KR970003821B1 - Rotor time constant measurement method and the apparatus - Google Patents

Abstract

The rotator time constant measuring method of an induction motor, in which a direct current source(15), a condenser(160, and a switch(14) are installed on the two of three phases of the induction motor, comprises the steps of: under the assumption that the current generated upon the turning on/off of the switch(14) is ir(off), obtaining an equation(1) as follows: ir(off) = Ioe-t/Tr, under the assumption that a voltage waveform of a stator shaft at this time is VLm, obtaining an equation(2) as follows: VLm = Lm (dir(off)/dt) = -Io(Lm/T) e-t/Tr, and obtaining a rotator time constant at a voltage of 36.8% upon turning-off of the switch(14); and measuring a momentary voltage upon the turning-off of the switch(14), and under the assumption that the voltage is Vs(off), inducing an equation(3) Vs(off) = -Io(Lm/T) from the equation(2), and obtaining a stator magnetization inductance Lm.

Description

Rotor time constant measurement method of induction motor and its device

An object of the present invention is to measure the rotor time constant so that the rotor time constant of the induction motor can be easily and accurately measured in the vector control required to improve the control response characteristics as the DC motor. It is intended to provide the device.

The present invention is provided with a switch in any two phases of the three phases of the induction motor to realize the above object, and applying and blocking a DC voltage of several to several tens of volts in the two phases according to the on-off state of the switch for a short time. When the energy accumulated in the magnetizing inductance in the motor is released to the rotor by detecting the voltage waveform on the stator side, the method and apparatus for measuring the rotor time constant are characterized.

1 is an embodiment of a system for measuring characteristic parameters of an induction motor according to the present invention.

2 is a more detailed circuit block diagram of FIG.

3 is an equivalent circuit diagram of an induction motor for explaining the present invention.

4 is a reference diagram showing the rotor current at the time of switching off in relation to FIG.

5 is a diagram of 1/4 hp (a) and 2 hp (b) induction motor oscilloscope stator voltage waveforms during switch-off according to the present invention.

* Description of the symbols for the main parts of the drawings *

1: time constant measuring device, 11: induction motor,

12: time constant detector, 13: vector slip calculator,

14 switch, 15 DC source,

16: condenser

Hereinafter, more specific features of the present invention will be understood by referring to the accompanying drawings in more detail.

That is, the method of measuring the time constant of the rotor according to the present invention is as follows.

Here, the rotor current from the moment the switch is temporarily turned on and off is reduced to the form shown in FIG. 4 when assuming that FIG. 3 is an equivalent circuit of an induction motor.

If the current at this time is i _{r (off)}

i_{r (off)}= I_oe^{t / Tr} (3)

The stator voltage waveform at this time is

V _Lm =

It becomes Since a voltage waveform of a voltage type is obtained in which the voltage form decreases exponentially from the initial DC level value, T _r is the time when the voltage value at the time of switch-off becomes 36.8%, and when the time is measured, _r can be found.

When the voltage at the time of switching off is measured and the voltage at that time is V _{s (off)} ,

Where the magnetization inductance L _m is

Since the rotor time constant and magnetization inductance, which are parameters used in equations (1) and (2), are obtained.

1 shows a time constant measuring apparatus 1 for a rotor according to the present invention.

Here, a rotor time constant detector 12 is connected to a conventional induction motor 11 having three phases a, b and c, and a rotor time constant detector 12 is connected to two phases a and b of three phases. Then, the parameters (rotor time constant and mutual inductance L _m ) calculated from the rotor time constant are input to the slip calculator 13.

In addition, the two-phase a, b stages were provided with a direct current source 15, a condenser 16 and a switch 14 in parallel connection.

FIG. 2 is an embodiment rotation block diagram showing the rotor time constant detector 12 of FIG. 1 in more detail.

