KR100392390B1 - Air conditioner and control method thereof - Google Patents

Abstract

The present invention is applied to an air conditioner having a variable capacity compressor. The present invention includes a compressor whose capacity is changed in accordance with the duty control signal, and a control unit for controlling the compressor in accordance with the change in the room cooling requirement. The control unit determines the unloading time and the loading time according to the changed indoor cooling requirements even if the indoor cooling demand is changed and generates a duty control signal, and controls the PWM valve according to the generated duty control signal. Adjust the refrigerant discharge amount of the compressor. Therefore, the present invention can quickly adjust the capacity of the compressor according to the changed room cooling demand ability even if the room cooling demand is changed rapidly, there is an effect that can increase the reliability for the compressor.

Description

Air conditioner and its control method {AIR CONDITIONER AND CONTROL METHOD THEREOF}

The present invention relates to an air conditioner and a control method thereof, and more particularly, to an air conditioner employing a pulse width modulation type compressor and a control method thereof.

As buildings are enlarged, consumer demand for multi-air conditioners in which a plurality of indoor units are connected to one outdoor unit is increasing. In the multi-air conditioner, the cooling requirements are different for each indoor unit, and since each indoor unit is operated independently, the total cooling requirement combined with the cooling requirements of all indoor units is also changed. Therefore, by adjusting the capacity (capacity) of the compressor in accordance with the change in the cooling demand capacity, and by controlling the opening degree of the electric expansion valve installed upstream of the indoor heat exchanger, e.

BACKGROUND ART A variable speed compressor is known as a compressor capable of varying a capacity (capacity) according to a variable cooling demand. The variable speed compressor can adjust the capacity of the compressor according to the change in cooling demand by controlling the number of revolutions of the motor by changing the frequency of the current applied to the motor through inverter control. However, the conventional variable speed compressor has a circuit portion for controlling the rotation of the motor in accordance with the cooling requirements. The circuit section includes a converter section for converting an AC power source into a DC power source, and an inverter section for converting a DC power source into an AC power source. However, there is a problem that the loss in this circuit portion is excessive and the efficiency is lowered.

Another type of variable capacity compressor is a pulse width modulated compressor disclosed in US Pat. No. 6,047,557 and Japanese Patent Laid-Open No. 8-334094. However, such a compressor is used in a refrigeration system having a plurality of refrigerating chambers or freezing chambers and cannot be applied to an air conditioning system of a building whose control environment is different from that of the refrigeration system.

Figure 8a shows the control operation of the compressor and the suction pressure of the compressor when the indoor cooling demand capacity is reduced in the unloading state according to the prior art, Figure 8b is a compressor when the indoor cooling demand capacity is reduced in the loading state according to the prior art The control operation of and the suction pressure of the compressor are shown.

In FIG. 8A, when the indoor cooling demand ability decreases in the unloading state (the PWM valve is OFF without discharging the refrigerant) in the corresponding period (Nth cycle) (Ta), the amount of refrigerant sucked into the compressor from the indoor unit decreases. In the cycle (Nth cycle), the compressor discharges more refrigerant than the actual cooling demand since the loading time A of the compressor is maintained before the cooling demand is reduced. In addition, in FIG. 8B, the compressor is loaded in the corresponding period (Nth cycle) even when the indoor cooling demand capacity decreases (Ta) while the corresponding period (Nth cycle) is loaded (the PWM valve is turned off while the refrigerant is discharged). As time A is maintained in the previous state, the compressor discharges more refrigerant than the actual cooling demand. Accordingly, the suction pressure of the compressor is excessively lowered in the corresponding period (Nth cycle) (see D).

In the prior art, even though the actual cooling demand is reduced in a certain cycle, the capacity of the compressor is not adjusted to the state before the cooling demand has changed (unreduced) during that cycle, and the indoor cooling requirement has changed since the end of the cycle. Correspondingly varying the capacity of the compressor.

