JP2002199798A - Measuring method for motor constant of induction motor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To identify the constants of an induction motor with accuracy, without having the induction motor run. SOLUTION: Time constant is determined from the rising waveform of an estimated excitation current value by two different methods, and measurement is repeatedly carried out, with the value of a secondary resistor R2 varied. The value of the secondary resistor R2, obtained when the two time constants match with each other, is used as the result of identification of the secondary resistor R2.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for measuring a motor constant of an induction motor.

[0002]

2. Description of the Related Art As a conventional technique, a method of obtaining a motor constant by performing a winding resistance measurement, a constraint test, and a no-load test as shown in JEC-37 is incorporated in inverter control software (conventional example). 1). As a method for identifying the constant of the induction motor while the induction motor is stopped, there is JP-A-7-55899 (conventional example 2). In this method, a single-phase alternating current is supplied to an induction motor,
The detected value of the d-axis current or the detected value of the q-axis current is subjected to Fourier series expansion to determine the constant of the induction motor.

[0003]

In the method shown in the conventional example 1, work such as fixing and releasing the rotor of the induction motor is required between the constraint test and the no-load current test.
Some aspects are not suitable for automatic measurement by inverter drive. Also, in the no-load current test, it is necessary to operate the induction motor alone, and if the load is already connected,
There is a problem that it is necessary to perform an operation of once disconnecting the load and rotating the electric motor alone, resulting in poor efficiency. In Conventional Example 2, since a single-phase alternating current is applied and the Fourier series expansion is used for the calculation, the software is complicated, the processing time of the software is lengthened, and the software requires a large storage capacity. In addition, in any of the methods, a voltage detection value or a voltage command value is used at the time of measurement, so that there is a problem that the measurement accuracy is not improved due to the influence of the voltage accuracy of the driving device.

SUMMARY OF THE INVENTION An object of the present invention is to provide a method for measuring the constant of an induction motor, in which the constant of the induction motor can be identified with high accuracy while the induction motor is stopped without rotating, and the measurement calculation is simple. It is in.

[0005]

SUMMARY OF THE INVENTION In order to solve the above problems, the present invention provides an induction motor driving device for supplying a variable frequency and a variable voltage to an induction motor and performing a variable speed operation of the induction motor. A power converter that outputs a three-phase alternating current based on the output voltage command value v_ref and the voltage output phase θv, a current detector that detects a current flowing through the induction motor, and a primary current based on the current value detected by the current detector. A primary current calculator for calculating the current, and a motor constant calculator for inputting the primary current and outputting the output voltage command value and the voltage output phase, wherein the voltage phase θv is an arbitrary fixed value set in advance. ,
A predetermined constant value is given as the voltage command v_ref, and at this time, a primary current detection value i1 flowing through the induction motor is read,
The value when the primary current value i1 converges to a constant value is

[0006]

[Outside 19] Then, the current im flowing through the mutual inductance M is calculated using the primary current value i1 and the primary resistance value R1 and the secondary resistance value R2 given by another means.

[0007]

(Equation 6) And this current estimate

[0008]

[Outside 20] Time constant in two ways from the rising waveform of

[0009]

[Outside 21] And the time constant at this time

[0010]

[Outside 22] Each

[0011]

[Outside 23] And repeated measurement is performed while changing the value of R2.

[0012]

[Outside 24] In this case, the value of the secondary resistance R2 at the time of is used as the identification result of R2.

Further, the mutual inductance M is

[0014]

(Equation 7) Is determined by: This mutual inductance M or time constant

[0015]

[Outside 25] And a primary resistance value R1, a leakage inductance L, a secondary resistance value R2, a rated voltage Vrate given as a rating of the motor, and a rated frequency fra given to another means.
The no-load current I0 is obtained using te and the mutual inductance.

The value when the primary current value i1 converges to a constant value is

[0017]

[Outside 26] In this case, the current im flowing through the mutual inductance M is determined using the primary current value i1 and the primary resistance value R1 and the secondary resistance value R2 given by another means.

[0018]

(Equation 8) In this configuration, the current estimation value

[0019]

[Outside 27] Is used as i1x

[0020]

(Equation 9) Then, the secondary resistance value R2 is obtained.

