JPH11248568A - Torque detector for induction motor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To detect a torque with good sensitivity and linearity by measuring a primary current of an induction motor. SOLUTION: A sine wave AC of the same frequency, phase, and amplitude as the output of a current sensor A in a torque which is a reference is outputted from a sine wave AC oscillator 12, and a difference from the output of the current sensor A is taken by a subtractor 13 for detection/rectification, so that a torque change is detected as a vector difference between a primary current of the torque which is a reference and a primary current at torque change.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a torque detector for detecting a change in torque of an induction motor, and more particularly, to a secondary current of an induction motor by detecting a primary current (power supply current) of the induction motor. The present invention relates to a torque detection device for an induction motor, which calculates a signal proportional to a change in the output torque, and outputs a signal proportional to a change in the load torque of the induction motor.

[0002]

2. Description of the Related Art Conventionally, as a method of detecting the torque of an induction motor, a method of installing a torque sensor on a motor shaft to detect a torque applied to the shaft, a method of measuring an input current or active power of the motor by an ammeter, There is a method of calculating the motor load torque by detecting with a meter, and among these methods, the torque estimation by current measurement is widely performed as the lowest cost and simple method.

[0003]

[SUMMARY OF THE INVENTION However, the primary current I _1-1 of the induction motor, as shown in FIG. 2 described later, the primary excitation current I ₀ unrelated to torque substantially proportional to the torque _Is the composite current of the primary load current I ₁ ′ _-1
It cannot be detected separately. In general, the primary exciting current I ₀ is large and occupies about half of the primary current I _1-1 even in a full load state, and the primary exciting current I ₀ and the primary load current I ₁ ′ ₋₁
Is about 90 °, the torque estimation by detecting the amplitude (effective value or the like) of the primary current has a problem that sensitivity is small and linearity is poor.

[0004] The present invention has been made in view of the above points, and has as its object to provide a torque detection device that measures current with high sensitivity and good linearity.

[0005]

In order to achieve the above-mentioned object, the present invention is configured as follows.

That is, according to the present invention, as will be described later, the vector difference between the primary current vector when the induction motor is operated at a certain load torque and the primary current vector when the torque changes. The torque is detected by utilizing a phenomenon that the torque is proportional to a secondary current and a torque change of the induction motor, and has the following configuration.

That is, according to the first aspect of the present invention, there is provided an induction motor torque detecting device for detecting a torque change based on a certain torque based on an output of a current sensor for detecting a primary current of the induction motor. A torque detection device for an electric motor, wherein the torque change is detected as a primary current vector difference based on a reference output of a current sensor at the certain torque and a detection output of the current sensor when the torque changes. Things.

According to a second aspect of the present invention, there is provided an induction motor torque detecting apparatus according to the first aspect, further comprising an output means for providing an output corresponding to a reference output of the current sensor at the certain torque.

According to a third aspect of the present invention, in the torque detecting device for an induction motor according to the second aspect, the output means includes:
A sine wave AC oscillator that outputs a sine wave AC having the same frequency, phase, and amplitude as the reference output from the current sensor at the certain torque.

According to a fourth aspect of the present invention, there is provided an induction motor torque detecting device according to the second aspect, wherein the output means includes:
A voltage-controlled oscillator that outputs a sine wave alternating current having the same frequency and phase as the reference output from the current sensor at the certain torque, and a sample that provides the same DC output as the amplitude of the reference output from the current sensor at the certain torque And a hold circuit.

According to a fifth aspect of the present invention, there is provided an induction motor torque detecting apparatus according to any one of the second to fourth aspects, further comprising a determining means for determining a direction of a torque change based on the certain torque. The discriminating means includes a phase shift circuit that shifts the output of the output means, a multiplier that multiplies the output of the phase shift circuit by a detection output of the current sensor, and an average that calculates an average value of the output of the multiplier. A value calculation circuit.

According to the torque detection device for an induction motor of the present invention, the primary current is determined based on the reference output of the current sensor at a certain torque and the detection output of the current sensor when the torque changes. Since the change in torque is detected as the vector difference of, the torque can be detected with high linearity and sensitivity.

According to the second aspect of the present invention, the torque detecting device for an induction motor includes an output means for providing an output corresponding to the reference output of the current sensor. , The torque change can be easily detected.