As described above, when the pulse width modulation type compressor is used for the air conditioner, even when the compressor is operated, since the loading time for discharging the refrigerant and the unloading time for discharging the refrigerant are repeated periodically, the flow of the refrigerant in the cycle is periodically Yes or no. Therefore, if the compressor capacity (capacity) is not rapidly adjusted to correspond to the indoor cooling demand, the suction pressure of the compressor may be drastically lowered or raised, which may cause damage to the compressor and stop operation.

In addition, despite the decrease in the cooling capacity of the room, the discharge of excess refrigerant from the compressor still makes the indoor heat exchanger easy to freeze and even freezes. There is a burden.

SUMMARY OF THE INVENTION An object of the present invention is to provide an air conditioner and a method of controlling the same according to a rapidly changing cooling demand when the cooling demand is changed during operation of a pulse width modulated compressor.

1 is a refrigeration cycle of an air conditioner applied to the present invention.

Figure 2a shows the loading state of the pulse width modulation compressor employed in the air conditioner of the present invention, Figure 2b shows an unloading state.

3 illustrates a relationship between a loading state and an unloading state and a refrigerant discharge amount during operation of the compressor of FIG. 2.

4 is an overall block diagram of an air conditioner applied to the present invention.

Figure 5a shows the control operation of the compressor when the indoor cooling demand capacity is changed in the unloading state according to the present invention, Figure 5b shows the control operation of the compressor when the room cooling demand capacity is changed in the loading state .

6 is a flowchart illustrating the operation of the indoor unit of the air conditioner according to the present invention.

7A, 7B and 7C are flowcharts for explaining the operation of the outdoor unit of the air conditioner according to the present invention.

Figure 8a shows the control operation of the compressor and the suction pressure of the compressor when the indoor cooling demand capacity is reduced in the unloading state according to the prior art, Figure 8b is a compressor when the indoor cooling demand capacity is reduced in the loading state according to the prior art The control operation of and the suction pressure of the compressor are shown.

* Description of symbols on the main parts of the drawings *

2: compressor 5: evaporator

8: outdoor unit 9: indoor unit

27: outdoor control unit 30: indoor control unit

The air conditioner according to the present invention as described above includes a compressor whose capacity varies according to a duty control signal having a loading time that the loading state continues in a given period and an unloading time that the unloading state continues; If the indoor cooling demand capacity changes in the corresponding cycle during the operation of the compressor, the load time and unloading time are determined according to the change of the indoor cooling demand capacity even before the end of the cycle to generate the duty control signal and according to the generated duty control signal. Achieved by a control unit that controls the compressor.

In addition, the control method of the air conditioner according to the present invention as described above, in the control method of the air conditioner having a compressor having a variable capacity according to a duty control signal having a loading time and an unloading time in a given period, Driving a; Determining whether the indoor cooling requirement changes; In the determination step, if the indoor cooling demand capacity changes in the corresponding period, the loading time and the unloading time are determined according to the change of the indoor cooling demand capacity even before the end of the cycle to generate a duty control signal and according to the generated duty control signal Controlled by the compressor.

Hereinafter, with reference to the accompanying drawings will be described embodiments of the present invention;

1 is a refrigeration cycle of an air conditioner applied to the present invention. The air conditioner 1 according to the present invention includes a compressor 2, a condenser 3, an electric expansion valve 4, and an evaporator 5 which are sequentially connected by a refrigerant pipe to form a closed circuit. Among the refrigerant pipes, the refrigerant pipe connecting the discharge side of the compressor 2 and the inflow side of the electric expansion valve 4 is a high pressure tube 6 for guiding the flow of the high pressure refrigerant discharged from the compressor 2, and the electric expansion valve ( The refrigerant pipe connecting the outlet side of 4) and the suction side of the compressor 2 is a low pressure tube 7 for guiding the flow of the low pressure refrigerant expanded by the electric expansion valve 4. The condenser 3 is installed in the middle of the high pressure tube 6, and the evaporator 5 is installed in the middle of the low pressure tube 7. When the compressor 2 operates, the refrigerant flows in the direction of the solid arrow.