[0021]

Next, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a block diagram of an induction driving apparatus for implementing a method for measuring a motor constant of an induction motor according to the first and second aspects of the present invention. When the induction motor is driven, the power converter 2 supplies a variable frequency and a variable voltage to the induction motor 2. The power converter 2 uses the voltage command v_ref and the voltage phase θv given from the motor constant calculator 1 to convert the power into three-phase AC power U, V, W, and supplies the three-phase AC power to the induction motor 3. The primary current calculator 6 is a current detector 4 provided for the U phase.
Current iu detected in step 5 and current detector 5 provided in the V phase
The primary current is calculated by taking in the current iv detected in (1) as data. First, the primary current calculator 6 calculates the equations (1) and (2) using the current iu and the current iv, and converts them into two-phase alternating currents iα and iβ.

[0023]

(Equation 10) The reason why (2/3) is multiplied in the expression (2) is to make the amplitudes equal before and after the conversion. The phase for detecting the current is not limited to the combination of the U phase and the V phase, and any two or all three phases may be detected. Next, the primary current calculator 6 calculates the primary current detection value i1 as the square root of the sum of the squares of iα and iβ. Further, in the method of the present invention, since the output phase is determined in advance, the primary current can be calculated by another calculation method such as obtaining from an arbitrary one-phase current value. The primary current value i1 is input to the motor constant calculator 1.

First, the principle of claim 1 will be described.
FIG. 2 shows a T-1 type equivalent circuit per phase when the induction motor is stopped (slip s = 1). R1 is the primary resistance, L is the leakage inductance, R2 is the secondary resistance, M is the mutual inductance, v is the applied voltage, i1 is the primary current of the motor, i2 is the secondary current of the motor, im is the mutual inductance M (Excitation current) flowing through the motor.
The electromotive force generated by a change in the current flowing through the mutual inductance M as e _m, the formulate an equation based on the Kirchhoff's law in the equivalent circuit of FIG. 2

[0025]

(Equation 11) It becomes.

Since the leakage inductance L is smaller than the mutual inductance M, ignoring the leakage inductance L for simplicity, the equation (3) becomes

[0027]

(Equation 12) It becomes. From equations (4) and (5),

[0028]

(Equation 13) Substituting equations (4) and (7) into equation (6),

[0029]

[Equation 14] At time t = 0, im0 = 0 (9) and solving for im,

[0030]

(Equation 15) It becomes. Here, τ is a time constant. Therefore

[0031]

(Equation 16) The time constant τ is obtained from the current im flowing through the mutual inductance M, and the mutual constant M can be obtained by substituting the time constant τ into the equation (12).

The principle according to claim 2 will be described. The current im flowing through the mutual inductance is a current flowing inside the induction motor, and cannot be directly measured from the induction motor input terminal side. Therefore, a method for estimating the current im flowing through the mutual inductance M will be described. From equations (4) and (6)

[0033]

[Equation 17] Substituting equation (13) into equation (5),

[0034]

(Equation 18) (14) Rearrange the equation

[0035]

[Equation 19] It becomes. Therefore, the current im can be obtained by the equation (15) using the voltage v applied to the motor and the primary current i1 flowing through the motor, and the time constant τ is obtained from the change in the current im and substituted into the equation (12). To obtain the mutual inductance M. In a state where a direct current flows, the equivalent circuit of the induction motor can be regarded as only a primary resistance. Therefore, immediately after the application of the DC voltage, current also transiently flows through the secondary resistance, but when a sufficient time has elapsed, only the primary resistance is present.
Current value when

[0036]

[Outside 28] Voltage

[0037]

[Outside 29] And equation (15) is

[0038]

(Equation 20) Can be rewritten.

The no-load current I0 is a current that flows when a power source having a rated voltage and a rated frequency is supplied to the induction machine and rotated without load, and the equivalent circuit at this time is a T-1 type equivalent circuit in FIG. Is represented as a series circuit of R1, L, and M. Therefore, the relationship between the voltage v and the current i1 at this time is as follows.

[0040]

(Equation 21) When the rated voltage is V and the equation (16) is rewritten by focusing only on the magnitudes of the voltage and the current,

[0041]

(Equation 22) V and I are numerical values representing the magnitudes of the voltage and the current, respectively, and may be either the effective value, the maximum value, or the average value, as long as the voltage and the current are the same. Solving equation (18) for I0 gives:

[0042]

(Equation 23) And the no-load current I0 is obtained. (16), (1
8) and (19) consider R1 and L,
R1 and L may be ignored for simplicity.

FIG. 3 shows a waveform of a current value when a DC voltage v is applied.

