JP3778877B2 - Motor control device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a motor control device having a function of detecting a load state.
[0002]
[Prior art]
In order to rotate an AC motor, such as an induction motor, at a target speed, a motor control device that controls the phase of a switching element connected to the motor based on a deviation between the target rotational speed and the actual rotational speed has been put into practical use.
[0003]
When the motor has a torque characteristic a as illustrated in FIG. 4, the motor control device adjusts the output torque of the motor as indicated by a line b. Therefore, the rotational speed of the motor is maintained at the target rotational speed until the output torque becomes the torque at the intersection P ₁ between the regulation line b and the characteristic a.
[0004]
In FIG. 4, the rated torque T _O indicates a torque that allows a continuously rated motor to be operated stably for a long time without overheating. The rated operation region is a region where the motor is operated with a torque equal to or less than the rated torque T _O , and the overload operation region I is a torque where the motor is larger than the rated torque T _O and equal to or less than the torque at the point P _1. Further, an overload operation region II indicates a region where the motor is operated with a torque greater than the torque at the point P ₁ and less than the stop torque (the torque at the P ₂ point).
[0005]
[Problems to be solved by the invention]
When the motor is operated for a long time in an overload state, inconveniences such as damage to the motor due to overheating occur. Therefore, in order to properly operate the motor, it is necessary to detect the load state and take measures to cancel the state in an overload state.
[0006]
According to the above-described conventional motor control device, when the motor is operated in the overload operation region II, it is possible to detect the overload operation state based on a decrease in the actual rotational speed of the motor. However, when the motor is operated in the overload operation region I, the actual rotational speed does not decrease, and therefore it is impossible to detect the overload operation state based on the decrease phenomenon.
[0007]
In view of such a situation, an object of the present invention is to provide a motor control device capable of reliably detecting a load state of a motor.
[0008]
[Means for Solving the Problems]
The present invention is a control device for phase-controlling a switching element connected to a motor based on a deviation between a target rotational speed of the motor and an actual rotational speed, and a load state of the motor based on a conduction time of the switching element It is characterized by providing a load state determination means for determining the above.
[0009]
The load state determination means may include timer means for measuring the conduction time, and comparison means for comparing the time value of the timer with a predetermined load state determination value to determine the load state. Further, display means for displaying the load state can be further provided.
[0010]
The present invention is a control device that controls the phase of a switching element connected to a motor based on a deviation between a target rotational speed and an actual rotational speed of the motor, and determines a load state of the motor based on the deviation It is characterized by providing state determination means.
The load state determination means may comprise comparison means for comparing the value of the signal indicating the deviation with a predetermined load state determination value to determine the load state. Further, display means for displaying the load state may be further provided.
[0011]
DETAILED DESCRIPTION OF THE INVENTION
A preferred embodiment of a motor control apparatus according to the present invention will be described below with reference to the drawings.
[0012]
First Embodiment As shown in FIG. 1, the motor control device according to the first embodiment includes a speed control unit 10 and a load state detection unit 20.
In the speed control unit 10, a motor (in this example, an induction motor) M is connected in series to an AC power source 13 via a switching element 12 such as a one-way control rectifier (thyristor) or a bidirectional control rectifier. The speed detection unit 14 outputs a signal corresponding to the actual rotation speed V _C of the motor M based on the output of the tacho generator 15 that rotates together with the motor M, and the speed setting unit 16 sets the target rotation speed V _R of the motor M. Set the corresponding signal and output.
[0013]
The comparison amplifier 11 forms a voltage signal S ₁ corresponding to the deviation V _R −V _C between the target rotation speed V _R and the actual rotation speed V _C and outputs the voltage signal S ₁ to the comparison section 17. Incidentally, the voltage signals S ₁ is a voltage referenced to the zero level line shown in FIG. Therefore, the signal voltage S ₁ as shown in the figure is changed to downward-sloping indicates that the deviation V _R -V _C with time is increased.
[0014]
The comparison unit 17 compares the voltage signal S ₁ with the triangular wave signal S ₂ output from the triangular wave generation unit 18 (see FIG. 2B), and when the triangular wave signal S ₂ crosses the signal S _1. A trigger signal (ignition signal) S _{3 shown} in FIG.
The switching element 12 is triggered by the trigger signal S ₃ , and as a result, the voltage shown in FIG. 2D is applied to the motor M via the switching element 12.
[0015]
The power supply synchronization signal unit 19 shows the “H” level in the period from the power supply synchronization signal shown in FIG. 2E, that is, from the zero cross point of the power supply voltage shown in FIG. It is configured to output a signal. Then, the triangular wave generating unit 18, based on the power-supply sync signal, for generating the triangular wave signal S ₂ for each half cycle of the supply voltage.
