JPS6147078B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an AC power control circuit that controls AC power supplied to an induction motor using a switching circuit.

The present invention cuts the AC power supplied to the induction motor for a very short time every predetermined period using a simple circuit without using a complicated circuit such as a phase control method, thereby smoothly and An object of the present invention is to provide an AC power control circuit for an induction motor that can precisely and stably control the speed, etc. of the induction motor.

Below, based on drawings showing embodiments of the present invention,
The present invention will be explained.

In FIG. 1, 1 is an AC power source with a predetermined frequency;
2 is an induction motor. 3 is a switching circuit such as a thyristor, a triax, or an SSR (solid state relay), and is a circuit for controlling the power supplied from the AC power supply 1 to the induction motor 2. S is an AC power supply circuit. 4 is a waveform shaping circuit, which is shown in FIG. 2A of the AC power supply 1.
This circuit inputs an output wave a as shown in FIG. 2 and outputs a periodic wave b as shown in FIG. Reference numeral 5 denotes a cutting cycle setting circuit for setting a cutting cycle T of an arbitrary size such as 1 second or 0.9 seconds. 6 is the cutting cycle setting circuit 5
The cutting period display signal f outputted from the cutting period display signal f is inputted, and the periodic wave b outputted from the waveform shaping circuit 4 is inputted and the wave number is counted. , cutting period T), the counting circuit generates an output signal c as shown in FIG. 2C and at the same time performs a new counting operation. Therefore, if the output frequency of power supply 1 is 60Hz and the cutting period T is 1 second, then
Every time the count reaches 60, the counting circuit 6 outputs an output signal c. 7 issues an opening command d to the switching circuit 3 to open the switching circuit 3 for a predetermined time width smaller than the cutting period T, for example, 1/60 seconds, based on the output signal c from the counting circuit 6. This is a cutting command circuit. Note that when the switching circuit 3 is opened/closed by the opening/closing command d from the cutting command circuit 7, the timing is of course not limited to when the output signal c is input to the cutting command circuit 3. , it is desirable that the first alternating current after that time is at zero potential. In that case, the time width during which the switching circuit 3 is turned on is preferably a half cycle of the alternating current or an integral multiple thereof. For example, when the opening time width is a half cycle, the switching circuit 3 opens the switching circuit 3 for a half cycle starting from the zero potential period of the AC, and the voltage waveform of the AC supplied to the induction motor 2 is as shown in FIG. This results in a discontinuous waveform e as shown in EF.
As mentioned above, as a method of cutting for half a cycle or an integral multiple thereof starting from the zero potential period of AC, there are two methods: issuing the opening command d in accordance with the zero potential period of AC, and using the zero voltage control function. There is a method such as having it in the switching circuit 3. Further, as the opening command d, for example, as shown in _d1 in FIG. 2D,
A pulse signal synchronized with the periodic wave b or a DC signal as shown in _d2 is constantly input to the switching circuit 3, and the output signal c is sent to the cutting command circuit 7.
When the output signal c is input to the cutting command circuit 7, the pulse signal or DC signal is not output for a predetermined time period as shown by the symbol X or _Y , or the output signal c is There are some that output a rectangular wave signal Z having a predetermined time width when the signal is input to the signal Z. Reference numeral 8 indicates that, while the switching circuit 3 is opened for a predetermined time width, the switching circuit 3 is turned off for a time width shorter than the predetermined time width in accordance with the opening command d from the cutting command circuit 7. This is a cutting interruption command circuit which issues a closing command g to the switching circuit 3 to close the cutting circuit more than once. The closing command g is, for example, the opening command d,
In the case shown at _d2 in FIG. 2D, the signal is as shown at g in FIG. 2D. It goes without saying that the cutting interruption command circuit 8 may be constructed integrally with the cutting command circuit 7, and the circuit may issue a signal as shown at i in FIG. FIG. 3 is a diagram showing an embodiment of another aspect of the present invention, in which 9 is an induction motor 2.
An overcurrent relay 10 is installed near the induction motor 2 to detect overcurrent of the alternating current flowing through the induction motor 2, and the overcurrent relay 10 is turned on and off based on the signal from the overcurrent relay 9.
The switch 11 that operates is a small signal power supply. A signal detector 12 is installed near the AC power source 1 and detects a small signal flowing from the AC power source 1 to the AC power supply circuit S to the induction motor 2, and transmits the detection result to the cutting cycle setting circuit 5. and is output to the cutting command circuit 7. The cutting cycle setting circuit 5 and the cutting command circuit 7 shorten the cutting cycle or lengthen the cutting time based on the signal input from the signal detector 12.