According to the third aspect of the present invention, there is provided a sine wave AC oscillator for outputting a sine wave AC having the same frequency, phase and amplitude as a reference output from a current sensor at a certain torque. As a result, a torque change can be detected as a differential output between the sine wave AC and the detection output of the current sensor.

According to a fourth aspect of the present invention, there is provided a voltage detecting oscillator for outputting a sine wave alternating current having the same frequency and phase as a reference output from a current sensor at a certain torque. A sample-and-hold circuit for providing the same DC output as the amplitude of the reference output from the current sensor in torque, so that a vector of the primary current is obtained from the sine wave AC, the detection output of the current sensor, and the DC output of the sample-and-hold circuit. The difference can be calculated.

According to the torque detecting device for an induction motor of the present invention, since the discriminating means for discriminating the direction of the torque change based on a certain torque is provided, the torque can be determined based on the certain torque. Whether the change is an increase or a decrease can be detected.

[0017]

Embodiments of the present invention will be described below in detail with reference to the drawings.

FIG. 1 is a view showing a state in which a torque detecting device for an induction motor according to one embodiment of the present invention is installed, 1 is an induction motor (hereinafter referred to as “motor”), and 3 is a motor. The first power supply is, for example, a commercial power supply or an inverter device.

A is a current sensor for detecting a motor AC current when the motor 1 is operated by supplying power thereto. The current sensor A is a sensor for detecting the motor AC current as it is. Anything may be used, for example, a current transformer (CT), a magnetic flux detection type current sensor, a resistor, or the like can be used.

The installation location of the current sensor A is
It may be inside the power source 3 as well as the wire portion 4 which is an intermediate portion between the power source 3 and the power source 3.

The torque detecting device 2 according to the present invention detects a change in the secondary current of the motor and a change in torque (load torque, generated torque) from the output of the current sensor A. The change in the torque of the motor 1 is displayed, and an increase / decrease direction display 56 indicates whether the torque is increasing or decreasing based on a certain torque.

Here, prior to the description of the specific embodiment, the principle of torque detection of the present invention will be described.

First, the reason why the secondary current is proportional to the torque will be described.

The torque generated by the motor is Lorentz force acting between the rotor current (secondary current) and the stator magnetic flux.

Incidentally, the stator magnetic flux is generated by the stator winding (1).
Secondary winding), and since the stator winding is connected to the power supply, the stator magnetic flux is constant because it is an amount necessary to generate a counter electromotive force that matches the power supply voltage. This is because the back electromotive force of the stator winding is e = − (dφ / dt) according to Lenz's law.

When the power source is a commercial power source, φ is constant because the voltage and frequency are constant, and when the motor is driven by the inverter power source, the inverter is usually v / f = -constant. Also in this case, the magnitude of φ is constant.

The Lorentz force is represented by the general formula F = BIL (F is force, B is magnetic flux density, I is current, and L is the effective length of a conductor) when the magnetic flux and the current are orthogonal to each other. In this case, since L in the above equation is determined by the length of the rotor and the number of rotors, it is a constant value for each motor. Further, B is constant in each motor for the above-mentioned reason, and I is a secondary current (rotor current).
And I are proportional, that is, in each motor, the torque and the secondary current are proportional.

Next, the principle of torque detection of the present invention will be described with reference to the vector diagram of FIG. In this FIG.
The current of each phase is described, and the secondary current is all 1
The primary iron loss, the primary copper loss, the secondary iron loss, the secondary copper loss, and the leakage reactance are small and unnecessary for the description, and are omitted here.

When the motor is completely unloaded and the slip is 0, the primary current (power supply current) of the motor is the primary exciting current I
Only ₀ flows. The primary exciting current I ₀ is delayed by 90 ° in phase from the primary supply voltage V ₁ .

When a torque is applied from this, slip occurs, an induced electromotive force is generated in the rotor, and a secondary current _I2-1 flows. The secondary current I _2-1 further delayed in phase 90 ° from the primary excitation current I _0.

However, as described above, since the magnetic flux must be kept constant, the primary load current I ₁ ′ ₋₁ that cancels out the magnetic flux generated by the secondary current I _2-1 .
Flows out of phase with the secondary current _I2-1 . Then, in the primary winding, the primary excitation current I ₀ and the primary load current I ₁ 'which is a combined current of _-1 primary current I _1-1 flows.