The air conditioner 1 of the present invention includes an outdoor unit 8 and an indoor unit 9. The outdoor unit 8 includes the compressor 2 and the condenser 3 described above, and several indoor units 9 are arranged in parallel. Each indoor unit 9 includes an electric expansion valve 4 and an evaporator 5. Therefore, a plurality of indoor units 9 are connected to one outdoor unit 8. The capacity and shape of each indoor unit 9 may be the same or different.

Meanwhile, an evaporator inlet temperature sensor 31 is installed at the inlet of the evaporator 5 to measure the temperature of the refrigerant flowing in, and an evaporator outlet temperature sensor for measuring the temperature of the refrigerant flowing out at the outlet of the evaporator 5. 32) is installed. These temperature sensors are means for measuring the superheat degree of the refrigerant.

In addition, the indoor unit 9 includes an indoor fan 37 provided near the evaporator 5. The indoor fan 37 allows heat exchange in the evaporator 5 by allowing the indoor air to pass through the evaporator 5.

As shown in Figs. 2A and 2B, the compressor 2 uses a variable capacity compressor controlled by a pulse width modulation method. The compressor (2) has a casing (20) provided with an inlet (18) and an outlet (19), a motor (21) provided inside the casing (20), and a rotating scroll (22) rotating under the rotational force of the motor (21). ) And a fixed scroll (24) for forming a compression chamber (23) between the orbiting scroll (22). The casing 20 is provided with a bypass tube 25 connecting the upper side of the fixed scroll 24 and the inlet 18, and the bypass tube 25 has a PWM valve in the form of a solenoid valve; 26) is installed. Fig. 2A shows a state where the PWM valve 26 is turned off to block the bypass pipe 25. In this state, the compressor 2 discharges the compressed refrigerant. This state is called a loading state and the compressor 2 operates at a capacity of 100%. 2B illustrates a state in which the PWM valve 26 is turned on to open the bypass pipe 25, in which the refrigerant is not discharged from the compressor 2. This state is called an unloading state and the compressor 2 is operated at a capacity of 0%. The compressor 2 is supplied with power, whether loaded or unloaded, and the motor 21 rotates at a constant speed. When the power supply to the compressor 2 is cut off, the motor 21 does not rotate and the operation of the compressor 2 is stopped.

As shown in FIG. 3, the compressor 2 repeats the loading state and the unloading state during operation, and the loading time and the unloading time change according to the room cooling demand capability, and the compressor 2 at the loading time Since the temperature of the evaporator 5 is lowered, and the compressor 2 does not discharge the refrigerant at the unloading time, the temperature of the evaporator 5 increases. In FIG. 3, the area of the hatched portion represents the amount of refrigerant discharged. The signal controlling the loading time and the unloading time is called a duty control signal and is generated by an outdoor controller to be described later.

4 is a block diagram of an air conditioner control system according to the present invention. As shown in FIG. 4, the outdoor unit 8 includes an outdoor controller 27 connected to the compressor 2 and the PWM valve 26 to enable signal transmission. The outdoor controller 27 is connected to the outdoor communication circuit 28 to transmit and receive data. Each indoor unit 9 includes an indoor control unit 30, and an input port of the indoor control unit 30 includes an evaporator inlet temperature sensor 31, an evaporator outlet temperature sensor 32, an indoor temperature sensor 34, and a desired temperature. The setting part 35 is connected, and the electric power expansion valve 4 and the indoor fan driving part 36 are connected to the output port. The evaporator inlet temperature sensor 31 detects the temperature of the refrigerant passing through the electric expansion valve 4 and enters the evaporator 5, and the evaporator outlet temperature sensor 32 detects the temperature of the refrigerant passing through the evaporator 5. In addition, the indoor temperature sensor 34 detects a temperature of a room, which is a harmonic space, and the detected temperature information is input to the indoor controller 30, respectively. The indoor control unit 30 controls the indoor fan driver 36 to turn on the indoor fan 37 when the indoor unit is turned on, and according to the degree of superheat calculated based on the outlet temperature of the input evaporator and the inlet temperature of the evaporator. The target opening degree of the expansion valve 4 is adjusted. In addition, when the indoor unit is turned off, the indoor control unit 30 closes the electric expansion valve 4 and controls the indoor fan drive unit 36 to turn off the indoor fan 37.

