BACKGROUND OF THE INVENTION The present invention is related to providing a compressor control circuit, more particularly, providing a circuit for controlling a compressor adapting a brushless D.C. motor.

In general, it is known that a brushless D.C. motor has advantages; the superior control characteristics are the same as a D.C. motor, and the reduction of noise and power consumption are significant. Therefore, nowadays there is a c tendency to adapt the brushless motor to home appliances, but the adaption has lagged behind in respect to the cost and the control techniques beyond the satisfaction to users until now. Almost all home appliances are accustomed to being adapted an A.C. motor. For example, an A.C. induction motor adapted to compressor of a refrigerator always constitutes a two pol motor which is fixed at the synchronizing speed of around 3500 rpm under the application of an alternative current powe having the frequency of 5-0 to 60 Hz. Therefore, the temperatur adjustment in chambers is performed at an on-off interval period that the operation of the compressor is repeatedl turned on and off with a sensor detecting the temperature i a freezing chamber. But, the operation causes the refrigerator to. have th temperature ripple (1— °C). It shortens the storing time fo keeping the freshness of refrigerating foodstuffs such a vegetables and fruits, etc. At the start of the operatio shifted from the non-operation condition accompanying with th

on-off operation of the inductive motor, the rush current is relatively greater, thereby requiring a larger amount of the consumption power. At this time, the winding current density is five times to ten times over that flowing at the normal operation period. It results in increasing the induction vibration and the electromagnetic noise between a rotator and a stator. Furthermore, the operation noises are more amplified at the band which is resonant with the mechanical inherent vibration frequency of the compressor. The induction motor has a greater induction loss. It causes higher winding heating than that of a D.C. motor to thereby raise the inner temperature of the compressor, thereby deteriorating the operation efficiency thereof and easily degenerating the substance of the compressor. The compressor has disadvantages due to the property of the A.C. induction motor in that it is difficult to operate at a continuous variable speed, the operation efficiency is relatively lower, the electromagnetic noise is greater, and the optimum operation range according to the load fluctuation is relatively narrower. Similarly, a compressor adapted to an air conditioner has the same problems.

The refrigerator adapting the same compressor has a relatively greater amount of load fluctuation over 100% at maximum related with the setting of a circumference temperature and chamber temperature. It requires the optimum- efficiency operation according to the load fluctuation ratio.

An object of the present invention is to provide a compressor control circuit including a brushless D.C. motor, for enabling the operation speed control of a compressor to

lead to an ideal continuous operation according to the load fluctuation without the intermittent on-off operation.

The other object of the present invention is to provide a compressor control circuit including a brushless D.C. motor of a high efficiency and a low noise, further comprising a control apparatus for varying the operation speed of the brushless motor and an operation control circuit for optimizing the operation input of the brushless motor dependent upon the load fluctuation to reduce the consumption power, greatly.

SUMMARY OF THE INVENTION In order to accomplish the objects and features, a compressor control circuit adapted to a refrigerator according to the present invention comprises a compressor including a brushless D.C. motor; a circuit for separating an A.C. power source from a D.C. power source to drive the brushless D.C. motor; a two phase control circuit for varying the operation speed of the brushless D.C. motor in response to the temperature of a freezing chamber; a voltage adjustment switching circuit for selecting the voltage of a power source circuit responsive to the load condition; an operation control circuit for enabling the on-off operation of the brushless D.C. motor to be continued according to the on-off of a load sensor in the freezing chamber; and a protecting circuit for stoppin the brushless D.C. motor and cutting off the power source unde the overload or binding condition of the compressor.

BRIEF DESCRIPTION OF THE DRAWINGS The present invention will be explained below in detail

with reference to the accompanying drawings, in which:

Fig. 1 is a circuit configuration illustrating one embodiment of an operation control circuit adapted to a refrigerator according to the invention; Fig. 2 is a control circuit of a brushless D.C. motor illustrating a part of Fig. 1;

Fig. 3 is a graph illustrating the speed control range of the brushless D.C. motor according to the temperature of an evaporator in a freezing chamber; Fig. 4 is a graph illustrating the freezing speed of the evaporator according to the operation speed of the brushless D.C. motor;

Fig. 5 is a graph illustrating the temperature change of the evaporator according to the continuous operation control of the brushless D.C. motor; and

Fig. 6 is a graph illustrating the corelationship between the temperature change period of the evaporator and the operation speed ratio of the brushless D.C. motor according to the intermittent operation control at an operation speed.