From this, when the load torque of the motor increases, more secondary current flows. That is, the secondary current I _2-1
The to I _2-2, the primary load current I _{1 '-1} are I _1' to the _-2, primary current I _1-1 are to I _1-2, respectively, changes.

Here, the current that can actually be measured directly is I
_1-1 and I _1-2 only.

The vector difference (length of ab) between the primary current I _1-1 and the primary current I _1-2 is equal to the magnitude of the secondary current I _2-1 and the secondary current I _2-2 . Equal to the difference. Therefore, the primary current I _1-1
When vector difference mentioned the primary current I _1-2 is equal to the difference between the magnitude of the secondary current, it can be seen equal to the change in the motor torque.

FIG. 3 is an example of a graph illustrating the effective value of the primary current and the vector difference of the primary current with respect to the motor load torque.

The vector difference of the primary current is 2 as described above.
Since it is proportional to the difference in the secondary current, it is proportional to the change in the motor load torque.

On the other hand, since the effective value of the primary current is represented by {(primary exciting current) ² + (secondary current) ² } ^1/2 in FIG. 2, it is not proportional to the motor load torque. As shown in FIG. 3, especially at a light load, the sensitivity becomes small and the linearity is poor. Further, since the shape of the graph is greatly affected by the primary excitation current, it is greatly affected by variations in the individual motors, which causes the problems as described in the above-described conventional example.

The present invention focuses on the fact that the vector difference of the primary current is proportional to the change in the motor load torque because it is proportional to the difference in the secondary current. The vector of the primary current when the motor is operated at a certain torque is stored by an electrical means, and the vector difference between the vector and the primary current vector when the torque is changed is calculated to change the torque of the motor. Is to be detected.

Hereinafter, specific embodiments will be described with reference to the drawings.

(Embodiment 1) FIG. 4 is a block diagram of a torque detecting device according to Embodiment 1 of the present invention.
Are assigned the same reference numerals.

The current sensor A detects an alternating current flowing through the electric wire 4 for supplying power to the motor. The output of the current sensor A is of a type proportional to the current to be measured. It is a sine wave alternating current of the same frequency as.

11 amplifies the output signal of the current sensor A,
This is an amplifier circuit for setting a signal level appropriate for a dynamic range of a subsequent circuit.

Reference numeral 12 denotes a sine-wave AC oscillator as output means for outputting a sine-wave AC corresponding to the reference output of the current sensor A at a certain reference torque, which can manually change the frequency, phase, and amplitude. It is.

Reference numeral 13 denotes a subtracter for subtracting the output signal of the sine wave AC oscillator 12 from the output signal of the amplifier circuit 11.

Numeral 14 denotes a detection circuit or an absolute value circuit.
Reference numeral 15 denotes a rectifier circuit. That is, it outputs a DC signal proportional to the amplitude of the output of the subtractor 13.

FIG. 5 is an example of a flowchart of the adjustment method according to the embodiment of FIG.

The operator attaches the current sensor A (step 21) and operates the motor 1 with a certain reference load, preferably a light load (step 22). Next, while operating at a constant load, the sine wave AC oscillator 1
The output of the rectifier circuit 15 becomes zero by adjusting the frequency, amplitude, and phase of No. 2. At this time, the output of the sine wave AC oscillator 12 is the current sensor A at the reference torque.
(Step 23).

When the adjustment is completed, the load torque of the motor is changed (step 24).
Is obtained as the vector ab in FIG. 2. By obtaining the length of the vector ab by the detection circuit 14 and the rectification circuit 15, a signal proportional to the load torque of the motor can be extracted.

(Embodiment 2) FIG. 6 is a block diagram of a torque detecting device according to Embodiment 2 of the present invention. Parts corresponding to those of Embodiment 1 described above are denoted by the same reference numerals. .

In this embodiment, the direction in which the load torque increases / decreases can be determined, and the procedure for adjusting the sine wave AC oscillator 12 is shown in FIG. 5, as in the above-described embodiment.