[0044]

[Outside 30] Where the value of is 0

[0045]

[Outside 31] Is almost identical to im,

[0046]

[Outside 32] Is from 0

[0047]

[Outside 33] The time constant at the time of rising can be treated as the time constant of the rising of im.

From the above, the no-load current is obtained by applying a DC voltage and calculating the primary current value according to equation (15).

[0049]

[Outside 34] Is calculated, the rising time constant is obtained, and the time constant can be obtained by using the equation (19). In equation (15)

[0050]

[Outside 35] Think of when.

[0051]

(Equation 24) (15) 'is

[0052]

(Equation 25) Solving this for k gives

[0053]

(Equation 26) Substituting equation (22) into equation (20)

[0054]

[Equation 27] It becomes.

When the voltage v = V1 is given in steps, the primary current i1, the current im flowing through the mutual inductance, and the estimated value of im obtained by equation (15) using the primary current i1 and the resistance values R1 and R2.

[0056]

[Outside 36] FIG. 3 shows the waveform of the time change of the above. i1, im,

[0057]

[Outside 37] Converge value of

[0058]

[Outside 38] Is (V1 / R1),

[0059]

[Outside 39] Is from 0

[0060]

[Outside 40] It can be confirmed that the waveform when changing to approximately coincides with the waveform of im. Therefore, at this time

[0061]

[Outside 41] Change from time constant

[0062]

[Outside 42] Should be obtained.

From here, a method based on the above principle is described in 200
A specific example realized for an induction motor of 2.2 V and 2.2 kW will be described with reference to FIGS. 1, 4 and 5. The motor constant of the induction motor used here is R1 = 0.86
Ω, R2 = 0.65Ω, L = 6.2 mH, M = 95.0
mH. The no-load current obtained by the no-load test is 3.
0A. In the following, a description will be given assuming that the phase when the U phase reaches a peak is 0 °. In this embodiment, the phase of the voltage phase θv is set to 0 °.

First, a method of determining the magnitude of the predetermined voltage V1 applied to the motor will be described. The voltage V1 applied to the motor may be an arbitrary value, but it is necessary that the voltage V1 be in a range that does not actually burn the induction motor due to heat generated by the current. Therefore, here, a case where V1 is given so that the current value becomes 50% of the rated motor current will be described with reference to an example of a method of determining V1. First, the voltage command v_ref is given as zero, and while measuring the current detection value i1, v_ref
Is added in increments of one thousandth of the rated voltage of the induction motor to increase the value. Then, when the current detection value i1 reaches 50% of the rated current of the induction motor, v_
The value of ref is stored as V1, and the supply of power to the motor is cut off. The amount of increase in the voltage command may be arbitrarily set to such a value that the current does not change abruptly. When a current controller is provided, a value of 50% of the rated current is given as a current command, and when the detected current value matches the current command value, the voltage command value at that time may be set to V1. However, when the primary resistance is measured by passing a direct current before the identification of the mutual inductance or the no-load current described in the present invention, the current value and the voltage command value at that time may be used. Of course, the current value is 50% of the rated current
It may be a value other than. R1, R2, and L will be described as being known by another means such as completion of measurement by a conventional measurement method before the start of this processing.

A specific example of claim 1 will be described. V1 is given as a voltage command v_ref, and a voltage is applied to the induction motor in steps. Here, for the sake of explanation, V1 = 1 (V), but in practice the voltage value is set to a value appropriate for measurement. An appropriate current value is a value within a range that is not excessively large or small with respect to the rating of the motor. At this time, the primary current value i1 is measured, and
According to the expression 5 ′),

[0066]

[Outside 43] Ask for.

[0067]

[Outside 44] Τ is determined from the rising waveform of. Here is the time constant

[0068]

[Outside 45] Is

[0069]

[Outside 46] Is from 0 to the final (convergence) value {1- (1 / e)} 0.6
The time required to reach 32 times is measured and obtained. Also, the time constant

[0070]

[Outside 47] Is

[0071]

[Outside 48] Is greater than 0 to 20.0% of the final (convergent) value.
Measure the time to reach 0.6% and calculate this

[0072]

[Outside 49] And Here, the fact that the time for changing from 20.0% to 70.6% matches the time constant is used.
The change width corresponding to the time constant is easily obtained by calculation,
In addition, 30.0% to 74.2%, 40.0% to 77.
The time required between 9% also corresponds to a time constant. Therefore, measurement may be performed under these conditions and an average value may be obtained.
FIG. 4 shows the results of measurement using the motor constants.

