Starting methods for BLDC motors applied on reciprocating compressors

A starting method with two-levels discrete fixed-time or fixed frequency hysteresis current control, under high load conditions, of a BLDC motor (10) with trapezoidal shaped induced voltages, the BLDC motor (10) being driven by an inverter bridge (30) with only one current sensor (20) positioned in the busbar, controlled by means of a processing unit associated to an analog-digital converter, comprising:

• driving the BLDC motor (10) by a six-step driving technique, wherein only two phases are driven at a certain electric position;
• applying, by means of a closed mesh of current control, a current in the BLDC motor (10) of maximum intensity in order to generate a maximum torque in said BLDC motor (10);
• applying the unipolar switching pattern of an ON_PWM type, wherein each switch is driven during 120° electrical in the following way:
• each switch is maintained switched on continuously during a first 60° electrical and is modulated by pulse width modulation during a final 60° electrical;
• wherein the method further comprises:
• controlling, by means of the two-levels discrete fixed-time or fixed frequency hysteresis current control, an intensity of the BLDC motor current (Im),
• wherein a first protecting level comprises:
• turning off a first switch, said first switch belonging to a portion of the inverter bridge associated with the two phases driven at a certain electric position, during a first protecting time (Toff1), when the BLDC motor current (Im), measured in a measuring instant (X), surpasses a first maximum current limit (Imax1);
• and
• keeping the first switch turned off and turning off a second switch, said second switch belonging to the portion of the inverter bridge associated with the two phases driven at a certain electric position, during a second protecting time (Toff2), in the end of the first protecting time (Toff1);
• wherein a second protecting level comprises:
• turning off the first switch and the second switch, during a third protecting time (Toff3), when the BLDC motor current (Im), measured in a measuring instant (X), surpasses a second maximum current limit (Imax2),
• wherein the first maximum current limit (Imax1) is lower than the second maximum current limit (Imax2);
• and
• wherein the second protecting level actuates after the actuation of first protecting level.