Since the present invention is configured as described above, it operates as shown below.

An alternating current wave a output from an alternating current power source 1 is shaped into a periodic wave b by a waveform shaping circuit 4, and is input to a counting circuit 6. Of course, the periodic wave b is synchronized with the alternating current wave a. On the other hand, a cutting cycle display signal f is input from the cutting cycle setting circuit 5 to the counting circuit 6. The counting circuit 6 issues an output signal c and at the same time performs a new counting operation every time the number of waves of the periodic wave b reaches a number corresponding to the magnitude of the cutting period display signal f. When the cutting command circuit 7 receives the output signal c from the counting circuit 6,
Based on the signal c, an opening command d is issued to the switching circuit 3 to open the switching circuit 3 for a predetermined time width. Since the switching circuit 3 is opened for a predetermined period of time in accordance with the opening/closing command d, the AC power supplied to the induction motor 2 becomes zero for a predetermined period of time, as shown in FIG. 2E, for example. Note that when the closing command g is issued from the cutting interruption command circuit 8, the switching circuit 3 is closed even if the opening command d is issued, so that the induction motor 2
As shown at e' in FIG. 2G, the AC power supplied to the AC power becomes zero intermittently only during the predetermined time width.
In this way, the cutting of the AC power supplied to the induction motor 2 is performed periodically. In addition, in the case of the configuration shown in FIG. 3, when an overcurrent flows through the induction motor 2, the overcurrent relay 9 detects it, the switch 10 is closed by the signal from the overcurrent relay 9, and a small signal is output. It flows into the AC power supply circuit S. By the way, during the time when large power is not flowing from the AC power supply 1 to the induction motor 2 (during the cutting time), only a small signal is flowing through the AC power supply circuit S, as shown in h of Fig. 2H. Since there is no signal, the signal detector 12 can detect the small signal, and as a result,
Overcurrent control is performed by shortening the cutting cycle and lengthening the cutting time width. In this way, when large power is not flowing through the AC power supply circuit S, the AC power supply circuit S can be used to perform automatic control to prevent overcurrent, which is very convenient.

As shown above, since the AC power control circuit in the induction motor according to the present invention (hereinafter referred to as the circuit according to the present invention) is configured, it produces the following effects.

Since the present invention cuts the AC supply to the induction motor for a predetermined time width of, for example, around 1/60 seconds at each predetermined cutting period, the cutting period and the cutting time width can be varied manually or automatically. , the speed of the induction motor can be controlled smoothly, accurately and stably, and the induction motor connected to the circuit of the present invention can control the speed of the induction motor by the inertial action of the rotor without causing synchronization unlike a synchronous motor. In addition to continuing to rotate smoothly, it is possible to save energy compared to the case where no cutting is performed. Furthermore, when the timing and time width for cutting the supply of AC are set to a half cycle starting from the zero potential period of AC or a time width that is an integral multiple thereof, compared to the case where AC power is controlled by a phase control method, As a result, the generation of radio noise can be reduced to an extremely low level, and the rush current can also be suppressed to a minimum, resulting in an energy-saving effect. Further, the effects when the present invention is applied to a cooler will be described below.

