JPH0621826B2 - Induction motor load condition detector - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Object of the Invention (Industrial field of application) The present invention relates to an induction motor load state detection device for detecting the load state of an induction motor based on the phase difference between the coil current and its applied voltage. Regarding

(Prior Art) As a method of detecting a load state such as load fluctuation of an induction motor (hereinafter, simply referred to as an electric motor), there is a method of detecting a rotation speed as a conventional target. As a means for implementing this method, there is a structure such as a tachometer which takes out a mechanical movement of the rotor and converts it into an electric signal, but this one has a mechanical driving portion and thus is inferior in long life. On the other hand, there is a pure electric means for detecting the input current of the electric motor, but there is a drawback that the detection accuracy is low because the input current changes due to external conditions such as fluctuation of the power supply voltage and temperature change of the electric motor.

(Problems to be Solved by the Invention) As described above, in the case where the rotational speed is detected,
There is a problem that the long life is inferior and the detection accuracy is low in the case where the input current of the electric motor is detected.

The present invention has been made in view of the above circumstances, and an object thereof is to obtain a signal dependent on the load state of a motor with high accuracy by detecting a phase difference between a coil current of the motor and an applied voltage. At the same time, it is an object of the present invention to provide a load state detection device for an induction motor, which can achieve a long life and can contribute to the cost reduction.

[Structure of the Invention] (Means for Solving Problems) The present invention relates to a phase detection unit that detects a phase difference between a coil current of an induction motor and an applied voltage by a difference between respective zero-cross points, and a phase detection unit. The present invention has a first feature in that it includes a load state determination unit that compares a phase detection signal output from the detection blower with a reference value and converts the phase detection signal into a load state signal. , A first comparator and a second comparator which convert the coil current and the applied voltage into a rectangular wave signal which rises and falls at each zero gloss time and outputs the rectangular wave signal, and a level difference between the output from the first comparator and the second comparator. A first voltage dividing circuit for giving a second voltage dividing circuit for giving a level difference to the output from the second comparator, an output from the first comparator and a voltage dividing output from the second voltage dividing circuit. Is in The third comparator that outputs the comparison result corresponding to each input, the output from the second comparator, and the divided output from the first voltage dividing circuit are input, and the comparison result corresponding to each input is output. A second characteristic is that the fourth comparator is provided, and the theoretical sum of the comparison results of the third and fourth comparators is used as the phase detection signal.

(Operation) According to the first characteristic configuration of the present invention, the phase difference between the coil current of the electric motor and the voltage applied to the coil is detected by the difference between the respective zero-cross points, and the phase detection signal is appropriately detected. By comparing with the reference value, various load states such as the magnitude of the motor torque or the rotation speed or the rate of change thereof are detected.

According to the second characteristic configuration of the present invention, the phase detection unit can be configured by four comparators, and the manufacturing cost can be reduced.

(Embodiment) A first embodiment of the present invention will be described below with reference to FIGS. 1 to 6 by applying the present invention to a capacitor-type induction motor. In FIG. 1, reference numeral 1 is an electric motor composed of a main coil 2, an auxiliary coil 3 and a capacitor 4, and in this embodiment, it serves as a drive source for a dehydrating basket of a two-tub type washing machine. Reference numeral 5 is a power source for applying a voltage to the electric motor 1 by connecting the normally open contact 7 of the relay 6. 8 is a phase detector, which is a current transformer 9,
A first comparator 10 including a resistor 10a and a resistor 11
It is configured to have a second comparator 11 including a and 11b, a first voltage dividing circuit 12, a second voltage dividing circuit 13, a third comparator 14 and a fourth comparator 15. The first comparator 10 converts the main coil current im into a pulse voltage Ui which is a rectangular wave signal that rises and falls at the time of the zero cross, and outputs it. The pulse voltage Ui is input to the inverting input terminal (−) of the third comparator 14, and also divided by the first voltage dividing circuit 12 and output as the divided voltage Uw having a level difference. The divided voltage Uw is input to the non-inverting input terminal (+) of the fourth comparator 15. On the other hand, the second comparator 11 converts the power supply voltage Vac into a pulse voltage Uv which is a rectangular wave signal that rises and falls at the time of its zero cross, and outputs it. The pulse voltage Uv is input to the inverting input terminal (−) of the fourth comparator 14, and also divided by the second voltage dividing circuit 13 and output as the divided voltage Uj having a level difference. This divided voltage U
j is input to the non-inverting input terminal (+) of the third comparator 15. Here, each divided voltage Uw and pulse voltage Uv
Is set so that its peak value is Uw <Uv, and the peak value of the divided voltage Uj and the pulse voltage Ui is Uj <U.
i is set to be i.

