JPS6059836B2 - Protection device for air conditioners - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a protection device for motor current fluctuations of an air conditioner using a DC motor.

Conventionally, induction motors have generally been used as electric motors for air conditioners.

As is well-known in induction motors, the motor rotation speed is determined by the commercial power supply frequency and the number of motor poles, so the motor rotation speed can only be controlled ON-OFF, which results in poor performance as an air conditioner compared to continuous control of the motor rotation speed. If the coefficient is bad,
It had some drawbacks. In order to significantly improve the coefficient of performance of an air conditioner, as an electric motor for an air conditioner,
If a DC motor is used instead of an induction motor, when the temperature on the outside air side of the air conditioner becomes abnormally high,
The load on the compressor increases and the DC motor produces a large torque, so a large current flows through the motor.

Furthermore, when refrigerant leaks, the load becomes lighter and the motor current becomes smaller. That is, when a DC motor produces a large torque, a large current flows through the motor, but at this time the brushes, armature windings, etc. of the motor burn out, and if a DC brushless motor is used as the DC motor,
This has the disadvantage that the semiconductor elements of the DC motor drive circuit are damaged by the large current.

In addition, when the motor current is small, the air conditioner is in a state of refrigerant leakage as described above, and in the air conditioner, the refrigerant is used to cool the motor and suppress the temperature rise of the motor. If the air conditioner is operated under such conditions, the temperature of the electric motor will rise and furthermore, it will burn out. SUMMARY OF THE INVENTION An object of the present invention is to eliminate the above-mentioned drawbacks of the prior art and to provide a protection device that prevents damage to a DC motor and its motor drive circuit even if the motor current fluctuates. The present invention is constructed as follows.

Detects the motor current and inputs it to two comparators after amplification.
A reference voltage corresponding to the upper and lower limit current settings has already been input to the comparator, and when the motor current is too large or too small than the set reference current, the motor drive circuit is activated by the motor stop command signal. There is a device that shuts off the driver and inverter circuits and stops the motor.
An example of the protection device for an air conditioner according to the present invention is when a DC brushless motor is used as the motor. I will explain about it.

The configuration of an air conditioner is shown in FIG. 1, a block diagram showing an embodiment of the protection device according to the invention applied to the motor drive circuit system of the air conditioner is shown in FIG. 2, and a specific circuit example of the protection device of the invention is shown in FIG. 3, and FIG. 4 shows an operating waveform diagram of FIG. 3.
In the air conditioner shown in FIG. 1, the left side of the dashed-dotted line indicates the outdoor side, and the right side indicates the indoor side. The refrigeration cycle uses a compression refrigerator, and the compressor is a completely hermetic compressor that includes a drive motor and a compressor. The refrigerant compressed by the compressor 1 becomes a high-temperature, high-pressure gas, and is condensed and liquefied by the condenser 2. Further, the liquefied refrigerant is depressurized through the capillary 3, becomes low temperature and low pressure, enters the evaporator 4, cools and dehumidifies the indoor air, evaporates and becomes gaseous, and returns to the compressor 1 where it is compressed.
This circulation is repeated to perform the cooling effect. In FIG. 2, a portion 13 surrounded by a dashed line indicates the protection device of the present invention. Further, in FIG. 2, the commercial power supply 6 passes through a rectifying and smoothing circuit 7 to become a DC voltage containing some ripple, and is applied to a three-phase bridge-connected semiconductor inverter circuit (hereinafter abbreviated as an inverter circuit) 8. The inverter circuit 8 switches the semiconductor element based on a signal detected from a rotor using a permanent magnet to detect the rotational position at which the torque should be maximum.
The armature current of the electric motor 9 is controlled. A back electromotive voltage detection circuit 10 detects the rotational position, and the detection signal is sent to a signal distribution circuit 11 to supply a signal to the inverter circuit.
The signal is distributed by . Conventionally, the driver circuit 12 as shown by the broken line
It was added to the inverter circuit 8 through the inverter circuit 8.

In the present invention, a current detection circuit 14 with a low resistance is configured between the rectification and smoothing circuit 7 and the inverter circuit 8 as shown in FIG. 3 to detect the motor current.

