Research On Predictive Direct Power Control Of Grid-connected Dfig Wind Turbines

With the rapid development of society and economy, conventional energy becomesscarce; vigorously develop renewable energy sources such as wind power is the inevitabletrend. Doubly fed induction generator (DFIG) has become the mainstream model of Windpower generation system with its low cost, small inverter capacity. In recent years, directpower control (DPC) has become a focus of DFIG inverter’s control due to its simplecontrol structures, fast dynamic response and robustness to parameters. This paper is focuson predictive direct power control (P-DPC) of DFIG system, the main content of the studyhas been summarized as follows:In this paper grid side converter (GSC) and rotor side converter (RSC) of DFIG havebeen studied respectively. Firstly, Lookup Table direct power control (LUT-DPC) as theconventional direct power control has been introduced. This strategy has simple structureand is high dynamic to follow. However, it also has some disadvantages. For reducing thepower oscillation, current harmonic and obtaining variable switching frequency, two kindof predictive direct power control are proposed, they are three vector predictive directpower control (TV-PDPC) and power predictive optimizing control (PPOC). Thesestrategies greatly reduce the current harmonic and obtain constant switching frequency.This paper adopts direct virtual power control (DVPC) as the grid connection method ofDFIG. This method maintains the controller structure unchanged before and after gridconnection. At the same time, stator voltage and grid voltage can quickly realizesynchronization, interconnection process smooth and no impact on the stator basic current.Under unbalanced grid voltage, conventional DPC can maintain the active andreactive power to a constant; however the content of current harmonic exceeds thestandard of grid. This article adds power command compensation terms to achieve thecorresponding control objectives. This method is easy to control, only need to extract thepositive-sequence content of current and negative-sequence content of voltage. Thismethod does not need to change the controller structure. Finally, a prototype has been built in MATLAB and dSPACE, simulations andexperimental results validate the correctness and feasibility of these proposed predictivedirect power control strategies.