On the other hand, 16 is a load state determination unit, which includes operational amplifiers 17 and 18, capacitors 19 and 20, a resistor 21,
22, 23, diode 24, and analog switch 2
5 is included, and in particular, the operational amplifier 17,
The capacitor 20, the diode 24 and the analog switch 25 form a peak value or minimum value holding circuit 26. Reference numeral 27 denotes a dehydration timer, which is for defining the dehydration time, and energizes the relay 6 at the same time when the power is turned on to form the normally open contact 7.

Next, the operation of the above configuration will be described. First, referring to FIGS. 4 to 6, the main coil current im and the power supply voltage V of the motor are shown.
The relationship between the phase difference θm with respect to ac and the magnitude of the load will be described. FIG. 4 shows an equivalent circuit of the electric motor 1, and FIG.
The figure is the vector diagram. In FIG. 4, the electric motor 1
If the rotation speed of the motor increases as the load decreases, the slip S
, The equivalent load resistance R ₂ increases and the secondary load current I ₂ decreases. However, the primary excitation current I ₀ is constant. If the change of I ₂ under the constant of I ₀ is applied to the vector of FIG. 5, it is clear from the change of the vector of Im that θm increases with the decrease of I ₂ , that is, the rotation speed increases. It can be seen that it increases with the increase. FIG. 6 shows the relationship between the phase difference θm, the rotation speed N and the torque T. In FIG. 6, 28 is a phase curve, 29 is a torque curve, Tm is the maximum torque, and Nm is the rotation speed at the maximum torque. What should be noted in FIG. 6 is θ
The point m is that the rotational speed N is almost constant until the rotational speed N passes the maximum torque Tm, but the rotational speed changes significantly after the rotational speed N passes through Tm as the rotational speed increases.