The indoor control unit 30 receives the indoor temperature detected by the indoor temperature sensor 34 and the set temperature set by the desired temperature setting unit 35. The indoor control unit 30 has information on its cooling capacity, and when calculating the cooling demand capacity, the indoor control unit 30 may calculate the cooling demand capacity based on the difference between the room temperature and the set temperature and the own cooling capacity. The cooling demand can also be calculated based on the cooling capacity alone.

The cooling request capability calculated by each indoor unit 9 is transmitted to the outdoor control unit 27 through the communication circuit unit 29 and 33, and the outdoor control unit 27 sums the cooling request capability of each indoor unit 9 in total. The compressor 2 and the PWM valve 26 are controlled by calculating the cooling demand. Table 1 shows the loading and unloading times set according to the total cooling requirements in the 20 second period.

TABLE 1

Loading time (sec) Unloading time (seconds) Total cooling requirement Loading time (sec) Unloading time (seconds) Total cooling requirement 20 0 148.5 ?? 10 10 69.5-77.5 18 2 135.5-148.5 9 11 60.5-69.5 17 3 126.5-135.5 8 12 51.5-60.5 16 4 118.5-126.5 7 13 43.5-51.5 15 5 110.5-118.5 6 14 34.5-43.5 14 6 102.5-110.5 5 15 26.5-34.5 13 7 93.5-102.5 4 16 17.5-26.5 12 8 85.5-93.5 3 17 17.5 ?? 11 9 77.5-85.5 - - -

The outdoor controller 27 outputs a duty control signal for determining the loading time and the unloading time of the compressor to the PWM valve 26 according to the total cooling demand capacity, that is, the indoor cooling demand capacity, to adjust the capacity of the compressor 2. . The outdoor controller 27 checks the indoor cooling demand ability periodically or continuously, and generates a duty control signal determined by the corresponding loading time and unloading time when the indoor cooling demand capability changes, and generates the generated duty control. The signal is output to the PWM valve 26 to adjust the capacity of the compressor 2. On the other hand, the operation of determining the loading time according to the unloading state or the loading state when the indoor cooling demand is changed according to the unloading state or the loading state is described in more detail with reference to FIGS. 5A and 5B. Explain.

The outdoor control unit 27 changes the loading time as shown in FIG. 5A when the indoor cooling requirement changes in the unloading state. Here, (A) of FIG. 5A corresponds to a case in which the loading time T3 in the corresponding cycle is shorter than the loading time T2 of the previous state so as to correspond to the reduced indoor cooling demand ability, and (B) is an increased indoor cooling demand ability. Correspondingly, the loading time T4 in the corresponding period is longer than the loading time T2 in the previous state, and (C) is the case in which the loading time T5 is longer to correspond to the increased indoor cooling demand. Since (T5) is larger than the remaining time (Tb) in the case where the indoor cooling demand capacity is increased (Ta), a new period (Na cycle) starting from the changing point Ta is applied.

In addition, the outdoor control unit 27 changes the loading time as shown in FIG. 5B when the indoor cooling requirement is changed in the loading state. Here, (A) of FIG. 5B is a case in which the loading time T6 in the corresponding cycle is shorter than the loading time T2 of the previous state so as to correspond to the reduced indoor cooling requirement, and (B) is a reduced room cooling requirement. Correspondingly, the loading time T7 in the period is shorter than the loading time T2 in the previous state, and the loading time T7 is greater than the loading time elapsed until the time Ta at which the indoor cooling demand is reduced. (C) is a case where the loading time (T8) corresponding to the increased indoor cooling requirement is greater than the previous loading time (T2) and increased until the end of the cycle. The loading time Td corresponding to the cooling demand is exceeded and the period Nb becomes longer than the previous period (N-1 cycle).