In this embodiment, when adjusting the sine-wave AC oscillator 12 with the motor fixed to a fixed reference load, if the lightest load cannot be fixed, the torque increases from the load at the time of this adjustment. In this case, a positive output can be output when the output is reduced, and a negative output can be output when the output is reduced.

The reason is, as can be seen from FIG. 2, it is clear that the phase of the primary current increases as the load torque increases. Because, when the motor is completely unloaded, the phase of the primary current is delayed by 90 ° from V1, and as the load increases, the phase of the primary current approaches V1 but does not exceed V1. Therefore, the change in the phase of the primary current is from 0 to 90 °, and it is possible to determine whether the phase is advanced or delayed.

Therefore, in this embodiment, a discriminating means B for discriminating the direction of the torque change from the reference torque is provided. In this discriminating means B, the AC signal of the sine wave AC oscillator 12 is shifted by + 90 °. The phase is advanced by 90 ° in the circuit 16, and this is multiplied by the AC signal of the amplifier circuit 11 in the multiplier 17. Further, when the average value is calculated by the average value calculation circuit 18, the output of the average value calculation circuit 18 is
If the phase of the amplifier circuit 11 is ahead of the phase of 2, the output becomes positive, and if it is delayed, the output becomes negative.

The positive / negative discrimination by the multiplication and the average value calculation will be further described.

Assume that a sine wave corresponding to the output of the sine wave AC oscillator 12 is Asin (ωt), and a sine wave having the same frequency corresponding to the output of the amplifier circuit 11 and having a different phase is Bs
Assuming that in (ωt + θ), the output of the + 90 ° phase shift circuit 16 shifts Asin (ωt) by + 90 °.
sin (ωt + 90 °) = Acos (ωt). By multiplying this by Bsin (ωt + θ), ABsin (ωt + θ) · cos (ωt) = (AB / 2) {sin (ωt + θ + ωt) + sin (ωt + θ−ωt)} The addition theorem = (AB / 2) {sin (2ωt + θ) + sinθ}, and on average, sin (2ωt + θ) is zero, so that (AB / 2) sinθ.

Therefore, the output of the average value calculation circuit 18 is positive when the phase of the amplifier circuit 11 is ahead of the phase of the sine wave AC oscillator 12 (θ> 0), and when the phase is delayed (θ <0). It will be negative.

Reference numeral 19 denotes a sign determination circuit which outputs +1 when the input is a positive number and -1 when the input is a negative number. 20 is a multiplier. The magnitude of the output of the multiplier 20 is the magnitude of the vector difference of the primary current, and the sign is positive when the torque increases from the reference torque when the sine wave AC oscillator 12 is adjusted. , Decreasing it becomes negative.

Although the phase shift circuit 16 has a phase shift of + 90 °, the general formula is (3)
What is necessary is just to shift the phase by 60k + 90) degrees. Here, k is 0, a positive or negative integer. in this case,
As described above, when the torque increases from the reference torque, the output of the average value calculation circuit 18 becomes positive.

The phase shift circuit 16 has a phase shift of -90 °,
That is, in the general formula, a circuit that shifts the phase by (360k-90) degrees may be used. In this case, contrary to the above description,
When the torque increases from the reference torque, the average value calculation circuit 1
The output of 8 becomes negative, and decreases when it becomes positive.
(However, k is 0, a positive or a negative integer.) (Embodiment 3) FIG. 7 is a block diagram of a torque detection device according to Embodiment 3 of the present invention, and is described in the above embodiment. 2 are denoted by the same reference numerals.

In each of the above-described embodiments, the sine wave AC oscillator 12 is manually adjusted so that the output of the current sensor A when operating at a certain reference load torque has the same amplitude, frequency and phase. Although a sine wave AC signal was generated and a differential output between the sine wave AC signal and the output of the current sensor A during an arbitrary torque operation was obtained, in this embodiment, it is only necessary to input a sample capturing signal (such as a pulse). The oscillator can be automatically adjusted.

When the sample receiving signal is received from the sequencer, for example, when the motor is operated by a sequencer or the like, the present torque detecting device is automatically taught and is operated when the motor is operated at a certain reference load torque. Output means C is provided that outputs a sine wave AC having the same frequency and phase as the output of the current sensor A, and outputs a DC output having the same amplitude as that of the current sensor A when operated at the certain load torque. .