[0073]

[Equation 28] R2 at this time is adopted as it is as the identification result. FIG. 5 shows a case where the value of R2 used in the expression (15 ′) is set to a half of a correct value.

[0074]

(Equation 29) And the difference between the two is large. In this case, change the value of R2 and apply the DC voltage again in the same manner in steps.

[0075]

[Outside 50] Measurement. At this time, the value of R2 to be newly used may be obtained by adding or subtracting a predetermined ratio of the value of R2 from the previous time. As a result, when the difference is further increased, the value is added and subtracted. In the next step, the reverse process is performed. Also,

[0076]

[Outside 51] When the magnitude relationship changes, the width of the value to be added to or subtracted from R2 is reduced, and this is repeated.

[0077]

[Outside 52] The value of R2 when the values of are substantially equal is adopted as the identification result of R2. This is a general idea, but here

[0078]

[Outside 53] As a result, a relationship approaching R2 was found, so the value of R2 to be used next in this equation was determined. Using the value of FIG. 5, as the next value of R2, for example, 20% of R2 (1/2/3 of the correct value: 0.325Ω) at this time is added to be 0.
39Ω is used as the next value. This is repeated. Or (0.384 / 0.261) .0.3
The process is performed again using 25 = 0.478Ω, and similarly repeated until the difference in the time constants becomes small. In such a method, it is clear that the error decreases as the number of repetitions increases, so a method of determining the number of repetitions may be used.

A specific example of claim 2 will be described. The mutual inductance M is obtained by the above equation (12) using the result obtained in the specific example of the first aspect. R1,
Substituting R2 into a known value, (12) using the value (average of two) shown in FIG.

[0080]

[Equation 30] It becomes.

A specific example of claim 3 will be described. Rated voltage Vrate and rated frequency frat of induction motor
Since e is given as the specification of the induction motor, it is determined by using R1 and L given by the test result table of the induction motor or another existing identification means and R2 and M identified by the above-described method. Then, when applied to equation (19),

[0082]

[Equation 31] And the no-load current I0 is obtained. When a certain error can be tolerated, for simplicity, the calculation may be performed with R1 and L omitted. Similarly, when applying the measurement results,

[0083]

(Equation 32) It becomes. here,

[0084]

[Outside 54] Is for conversion per phase.

A specific example of claim 4 will be described. In the specific example of claim 1,

[0086]

[Outside 55] Is recorded as i1x. The final value of the current value i1 is

[0087]

[Outside 56] And if

[0088]

[Equation 33] To determine the secondary resistance R2. Realistically

[0089]

[Outside 57] It is difficult to detect the moment

[0090]

[Outside 58] When i changes from negative to positive, i1x is recorded. Alternatively, when the value changes from negative to positive, the average value of the immediately preceding negative value and the immediately following positive value is used as i1x. At this time, as shown in FIG. 4, i1x = 0.665,

[0091]

[Outside 59] So

[0092]

(Equation 34) Due to the influence of reading errors and the like, the values are not exactly the same. In addition, since there are variations in the measured values, R2 recalculated here is

[0093]

[Outside 60] A method of using the average value of R2 used in the calculation as the result of identifying R2 is also effective.

[0094]

As described above, according to the present invention, the voltage of the fixed output phase is applied to the induction motor in steps, and the motor constant is measured from the time change of the current value at that time. That is, since only a DC current is applied and no rotating magnetic field is applied to the induction motor, the mutual inductance M of the induction motor is not increased without rotating the induction motor and regardless of the voltage accuracy of the motor driving device. Alternatively, the no-load current I0 can be identified with high accuracy,
Further, there is an effect that the accuracy of the identification result of the secondary resistor R2 measured based on the conventional technique can be improved.

[Brief description of the drawings]

FIG. 1 is a block diagram of an induction motor driving device to which a method for measuring a motor constant of an induction motor according to the present invention is applied.

FIG. 2 is a circuit diagram of a T-1 type equivalent circuit of the induction motor.

FIG. 3 is a diagram showing a time change of a current when a DC voltage is applied to an induction motor.

FIG. 4 is a diagram showing a current waveform (when a known constant used for calculation is correct) applied to an induction motor of 200 V and 2.2 kW.

