A method of synchronizing a synchronous reluctance electric machine, wherein said electric machine (E) is speed and/or residual magnetization voltage sensorless and comprises power terminals (T) and rotating masses (M) whose mechanical rotation frequency (fM) is subjected to speed transients caused by power cut-off conditions, the method comprising:
- applying a control voltage (Vc) with predetermined amplitude (vc) and duration (Tc) to the power terminals after the speed transients, for inducing an electric current (Ii), wherein said electric current has a harmonic spectrum (S) that is a function of a frequency differential between a frequency (fc) of said control voltage (Vc) and a mechanical rotation frequency (fM) of the rotating masses;
- and detecting said induced electric current (Ii) to restore power and synchronous rotation control of the electric machine (E), wherein said harmonic spectrum (S) of said induced current (Ii) has substantially null or negligible harmonic components in an audible range, in response to the application of said control voltage (Vc) to the power terminals (T);
- decomposing said induced electric current (Ii) into a pair of vector currents (Id, Iq) offset by substantially 90°;
- filtering said pair of vector currents (Id, Iq) using a high-pass filter (HPF) to filter out a direct current component and obtain respective filtered vector components (I′d, I′q) dependent on an instantaneous rotation speed of the rotating masses (M);
- detecting an instantaneous rotation angle (θist) of said rotating masses (M) of the electric machine (E);
- setting an initial value (θin) of the instantaneous rotation angle (θist) and adjusting said instantaneous rotation angle (θist) to determine a synchronized rotation angle (θsin c), substantially in phase with a mechanical rotation angle (θM) and having an angular error (εθ) relative to the mechanical rotation angle (θM);
- supplying the electric machine (E) with a vector current (lai) having an electric rotation angle (θai) which is a function of said synchronized angle (θsin c) and a torque component (Iai torque) increasing from zero to a nominal value in a predetermined interval of time,
- wherein the step of adjusting said instantaneous rotation angle (θist) comprises a step of iteratively minimizing said angular error (εθ) from the initial value (θin),
- wherein the step of iteratively minimizing is obtained through a first phase-lock loop algorithm (PLL1) for generating said synchronized rotation angle (θsin c) as an output thereof,
- wherein the step of supplying the electric machine (E) with a vector current (Iai) comprises a step of conditioning said synchronized rotation angle (θsin c) generated by the first phase-lock loop algorithm (PLL1) as a function of a number of poles of the electric machine (E),
- wherein the step of supplying the electric machine (E) with a vector current (Iai) comprises a step of providing a fine adjustment of said synchronized rotation angle (θsin c) obtained using a second phase-lock loop algorithm (PLL2), having an initial transient in which said vector current (Iai) has a substantially zero torque component (Iai torque) and a flux component (Iai flux) having a predetermined value, for generating a flux lower than a nominal flux in the electric machine (E),
- wherein the step of applying the control voltage (Vc) is carried out when the masses are rotating and after the speed transient;
- and wherein said harmonic spectrum (S) is a function of a frequency differential between said frequency (fc) of said control voltage (Vc) and said mechanical rotation frequency (fM) of the rotating masses.