In FIG. 7, the sample hold circuit (S
/ H) 35 and 38 are circuits that output the input signal as it is when the sample capturing signal is on, and output the input immediately before the sample capturing signal is off when the sample capturing signal is off.

First, a description will be given of the operation when the sample capturing signal is ON, that is, at the time of teaching.

In this embodiment, in FIG. 7, the multiplier 32-the average value calculating circuit 34-the sample / hold circuit (S / H) 35-the voltage controlled oscillator (VCO) 36- + 9 in FIG.
The loop of the 0 ° phase shift circuit 37 and the multiplier 32 constitutes a so-called phase difference controlled oscillator (PLL), and has the same frequency as the output signal (AC) of the amplifier circuit 11 at the time of sampling.
A sine wave alternating current having a phase and an amplitude of a unit amplitude is output from a voltage controlled oscillator (VCO) 36. FIG. 8 shows only this portion taken out for explanation.

The voltage controlled oscillator (VCO) 36 is an oscillator that increases the frequency and advances the phase when the input is positive, and decreases the frequency and delays the phase when the input is negative. + 90 °
The phase shift circuit 37 is for shifting the phase of the output of the voltage controlled oscillator (VCO) 36 by + 90 °.
+90) degrees (k is 0, a positive or negative integer). Reference numeral 32 denotes the output of the amplifier circuit 11 and +90.
° multiplier for multiplying the output of the phase shift circuit 37. Reference numeral 34 denotes an average value calculation circuit that calculates the average of the output of the multiplier 32.

The operation of the PLL loop during teaching will be described with reference to FIG.

The output (AC) vector of the amplifier circuit 11 is OD, and the output (AC) vector of the voltage controlled oscillator (VCO) 36 is OE. The output of the + 90 ° phase shift circuit 37 is the vector OF because the vector OE is shifted by + 90 °.

Here, the phase of the vector OD is the vector O
When the phase is ahead of E by δ, the output (ODsin δ) of the average value calculation circuit 34 becomes a positive value, which is input to the voltage controlled oscillator (VCO) 36, so that the voltage controlled oscillator (VCO) 36 The output frequency increases to advance the phase of the vector OE.

Conversely, the phase of the vector OD is the vector OE
If it is later than that, that is, if δ <0, the output (OD sin δ) of the average value calculation circuit 34 becomes a negative value, which is input to the voltage controlled oscillator (VCO) 36, so that the voltage controlled oscillator 36 The frequency of the output goes down and the phase is delayed. Since this is repeated, the phases of the vector OD and the vector OE gradually match, and the lock state is finally attained. A vector diagram at this time is shown in FIG.

FIG. 10 shows a state of the PLL loop when the vector OD and the vector OE have phases.

Next, the PLL loop operates, and the vector O
When the phase of D and the vector OE match (immediately before the end of teaching), the sample and hold circuit (S / H) 35, 3
8. About the outputs of the average value calculation circuits 33 and 34, FIG.
This will be described with reference to FIG.

Immediately before the end of the teaching, the output of the voltage controlled oscillator (VCO) 36 is a sine wave AC OE whose frequency and phase are equal to the output OD of the amplifier circuit 11 and whose amplitude is the unit amplitude. The output of the + 90 ° phase shift circuit 37 is a sine wave AC OF.

Therefore, the output of the average value calculation circuit 33 is the average of the result of multiplication of the sine wave AC OD and the sine wave AC OE having the unit amplitude, so that ODcos δ = OD. Therefore, the output of the sample hold circuit (S / H) 38 also becomes OD.

The output of the average value calculating circuit 34 is the average of the result of multiplication of the sine wave AC signal (OF) of unit amplitude obtained by shifting the sine wave AC OE by 90 ° and the OD.
nδ = 0 (zero). Therefore, the output of the sample / hold circuit (S / H) 35 also becomes 0 (zero).

Next, the operation when the teaching is completed, the sample capturing signal is turned off, and the load on the motor changes as described above will be described with reference to FIGS.

The output of the sample and hold circuit (S / H) 35 at the time of teaching (when the sample capturing signal is on) is 0
(DC), the output of the sample and hold circuit (S / H) 38 is OD (DC), the output of the voltage controlled oscillator (VCO) 36 is OE (AC), and the output of the + 90 ° phase shift circuit 37 is OF.
(AC).

