The method: determines, within the switching cycle, when current is not provided to the DC-bus capacitor, determines, for each switching cycle, the sector of a reference vector, active vectors durations and null voltage vectors durations, determines from the determined durations, sampling instants, samples the currents through the three phases and the DC-bus voltage at the determined sampling instants, determines, from the phase currents sampled at the determined sampling instants, the current flowing through the DC-bus capacitor during the active vectors, estimates the capacitance value and/or the equivalent series resistance value of the DC-bus capacitor, compares the capacitance value and/or the equivalent series resistance value to a threshold and determines if the DC-bus capacitor reaches its end of life according to the comparison result.