The operation of the apparatus shown in FIG. 1 will be described below. It is now assumed that the electric motor 1 is energized by the power source 5 to drive the dehydration basket. In this state, the main coil current im is detected by the current transformer 9 and the zero-cross comparison is performed by the first comparator 10, and the pulse voltage Ui (shown in FIG. 2) is changed at the time of the zero cross.
Is converted to and output. Similarly, the applied voltage Uac shown in FIG. 2 is converted into a pulse voltage Uv (shown in FIG. 2) that rises and falls at the time of the zero cross comparison by the second comparator 11, and is output. Thus, the pulse voltage Ui is applied to the inverting input terminal (-) of the third comparator 14 and is divided (stepped down) by the first voltage dividing circuit 12 to generate the divided voltage Uw.
As the non-inverting input terminal (+) of the fourth comparator 15
Given to. The pulse voltage Uv is applied to the inverting input terminal (-) of the fourth comparator 15 and is divided (stepped down) by the second voltage dividing circuit 13 to generate a divided voltage Uj of the third comparator 14. It is given to the non-inverting input terminal (+). The third comparator 14 compares the pulse voltage Ui, which is an input given to each terminal thereof, with the divided voltage Uj, and outputs the comparison result as a signal Uk. This signal Uk has a second value when its peak value is Ui <Uj.
As shown in the figure, the level becomes high, and the pulse width of this high-level signal detects the difference between the negative and positive zero-cross points. The fourth comparator 14 compares the pulse voltage Uv, which is an input given to each terminal thereof, with the divided voltage Uw, and outputs the comparison result as a signal Ux. When the peak value of this signal Ux is Uv <Uw, it becomes a high level as shown in FIG. 2, and the difference between the positive and negative zero crossing points is detected by the pulse width of this high level signal. These third comparator 14 and fourth comparator 15
Since the output terminals of the comparator 14 and the output terminal of the comparator 15 are commonly connected to each other, the signals Uk and Ux, which are the results of the comparisons, are ORed at the connection point 8a and are shown in FIG. As described above, the load state determination unit 16 outputs the phase detection signal U _θ depending on the magnitude of the phase difference θm.
To be given to. This phase detection signal U _θ
Are averaged by being charged in the capacitor 19 via the resistor 21 and converted into the analog voltage U _θ a shown in FIG. This analog voltage U _θ a is applied to the load state determination unit 1
6 and the resistors 22 and 2
It is divided by 3 and converted into U _θ a ′. On the other hand, since the analog switch 25 is temporarily turned on when the control power is turned on, V _θ a corresponding to the phase difference θm ₀ in the initial rotation of the electric motor 1 shown in FIG. Through the capacitor 2
It is charged to 0 as an initial value. After this, the diode 24
Because there is, the terminal voltage of the capacitor 20 is fixed in only this U _theta a when U _theta a is smaller than the terminal voltage of the capacitor 20. That minimum value U _theta m in the capacitor 20 is always the peak value of U _theta a is held. The phase detection signal U _θ a ′ that changes moment by moment is compared with U _θ m by the operational amplifier 18, and U _θ a ′> U
_The state determination signal U ₀ is output when _θ m. And
The dehydration timer 27 receives the state determination signal U ₀ , disconnects the relay 6 after the set time, the normally open contact 7 is turned off, the electric motor 1 is disconnected, and the dehydration operation ends.

The above is described with the progress of the dehydration operation.
As understood from the figure, if the electric motor 1 is started at time t ₀ , the rotation speed of the electric motor 1 gradually increases as shown by the curve 30, and along with this, U _θ a and U _θ a ′ also change.
As is clear from the comparison with FIG. 6, these are times T _{1 at} which the rotation speed passes the speed Nm corresponding to the maximum torque Tm.
It begins to increase rapidly from. On the other hand, the minimum value U _θ m of the phase detection signal is a value of a constant phase difference θ m that hardly changes until the rotation speed reaches Nm. Therefore, when the rotation speed exceeds Nm at time t ₁ , θm increases rapidly, and U _θ a ′> U _θ
Thus, the operational amplifier 18 outputs the above-mentioned state determination signal U ₀ at time t ₁ (see FIG. 3). The generation of this state determination signal U ₀ determines the completion of riding through the maximum torque Tm. Dehydration basket has this maximum torque T
An imbalance of the distribution cloth in the dewatering basket can be considered as a cause of continuing the rotation at a rotation speed that does not pass m, that is, a range of Nm or less. If there is this imbalance, the dehydration basket causes a swinging motion and is difficult to accelerate in an unstable region of less than the maximum torque Tm, so it takes a long time to reach the original high speed region (Nm or more), and during this period, it is low speed. Therefore, it hardly contributes to dehydration. When the rotational speed of the electric motor 1 is eventually accelerated to Nm or higher corresponding to the maximum torque Tm, the operational amplifier 18 outputs the state determination signal U ₀ at time t ₁ as described above. In this way, the dehydration timer 27 starts the timing operation after the motor 1 reaches the stable region in which the maximum torque Tm is exceeded and the dehydration action is exerted, so that the dehydration timer is not inadequate. As described above, the detection of the rotation speed of the electric motor 1 passing through the maximum torque Tm point cannot be performed by the method in which the rotation speed of the electric motor 1 is used as the detection target, and can be detected only by the phase detection. I understand.

