Screw compressor and control method therefor

Control method for the screw compressor (100), characterized in that it comprises:

• a) setting the working frequency parameter F and the working internal volume ratio parameter Vi of the screw compressor (100) based on the target load, wherein the working frequency parameter F corresponds to a predetermined working suction capacity R;
• and
• b) determining whether the working frequency parameter F is lower than the working frequency threshold Ft, wherein the working frequency threshold Ft corresponds to a threshold suction capacity Rt;
• and
• c) adjusting the position of the spool valve (120) based on the set working frequency parameter F and the working internal volume ratio parameter Vi, wherein:
• c1) when the working frequency parameter F is no lower than the working frequency threshold Ft,
• (i) the working frequency of the screw compressor (100) is taken as the working frequency parameter F, to adjust the speed of the screw rotor (110) of the screw compressor (100), so that the suction capacity of the screw compressor (100) is adjusted to the predetermined working suction capacity R, and the displacement L1 of the spool valve (120) moving to the internal volume ratio adjusting position (220) corresponding to the working internal volume ratio parameter Vi is determined based on the set working internal volume ratio parameter Vi, and
• (ii) the spool valve (120) is moved to the internal volume ratio adjusting position (220) based on the displacement L1, and, when it is in the internal volume ratio adjusting position (220), the spool valve head end (121) of the spool valve (120) is located at the outer side of the suction head end (111) of the screw rotor (110) of the screw compressor (100) or aligned with the suction head end (111), so that the spool valve (120) can shield a section of the screw rotor (110) extending from the suction head end (111) to the exhaust tail end (112);
• and
• c2) when the working frequency parameter F is lower than the working frequency threshold Ft,
• (i) the working frequency of the screw compressor (100) is taken as the working frequency threshold Ft, to adjust the speed of the screw rotor (110), and the displacement L2 of the spool valve (120) moving to the suction capacity adjusting position (240) corresponding to the predetermined working suction capacity R is determined based on the set working internal volume ratio parameter Vi, and
• (ii) the spool valve (120) is moved to the suction capacity adjusting position (240) based on the displacement L2, and, when it is in the suction capacity adjusting position (240), the spool valve head end (121) is located at the inner side of the suction head end (111) of the screw rotor (110), and a suction capacity adjusting distance (D2) is formed between the spool valve head end (121) and the suction head end (111), so that the threshold suction capacity Rt corresponding to the working frequency threshold Ft can be adjusted to the predetermined working suction capacity R.