Novel Bearing Current Suppression Approach in Doubly-Fed Induction Generators

Doubly-fed induction generators (DFIGs) are widely used in the wind power generation systems. However, due to the use of the power electronic devices, such as insulated gate bipolar transistor (IGBT), it is inevitable to generate a non-zero common mode voltage on the rotor side. The common mode voltage can induce the bearing voltage through the stray capacitances and result in the bearing currents, which seriously affect the efficiency and the safety of wind power generation system. This paper proposes a new bearing current suppression method in DFIGs. The key is to design the electrostatic shield on the rotor side of DFIGs and based on the bearing voltage ratio to effectively mitigate the bearing voltage ratio in the generator. This paper firstly investigates the bearing current equivalent circuit and the stray capacitance calculation method. The sensitivity analysis on the bearing voltage ratio is carried out, which shows that the capacitance between the rotor winding and the rotor core is a key parameter to mitigate the bearing voltage and bearing currents. The electrostatic shield on the rotor side of DFIGs is designed to regulate the capacitance value and hence the bearing currents. Finally, the bearing current of the converter-DFIG system is simulated and analyzed. The results verify that the new suppression method can effectively suppress the bearing currents.