An operating method (10) for a compressor (101) of a refrigerating machine (100), said compressor (101) comprising an electric motor (102) and a power supply device (103) configured to modulate a supply voltage (V) and/or current (I) and/or frequency (F) for driving said electric motor (102);
- said method (10) being characterized by the following steps:
- setting (A) a stator resistance calibration value (Ro) and at least one threshold value (S1, S2, S3, S4) for a control parameter (R), said threshold value (S1, S2, S3, S4) being correlated to said calibration value (Ro);
- injecting (B), continuously during operation of said electric motor (102), a disturbance signal (V1, I1) into said electric motor (102) by means of said power supply device (103), said disturbance signal (V1, I1) consisting of a disturbance of said supply voltage (V) and/or current (I);
- detecting (C), by means of voltage and current measurements at the phases of said electric motor (102), a resulting voltage signal (V2) and a resulting current signal (I2), corresponding to said disturbance signal (V1, I1);
- associating (D) with said control parameter (R) a value calculated as a function of said resulting voltage signal (V2) and the resulting current signal (I2);
- regulating or interrupting (E) said supply voltage (V) and/or current (I) and/or frequency (F) depending on the value of said control parameter (R) with respect to said at least one threshold value (S1, S2, S3, S4);
- wherein said electric motor (102) is a three-phase motor;
- said disturbance signal (V1) being a voltage signal;
- wherein said disturbance signal (V1) is a voltage signal consisting of a disturbance in a first component V1x and/or a disturbance in a second component V1y in a system with two orthogonal components x, y;
- said supply voltage (V) having a first component Vpx and a second component Vpy in said system with two components x, y;
- said injection step (B) involving injecting said disturbance signal (V1) selectively in a first mode, in a second mode or in a third mode, wherein:
- said first mode involves injecting said disturbance in the first component V1x into said first component Vpx;
- said second mode involves injecting said disturbance in the second component V1y into said second component Vpy;
- said third mode involves injecting said disturbance in the first component V1x into said first component Vpx and said disturbance in the second component V1y into said second component Vpy;
- said step of detecting (C) a resulting signal (I2) involving measuring phase currents Ia, Ib, Ic of said electric motor (102), deriving equivalent currents Ix, Iy from said phase currents Ia, Ib, Ic by means of conversion of said phase currents Ia, Ib, Ic into said system with two components x, y and deriving from said equivalent currents Ix, Iy respective components Ix-meas and/or Iy-meas corresponding to said disturbances in the first component V1x and/or in the second component V1y, respectively;
- said detection step (C) comprising selectively:
- deriving said current component Ix-meas, of the equivalent current Ix, if said disturbance signal (V1) has been injected in said first mode,
- deriving said current component Iy-meas, of the equivalent current Iy, if said disturbance signal (V1) has been injected in said second mode,
- deriving both said current components Ix-meas and Iy-meas if said disturbance signal (V1) has been injected in said third mode;
- wherein said method comprises a derivation operation which involves selectively determining:
- a component x of voltage Vx-meas, if said disturbance signal (V1) has been injected in said first mode, or
- a component y of voltage Vy-meas, if said disturbance signal (V1) has been injected in said second mode, or
- the component x of voltage Vx-meas and the component y of voltage Vy-meas, if said disturbance signal (V1) has been injected in said third mode;
- wherein said component x of voltage Vx-meas and/or said component y of voltage Vy-meas are derived by means of a processing operation which involves
- measuring at least one line-to-line stator voltage Vab, Vbc, Vca between terminals of the phases of said electric motor (102);
- determining a direct current component for each of said at least one line-to-line voltages Vab, Vbc, Vca;
- wherein the value associated with said control parameter (R) is an electrical resistance value calculated, by Ohm's law, selectively:
- as the ratio between the component x of voltage Vx-meas and said component x of current Ix-meas where said component x of voltage Vx-meas is calculated on the basis of at least one of said direct current components of said at least one line-to-line voltage Vab, Vbc, Vca, if said disturbance signal (V1) has been injected in said first mode,
- as the ratio between the component y of voltage Vy-meas and said component y of current Iy-meas where said component y of voltage Vy-meas is calculated on the basis of at least one of said direct current components of said at least one line-to-line voltage Vab, Vbc and/or Vca, if said disturbance signal (V1) has been injected in said second mode;
- as a ratio between said component x of voltage Vx-meas and said component x of current Ix-meas and/or as the ratio between said component y of voltage Vy-meas and said component y of current Iy-meas, if said disturbance signal (V1) has been injected in said third mode.