Control And Open-switch Fault Diagnosis Of Doubly-fed Wind Power Converter

As growing fears for the global climate change and energy crisis, low-carbon economy will dominate the trend of the world economic development. Wind energy is one of the best choices to develop low-carbon economy. The doubly-fed induction generator is one of the most widely used generators with wind turbine. In such a wind turbine the back-to-back converter is less robust than the generator and other mechanical parts. The wind turbine may be seriously damaged or have to stop once any switch failure occurs in the converter. Therefore, converter health monitoring and fault diagnosis are extremely important to improve system reliability. Moreover, to avoid shutting down the wind turbine, converter fault diagnosis may reconfigure the power converters to permit post-fault operation.This research focuses on the control, open-switch faults diagnosis and post-fault operation for the converters of the doubly-fed induction generator. The fault diagnosis methods are implemented through signal processing of current before and after the happening of open-switch fault. In order to simulate the open-switch faults of power switches, the whole software simulation platform is built using MATLAB/Simulink, and a hardware design of DFIG is also proposed. The usual method used to control rotor side converter is stator-flux vector control, and the control method used in grid side converter is voltage vector control. The space vector pulse width modulation method is used to modulate back-to-back converter. The steady-state operating of the whole system is simulated. Simulation results show that the control method is available. The effects of open-switch faults in different locations on DFIG are analyzed in detail.Several open-switch fault diagnosis methods used in general converter have already existed but are found to be unsuitable for the doubly-fed induction generator. These methods can easily result in false alarms, and these alarms can not be eliminated through implement a dead time when being applied in the rotor side converter. The causes of false alarms with these methods are investigated. Two new open-switch fault diagnosis methods,which are capable of detecting one or two open circuit faults of wind power converter,are proposed through investigating the characters of current signals. And the methods can eliminate the false alarms happened around synchronous speed completely. Simulation results show that the methods could detect the locations and styles of open-switch faults precisely, and the system reconfiguration strategy could restore the DFIG to the normal operation anew.