetic flux d axis component, q axis component R1, R2: Motor primary and secondary resistances L1 and L2: Motor primary and secondary inductances M: Mutual inductance σ: Leakage coefficient ω0: Power frequency (= ωm + ωs) ωm: Motor speed ωs: Slip frequency P: Differential operator (= D / dt). Considering the steady rotation state of the motor, equation (6) becomes equation (7).

When the secondary resistance value R2 fluctuates, the slip coefficient K given by the equation (4) deviates from the actual value and the slip frequency ω
s becomes incorrect. The motor currents id and iq among the control state quantities of the vector control are controlled to the current commands idc and iqc by the feedback control regardless of the fluctuation of R2, but deviate from the exciting current control voltage command Vdc and the torque current control voltage command Vqc. If there is no coordinate conversion error, it is considered that the voltages Vd and Vq applied to the induction motor match the voltage commands Vdc and Vqc. Therefore, id, iq, Vd, Vq, ω0, and ωs in the steady state are all vector control. Is a state variable and is a known quantity. Therefore,
From the first and second equations of equation (7), the motor secondary magnetic flux Φ2
d and Φ2q can be calculated as in Expression (8).

[0021]

Next, assuming that the value of the secondary resistance of the induction motor fluctuates by γ times, the slip coefficient of the equation (4) becomes 1 / γ times the proper value.

[0023]

Γ can be calculated from any of the equations (11), and the value of the secondary resistance of the induction motor is calculated as γ × R2. As described above, the secondary resistance estimation means 11 causes the vector control unit 5 to perform vector control state variables id, iq,
By inputting Vd, Vq, ω0 and ωs, equation (8) and equation (1
According to 1), the secondary resistance value of the induction motor 1 is estimated as γ × R2.

The secondary resistance / temperature converting means 12 obtains the corresponding motor temperature from the secondary resistance value estimated by the secondary resistance estimating means 11. The secondary resistance-temperature characteristics of the induction motor are measured in advance as shown in FIG.
The motor temperature is output by the secondary resistance value using the secondary resistance / temperature conversion table.

[0026]

As described above, the induction motor control device of the present invention utilizes the fact that the secondary resistance value of the induction motor fluctuates depending on the motor temperature. By estimating the secondary resistance value and obtaining the temperature of the induction motor from the estimated secondary resistance value, it is possible to detect the overheat of the induction motor and to predict the occurrence of overheat without using a special temperature detector. Become.

[Brief description of drawings]

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

FIG. 2 is a characteristic diagram of secondary resistance-temperature of the induction motor of this embodiment.

FIG. 3 is a block diagram of an example of a conventional induction motor control device.

[Explanation of symbols]

 1 Motor 2 Encoder 3 Differentiating Means 4 Speed Control Unit 5 Vector Control Unit 6 Motor Cooling Means 7 Temperature Detector Part 11 Secondary Resistance Estimating Means 12 Secondary Resistance / Temperature Converting Means

Claims (1)

[Claims] 1. An encoder for detecting a rotational position of an induction motor and outputting it as position information, a differentiating means for differentiating the position information, a speed control unit for controlling a rotation speed of the induction motor, and a torque of the induction motor. Is controlled by vector control, a secondary resistance estimating means for estimating a secondary resistance value of the induction motor by inputting a state variable of the vector control portion, and a secondary resistance estimating means for estimating 2 Secondary resistance to find the motor temperature corresponding to the secondary resistance value /
An induction motor control device comprising: a temperature conversion means.