Optimized Reactive Power Flow of DFIG Power Converters for Better Reliability Performance Considering Grid Codes

If there is no reactive power exchange between the Doubly-Fed Induction Generator (DFIG) and the grid, the various characteristics of the power converters in the DFIG wind turbine system cause the lifetime expectancy of the rotor-side converter significantly less than the grid-side converter. In order to fulfill the modern grid codes, over-excited reactive power injection will further reduce the lifetime of the rotor-side converter. In this paper, the additional stress of the power semiconductor due to the reactive power injection is firstly evaluated in terms of modulation index and the current loading. Then an optimized reactive power flow is proposed in the case an over-excited reactive power support is applied with the joint compensation from both the rotor-side converter and the grid-side converter. Finally, some experimental validations are performed at a down-scale DFIG prototype. It is concluded that, among the different combined reactive power support strategies, the best scheme will trade-off the lifetime between the grid-side converter and the rotor-side converter.