Here, the time constant detector 12 inverts the sign of the amplifier 12a for amplifying the voltage generated in the two phases of the three-phase induction motor 11 when the switch 14 is turned on and off, and for inverting the sign of the output value of the amplifier 12a. DC voltage level detector 12c for maintaining a constant voltage of 36.8% of the voltage at the time of switching off from the inverter 12a and the output waveform of the amplifier 12a, the inverter 12b and the level detector 12c. The comparator 12d generates a predetermined pulse width output by comparing the outputs of each of the < RTI ID = 0.0 >), < / RTI > An AND gate 13a receiving the output of the generator 13c as another input and the output of the AND gate 13a are measured to measure the number of pulses, and the number of pulses measured is multiplied by the period of the clock generator. The time corresponding to the pulse width, that is, the time of the rotor It is comprised by the time constant indicator 13b which displays an integer.

The present invention has the following effects and effects.

In other words, in order to separate the currents from the AC motors without interference from each other, it is necessary to know the parameter values of the rotor time constant T _r = L _r / R _r and the stator magnetization inductance L _m as shown in Equations (1) and (2) above. The motor can be driven at the same fast response speed as the DC motor.

At this time, in the rotor time constant measuring method according to the present invention, an exponentially decreasing current value is obtained at a short moment of turning on and off the switch 14, and an exponentially fault-side voltage waveform is obtained to obtain the T _r and L _m. It will be easy to know.

In order to prove the validity of the present invention, only the rotor time constant was measured by the method according to the present invention and the method according to the no-load and restraint experiment with a 1/4 horsepower and two horsepower flow motors. 5 shows the voltage waveform displayed on the stator side when the switch of FIG. 1 is temporarily turned on and off for 1/4 horsepower (a) and 2 horsepower (b). The y-axis represents voltage and the x-axis represents time. Point A is the voltage and time when the switch is off and point B indicates the time of the voltage 36.8% to this voltage. Therefore, the comparator 12d output maintains the logic 1 state when the switch 14 of FIGs. 1 and 2 is turned off for the first time, and the comparator is at a time when the output signal of the level detector 12c coincides with the output of the inverter 12b. The output of (12d) is maintained at logic 0, thereby obtaining the time for the voltage at 36.8% of the stator side in pulse width.

The pulse width output provided by the comparator 12d is applied to one input of the two input and gate 13a, and the input of the clock frequency generator 13c having a predetermined clock frequency is input to the input. At this time, measure the number of pulses coming from the output of the AND gate. For example, assuming that the frequency of the clock generator is 100 kHz, the rotor time constant is obtained by multiplying the pulse output from the AND gate output by 1 / 100k [sec] of the pulse generator.

On the other hand, the following Table 1 and Table 2 shows an experimental example applied to 1/4 horsepower and 2 horsepower induction motor using the measuring method and the device according to the present invention.

TABLE 1

Parameters of Whole Induction Motor by No Load and Restraint Test

TABLE 2

Comparison of time constant value according to the conventional no-load, restraint test and the present invention

The experimental condition at this time was observed with the oscilloscope the voltage waveform of FIG. 4 shown on the stator when the switch 14 was turned on for a while and off. In FIG. 4, the y axis represents voltage and the x axis represents time.

In addition, Table 1 records the average value over several repeated experiments, and Table 2 shows the conventional rotor time constant measurement values obtained by no load and restraint experiments, and the rotor time constant measurement values according to the present invention. have.

The value was slightly different for each measurement, but did not deviate significantly from the mean value.

As can be seen from Table 1 and Table 2, the measured values according to the present invention and the conventional measured values correspond to each other.

However, through the conventional means, it is difficult to measure the time and power required for measuring the power and voltage values during no-load and restraint experiments, or for the task of restraining the rotor from rotating while the three-phase power is applied. In consideration of the above, it can be estimated how easily the measuring means of the present invention can be made.

Such a means for measuring the rotor time constant of the induction motor of the present invention can be realized by a simple method and a device, which is advantageous in that the ease and convenience of the measuring means can be provided well.