Here, since the phase detection unit 8 is configured to have four comparators and output the phase detection signal U _θ a, the phase detection unit 8 is a general-purpose commercially available general-purpose four-circuit operational amplifier IC. It can be configured by using one (quad type), that is, the number of logic ICs to be used is one, which can contribute to the reduction of manufacturing cost.

The second embodiment will be described with reference to FIGS. In FIG. 7, reference numeral 31 is a sampling circuit as a load state determination unit, which has the same configuration as the load state determination unit 16 of FIG. Since the analog switch 25 of the sampling circuit 31 is given a sampling signal φ shown in FIG. 8 peak value U _theta p of the capacitor 20 is changed stepwise as shown in FIG. 8, which is U _theta at operational amplifier 18 a ', and a pulse-like state determination signal U ₀ having a time width corresponding to the rate of change of U _θ a is output as shown in FIG. In this embodiment, the time t _{1 when the} state determination signal U ₀ is first output
The dehydration timer 27 starts the timing operation from (at the time point when the maximum torque Tm has passed). In this way, the sampling circuit 3
The peak value U _θ p of the phase detection signal sequentially stored in the capacitor 20 of No. 1 by the sampling signal φ serves as a reference value, and the newly detected phase detection signal U _θ a ′ is compared with this to obtain the maximum torque. Phase difference θm when passing through Tm
Therefore, the state determination signal U _{0 in} this embodiment corresponds to the change rate signal of the phase detection signal U _θ a.

Next, a third embodiment in which the present invention is applied to a belt slack detecting device will be described with reference to FIG. 9 in which the same parts as those in FIG. In FIG. 9, reference numeral 32 denotes a load state determination unit, which is a reference value Vr set by the resistors 33 and 34 and a phase which is a terminal voltage of the capacitor 19 similar to that shown in FIG. 1, that is, an analog voltage. It is composed of an operational amplifier 35 for comparing the detection signal U _θ a,
The output of the operational amplifier 35 is applied to a display device, for example, a light emitting diode 37 via a resistor 36.

Considering a state where the electric motor 1 is driving a load via a belt, the magnitude of the load torque is now T ₁ (see FIG. 6).
If the belt tension is normal and the belt slip does not occur, the output torque of the electric motor 1 is the same T.
It is ₁ . On the other hand, when the belt becomes loose and the belt slips, the load torque seen from the electric motor 1 decreases from T ₁ to T ₀ . This change in torque changes or increases the phase difference θm. As a result, when the phase ticket type signal U _θ a in FIG. 9 increases and exceeds the preset reference value Vr in anticipation of the normal load fluctuation with respect to the torque T ₁ , the operational amplifier 35 outputs the state determination signal U ₀ and emits light. The diode 37 is turned on to warn of belt loosening.

The third embodiment simply represents the features of the present invention. That is, as shown in FIG. 6, generally, the continuous operation becomes possible only when the load operation of the electric motor is performed in the Th-Tl region, that is, the stable region, which has exceeded the maximum torque Tm. By the way, in this stable region (region of Nm or more), the torque changes drastically, but the rate of change of the rotational speed is extremely small. In such a situation, it is extremely difficult to detect the belt slack as described above by detecting the rotational speed of the electric motor, and it can be easily realized by the phase detection as in the third embodiment. This is also true for the detection of the maximum torque weathered time t ₁ of Tm described in FIG. 3, it is almost impossible to detect the time t ₁ with a rotational speed detection of the prior art.

