Abstract: This paper introduced the advantages of the stepless capacity regulation system and its influence on the reciprocating compressor firstly. Then it analyzed the concept and calculation method of the motor current pulsation. Through an example,the paper calculated the torque of the compressor crankshaft and the motor stator current pulsation under different loads when using the stepless capacity regulation system. It was concluded that as the capacity decreased, the motor current pulsation increased accordingly. Therefore, it is suggested that when the stepless capacity regulation system is newly installed, the reverse angle, rotation unevenness and stator current pulsation of the drive motor should be checked for the compressor unit. This paper is informative for the operation, selection calculation and check calculation of compressors.

Key words: stepless capacity regulation system, reciprocating compressor, current pulsation, synchronous motor, crankshaft torque