JPH06303791A - Method of compensating temperature of secondary resistor of induction motor - Google Patents

Abstract

PURPOSE:To simplify the method of compensating the temperature of a secondary resistor by seeking the data on the thermal time constant of the secondary conductor of an induction motor and the stationary temperature rise value by an input current beforehand, and seeking the temperature of the secondary conductor at start of each operation from the mean square value in operation period of input currents and the measured value of ambient outside air temperature. CONSTITUTION:A mean square arithmetic unit 5 seeks the mean square Ims current Ims in one cycle of motor operation of the input currents i1 detected with a current detector 4. Next, an arithmetic unit 6 for temperature rise value at operation end seeks the stationary temperature rise value at the time of its input current from this means square current Ims, the thermal time constant Ia of the secondary conductor of a motor IM obtained in advance, and the stationary temperature rise value DELTATA, and seeks the temperature rise value of the secondary conductor at the end of operation. Next, an arithmetic unit 7 for the temperature rise value at operation start seeks the temperature rise value DELTATA at operation start from this conductor temperature rise value and the thermal time constant ta, and an adder 8 adds ambient outside air temperature to it so as to make the secondary conductor temperature Ta+DELTATR at operation start, and it outputs the value to a vector operation unit 1.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a secondary resistance temperature compensation method for an induction motor in inverter control.

[0002]

2. Description of the Related Art When controlling an induction motor (hereinafter simply referred to as an electric motor) with an inverter, a vector control system is often used. In that case, the secondary resistance of the electric motor is involved in the vector calculation, but since the secondary resistance of the electric motor changes with temperature, its temperature compensation is necessary.

Conventionally, as a temperature detecting method for temperature compensation, a temperature sensor is embedded in a primary coil or a frame of an induction motor to detect the temperature of a secondary rotor in a pseudo manner, or a current is supplied to the motor. A method is used in which the temperature of the secondary resistance is calculated by flowing the current and electrically calculating the transient characteristic.

[0004]

However, the method of embedding the temperature sensor in the primary coil or frame of the electric motor requires the temperature sensor and wiring from the sensor. Further, the method of electrically calculating from the transient characteristic requires complicated electric calculation, and none of them is easy.

The present invention has been made in view of the above problems of the prior art, and an object of the present invention is to detect a secondary current of an induction motor by detecting an input current without using a temperature sensor. It is an object of the present invention to provide a secondary resistance temperature compensation method for an induction motor that can easily perform temperature compensation.

[0006]

In order to achieve the above object, in the method for compensating the secondary resistance temperature of an induction motor according to the present invention, the temperature of the secondary side conductor of the induction motor is input to a vector computing section. In the one that compensates the secondary resistance of the induction motor, the thermal time constant of the secondary conductor of the induction motor and the data of the steady temperature rise value due to the input current are obtained by calculation or actual measurement, and the input current is detected. The secondary-side conductor temperature at the start of each operation of the induction motor is obtained using the root mean square value of the input current during operation, the above-mentioned data, and the ambient outside air temperature, and the secondary resistance temperature compensation of the induction motor is performed using this temperature. To do.

[0007]

Embodiments of the present invention will be described with reference to the drawings.
FIG. 1 shows a control circuit of an induction motor using an inverter, and FIG. 2 shows the relationship between the input current of the motor and the temperature rise of the secondary side conductor.

1 and 2, 1 is a voltage vector calculation unit, 2 is a PWM circuit, 3 is an inverter main circuit, 4 is an input current detector of the induction motor IM, and 5 to 8 are secondary conductor temperature detection circuits. 5 is the input current i ₁ detected by the current detector 4.
Root mean square calculation unit that calculates the _root mean square current I _ms during Δt _K (K represents the _Kth operation) during one cycle of the motor operation,
_{Reference numeral} 6 denotes the input from the _root mean square current I _ms , the thermal time constant t _A of the secondary conductor of the electric motor IM previously calculated or actually measured, and the steady temperature rise value ΔT _A due to the input current (root mean square current). A temperature rise value calculation unit at the end of operation that obtains a steady-state temperature rise value ΔT _AK at the time of current, and obtains a secondary side conductor temperature rise value ΔT _RK at the end of operation using equation (1)

[0009]

[Equation 1]

7 is the secondary conductor temperature rise value ΔT at the end of operation
_{From the RK-1} and the thermal time constant t _A , 2 at the start of operation according to the equation (2)
Operation start temperature rise value calculation unit for obtaining the secondary conductor temperature rise value ΔT ′ _RK , and 8 is the secondary conductor temperature rise value ΔT ′ at the start of operation
An adder for outputting the motor IM ambient outside air temperature T 2 primary conductor temperature at the start of operation by adding the _a T _R of _{(= T a + ΔT 'RK} ) to the voltage vector control unit 1 to _RK.

With the above configuration, the secondary resistance temperature compensation of the electric motor IM is compensated by the temperature at the start of each operation. If the temperature of the secondary conductor of the induction motor IM is repeatedly operated as shown in FIG. 2A, the temperature gradually rises as shown in FIG. 2D, but each temperature rise ΔT _R1 , ΔT _R2 −ΔT ′ _R1 , ΔT _Ra −Δ
Since _T'R2 , ... Is not so large, there is no problem in temperature compensation if temperature compensation of the secondary resistance is performed at the temperature at the start of each operation.

The ambient outside air temperature T _a can be represented by an average temperature when the temperature change is small.

[0013]

Since the present invention is configured as described above, it has the following effects.

(1) The secondary resistance can be simply temperature-compensated only by detecting the input current of the induction motor.

(2) Since temperature sensors and calculations based on complicated transient characteristics are not used, inexpensive temperature compensation can be performed.

[Brief description of drawings]

FIG. 1 is a block circuit diagram showing a secondary resistance temperature compensation circuit of an induction motor according to an embodiment.

FIG. 2 is an explanatory diagram showing a relationship between an input current and a temperature rise of a secondary conductor.

[Explanation of Codes] IM ... Induction motor 1 ... Vector calculation unit 2 ... PWM circuit 3 ... Inverter main circuit 4 ... Current detector 5 ... Root mean square calculation unit 6 ... Operation end temperature rise value calculation unit 7 ... Operation start Temperature rise value calculation unit 8 ... Adder t _A ... Thermal time constant ΔT _A ... Steady temperature rise value _Ta ... Outside air temperature

Claims (1)

[Claims] 1. In a method for compensating the secondary resistance of an induction motor by inputting the temperature of a secondary side conductor of the induction motor to a vector calculation unit, a steady state due to a thermal time constant and an input current of a secondary side conductor of the induction motor. The data of the temperature rise value is calculated or actually measured, and the input current is detected.
An induction motor characterized in that a secondary-side conductor temperature at the start of each operation of the induction motor is obtained using the root mean square value, the above-mentioned data, and the ambient outside temperature, and the secondary resistance temperature of the induction motor is compensated using this temperature. Secondary resistance temperature compensation method of.