Next, a fourth embodiment of the present invention will be described with reference to FIGS. In the structure of the apparatus shown in FIG. 10, reference numeral 38 is an electric motor for driving a rotating tub or a dewatering tub which is a dewatering basket provided in the washing machine, and includes a main winding 39, an auxiliary winding 40 and a capacitor. 41 as a condenser motor. FIG. 11 shows the relationship between the rotational speed N, the torque T, and the phase difference θ of the electric motor 38 in the fourth embodiment as a result of actual measurement. That is, 42 is a torque curve and 43 is a phase curve. A curve 44 shown in FIG. 12 shows a temporal change of the rotation speed N when the electric motor 38 is driven by putting laundry in the dehydration tub, and N ₁ shown in FIG. It is shown as a value equal to N ₁ shown in the figure. As shown in FIG. 12, the rotation speed of the electric motor 38 increases at a relatively large rate of change with time from time T ₀ to time T ₁ when the dehydration amount is large because the load decreases as the dehydration progresses. On the other hand, the degree of acceleration gradually decreases after the time T _{1 when the} dehydration is sufficiently performed. As a result, in the region where the rotational speed is N ₁ or higher, the temporal increase rate of the phase difference decreases as the temporal increase rate of the rotational speed decreases, as shown in FIG. Therefore, unlike the cases of the first and second embodiments, the temporal change rate of the phase difference can be used as a judgment element for completion of dehydration, and the fourth embodiment is constructed based on this principle. . This embodiment will be described below with reference to FIG. Reference numeral 45 denotes a phase detection unit, the internal circuit configuration of which is the same as that of the phase detection unit 8 described above, and therefore has four comparators 10, 11, 14, 15 and two voltage dividing circuits 12, 13. Is configured. The phase detector 45 is an electric motor 38 in a state where laundry is put in the dehydration tub.
The phase difference θ is constantly detected from the driving start time of 1 and the phase detection signal θx is given to the phase comparison unit 46 and the change rate determination circuit (load state determination unit) 47. A reference phase setting unit 48 sets a reference phase difference θ ₁ . Here, when the phase difference of the rated load is θ ′, θ ₁ is determined so as to satisfy the relationship of θ ₁ /θ′=0.9. And the aforementioned N ₁
Is the rotation speed when the phase difference is θ ₁ , and is the value at the time when the phase difference starts to change. When the phase comparison unit 46 determines that θx> θ ₁ , the determination command signal S ₁ is sent to the change rate determination circuit 4
Give to 7. Then, the change rate determination circuit 47 compares the reference change rate dθ, which is the reference value of the time change rate of the phase difference set in the reference change rate setting unit 49, with the time change rate dθx of the phase detection signal θx. To do. The result is dθx <
At the time when dθ is reached, the dehydration completion signal S ₂ is output, and this is given to the motor stop control circuit 50. The motor stop control circuit 50 receives the dehydration end signal S ₂ and immediately
Alternatively, the electric motor 3 may be used after a predetermined time delay for the dehydration compensation.
Turn off 8. A microcomputer can be substituted for the structure shown in FIG. The program flow chart in this case is shown in FIG. In FIG. 13, a routine shown by an arrow A is a program routine for sequentially rewriting the content θa of the memory into a phase detection signal θx each time the detecting section is used, and a routine consisting of arrows B and C is a previous phase detection signal. Value θa and new phase detection signal θ
It is a program routine that takes the difference from x and judges the temporal change rate of the phase difference from the difference.

In particular, in the routine A, the determination part for θa> 0 is a part for determining that the θx should be substituted into θa after the value θ ₁ or more at which the phase starts changing after passing the invariant region in the routine A. Is.

Further, regarding the fourth embodiment, if the value of dθ can be switched and selected, the dehydration strength can be selected.

As described above, as can be understood from the fourth embodiment, according to the present invention, the phase difference has a characteristic that it greatly changes with a slight change in the rotation speed in the stable region of the rotation speed at the maximum torque point or higher. Therefore, a slight change in the rotation speed in this stable region can be easily and highly accurately determined by the phase detection signal. Moreover, since the phase difference hardly changes depending on the power supply frequency, its voltage fluctuation, temperature change, etc., there are few error factors and highly accurate detection becomes possible. By the way, the fluctuation rate of the phase difference is ± 2% for the fluctuation between the frequencies of 50 Hz and 60 Hz, and ± 10% at the voltage of 100 V.
± 2% for fluctuations in%, ± 1% or less for fluctuations from 20 ° C to 70 ° C, and ± 10% for fluctuations of the capacitor 4 for reference. 3%
It is degree.