The operation of each indoor unit 9 will be described with reference to FIG. 6. First, the indoor controller 30 determines whether the indoor unit off signal is input by the user (S101). As a result, if the indoor unit off signal is not input, the inlet temperature and the outlet temperature of the evaporator are detected through the evaporator inlet temperature sensor 31 and the outlet temperature sensor 32, and the room temperature sensor 34 detects the indoor temperature. The set temperature set through the temperature setting unit 35 is detected (S102). Subsequently, the indoor control unit 30 calculates the superheat degree of the evaporator according to the difference between the detected inlet temperature and the outlet temperature (outlet temperature-inlet temperature) of the evaporator, and the target opening degree of the electric expansion valve 4 corresponds to the calculated superheat degree. Adjusting the indoor fan driving unit 36 to control the indoor fan 37 to turn on (S103). Subsequently, the indoor control unit 30 calculates the cooling demand capability of the indoor unit based on the cooling capability of the indoor unit and the detected temperature difference (S104), and transmits the cooling request capability calculated through the indoor communication circuit unit 33 to the outdoor unit 8. (S107).

When the indoor unit off signal is input in step S101, the indoor control unit 30 closes the electric expansion valve 4 and controls the indoor fan driving unit 36 to turn off the indoor fan 37, and accordingly, in the evaporator 5 The heat exchange is stopped and the pressure of the refrigerant sucked into the compressor 2 drops (S105). Subsequently, since the indoor unit 9 is in the off state, the indoor control unit 30 calculates the indoor unit cooling demand capability as 0 (S106), and proceeds to step S107 to transmit the calculated value (cooling demand capability = 0) to the outdoor unit.

The operation of the outdoor unit 8 will be described with reference to Figs. 7A, 7B and 7C. The outdoor control unit 27 calculates the indoor cooling requirement (total cooling requirement) by summing the cooling request capabilities transmitted from each indoor unit 9 (S200). Subsequently, it is determined whether the sum of indoor cooling requirements is 0 (S210). If the indoor cooling requirement is 0 as a result of the determination, the compressor is stopped (S211) and then returned.

If the indoor cooling demand is not 0, the outdoor controller 27 turns on the compressor, determines the loading time and the unloading time according to the indoor cooling demand, generates a duty control signal, and then generates a PWM valve (26). ) To control the compressor 2 (S220).

Subsequently, the outdoor control unit 27 determines whether the indoor cooling demand ability has changed (S220). If the indoor cooling demand ability has not changed as a result of the determination, the outdoor control unit 27 maintains the loading time and the unloading time of the current duty control signal. Subsequently, the flow proceeds to step S200 to control the compressor 2.

As a result of the determination of step S220, when the indoor cooling demand capacity is changed, the outdoor controller 27 determines whether the time when the indoor cooling demand capacity is changed is an unloading state or a loading state of the corresponding cycle (S240). As a result of the determination, when the cooling demand capacity is changed in the unloading state, it is determined whether the cooling demand capacity is reduced from the previous state (S250).

When the cooling request ability decreases as a result of the determination in step S250, the outdoor controller 27 determines the loading time T3 corresponding to the reduced cooling request ability as shown in FIG. 5A (S260), and the loading time T3. ) Generates a duty control signal corresponding to (S270), and applies the duty control signal generated in the cycle to the PWM valve 26, where the loading time (T3) of the cycle is shorter than in the previous state. Since the amount of refrigerant to be discharged is reduced (S280).

If the cooling request ability does not decrease as a result of the determination of step S250, it is determined whether the cooling demand capacity has been increased (S290). If the cooling request ability does not increase, the determination is returned as it is.

If the cooling demand capability is increased as a result of the determination of step S290, as shown in (B) (C) of FIG. 5A, the loading time T4 or T5 corresponding to the increased cooling demand capability is determined (S300), and the increased time point Ta is determined. It calculates the remaining time (Tb) at (S310), and determines whether the determined loading time (T4 or T5) is greater than the calculated remaining time (Tb) (S320), the determination result that the loading time (T4) remaining time If not greater than (Tb) generates a duty control signal corresponding to the loading time (T4) (S330), and applies the duty control signal generated within the period to the PWM valve 26, the excitation loading time (T4) ) Is longer than the previous state, so the amount of refrigerant discharged from the compressor increases, thereby increasing the compressor capacity (S340). If the loading time T5 is greater than the remaining time Tb as a result of the determination in step S320, a duty control signal corresponding to the loading time T5 is generated (S350), and a new period (started at an increased time Ta) The duty control signal generated from Na) is applied to the PWM valve 26, and the compressor capacity is increased because the loading time T5 is longer than the previous state (S360).