Conventional coolers use temperature sensors to turn on and off power at predetermined time intervals, as shown in Figure 4a.
The temperature was controlled by repeatedly turning it off. However, in that case, as shown in FIG. 2B, the temperature changed drastically and the purpose of maintaining the temperature at an appropriate level could not be achieved.
Especially during the OFF time, the temperature rose and was uncomfortable.
Therefore, by utilizing the present invention, temperature control is performed by cutting AC power for a predetermined time width at a predetermined cutting cycle to maintain an appropriate temperature while continuously supplying alternating current as described above. Since the OFF time does not continue continuously, it is possible to make the room more comfortable. Furthermore, since the cutting time width is short, the induction motor continues to rotate without stopping due to inertia.
There is no need to stop the compressor during the OFF time and restart it again, as in the past. As a result, there is no need to flow a rising current when restarting the induction motor, and the peak current is small, so the allowable capacity of wiring equipment, etc. is small, and costs can be reduced. In addition, the present invention
Although the AC power control is for an induction motor, it is also possible to perform AC power control not only for the induction motor but also for, for example, a heater load.

[Brief explanation of the drawing]

The drawings are all for explaining the embodiments of the present invention, and FIG. 1 is a block diagram of the circuit of the present invention, and FIG. 2 is a signal waveform diagram at various points in the circuit. A diagram of the output wave a of the power supply, B is a diagram of the periodic wave b whose waveform has been shaped, C is a diagram of the output signal wave c from the counting circuit, and D is a diagram of the opening/closing command d from the cutting command circuit and the cutting interruption command circuit. E is a diagram of the AC wave e cut by a predetermined time width, F is an enlarged diagram of the AC voltage waveform portion surrounded by the dashed line in the diagram E, G
is an enlarged view of the AC wave e' cut in a different manner, H is an enlarged view of the current waveform flowing through the AC power supply circuit when a small signal is passed through the AC power supply circuit during cutting, and I is an enlarged view of the switching circuit. Opening,
A diagram of the command signal wave of another mode of closing, FIG. 3, is as follows.
A block diagram of a circuit according to another embodiment of the present invention, A of FIG.
A graph showing ON and OFF, and B is a graph showing changes in indoor temperature. DESCRIPTION OF SYMBOLS 1... AC power supply, 2... Induction motor, 3... Switching circuit, 4... Waveform shaping circuit, 5... Cutting cycle setting circuit, 6... Counting circuit, 7...
... Cutting command circuit, 8 ... Cutting interruption command circuit, a ... continuous AC wave, b ... periodic wave,
c... Output signal, d... Opening command, e, e'... Discontinuous AC wave, f... Cutting period display signal,
g...Closing command, 9...Overcurrent relay, 10...
Contact, 11...Small signal power supply, 12...Small signal detector.

Claims (1)

[Scope of Claims] 1. In an AC power control circuit that uses a switching circuit to control AC power supplied to an induction motor from an AC power source of a predetermined frequency, a cutting cycle setting circuit that sets a cutting cycle in advance;
A counting circuit that counts the number of periodic waves synchronized with the output of the AC power source and generates an output signal every time the counted number reaches a quantity corresponding to the magnitude of the cutting cycle display signal inputted from the cutting cycle setting circuit. and a cutting command circuit that issues an opening command to the switching circuit to open the switching circuit for a predetermined time width shorter than the cutting period based on the output signal from the counting circuit. AC power control circuit for an induction motor. 2. The cutting command circuit issues, based on the output signal from the counting circuit, an opening command to the switching circuit to open the switching circuit for a time width of a half period starting from the zero potential period of the alternating current or an integral multiple thereof. An AC power control circuit for an induction motor according to claim 1, characterized in that the circuit emits an AC power. 3. A closing command for closing the switching circuit one or more times for a time width shorter than the predetermined time width while the switching circuit is open for a predetermined time width due to the opening command from the cutting command circuit; 2. The AC power control circuit for an induction motor according to claim 1, further comprising a cutting interruption command circuit that issues a cutting interruption command to the switching circuit, either integrally or separately from the cutting command circuit.