[0016]
The speed control unit 10 configured as described above controls the phase of the switching element 12 so that the power supplied to the motor increases as the deviation V _R -V _C of the rotation speed of the motor M increases, so that the actual rotation speed of the motor M increases. V _C is brought close to the target rotational speed V _R.
That is, when the motor M has the torque characteristic a illustrated in FIG. 4, the speed control unit 10 adjusts the output torque of the motor M as indicated by a line b. Therefore, the rotational speed of the motor M is maintained at the target rotational speed V _R until the output torque reaches the torque at the intersection P ₁ between the regulation line b and the characteristic a.
[0017]
On the other hand, the load state detection unit 20 includes a counter 22 that counts clock pulses output from the pulse generation unit 21, a threshold setting unit 23 that sets a threshold for the count value of the counter 22, and the count A comparison unit 24 for comparing the value and the threshold value and a display unit 25 for displaying the comparison result of the comparison unit 24 are provided.
[0018]
By the way, as the load torque of the induction motor M increases, the effective value of the applied voltage increases and the output torque thereof increases. An increase in the effective value of the applied voltage means that the conduction time of the switching element 12 becomes longer.
Therefore, if the conduction time of the switching element 12 in each half cycle of the power supply voltage in FIG. 2A is measured, the effective value of the voltage applied to the motor M in each half cycle, and hence the load state of the motor M, can be obtained. I can know.
[0019]
Therefore, in this embodiment, the counter 22 is operated to measure the conduction time of the switching element 12. That is, the counter 22 starts counting the clock pulse when the power supply synchronization signal changes from “L” level to “H” level (zero cross point of the power supply voltage), and the power supply synchronization signal is changed from “H” level. The count operation of the counter 22 is stopped at the time of changing to the “L” level (the trigger time of the switching element 12). The counter 22 is reset at the next zero crossing time of the power supply voltage, and then starts a counting operation in the next cycle.
[0020]
As is apparent from the above description, the counter 22 functions as a timer that measures the time during which the power supply synchronization signal is in the “H” level, that is, the non-conduction time of the switching element 12 in the half cycle of the power supply voltage. Have.
The conduction time of the switching element 12 is a time obtained by subtracting the non-conduction time from a half cycle of the power supply voltage. Therefore, measuring the non-conduction time is substantially equivalent to measuring the conduction time. Although the conduction time can be measured directly, it is advantageous to measure the non-conduction time in order to facilitate the measurement process.
[0021]
The threshold value setting unit 23 sets a threshold value for determining a load state. In this embodiment, non-conductive time of the first load state determining threshold value t _a of the switching element 12 when the motor M generates an arbitrary torque T _S less than the rated torque T _O shown in FIG. 4 The non-conduction time of the switching element 12 when the motor M generates the rated torque T _O is set as the second load state determination threshold t _b .
[0022]
The comparison unit 24 sets _a state where the non-conduction time t detected by the counter 22 is t ≧ ta as _a low load state, a state where t _b ≦ t <ta as _a medium load state, and further satisfies t <t _b Each state is determined as an overload state. When the comparison unit 24 determines the low load state, the medium load state, and the overload state in a half cycle of the power supply voltage, as shown in FIGS. 2 (g), (h), and (i), A signal indicating the determination result is output in the next period.
The number of threshold values is not limited to two, and may be one or three or more. Also, the threshold value can be set arbitrarily.
[0023]
The display unit 25 displays the load state based on the output signal from the comparison unit 24. That is, for example, the fact that the motor M is operating in a low load, medium load, and overload state is displayed to the outside by lighting of light emitting elements (for example, LEDs) of different colors or by sounds, characters, and the like.
[0024]
The indication “low load” on the display unit 25 recognizes that the motor M is being operated with a sufficient margin with respect to the rated torque T _O. The continuation of the display of “low load” is a material for design change determination that the motor M can be replaced with a low output one.
In addition, the indication “medium load” means that the motor M is being operated in a state where there is not much margin with respect to the rated torque T _O , that is, it is necessary to be careful not to increase the load any more. Recognize that.
[0025]
Further, the display of "overload" is that the motor M is operated beyond the rated torque T _O, i.e., mechanism elements provided on the periphery of the motor M and the motor M is continued for a long time operation anyway Recognize that there is a risk of damaging them. The continuation of the display of “overload” is a design change determination material that it is desirable to replace the motor M with a higher output one.
[0026]
By the way, the motor M controlled by the motor control device has a characteristic that the loss increases according to the effective value of the applied voltage, and the heat generation amount increases as the loss increases. This means that if the effective value of the applied voltage of the motor M is known, the tendency of the temperature rise (not the actual temperature but the temperature reached when the operation state continues) can be known.