The present invention is not limited to the above-mentioned embodiment, and for example, the phase difference detection target may be the auxiliary winding.

[Effects of the Invention] According to the present invention, as described above in detail, the direct object of detection is the phase difference between the coil current and the applied voltage.
It is possible to obtain with high accuracy a signal that depends on the load state such as a change in torque and a change in rotation speed of the electric motor, particularly in a stable region, and the number of logic ICs used in the circuit configuration of the phase detection unit is sufficient. The effect is that it is possible to contribute to cost reduction.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing a first embodiment of the present invention, FIG. 2 is a voltage / current waveform diagram of each part of FIG. 1, and FIG. 3 is a state determination signal mainly showing a rotation speed characteristic and a phase detection signal characteristic. FIG. 4 is a diagram shown together with a time chart of FIG. 4, FIG. 4 is an equivalent circuit diagram of an electric motor, and FIG.
Fig. 6 is a vector diagram thereof, Fig. 6 is a diagram showing torque, rotation speed, and phase difference curves of the electric motor, Fig. 7 is a circuit diagram showing a second embodiment of the present invention, and Fig. 8 is each part of Fig. 7. Showing the time characteristics of the signal of FIG. 10 together with the sampling signal and the state determination signal, FIG. 9 is a circuit diagram showing a third embodiment of the present invention, and FIG.
FIG. 13 to FIG. 13 show a fourth embodiment of the present invention, of which FIG. 10 is a block diagram of an operating circuit, and FIG.
FIG. 12 is a characteristic curve diagram showing the relationship between torque and phase difference with respect to rotation speed, FIG. 12 is a characteristic curve diagram showing the time change rate of rotation speed of the electric motor, and FIG. 13 is a flow chart when a microcomputer is used. . In the figure, 1 is an electric motor, 8 is a phase detector, 9 is a current transformer, and 10 is a current transformer.
Is a first comparator, 11 is a second comparator, 1
2 is a first voltage dividing circuit, 13 is a second voltage dividing circuit, 14 is a third comparator, 15 is a fourth comparator, 16 is a load state determination unit, 26 is a minimum value holding circuit, 27 is a dehydration timer. , 31 is a sampling circuit (load state determination unit),
32 is a load state determination unit, 38 is a motor, 45 is a phase detection unit, 46 is a phase comparison unit, 47 is a change rate determination circuit (load state determination unit), 48 is a reference phase setting unit, and 49 is a reference change rate setting unit. , 50 are motor stop control circuits.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Internal reference number FI Technical indication location H02P 7/36 S 9178-5H (56) References JP-A-63-35293 (JP, A) Special features Kai 63-31490 (JP, A) JP 62-2887 (JP, A) JP 61-191394 (JP, A) JP 61-82127 (JP, A) JP 51-113673 ( JP, A) JP 49-100547 (JP, A) JP 49-35085 (JP, A) JP-B-5-52233 (JP, B2)

Claims (1)

[Claims] 1. A phase detecting section for detecting a phase difference between a coil current of an induction motor and an applied voltage based on a difference between respective zero crossing points, and a phase detecting signal output from this phase detecting section is compared with a reference value. And a load state determination unit that converts the load current to a load state signal, wherein the phase detection unit converts the coil current and the applied voltage into a rectangular wave signal that rises and falls at each zero-cross point and outputs the rectangular wave signal. A first comparator and a second comparator, a first voltage dividing circuit that gives a level difference to the output from the first comparator, and a second voltage dividing circuit that gives a level difference to the output from the second comparator. And the output from the first comparator and the second
And a third comparator which receives the divided voltage output from the voltage dividing circuit and outputs a comparison result corresponding to each input, an output from the second comparator and a divided voltage output from the first voltage dividing circuit. And a fourth comparator that outputs a comparison result corresponding to each input, and is configured to use a logical sum of the comparison results of the third and fourth comparators as a phase detection signal. Electric motor load condition detection device.