Thereafter, the sample capturing signal is turned off,
Since the sample and hold circuits (S / H) 35 and 38 continue to output the voltage immediately before they are turned off, the output of the sample and hold circuit (S / H) 35 is 0 even during actual measurement (when the sample capturing signal is off). Yes, the output of the sample and hold circuit (S / H) 38 is OD. Further, the output of the voltage controlled oscillator (VCO) 36 has the input of 0, so that the output OE at the time of teaching is kept as it is. Therefore +9
The output of the 0 ° phase shift circuit 37 is also similar to the output during teaching.
OF.

Next, it is assumed that the load of the motor changes and the amplitude and phase of the motor current changes to become the vector Ot.
At this time, the output of the average value calculation circuit 33 is the size of the projection Au of Ot to the OE because OE is the unit amplitude (Otcos θ = Ou).

The output of the average value calculation circuit 34 is
Is the unit amplitude, and similarly, the projection ut of Ot onto the OF is
(Otsin θ = ut).

Therefore, the output of the subtractor 41 is Ou-OD
= Du, the output of the subtractor 42 is ut.

These are combined with the squaring circuits 43 and 4 as shown in FIG.
4, each squared, added by the adder 45, and the square root is obtained by the square root circuit 46, whereby the magnitude of Dt can be obtained.

Since the vector OD is a current vector at the time of teaching (at the time of reference torque) and the vector Ot is a current vector at the time of changing the torque from the time of teaching, the magnitude of Dt is as described above. Is proportional to a torque change from a reference torque at the time of teaching.

Next, the sign of the increase or decrease of the torque during the actual measurement with respect to the teaching (at the time of the reference torque) is determined. At the time of the actual measurement, the output of the subtractor 42 is Since the output is 0, the output is the same as the output of the average value calculation circuit 34, and the second embodiment is used.
Similarly to this, the sign is determined by the sign determination circuit 19 and the multiplier 20 determines the sign because the vector Ot has a positive value if the phase is ahead of the vector OE and a negative value if the phase is late. By multiplying with the output of the square root circuit 46,
The torque can be obtained with a sign.

Here, the output of the average value calculation circuit 33 is O
The fact that the output value becomes u and the output of the average value calculation circuit 34 becomes ut will be further described.

Now, when two sine waves having the same frequency and different phases are multiplied by a multiplier and an average value is obtained by an average value calculation circuit, the result is as follows.

If one sine wave is assumed to be Asin (ωt) and the other sine wave is assumed to be Bsin (ωt + θ), these two sine waves have the same frequency, and the phase of B is ahead of A by θ. become.

Thus, the result of the multiplication is: Asin (ωt) · Bsin (ωt + θ) = ABsin (ωt) · sin (ωt + θ) = (AB / 2) {cos (ωt−ωt−θ) −cos (ωt + ωt + θ)} Theorem = (AB / 2) {cos (-. Theta.)-Cos (2.omega.t + .theta.)} When these are averaged, the term cos (2.omega.t + .theta.) Becomes zero, so that (AB / 2) cos (-. Theta.) = (AB / 2) c
osθ.

When Asin (ωt) is shifted by + 90 °, Asin (ωt + 90 °) = Acos (ωt)
As described in the determination of the increase / decrease direction in the second embodiment, multiplication and averaging yield (AB / 2) sin
θ.

This is applied to FIG. 14 and FIG.

That is, if OE is 2 sinωt,
OF becomes 2cosωt, and Ot becomes Bsin (ωt +
θ).

Then, the output of the average value calculation circuit 33 is Bc
osθ = Ou, and the output of the average calculation circuit 34 is Bs
inθ = ut.

FIG. 16 is a flowchart of the operation procedure according to the third embodiment. As shown in FIG. 16, the motor is operated with a certain reference load, preferably a light load (step 50). Next, while operating at a constant load, the sample taking signal is turned on to start teaching (step 51), and after a predetermined time has elapsed, the sample taking signal is turned off to end teaching (step 52). At the start, a torque change is detected (step 53).

The induction motor to which the present invention can be applied is:
Any of a cage type and a winding type may be used, and any of a single phase, a three phase and a polyphase may be used.

