JPH07213100A - Sensorless inverter apparatus provided with resistance-change compensation - Google Patents

Abstract

PURPOSE:To restrain the control accuracy of a speed from being degraded by providing a resistance change estimation means which estimates a change in a secondary resistor on the basis of the current of an output from a current detection means and on the basis of the operating time so as to output the change to a speed operation means. CONSTITUTION:A resistance-change estimation device 111 to which a current is input estimates a rise in the temperature of an electric motor 4 by means of Formula I, it estimates a change in a secondary resistor by means of Formula II, and it outputs a corrected secondary resistor R2 to a current-system magnetic-flux operation device 62 and a speed operation device 72. A secondary resistor R2n in Formula II at this time is sent by a resistance measuring and setting device 12. Thereby, arithmetic is performed by using the corrected secondary resistor in the current-system magnetic-flux operation device 62 and the speed operation device 72.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a speed sensorless type device for driving an induction motor by an inverter, and more particularly to a sensorless inverter device with resistance compensation which suppresses characteristic changes due to temperature changes.

[0002]

2. Description of the Related Art A prior art sensorless inverter device for controlling the torque and speed of an electric motor with high accuracy and high speed without attaching a speed detector to the induction motor is shown in FIG. Figure 4
, 1 is an inverter, 2 is a current detector, 3 is a voltage detector, 4 is an induction motor (hereinafter simply referred to as an electric motor),
5 is a voltage-based magnetic flux calculator, 61 is a current-based magnetic flux calculator, 71 is a speed calculator, 8 is a torque calculator, 9 is a speed controller, and 10 is a torque-flux controller.

The inverter 1 receives a switching signal output from the torque flux controller 10, and the inverter 1 is operated according to the switching signal. The output of the inverter 1 is connected to the electric motor 4 via the current detector 2 and the voltage detector 3, and the inverter 1 can apply a voltage to the electric motor 4. The voltage system magnetic flux calculator 5 is the current detector 2
Input the output current i and the voltage detector 3 output voltage v, and also input the current system magnetic flux calculator 61 output magnetic flux ψi, and
Calculate v according to equation (1).

[0004]

[Equation 1]

Where L1 is the primary self-inductance,
L2 is a secondary self-inductance, M is a mutual inductance, R1 is a primary resistance, and K is a drift compensation gain.
The speed calculator 7 calculates the rotation speed ωm from the magnetic flux ψv and the current i according to the equation (2).

[0006]

[Equation 2]

Here, ω is the rotational angular velocity of the magnetic flux ψv, and R2 is the secondary resistance. The current system magnetic flux calculator 61 calculates the magnetic flux ψi by the equation (3).

[0008]

[Equation 3]

The torque calculator 8 calculates the torque T from the magnetic flux ψi and the current i, and outputs it to the torque magnetic flux controller 10. In addition to the torque command T *, the magnetic flux command ψ *, and the magnetic flux ψi, the torque magnetic flux controller 10 inputs a switching signal such that the torque and the magnetic flux follow these commands.
Output to. The speed controller 9 inputs the speed command ωm * and the calculated rotation speed ωm, and outputs the torque command T * such that the speed follows the command.

[0010]

As described above, in the prior art, the secondary resistance R2 is used to calculate the rotation speed ωm, but this value fluctuates depending on the temperature of the electric motor, and ω depends on the temperature fluctuation.
A calculation error occurs in m. Therefore, the speed control accuracy deteriorates.

[0011]

The present invention has the following construction in order to solve the above-mentioned problems. Therefore, in the sensorless inverter device, resistance measurement setting means for measuring the secondary resistance of the electric motor when it is cold and setting it in the inverter, and the secondary resistance fluctuation of the electric motor are estimated from the current output from the current detection means and the operating time to calculate the speed. And a resistance fluctuation estimating means for outputting to the means.

Further, in order to estimate the temperature rise of the motor immediately after the control power supply of the sensorless inverter device is turned on, the charge / discharge circuit of the resistor and the capacitor and the charge / discharge circuit of the sensorless inverter device after the control power supply of the sensorless inverter device are turned on. The time when the control power supply is off is estimated by measuring the capacitor voltage, and the motor temperature rise when the control power supply is turned on from that time and the motor temperature rise value of the resistance fluctuation estimation means output when the control power supply is turned off. A first initial value measuring unit that estimates a value and sets it as an initial value of the resistance variation estimating unit is configured.