As a result of the determination in step S240, when the cooling demand ability does not change in the unloading state, it is determined whether the cooling demand ability has changed in the loading state (S370). As a result of the determination, if the cooling demand ability does not change in the loading state, the process returns.

As a result of the determination in step S370, when the cooling demand capacity is changed in the loading state, it is determined whether the cooling demand capacity is reduced from the previous state (S380). If the cooling demand capacity is reduced as a result of the determination of step S380, the outdoor control unit 27 determines the loading time (T6 or T7) corresponding to the reduced cooling demand capacity as shown in (A) (B) of Figure 5b, (S390) After the loading is started, the loading time Tc elapsed until the reduced time Ta is calculated (S400), and it is determined whether the determined loading time T6 or T7 is greater than the elapsed loading time Tc (S410).

When the loading time T6 determined as a result of the determination in step S410 is greater than the elapsed loading time Tc, a duty control signal corresponding thereto is generated (S420), and the duty control signal generated within the period is converted into a PWM valve 26. ) To reduce the compressor capacity (S430). When the loading time T7 determined as a result of the determination in step S410 is not greater than the elapsed loading time Tc, the device immediately switches to the unloading state and maintains the unloading state until the corresponding period ends (S440).

If the cooling request ability is not reduced as a result of the determination of step S380, the outdoor control unit 27 determines whether the cooling request ability is increased (S450), and if it is determined that the cooling request ability is not increased, it is returned as it is. If the cooling demand capability is increased as a result of the determination of step S450, as shown in (C) of FIG. 5B, the loading time T8 corresponding to the increased cooling demand capability is determined (S460), and the previous loading time is determined at the determined loading time T8. Subtracting (T2) to calculate the excess loading time (Td) (S470), and maintains the loading state until the next calculated loading time (Td) to increase the push capacity (S480).

As described above, the present invention changes the indoor cooling demand by generating a duty control signal by varying the loading time to correspond to the changing indoor cooling demand, even before the end of the cycle, thereby controlling the operation of the PWM valve. The amount of refrigerant discharged from the compressor is adjusted according to the cooling demand. Therefore, the present invention can operate the compressor without a sudden change in the room cooling requirement when applied to the multi-air conditioner can increase the reliability for the compressor, it is not necessary to perform unnecessary freeze prevention operation for the indoor heat exchanger.

Claims (19)

