Thermal Analysis on IGBT Module Based Rotor Side Coverter of Doubly-fed Wind Turbine by Considering Inter-harmonic Current

When the connected grid is under sub-synchronous or low frequency oscillation, doubly-fed wind turbines are susceptible to grid background harmonics because the stator is directly connected to the power grid. Due to the coupling between stator and rotor magnetic fields, inter-harmonic currents (IHC) could be induced in rotor windings. However, the traditional analysis on loss and junction temperature of insulated gate bipolar transistor (IGBT) modules is considered only the fundamental current. In this paper, the effect of IHC on loss and junction temperature of IGBT modules in rotor side converter is studied. Firstly, the analytical model of rotor IHC is derived. Then, the calculation method of power loss and junction temperature is presented by considering IHC. Further, the power loss and junction temperature with and without rotor IHC are obtained. The comparison results show the IHC could result in the increase of the power loss and the junction temperature of IGBT module, especially for the low frequency IHC.