The technical field to which the invention belongs and the prior art in that field

The present invention relates to a means for measuring a rotor time constant of an induction motor used in an industrial field, which in particular measures the rotor time constant of such an induction motor to generate a magnetic flux of the current of the AC motor and torque generating current The present invention relates to a method and apparatus for measuring the rotor time constant of an induction motor, which can be separated by a vector control so as to expect a fast response speed such as a DC motor.

Induction motor is disadvantageous to have the same fast response speed as DC motor because it is AC motor load.

The AC motor load can be divided into a current component for generating a current and a current component for generating a torque in its driving. In the past, since there is no means to control the components of the driving current without interference, such as a DC motor It was disadvantageous to get fast response speed.

In addition, vector control is known as a means for controlling an AC motor in consideration of the characteristics of the AC motor as described above.

The vector control is a control method that separates the current of the AC motor into a magnetic flux generating current and a torque generating current and operates them independently. In order to realize such a control method, the rotor time constant is used to calculate the slip command value of the slip controller. Has been.

As an example, the relationship between the slip and the magnetic flux for the separation control is as follows.

Where T _r = L _r / R _r is the time constant of the rotor, L _m is the stator magnetizing inductance, Is the command value of the current component and torque generating current which make the magnetic flux, W _si is slip angular frequency, L _r is rotor magnetic inductance, R _r is rotor resistance, _r represents the rotor magnetic flux.

In the control of the induction motor by the vector control, knowing the values of the above parameters and the like has emerged as an important factor in controlling the induction motor. However, in the related art, such parameters (rotor time constant and magnetization inductance, etc.) are known. A lot of time and effort were required for the measuring means to know

For example, such a measuring means is to measure the parameters by the no-load test and the restraint test of the induction motor, and the effort, time and cost required for the measurement such as restraining the rotor from rotating with the three-phase power applied. This much unavoidable disadvantage was inevitable.

Claims (2)

When two of three phases of an induction motor are provided with a DC source 15, a condenser 16, a switch 14, and the like, the current generated when the switch 14 is momentarily turned on and off is i _{r (off)} . , i _{r (off)} = I | _o e ^{t / Tr} ...... (1) and stator voltage waveform at this time is V _Lm , (2) to obtain a rotor time constant by measuring the time at the time of 36.8% of the voltage at the time of switch-off in the form of a voltage which decreases exponentially from the switch o from (2); Measure the instantaneous voltage when the switch 14 is off, and when the voltage is V _{s (off)} , V _{s (0ff)} = ...... (3), where the stator magnetization inductance L _m is Rotor time constant and magnetization inductance measurement method of induction motor characterized by the method of obtaining from V _{s (off)} An induction motor rotary machine capable of automatically measuring the rotor time constant of an induction motor. The DC source 15 and the condenser are included in two phases (a, b) of the three phases (a, b, c) of the stator side of the induction motor 11. (16) are connected in parallel via a switch (14), and the time constant detector (12) for detecting the voltage generated at the stator side of the induction motor (11) to the two phases (a, b), and the time constant detector The slip calculator 13 which calculates the rotor time constant following the output of 12 is integrally formed, and the time constant detector 12 is connected to the two phases a and b so that the induction motor 11 An amplifier 12a for amplifying the voltage generated on the stator side of the circuit), a signal inverter 12b for inverting the signal amplified by the amplifier 12a, and a signal for inverting the signal amplified in the amplifier 12a. DC is measured by measuring the voltage at which the switch-off time is reduced by 63.2% from the voltage amplified by the inverter 12b and the amplifier 12a And a level detector 12c for maintaining the pressure level, and a comparator 12d for comparing the outputs of the signal inverter 12b and the level detector 12c. The time constant calculator 13 has a clock of several kHz. A clock generator 13c for generating a signal, a pulse width output of the comparator 12d is provided as one input, and the other end thereof is an AND gate 13a provided with the output of the clock generator 13c, and the AND gate 13a. Rotor time constant measuring device of an induction motor, characterized in that consisting of a time constant indicator (13b) to digitally display the time constant by multiplying the number of clocks output by the clock generator (13c)