Investigations of grid-connected wind power system : low voltage ride through and power quality issues

Abstract

This thesis presents an investigation on system architecture, control and analysis of wind turbine generators to improve grid integration performance. First of all, the main grid connection requirements have been reviewed in terms of safety operation of transmission systems as well as the wind turbine configurations. Due to these requirements, there have been conscious efforts made by wind turbine manufacturers to design grid compatible wind turbines, which are able to improve turbine operating performance and eliminate negative impacts on the utility, with features such as strong fault ride-through capability, flexible voltage regulation and good power quality performance. All these expectations provided the motivation to carry out the research described in this thesis. Doubly-fed induction generator (DFIG) wind turbine technology has been extensively applied by many turbine manufacturers due to the low cost of its partial-scale power electronics converter. However, enhancing ride-through capability under grid fault events has been worldwide recognized as a challenging problem of the DFIG-based wind generation systems. The operating principle and numerical simulation of DFIG-based wind turbine are thus reviewed, which give the fundamentals to analyze the essential behaviors during grid faults. Consequently, a ride-through enhancing solution is proposed based on series compensation principle. The compensator is in series with the stator windings of the DFIG in order to eliminate the impacts caused by grid voltage faults. Furthermore, an advanced ride-through control scheme based on ramp-function injection voltage is developed to significantly reduce the energy capacity requirement of the series compensator, which in turn reduces the capital cost. The performance of the developed architecture has been verified in simulation.