Furthermore, in place of the above-mentioned first initial value measuring means, the resistance of the electric motor is measured at the start of operation after the control power supply of the sensorless inverter device is turned on, and is set as the initial value of the resistance fluctuation estimating means. It is configured by including two initial value measuring means.

Further, firstly, the motor resistance measuring means in the second initial value measuring means applies the DC voltage from the inverter to the motor and measures the resistance of the motor from the current and voltage at that time. It is a thing. Secondly, a rectangular wave voltage for a short time is applied to the electric motor from the inverter, and the resistance of the electric motor is measured from the current rising characteristic at that time.

[0015]

Most of the heat generated from the electric motor is generated by the current flowing through the winding resistance of the electric motor, and it is considered that the generated heat is proportional to the square of the current I. Further, in consideration of the heat resistance and heat capacity with the outside air, the temperature rise θ of the electric motor can be approximated by a first-order delay as shown in equation (4).

[0016]

[Equation 4]

Here, K is a conversion gain, and T is a time constant. The resistance of the winding is almost proportional to the temperature, and therefore the secondary resistance R2 can be estimated by the equation (5).

[0018]

[Equation 5]

Here, K1 is a conversion coefficient between temperature and resistance, R2n is a secondary resistance when the temperature of the motor is the same as the ambient temperature, and is set by the resistance measuring means.
In this way, the resistance fluctuation estimating means described in the above-mentioned solving means estimates the fluctuation of the secondary resistance due to the temperature change by the above calculation.

If the control power supply of the sensorless inverter is turned off, the calculation of the equation (4) cannot be performed. Therefore,
The first initial value measuring means measures a value Vc1 of the capacitor voltage Vc of the charging / discharging circuit by the resistor and the capacitor immediately before the control power supply is turned off and a value Vc2 immediately after the control power supply is turned on, and the voltage ratio thereof is measured. Estimate the time when the control power supply was off, and from that time and the temperature increase value θ1 in equation (4) immediately before the control power supply was turned off, the motor temperature rise value immediately after the control power supply was turned on according to equation (4) And θ0 which is the initial value of the equation (4) can be obtained.

Further, in the second initial value measuring means, the DC voltage is applied to the electric motor by PWM control on average, and if the application time is long, the primary resistance can be measured from the applied voltage and the current. Temperature rise of primary resistance R1 and secondary resistance R
If the temperature rise of 2 is the same, from equation (6), equation (4)
The initial value of can be obtained.

[0022]

[Equation 6]

Here, R1n is the primary resistance when the motor or the ambient temperature is the same. When the application time is short, the current Ix after a fixed time is measured. The ratio of the fluctuation of the current value in the second initial value measuring means to the value of the current Ix0 by the similar method in the case of the secondary resistance R2n is almost the same as the ratio of the resistance fluctuation, and from the formula (7), the formula (7) The initial value of 4) can be obtained.

[0024]

[Equation 7]

That is, in the first and second initial value measurements, the temperature rise of the electric motor when the control power source is turned on is obtained, and the resistance variation estimating means estimates the temperature rise of the electric motor during operation, so that the temperature rise By estimating the fluctuation of the secondary resistance and correcting the secondary resistance used in the speed calculation means, the speed fluctuation due to the temperature fluctuation can be controlled. In addition, the second initial value measuring means can measure the resistance to accurately grasp the temperature rise of the electric motor even after the power failure is recovered, and the versatility is improved as compared with the first initial value measuring means.

[0026]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows a main structure of an embodiment of the present invention. 62 is a current system magnetic flux calculator, 72 is a speed calculator, 111 is a resistance fluctuation estimator, and 12 is a resistance measurement setting device. is there. In the figure, the same reference numerals as those in FIG. 4 indicate components having the same functions.

In such a circuit configuration, the resistance fluctuation estimator
111 inputs the current I, estimates the temperature rise of the electric motor 4 by the equation (4), estimates the secondary resistance variation by the equation (5),
The corrected secondary resistance R2 is output to the current system magnetic flux calculator 62 and the speed calculator 72. R2n in the equation (5) at that time is set by the resistance measurement setting device 12. As a result, the current system magnetic flux calculator 62 and the speed calculator 72 can be calculated using the modified secondary resistance.

In FIG. 1, the temperature rise value of the electric motor immediately after the control power source is turned on is undetermined, and the initial value of the temperature rise value of the equation (4) of the resistance fluctuation estimator 111 cannot be set. Therefore, the configuration as shown in FIG. 2 or FIG. 3 is adopted. FIG. 2 shows an example of a circuit in which an initial value measuring means according to the present invention is used. 112 is a resistance fluctuation estimator, 131 is an initial value measuring device,
14 is a charging / discharging circuit. That is, the resistance variation estimator 112
In addition, an initial value measuring device 131 as an initial value measuring means and a charging / discharging circuit 14 are added.

