Piston positioning processes of a reciprocating compressor

A positioning process of a piston (500) of a reciprocating compressor, applied before the beginning of a start procedure of a brushless direct current (BLDC) motor (100), the reciprocating compressor comprising:

• the BLDC motor (100) having a rotor (400) associated mechanically to the piston (500);
• a frequency inverter (200), used to drive the BLDC motor (100), that comprises six switches (S1-S6);
• a current sensor (201) positioned on a busbar;
• one or more processors (300) configured to:
• drive the motor using a six-step motor drive technique;
• and
• execute the positioning process comprised of a set of steps including a first step where piston (500) is at a bottom dead center position and one or more new steps that are performed sequentially after the first step and incrementally move the piston (500) towards a top dead center position;
• and
• drive the switches (S1-S6) based on a six-step control signal and a commuting sequency in a determined step of the set of steps, in order to control electrical currents (IA, IB, IC) applied to phases (FA, FB, FC), respectively, of the BLDC motor (100);
• characterized in that:
• the one or more processors (300) drives the switches (S1-S6) in 150 electrical degrees, wherein up to three switches can be actuated concurrently at each electrical position;
• characterized in that:
• in one or more new steps, a value of a new initial current is higher than the value of a previous initial current of a previous step;
• and
• in one or more new steps, a value of a new maximum current is higher or equal to the value of a previous maximum current of the previous step;
• characterized in that the value of the new initial current, the previous initial current, the new maximum current, and the previous maximum current depend on the position of the piston (500).