[0094]

As described above, according to the present invention, based on the reference output of the current sensor at a certain torque and the detection output of the current sensor when the torque changes, the torque is calculated as a vector difference of the primary current. Since the change is detected, the torque can be detected with higher linearity and sensitivity than in the conventional example in which the torque is estimated from the effective value or the average value of the current, and the sensitivity is improved particularly at a light load.

Further, since a sine wave AC oscillator is provided which outputs a sine wave AC having the same frequency, phase and amplitude as the reference output from the current sensor at a certain torque, the sine wave AC and the detection output of the current sensor are provided. Thus, a change in torque can be detected as a differential output from the above.

A voltage-controlled oscillator for outputting a sine wave alternating current having the same frequency and phase as the reference output from the current sensor at a certain torque, and a DC output having the same amplitude as the reference output from the current sensor at a certain torque , The vector change of the primary current can be calculated from the sine wave AC, the detection output of the current sensor, and the DC output of the sample and hold circuit to detect a torque change.

Further, it is possible to determine whether the torque change is increasing or decreasing from the reference torque.

[Brief description of the drawings]

FIG. 1 is a diagram showing an installation state of a torque detection device according to one embodiment of the present invention.

FIG. 2 is a vector diagram of a motor current for explaining a detection principle of the present invention.

FIG. 3 is a diagram showing a change in an effective value of a primary current and a vector difference of the primary current with respect to a motor load torque.

FIG. 4 is a block diagram of the first embodiment of the present invention.

FIG. 5 is a flowchart showing the operation procedure of FIG.

FIG. 6 is a block diagram according to a second embodiment of the present invention.

FIG. 7 is a block diagram according to a third embodiment of the present invention.

FIG. 8 is a block diagram showing a portion of a PLL loop during teaching.

FIG. 9 is a vector diagram corresponding to FIG.

FIG. 10 is a block diagram showing a portion of a PLL loop at the end of teaching.

FIG. 11 is a vector diagram corresponding to FIG. 10;

FIG. 12 is a block diagram showing a PLL loop and a sample-and-hold circuit at the end of teaching.

FIG. 13 is a vector diagram corresponding to FIG.

FIG. 14 is a block diagram corresponding to FIG. 12 after teaching is completed.

FIG. 15 is a vector diagram corresponding to FIG. 14;

FIG. 16 is a flowchart showing the operation procedure of FIG. 7;

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 induction motor 2 torque detector 3 power supply 11 amplifying circuit 12 sine-wave AC oscillator 13, 41, 42 subtractor 14 detection circuit 15 rectifier circuit 16, 37 + 90 ° phase shift circuit 17, 20, 31, 32 multiplier 18, 33 , 34 Average value calculation circuit 35, 38 Sample hold circuit 36 Voltage controlled oscillator 43, 44 Square circuit 45 Adder 46 Square root circuit A Current sensor B Discriminating means C Output means

Claims (5)

[Claims] 1. A torque detecting device for an induction motor for detecting a torque change based on a certain torque based on an output of a current sensor for detecting a primary current of the induction motor, the current detection device comprising: A torque detecting device for an induction motor, wherein the torque change is detected as a primary current vector difference based on a reference output of a sensor and a detection output of a current sensor when the torque changes. 2. The torque detecting device for an induction motor according to claim 1, further comprising an output unit for providing an output corresponding to a reference output of the current sensor at the certain torque. 3. The induction motor according to claim 2, wherein the output means includes a sine wave AC oscillator that outputs a sine wave AC having the same frequency, phase, and amplitude as a reference output from the current sensor at the certain torque. Torque detector. 4. The voltage-controlled oscillator for outputting a sinusoidal alternating current having the same frequency and phase as the reference output from the current sensor at the certain torque, and a reference output from the current sensor at the certain torque. 3. The torque detection device for an induction motor according to claim 2, further comprising: a sample-and-hold circuit that provides a DC output having the same amplitude as that of the torque. 5. A phase shifter for determining a direction of a torque change based on the certain torque, wherein the determiner includes a phase shifter for shifting the output of the outputter, and an output of the phase shifter. 5. The torque detection device for an induction motor according to claim 2, further comprising: a multiplier for multiplying the output of the current sensor by the current sensor and an average value calculation circuit for calculating an average value of the output of the multiplier.