In the charging / discharging circuit 14, 141 is a control power source, 142 is a charging resistor, 143 is a charging diode, and 14 is a charging diode.
4 is a discharge resistor and 145 is a capacitor. Initial value measuring instrument
Reference numeral 131 is for obtaining the output of the capacitor 145 of the charge / discharge circuit 14, and measures the capacitor voltage immediately before the control power supply 141 is turned off and immediately after it is turned on. Then, the initial value measuring device 13
1 estimates the time during which the control power supply is off from the voltage ratio, estimates the temperature rise θ 0 of the electric motor when the control power supply is on according to equation (4), and outputs it to the resistance variation estimator 112. The resistance variation estimator 112 uses this θ0 as the initial value of the equation (4).

FIG. 3 shows an example of a circuit in which another example of the initial value measuring means according to the present invention is used. 113 is a resistance fluctuation estimator, 132 is an initial value measuring device, and 15 is a switch. That is, the resistance variation estimator 113 is provided with an initial value measuring device 132 and a switch 15 as initial value measuring means. Then, the switch 15 can be closed to the initial value measuring instrument 132 side only when the operation is started immediately after the control power supply is turned on. Further, the inverter 1 can be operated by the switching signal output from the initial value measuring device 132. A DC voltage is applied to the electric motor 4 by this switching signal, and the initial value measuring device 132 measures the electric current Ix of the electric motor at this time, and also estimates the temperature rise value θ0 from the equation (7) to estimate the resistance variation estimator 113. Output to. Further, the switching signal output from the initial value measuring device 132 may be applied to the inverter 1 as a rectangular wave voltage for a short time to obtain the rising characteristic of the current at that time, and the resistance of the electric motor can be measured in the same manner. .

[0031]

As described above, according to the present invention, it is possible to provide a special device in which the deterioration of the speed control accuracy due to the secondary resistance fluctuation due to the temperature rise of the induction motor is suppressed.

[Brief description of drawings]

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

FIG. 2 is a block diagram showing an example of a circuit in which an example initial value measuring means according to the present invention is used.

FIG. 3 is a block diagram showing an example of a circuit in which an initial value measuring means of another example according to the present invention is used.

FIG. 4 is a block diagram showing a conventional sensorless inverter device.

[Explanation of symbols]

 1 Inverter 2 Current detector 3 Voltage detector 4 Induction motor (motor) 5 Voltage system magnetic flux calculator 61 Ammeter magnetic flux calculator 62 Ammeter magnetic flux calculator 71 Speed calculator 72 Speed calculator 8 Torque calculator 9 Speed controller 10 Torque flux controller 111 Resistance fluctuation estimator 112 Resistance fluctuation estimator 113 Resistance fluctuation estimator 12 Resistance measurement setting device 131 Initial value measuring device 132 Initial value measuring device 14 Charge / discharge circuit 15 Switch

Claims (3)

[Claims] 1. A current detection means for detecting an input current of an induction motor, a torque control means for controlling a torque of the induction motor, a speed calculation means for calculating a rotation speed of the induction motor, and a rotation of an output of the speed calculation means. In a sensorless inverter device comprising speed control means for making speed follow its command value, a resistance measurement setting means for measuring the secondary resistance of the induction motor at the time of cold temperature and setting it in the inverter, and a current detection means output. A sensorless inverter device with resistance variation compensation, comprising: a resistance variation estimating means for estimating a secondary resistance variation from an electric current and an operating time and outputting it to the speed computing means. 2. The time when the control power supply is off is estimated by measuring the capacitor voltage of the charging / discharging circuit by the resistance and the capacitor immediately after the control power supply of the sensorless inverter device is turned on, and the time and control are performed. First initial value measuring means for estimating the motor temperature rise value when the control power source is turned on from the estimated motor temperature rise value output from the resistance variation estimating means when the power is off, and setting it as the initial value of the resistance variation estimating means. The sensorless inverter device with resistance fluctuation compensation according to claim 1, wherein 3. A second initial value measuring means for measuring the resistance of the induction motor and setting the initial value of the resistance fluctuation estimating means at the start of operation after the control power source of the sensorless inverter device is turned on. The sensorless inverter device with resistance fluctuation compensation according to claim 1.