JP3237332B2 - Protection device for magnet motor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a protection device for a magnet motor used in a compressor for an air conditioner or the like.

[0002]

2. Description of the Related Art Conventionally, as an electric motor in an air-conditioning compressor driven by an inverter, there is a motor adopting a magnet motor which is a synchronous motor using a permanent magnet for a rotor. An air-conditioning compressor usually requires a relatively large output of 600 W or more, so that a magnet is required to have a high coercive force, and a ferrite-based magnet is generally used as the magnet material. The load of the air-conditioning compressor is not uniform, and an excessive load may suddenly occur due to various factors such as liquid suction. In such a case, an excessive current flows through the stator, and a magnetic field generated by the excessive current may demagnetize the ferrite magnet of the rotor. In order to prevent such demagnetization, the current value of the compressor is usually detected, and if an excessive current exceeding the set current is generated, the power supply is shut off and a device is installed to protect it from demagnetization. I was Since the set current value for demagnetization protection tends to decrease as the temperature decreases as the coercive force of commonly used strontium-based ferrite magnets lowers, it is set based on the lowest ambient temperature that the magnet rotor of the motor receives. There is a need to. Since most air-conditioning compressors are of a closed type, liquid refrigerant may also accumulate around the rotor magnets.
° C. For this reason, the power supply set value for demagnetization protection has generally been set on the basis of minus a number + ° C.

[0003]

In an air conditioner, as the temperature increases, the pressure increases, the load on the compressor increases, and the current flowing tends to increase. Therefore, if the current flowing through the compressor is limited for demagnetization protection, operation cannot be performed at a high load, and the operating load range is limited. Also, when a scroll compressor is used as a compressor, a larger starting current tends to flow as the ambient temperature is higher.Therefore, this starting current becomes larger than a set current for demagnetization protection, and starting mistakes may occur. is there. In addition, it is necessary to select a magnet having a large coercive force in order to make demagnetization less likely to occur, and it is necessary to sacrifice the maximum magnetic flux density, which leads to a decrease in compressor efficiency due to a decrease in motor efficiency. Accordingly, an object of the present invention is to provide appropriate demagnetization protection, expand the operating load range, and reduce starting failures.

[0004]

SUMMARY OF THE INVENTION The present invention solves the above-mentioned problems and achieves the object by controlling the demagnetization protection set current value of a magnet motor by temperature and changing it to an appropriate value. The operating load range is expanded and starting failures are reduced. In an air conditioner, a thermistor or the like is used as a temperature detecting means.

[0005]

The cut-off current set value for demagnetization protection is made variable by detecting the motor ambient temperature and detecting this temperature. In a ferrite magnet, the breaking current can be set to a higher current value as the temperature is higher due to its demagnetization characteristics. Therefore, when the ambient temperature rises in an air conditioner or the like, the load of the motor increases accordingly, so that a wider operating load range can be realized and starting failure can be reduced.

[0006]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to a schematic diagram taking an air conditioner as an example.

FIG. 1 is a diagram showing an embodiment of an air conditioner according to the present invention. Generally, an air conditioner is composed of an outdoor unit 1 and an indoor unit 2, and a compressor 3, a condenser 4, a throttle mechanism 5, and an evaporator 7 arranged in the outdoor unit 2 are sequentially connected to form a refrigeration cycle. are doing. As the electric motor 8 of the compressor 3, a magnet motor which is a synchronous motor using a magnet for a rotor is used. The power supply unit for the motor 8 is a schematic diagram of the present embodiment. Are represented by a power cutoff device 12 that operates when the air flows, and a temperature detector 13 that detects the outside air temperature. These power supply units are generally configured in an inverter circuit. The circuit breaker 12 is opened and closed by a power transistor, and the detection device 11 for the current flowing through the compressor 3 detects the current of the DC unit in the inverter circuit. Detected by CT. The protection device 5 is composed of a microcomputer that generally uses a thermistor to calculate the value of the temperature detector 13 based on the value of the current detected by CT, and issues an OFF instruction to the power transistor.

