Air conditioner and method of controlling the same

An air conditioner, comprising:

• a plurality of indoor devices, each of the plurality of indoor devices respectively including an indoor heat exchanger and an indoor expansion valve;
• a plurality of outdoor devices connected to the plurality of indoor devices via a gas pipe and a liquid pipe, each of the plurality of outdoor devices respectively including:
• a compression device including one or more compressors;
• a four-way valve that switches a flow direction of a refrigerant discharged from the compression device;
• a plurality of outdoor heat exchangers, each of the outdoor heat exchangers respectively including a plurality of heat exchangers including a first heat exchanger and a second heat exchanger;
• a common connection pipe connected to the four way valve;
• a first connection pipe that connects the common connection pipe to a first side of the first heat exchanger;
• a second connection pipe that connects the common connection pipe to a first side of the second heat exchanger;
• a third connection pipe connected to a second side of the first heat exchanger;
• a fourth connection pipe connected to a second side of the second heat exchanger;
• a first outdoor expansion valve disposed in the third connection pipe;
• a second outdoor expansion valve disposed in the fourth connection pipe;
• a joint pipe to connect the compression device to the four-way valve;
• a common pipe connected to the joint pipe;
• a first bypass pipe that connects the third connection pipe to the common pipe;
• a second bypass pipe that connects the fourth connection pipe to the common pipe;
• a first bypass valve disposed in the first bypass pipe;
• and
• a second bypass valve disposed in the second bypass pipe;
• and
• a controller that controls operation of the plurality of indoor devices and the plurality of outdoor devices, wherein the gas pipe connects the four-way valve with the indoor heat exchangers, wherein the liquid pipe connects the indoor expansion valves with the first outdoor expansion valve and the second outdoor expansion valve, wherein the controller controls the first bypass valve, the second bypass valve, the first outdoor expansion valve, and the second outdoor expansion valve to successively perform a defrosting operation, wherein the controller opens the first bypass valve and the second outdoor expansion valve and closes the second bypass valve and the first outdoor expansion valve, wherein refrigerant enters the first bypass pipe without passing through all of the plurality of indoor devices, the gas pipe and the liquid pipe, wherein refrigerant of the first bypass pipe passes through the first heat exchanger and flows into the four-way valve without passing through the second heat exchanger, when the first heat exchanger performs the defrosting operation, wherein the controller opens the second bypass valve and the first outdoor expansion valve and closes the first bypass valve and the second outdoor expansion valve, wherein refrigerant enters the second bypass pipe without passing through all of the plurality of indoor devices, the gas pipe and the liquid pipe, wherein refrigerant of the second bypass pipe passes through the second heat exchanger and flows into the four-way valve without passing through the first heat exchanger, when the second heat exchanger performs the defrosting operation, and wherein the controller opens the first expansion valve and the second expansion valve and closes the first bypass valve and the second bypass valve, when the air conditioner performs a heating operation.