DETAILED DESCRIPTION OF THE INVENTION

Fig., 1 shows a circuit for controlling a compressor

^" including a brushless D.C. motor adapted to a refrigerator according to one embodiment of the present invention. The refrigerator is examplified as a standard two door type including a freezing chamber and a refrigerating chamber. The refrigerator requires an A.C. power source for operating a defrosting heater, a fan motor and a chamber lamp as well as a compressor including a motor for compressing refrigerant, but

a refrigerator adapted to the present invention includes a control circuit for a compressor including a brushless D.C. motor to which a D.C. power source should be applied.

An A.C. power source plug 1 is connected to a power selection switch 2 for selecting any one of commercial voltages 110 V and 220 V, the power application path of each of which is represented as a dotted line and a solid line in the figure. The power selection switch 2 supplies the power voltage to the first winding of a power transformer 25. The power transformer 25 has a first winding provided with input taps for the power source of 110 V and 220 V and second winding including full-wave windings of three tap types, for example, 14 V, 28 V and 38 V. The first winding of the power transformer is connected in parallel to a defrosting heaters 7 and 8, a defrosting timer 5, a fan motor 9 and a chamber lamp 11. At the second winding, the power source of 14 V is rectified in a full-wave form through diodes 27 and 28 to be used as the power source V _L of a control logic circuit. The power sources of 28 V and 38 V are applied through a voltage adjustment selecting switch 23 called a double break, double make type to a full wave rectifying circuit 22. The rectified power scurces V _w is used for driving the brushless D.C motor 15 of the compressor. Herein, it is noted that these portions constituting a D. C. power source use a linear transformer to separate the power source of the first winding from that of the second winding, and the voltage adjustment and rectification is reliable and inexpensive free of the electrical noise with the exclusion of the use of a high frequency switching device (SMPS) for PWM: Pulse Width Modulation.

A compressor is connected through a refrigerant flow pipe to an evaporator and a condenser 34.

A two phase control circuit 14 for driving the brushless

D.C. motor 15 for the compressor comprises a two phase control circuit which is registered as U. S. Patent Nos. 4,472,564 and

4,584,505, issued to the inventor, Mr. Yeong C. Chung the same as that of this application, can be used.

Referring to Fig. 2,-, the two phase control circuit 14 is preferably provided with a two phase logic control circuit 29, a comparing circuit 30 for detecting the speed of a rotor, an on-off operation control circuit 31 synchronized through ports H- _j _ and H2 with the on-off operation of a thermostat or thermal switch 3 (Fig. 1), temperature sensors 19 and 20 for enabling the speed control of the brushless motor according to the detection of the temperature in a freezing chamber 33, temperature adjustment variable resistors 18 and 21 and an alternating switching amplification circuit 28 including a plurality of power transistors for driving the brushless motor 15. The two phase control circuit 29 generates two phase signals for driving the brushless motor 15 by means of a position ^" sensor 17, the detailed description of which is omitted, because the technical contents is known in the disclosure of u;S. Patent No. 4,584,505. Also, the two phase logic control circuit 29 adapted to a refrigerator includes variable resistors 18 and 20 for controlling the operation speed of the brushless motor and thermistors 19 and 20 mounted in the freezing chamber 33 or on an evaporator with being connected in parallel to each of the variable resistors 18 and

20. Thus, the compressor is driven at the operation spee increased or decreased in proportion to the difference betwee the detecting temperature and the room temperature at the star of the operation or during the normal operation. The variabl resistors 18 and 20 can adjust the increase ratio and th decrease ratio of the operation speed. Also these resistors ca be used to set the maximum and minimum speeds.

The alternating switching amplification circuit 28 output two phase D.C. power voltages V _M and -V _M in the form of the tw phase logic control signal to the brushless D.C. motor 1 mounted in the compressor.

The brushless D.C. motor 15 includes two coil windings 1 and the position sensor 17 for detecting the position of rotor. These winding and sensor lines are connected throug five pins mounted on the compressor to three output ports o the two phase logic control circuit 29 and two input ports o the alternating switching amplification circuit 28. Herein i is noted that four transistors are used for two phase bipola switching, but a general,single phase power source requires a eight bridged transistor operating circuit. The close compressor adapted to the present invention needs only fiv external electrical connection pins including three pins fo supplying the driving currents to the brushless D.C. motor 1 and two pins for sensor signals, but a general compresso requires at least eight pins in the case of a two phase an more than seven pins in the case of a three phase. Especially the number of the external electrical connection terminals i very important to the closed compressor which is under ver critical technical limitation for keeping the vacuum seal wit

respect to the internal pressure thereof.

