Compressor capacity control system

A method of controlling a compressor in a transport temperature control unit, the temperature control unit having a prime mover providing power to the compressor, and the compressor having a power requirement that varies depending on the loading conditions of the compressor, the method comprising:

• determining the maximum power available from the prime mover;
• operating the compressor at a first loading condition;
• determining the power requirement for the compressor at the first loading condition;
• comparing the power requirement for the compressor to the maximum power available to determine if the compressor should continue operating at the first loading condition;
• and
• if the compressor should not continue operating at the first loading condition, adjusting the loading conditions so that the power requirement of the compressor substantially equals the maximum power available from the prime mover by at least one of
• (a) while operating the compressor at a first speed setting, varying a suction pressure setting as permitted by the maximum amount of power available to run the compressor until the suction pressure setting reaches a predetermined suction pressure setting, and only after the suction pressure setting reaches the predetermined suction pressure setting, increasing the speed of the compressor as permitted by the maximum amount of power available to run the compressor;
• and
• (b) while operating the compressor at a first suction pressure setting, varying a compressor speed setting as required by the maximum amount of power available to run the compressor until the compressor speed setting reaches a predetermined speed setting, and only after the compressor speed setting reaches the predetermined speed setting, reducing the suction pressure setting as required by the maximum amount of power available to run the compressor.

A method of compressor control to maximize the pull-down capacity of a temperature control unit with respect to a predetermined maximum power available to run the compressor, the method comprising:

• starting the compressor at a low speed setting and at a suction pressure setting no greater than a predetermined maximum startup setting;
• varying the suction pressure setting as permitted by the maximum amount of power available to run the compressor until the suction pressure reaches a maximum suction pressure setting;
• and
• only after the suction pressure reaches a maximum suction pressure setting, increasing the speed of the compressor as permitted by the maximum amount of power available to run the compressor.

A method of compressor control to maximize the pull-down capacity of a temperature control unit with respect to a predetermined maximum power available to run the compressor, the method comprising:

• operating the compressor at a maximum suction pressure setting;
• varying a compressor speed setting as required by the maximum amount of power available to run the compressor until the compressor speed setting reaches a minimum speed setting;
• and
• only after the compressor speed setting reaches the minimum speed setting, reducing the suction pressure setting as required by the maximum amount of power available to run the compressor.