The thermistor for detecting the temperature can be commonly used as an outside air temperature sensor attached to the condenser 4 of the outdoor unit 1 of the air conditioner. The mounting place is
As shown in FIG. 4, it may be directly attached to the surface of the compressor 3, or may be attached to a piping of a refrigeration cycle or a ventilation circuit. The magnet used in the electric motor 8 is a strontium-based ferrite magnet, and its characteristic curve is represented by a magnetic flux density B and a coercive force H, and changes with temperature as shown in FIG. In particular, the coercive force H, which governs the demagnetization proof strength, tends to decrease as the temperature decreases.

In this embodiment having the above-described structure,
A current detector 11, a power supply breaker 12, and a temperature detector 13 for capturing the outside air temperature are connected to a protection device 10 for preventing demagnetization of a motor 8 that drives the compressor 3. The protection device 10 can take an appropriate demagnetization protection set value from the temperature data obtained by the temperature detector 13 by the setting in FIG. FIG. 3 is an example, but according to this, when the outside air temperature is equal to or higher than t ° C., the demagnetization protection set value of the protection device 10 takes α ampere, and when it is less than t ° C., the protection set value takes β ampere. It has become. That is, when the outside air temperature is high, the set value is high, and when the temperature is low, the set value is also low. This is because the demagnetization characteristics of the magnet are taken into consideration.

As described above, according to this embodiment, the protection device 10 for preventing demagnetization of the magnet reads the outside air temperature by the temperature detector 13, and when the outside air temperature is low, the protection device 10 has a low temperature corresponding to the demagnetization current. When the outside air temperature is high, a high current value can be set as the cutoff current setting value. Therefore, when a high load is generated in the compressor 3 at a high outside air temperature, an operation using a high current can be performed, and a large load range operation can be performed. In addition, even at the time of starting where a relatively large current is likely to flow, demagnetization is protected at low temperatures and at high temperatures,
For example, even when a high current flows as in a scroll compressor, a starting error does not occur because the set current value is high. In the present embodiment, the current protection set value is described as an example in which two stages are used. However, it is needless to say that the current protection set value may be multistage or may be changed by a function of temperature. With this protection device, a magnet having a low coercive force can be selected, the maximum magnetic flux density can be increased, and the efficiency of the motor can be increased.

The present invention is not limited to the above embodiment. For example, if the outside air temperature is taken as shown in FIG.
The thermistor can also be used for controlling the temperature of the air conditioner. If the temperature sensor 13 is directly provided on the compressor 3 and connected to the protection device 10 as shown in FIG. 4, switching along the ambient temperature of the magnet becomes possible. . Even when such a structure is adopted, the operation and effect are exactly the same as those shown above. In addition, it goes without saying that various modifications can be made without departing from the spirit of the present invention.

[0012]

As is apparent from the above description, the present invention provides the following effects in a synchronous motor in which the rotor of the electric motor is constituted by permanent magnets, by varying the setting of the cutoff current value of the power supply depending on the temperature. can get.

(1) Operation in a large load range becomes possible. (2) Poor starting can be reduced.

(3) Appropriate demagnetization protection can be provided. (4) Efficiency can be improved.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an example of a compressor using a magnet motor in an air conditioner according to the method of the present invention.

FIG. 2 is a characteristic diagram showing a demagnetization characteristic curve of a ferrite magnet due to a temperature change.

FIG. 3 is a characteristic diagram showing a demagnetization protection set current value with respect to a temperature change of the demagnetization protection device.

FIG. 4 is a block diagram showing a modification of the method of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 3 Compressor 8 Electric motor 9 Power supply 10 Protection device 11 Current detector 12 Circuit breaker 13 Temperature detector

Continuation of the front page (56) References JP-A-59-106882 (JP, A) JP-A-5-184192 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H02P 5 / 408-5/412 H02P 7/628-7/632 H02P 21/00 H02P 6/00-6/24 F24F 11/00-11/02 F25B 1/00 361

Claims (1)

(57) [Claims] An electric motor using a magnet having a temperature characteristic that is easily demagnetized in a low temperature range, a current detector for detecting a current of the electric motor, and a predetermined current value is obtained by a signal from the current detector. Current interrupting means for interrupting the current by detecting that
Used for refrigeration equipment such as air conditioners equipped with a temperature detector
Protection device for the magnet motor for hermetic electric compressors
And a current value at which the current cut-off means operates when the temperature detected by the temperature detector is lower than when the temperature is high.