An overload protection circuit 30 is preferably used as a known frequency comparing circuit. The position sensor 7 detects the N and S poles of a rotor to determine the switching frequency of the N pole and the S pole. Thus, assumed that the reference frequency necessary for the operation of the brushless D.C. motor 15 is already set, and the switching frequency of the N pole and the S pole is dropped below the reference frequency, the overload protection circuit 30 outputs the high.level signal "H" to enable an OR gate 32 to mute the output of the two phase logic control circuit 29. The muting state of the two phase logic control circuit 29 causes the alternating switching amplification circuit 28 to -be turned off, thereby cutting off the driving current of the brushless D.C. motor 15 and protecting it. The on-off operation control circuit 31 is turned off during the operation of the thermal switch 3, the defrosting heaters 7 and 8 and the timer 5.

On the other hand, a power switch 10 comprises a non- contact switch such as triac which prevents the induction surge voltage from being applied to the fan motor 9. The induction surge voltage is generated at door switches 12 and 13, when the doors of the freezing chamber 33 and the refrigerating chamber 33 are opened/closed. The door switches 12 and 13 are connected in series to the gate of the non-contact switch 10.. A refrigerator adapting the present invention is continuously controlled with the range of 2000 to 4000 rp according to the temperature of a freezing chamber 33 or an evaporator. Thermistors 18 and 19 control each phase of a two phase control logic circuit 29, so that the average energizing

current flowing through a brushless D.C. motor 15 is adjuste to control the operation speed. Variable resistors 18 and 21 connected in parallel to each of the thermistors 18 and 19 enable users to manually adjust the range of the automati operation speed, which is dependent upon the characteristic of the compressor and a refrigeration cycle. For example, whe the evaporator is started at the temperature of 25 °C near th room temperature, the compressor is operated at the maximu speed in the predetermined range. As the temperature of th evaporator is being dropped, the operation speed of th compressor is reduced- in proportion thereto. At this time, th refrigeration cycle load is reduced until the temperature o the evaporator reaches the lowest temperature. The compresso is operated at the speed to keep the appropriate temperatur of the chambers.

Fig. 4 shows the change of the operation times from t-^ t t ₃ until an evaporator becomes full down according to th operation speed setting of a compressor. A refrigerato adapting the present invention can control the cooling leve by auxiliary fixing the operation speed of a compressor, thereby .adjusting the refrigerating time, so that the optimu operation thereof may be selected dependent upon the chambe temperature and the circumference temperature. Then, brushless D.C. motor is changed at the operation efficienc characteristics according to the load fluctuation, and th refrigeration cycle of the refrigerator has the great width o the load fluctuation according to the circumference temperatur of the evaporator. It needs to keep the high operatio efficiency characteristics by adjusting the input voltage o

the brushless D.C. motor according to the load condition. Thus, the brushless D.C. motor can be operated at the appropriate dropped voltage during the weak load operation below the rate of output range thereof. For example, when the temperature of the evaporator reaches -18 C, the operation load is dropped by 40% over that at the room temperature. At this time, the brushless motor is changed into the low speed operation by dropping the input voltage thereof, so that its rate output is reduced by less than one-half. The operation efficiency of the brushless motor is lowered by more 10 to 20 % than the optimum efficiency of the rate of output operation. As shown in Fig. 1, if the temperature of the evaporator sensed by the thermistor 4 is below -18 °C _Λ a comparing circuit 24 operates a voltage adjustment selecting switch 23 to apply the low voltage of 28 V to a brushless motor 15. During the normal operation of the refrigerator, and the thermal switch 3 of the evaporator repeats the on-off operation based on the temperature setting.

Furthermore, the on-off operation of the thermal switch 3 selecting the power voltage of 110 V and 220 V enables the on-off control circuit 31 of two phase control circuit 14 to apply the low level " " or high level "H" signal to an OR gate 32 while to control a two phase control circuit 29, thereby synchronizing the operation of the compressor ^' therewith. Therefore, as shown in Fig. 6, the refrigerating speed of the evaporator is variable according to the operation setting speeds -^ to V3 of the brushless D.C. motor, so that the on-off period of the thermal switch 3 is changed, and its operation ratio is controlled.

The present invention adjusts the temperature of an evaporator by the continuous variable speed operation of a brushless D.C. motor, so that the continuous temperature control of the evaporator is performed as shown in Fig. 5, and the freezing and refrigerating chambers of a refrigerator are kept at a constant temperature without a temperature ripple.