FIG. 5 is a diagram showing a current waveform (when a half of a correct value is given as a secondary resistance) as a result of application to a 200 V, 2.2 kW induction motor.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Motor constant calculator 2 Power converter 3 Induction motor 4,5 Current detector 6 Primary current calculator

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Koujiro Sawamura 2-1 Kurosaki Castle Stone, Yawatanishi-ku, Kitakyushu-shi, Fukuoka F-term (reference) 2G016 BA03 BB01 BB02 BB10 BC05 BD06 5H576 BB06 DD02 DD04 EE01 GG04 HB01 LL22 LL29 LL40

Claims (4)

[Claims] 1. An induction motor driving device for supplying a variable frequency and a variable voltage to an induction motor and performing a variable speed operation of the induction motor, comprising a three-phase AC based on an output voltage command value v_ref and a voltage output phase θv. A power converter that outputs a current, a current detector that detects a current flowing through the induction motor, a primary current calculator that calculates a primary current from a current value detected by the current detector, and inputting the primary current. A motor constant calculator that outputs the output voltage command value and the voltage output phase, sets the voltage output phase θv to an arbitrary fixed value set in advance, and gives a predetermined constant value as the voltage command v_ref. When the primary current detection value i1 flowing through the induction motor is read and the voltage command v_ref is given, the value when the primary current value i1 converges to a constant value is expressed as follows. When the primary current value i1 and the known primary resistance value R1 and secondary resistance value R2 are used, an estimated value of the exciting current im flowing through the mutual inductance M is given by To In the method for measuring the motor constant of an induction motor, the excitation current estimated value Time constants from the rising waveforms in two ways. , And the time constant at this time Each [outside 6] Repeated measurement is performed by changing the value of R2. A method for measuring a motor constant of an induction motor, characterized in that the value of R2 at the time of is used as an identification result of R2 instead of the original R2. 2. An induction motor driving device for supplying a variable frequency and a variable voltage to an induction motor and performing a variable speed operation of the induction motor, the three-phase AC being based on an output voltage command value v_ref and a voltage output phase θv. A power converter that outputs a current, a current detector that detects a current flowing through the induction motor, a primary current calculator that calculates a primary current from a current value detected by the current detector, and inputting the primary current. A motor constant calculator that outputs the output voltage command value and the voltage output phase, sets the voltage output phase θv to an arbitrary fixed value set in advance, and gives a predetermined constant value as the voltage command v_ref. When the primary current detection value i1 flowing through the induction motor is read and the voltage command v_ref is given, the value when the primary current value i1 converges to a constant value is expressed as follows. In this case, using the primary current value i1, the known primary resistance value R1, and the secondary resistance value R2, an estimated value of the exciting current im flowing through the mutual inductance M. To In the method for measuring the motor constant of an induction motor, the excitation current estimated value Time constant from two rising waveforms And at this time, Each [outside 13] , And repeat measurement is performed by changing the value of R2. The time constant when And the mutual inductance M is A method for measuring a motor constant of an induction motor, characterized in that the method is obtained by: 3. The mutual inductance M or time constant. And a primary resistance value R1, a leakage inductance L, a secondary resistance value R2, a rated voltage Vrate given as a rating of the motor, and a rated frequency f given by another means.
The method for measuring a motor constant of an induction motor according to claim 2, wherein a no-load current I0 is obtained using the rate and the mutual inductance. 4. An induction motor driving device that supplies a variable frequency and a variable voltage to an induction motor and performs a variable speed operation of the induction motor, the three-phase AC being based on an output voltage command value v_ref and a voltage output phase θv. A power converter that outputs a current, a current detector that detects a current flowing through the induction motor, a primary current calculator that calculates a primary current from a current value detected by the current detector, and inputting the primary current. A motor constant calculator that outputs the output voltage command value and the voltage output phase, sets the voltage output phase θv to an arbitrary fixed value set in advance, and gives a predetermined constant value as the voltage command v_ref. When the primary current detection value i1 flowing in the induction motor is read and the voltage command v_ref is given, the value when the primary current value i1 converges to a constant value is expressed as Then, using the primary current value i1 and another known primary resistance value R1 and secondary resistance value R2, an estimated value of the exciting current im flowing through the mutual inductance M is expressed as follows. In the method for measuring the motor constant of an induction motor, the current estimation value Using the primary current value i1 at the time of i1x, A method for measuring a motor constant of an induction motor, wherein the secondary resistance R2 is obtained by: