Method for determining a state of a bearing, module for determining a state of a bearing, railway vehicle and system

Module for determining a state of a bearing of a three phase electric machine, the electric machine having a rotor, which is supported by the bearing, the electric machine being connected to a three phase inverter for supplying the electric machine with electric power, the three phase inverter being controlled to apply a pulse width modulation with a predefined scheme to create three phase currents, wherein the module is adapted to:

• determine a first phase current provided to the electric machine;
• determine a second phase current provided to the electric machine, the second phase current being different to the first phase current;
• determine the power spectral density of the park's vector of the current provided to the electric machine, based on the first phase current and the second phase current;
• determine an amplitude of the power at a predefined frequency of the power spectral density, wherein the predefined frequency depends on the rotational speed of the rotor and the scheme of the pulse width modulation;
• compare the amplitude of the power at the predefined frequency with a predefined power value;
• and
• determine, based on the comparison, whether a failure of the bearing has occurred or the bearing is degraded.

System of the energy supply of a three phase electric machine comprising a bearing, the electric machine having also a rotor, which is supported by the bearing, the electric machine being connected to a three phase inverter for supplying the electric machine with electric power, the three phase inverter being controlled to apply a pulse width modulation with a predefined scheme to create three phase currents, wherein the system comprising a bearing state detection module adapted to:

• determine a first phase current provided to the electric machine;
• determine a second phase current provided to the electric machine, the second phase current being different to the first phase current;
• determine the power spectral density of the park's vector of the current provided to the electric machine, based on the first phase current and the second phase current;
• determine an amplitude of the power at a predefined frequency of the power spectral density, wherein the predefined frequency depends on the rotational speed of the rotor and the scheme of the pulse width modulation;
• wherein the system is further adapted to:
• compare the amplitude of the power at the predefined frequency with a predefined power value;
• and
• determine, based on the comparison, whether a failure of the bearing has occurred or the bearing is degraded.