Improving the Reactive Power Capability of the DFIG-Based Wind Turbine During Operation Around the Synchronous Speed

The doubly fed induction generator (DFIG) equipped with self-commutated insulated gate bipolar transistor (IGBT) voltage source converter (VSC) is one of the most popular topologies used in wind power systems. It has the ability to control active and reactive power independently. The reactive power capability is subject to several limitations which change with the operating point. Around synchronous operating point, a special attention is needed since the limitation of maximum junction temperature of the IGBTs cause a reduction on maximum permissible output current at the rotor side. This paper investigates the thermal behavior of the converter using semiconductor losses and thermal model based on the IGBT manufacturer datasheet. Different pulse-width modulation (PWM) types, including continuous and discontinuous types are applied and the results of reactive power capability are compared. Simulation results show that appropriate selection of PWM type is necessary at around synchronous speed to increase the maximum permissible rotor current as well as reactive power capability.