A compressor whose capacity varies according to a duty control signal having a loading time in which a loading state continues in a given period and an unloading time in which an unloading state continues; If the indoor cooling demand capacity changes in the corresponding cycle during the operation of the compressor, the load time and unloading time are determined according to the change of the indoor cooling demand capacity even before the end of the cycle to generate the duty control signal and according to the generated duty control signal. An air conditioner comprising a control unit for controlling the compressor. The air conditioner of claim 1, wherein the controller applies a duty control signal generated within a corresponding period. The air conditioner according to claim 1, wherein the control unit applies a duty control signal generated in a new cycle starting immediately after the change in the indoor cooling requirement. The method of claim 1, wherein the control unit generates a duty control signal with a shorter loading time in response to the reduced indoor cooling demand when the indoor cooling demand is decreased in the unloading state of the corresponding cycle, Air conditioner characterized in that for reducing the compressor capacity in accordance with the duty control signal. The compressor of claim 1, wherein the control unit generates a duty control signal based on the remaining time of the corresponding cycle and the loading time corresponding to the increased indoor cooling requirement when the indoor cooling demand capability increases in the unloading state of the corresponding cycle. An air conditioner, characterized by increasing capacity. The air conditioner according to claim 5, wherein the controller increases the compressor capacity according to the duty control signal generated within the period if the loading time corresponding to the increased indoor cooling demand is not greater than the remaining time. The method of claim 5, wherein the control unit increases the compressor capacity according to the duty control signal generated from a new period starting from an increased time point when the loading time corresponding to the increased indoor cooling demand capacity is greater than the remaining time. Air conditioner. The method of claim 1, wherein the control unit generates a duty control signal based on the loading time elapsed in the corresponding cycle and the loading time corresponding to the reduced indoor cooling requirement when the indoor cooling demand is decreased in the loading state of the corresponding cycle. An air conditioner, characterized by reducing compressor capacity. The air conditioner according to claim 8, wherein the control unit reduces the compressor capacity according to the duty control signal generated in the period when the loading time corresponding to the reduced indoor cooling requirement is greater than the elapsed loading time. The compressor capacity of claim 8, wherein the control unit switches to an unloading state and maintains an unloading state until a corresponding cycle ends when the loading time corresponding to the reduced indoor cooling demand is not greater than the elapsed loading time. Air conditioner, characterized in that to reduce. The method of claim 1, wherein the control unit generates a duty control signal having a longer loading time to correspond to the increased indoor cooling demand when the indoor cooling demand is increased in the loading state of the period, and the increased loading time is terminated. Air conditioner to increase the compressor capacity by maintaining the loading state until. The air conditioner according to claim 1, wherein the control unit is installed in an outdoor unit connected to a plurality of indoor units, and determines whether to change the air conditioner according to the cooling request ability obtained by adding up the indoor cooling request capability transmitted from each indoor unit. A control method of an air conditioner having a compressor whose capacity varies according to a duty control signal having a loading time and an unloading time in a given period, Operating a compressor; Determining whether the indoor cooling requirement changes; In the determination step, if the indoor cooling demand capacity changes in the corresponding period, the loading time and the unloading time are determined according to the change of the indoor cooling demand capacity even before the end of the cycle to generate a duty control signal and according to the generated duty control signal. And controlling the compressor. 15. The method of claim 13, further comprising the step of summing the cooling demand capacity transmitted from the plurality of indoor units connected to one indoor unit during the operation of the compressor, and determines whether the change in the indoor cooling demand capacity for the combined cooling demand capacity Control method of an air conditioner, characterized in that. The control method of claim 13, wherein the determining of the change in the indoor cooling demand capability comprises determining whether the change timing is an unloading state or a loading state of the period. 16. The method of claim 15, wherein in the determining step, if the indoor cooling requirement decreases in the unloading state of the cycle, the compressor capacity is adjusted according to the duty control signal generated by the loading time corresponding to the reduced cooling requirement in the cycle. A control method of an air conditioner comprising the step of reducing. The method of claim 15, wherein if the indoor cooling requirement is increased in the unloading state of the cycle in the determining step, calculating the remaining time of the cycle, the loading time corresponding to the calculated remaining time and the increased indoor cooling requirement Comparing the step, and if the corresponding loading time is not greater than the remaining time, the compressor capacity is increased according to the duty control signal generated within the period. If the corresponding loading time is greater than the remaining time, the duty control generated from the new period is And increasing the compressor capacity according to the signal. The method of claim 15, wherein if the indoor cooling demand is reduced in the loading state of the cycle in the determination step, calculating the loading time elapsed in the cycle, the loading corresponding to the elapsed loading time and the reduced indoor cooling requirement Comparing the time, if the corresponding loading time is greater than the elapsed loading time, reduce the compressor capacity according to the duty control signal generated in the corresponding period, or if the corresponding loading time is not greater than the elapsed loading time, And controlling the compressor capacity by maintaining the unloading state until the cycle ends. The method of claim 13, wherein in the determining step, when the indoor cooling demand capacity increases in the loading state of the period, determining a loading time corresponding to the increased indoor cooling demand capacity, wherein the determined loading time exceeds a previous loading time. Calculating a loading time, maintaining the loading state until an excess loading time to increase the compressor capacity.