Furthermore, even if a current transformer is used as the detection element, the motor current can be similarly detected. The detection signal is amplified by an amplifier circuit 15 and then input to a comparator 16 and a comparator 17. Reference potentials corresponding to set reference currents have already been set in the comparators 16 and 17, respectively. For example, if the comparator 16 is set to a reference setting current of 15A,
When a current larger than the set current is input to the comparator 16, the motor stop signal changes from high level to low level and is input to the signal cutoff circuit 18, as shown in FIG. 4A.

In the present invention, the motor drive signal shown in FIG. 4B is inputted to the signal cutoff circuit 18 from the signal distribution circuit 11,
When the signal cutoff circuit 18 is configured with the AND circuit 18 shown in FIG. 3, as shown in FIG. 4A, the motor drive signal is output when the motor stop command signal is at a high level, and when the motor stop command signal is at a low level, it is output at a low level. This becomes an output signal and is input to the driver circuit 12. That is, when the motor stop command signal is at a high level, the signal from the signal distribution circuit 11 is directly input to the driver circuit 12, and when the motor stop command signal is at a low level, the input signal to the driver circuit 12 is also at a low level, and the inverter circuit 8, and the motor is therefore stopped. For example, when a current smaller than the set current is input to the comparator 17 set to the reference set current 1A, the motor stop command signal changes from a high level to a low level as shown in FIG. is input, and the electric motor 9 is similarly stopped.

The current values for the upper and lower limits of the reference setting current can be arbitrarily changed by changing the comparator setting potential using variable resistors 19 and 20 shown in FIG. As explained in detail above, when the motor current is too large or too small than a set current with an upper limit and a lower limit, after comparing the set current and the motor current, a motor stop command signal is sent to the driver circuit 12 and By cutting off the signal from the inverter circuit 8, the electric motor is stopped.

In this embodiment, a signal was applied to cut off the driver circuit 12 and inverter circuit 8 using the motor stop command signal, but in a general DC motor, a switch, etc. is installed at the commercial power switch of the air conditioner or the motor input power supply. However, it is clear that the electric motor can be stopped by applying the command signal to disconnect the switches.

According to the present invention, when a DC motor is used in an air conditioner,
It is possible to prevent burnout of the motor or damage to the motor drive circuit in a DC brushless motor caused by too large a motor current.

In addition, by detecting that the motor current is too small, it is possible to detect refrigerant leaks in the air conditioner, and prevent temperature rises and burnouts in the motor that occur when operating the air conditioner due to refrigerant leaks. can significantly improve reliability.

[Brief explanation of the drawing]

Fig. 1 is a block diagram of an air conditioner, Fig. 2 is a block diagram showing an embodiment of a protection device according to the present invention applied to a motor drive circuit system of an air conditioner, and Fig. 3 is a circuit diagram of a protection device according to the present invention. For example, FIG. 4 is a waveform diagram for explaining the operation of FIG. 3. 6... Commercial power supply, 7... Rectifier and smoothing circuit, 8... 3
Phase bridge connection semiconductor inverter circuit, 9... Motor, 10... Back electromotive voltage signal detection circuit, 11... Signal distribution circuit, 12... Driver circuit, 13... Protective device, 14... Current detection circuit, 15...Amplification circuit, 16
... Comparator, 17... Comparator, 18... Signal cutoff circuit.

Claims (1)

[Claims] 1. A DC motor, a signal distribution circuit that generates a motor drive signal, a driver circuit to which the motor drive signal is supplied from the signal distribution circuit, and an inverter circuit that is connected to the driver circuit and supplies current flowing through the DC motor to the DC motor. This is a protection device for an air conditioner used in an air conditioner having a DC motor. A first comparison circuit that compares the detection signal with a predetermined first reference signal and generates a DC motor stop signal when the detection signal exceeds the first reference voltage; prescribed second
a second comparison circuit that generates a DC motor stop command signal when the detection signal is lower than the second reference signal, and is connected to the first and second comparison circuits; , is connected between the signal distribution circuit and the driver circuit, and outputs a motor drive signal supplied from the signal distribution circuit to the driver circuit when a DC motor stop command signal is supplied from the first and second comparison circuits. A protection device for an air conditioner, comprising a signal cutoff circuit that cuts off the signal.