Therefore, a relationship between the count value of the counter 22 corresponding to the effective value of the applied voltage and the reached temperature is obtained in advance by experiment or simulation, and the reached temperature obtained from the relationship and the count value of the counter 22 is calculated. It is also possible to display on the display unit 25.
[0027]
When the motor M is a short-time rated specification motor, the continuous operation time of the motor corresponding to the effective value of the applied voltage is known based on the relationship between the temperature rise characteristic and the time rating. . Therefore, it is also possible to obtain the continuous operation possible time corresponding to the count value of the counter 22 from the above relationship and display it on the display unit 25.
[0028]
Second Embodiment FIG. 3 shows a second embodiment of the motor control apparatus according to the present invention.
The effective value of the applied voltage representing the load state of the motor M also corresponds to the deviation signal voltage S ₁ output from the comparison amplification unit 11. Therefore, the load state detection unit 20 'of the motor control device according to this embodiment is configured to detect a load state based on the deviation signal voltage S _1.
[0029]
That is, the load state detecting unit 20 ′ sets the threshold voltages S _a and S _b shown in FIG. 2 as threshold values for determining the first and second load states, deviation signal voltage S ₁ the threshold voltage S _a, and a comparison unit 24 'to be compared with the S _b. The threshold voltages S _a and S _b are voltages based on the zero level line shown in FIG. 2, and the threshold voltage S _a is an arbitrary value that the motor M is lower than the rated torque T _O shown in FIG. is set to the value of the deviation signal voltage S ₁ at the time of generating the torque T _S, the threshold voltage S _b is set to the value of the deviation signal voltage S ₁ when the motor M generates the rated torque T _O Has been. The number of threshold values is not limited to two, and may be one or three or more.
[0030]
The comparison unit 24 ′ sets the state where the deviation signal voltage S ₁ is S ₁ ≦ S _a as a low load state, sets the state where S _a <S ₁ ≦ S _b as a medium load state, and further sets the state where S ₁ > S _b . Each is determined as an overload state, and a signal indicating the determination result is output. Then, the display unit 25 ′ displays the load state on the outside with a light emitting element, sound, characters, etc. based on the output signal of the comparison unit 24.
[0031]
In the above, the deviation signal voltage S ₁ is directly compared with the threshold voltages S _a and S _b. Instead, the average value of the deviation signal voltage S ₁ in the half cycle of the power supply voltage is used as the threshold value. voltage S _a, it may be compared with S _b.
Also in this embodiment, it is possible to predict the temperature reached by the motor M and the continuous operation possible time based on the deviation signal voltage S ₁ and display them on the display unit 25 ′.
[0032]
The motor control devices according to the first and second embodiments can be configured by a digital circuit using a CPU or the like in addition to an analog circuit using an OP amplifier or the like.
In addition, the output signals (load state determination signals) of the comparison units 24 and 24 ′ in the first and second embodiments are used for controlling the operation state of the equipment using the motor M as a drive source. It can be output to a host controller such as a programmable controller or a computer.
The load state determination technique according to the present invention described above can also be applied to load state determination in a control system that performs PWM control of a brushless motor.
[0033]
【The invention's effect】
According to the motor control device of the present invention, since the load state of the motor is determined based on the conduction time of the switching element, even when the motor is rotating in the vicinity of the rotation target speed, that is, the motor is regulated. Even when the motor is overloaded, it is possible to reliably detect the overload of the motor.
Further, according to the motor control device of the present invention, since the load state of the motor is determined based on the deviation between the target rotational speed of the motor and the actual rotational speed, the same effect as described above can be obtained.
[Brief description of the drawings]
FIG. 1 is a block diagram showing a first embodiment of a motor control device according to the present invention.
FIG. 2 is a waveform diagram showing the operation of the motor control device.
FIG. 3 is a block diagram showing a second embodiment of the motor control device according to the present invention.
FIG. 4 is a graph showing an example of torque characteristics of a motor.
[Explanation of symbols]
M motor 10 speed control unit 11 comparison amplification unit 12 switching element 13 AC power source 14 speed detection unit 15 tachometer generator 16 speed setting unit 17 comparison unit 18 triangular wave generation unit 19 power supply synchronization signal unit 20 load state detection unit 21 pulse generation unit 22 counter 23, 23 'Threshold setting unit 24, 24' Comparison unit 25, 25 'Display unit

Claims (3)

A motor control device that performs phase control on a switching element connected to a motor based on a deviation between a target rotation speed and an actual rotation speed of the motor,
A motor control device comprising load state determination means for determining a load state of the motor based on a conduction time of the switching element during a power supply voltage application period . The load state determination means includes timer means for measuring the conduction time, and comparison means for comparing the time value of the timer means with a predetermined load state determination value to determine the load state. The motor control device according to claim 1.   The motor control device according to claim 1, further comprising display means for displaying the load state.

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