Research Of Gird Side Converter For Direct-Drive Wind Power Generation System In The Fault Grid

The wind has the unique advantage of being widely used to power generation, and this can solve the world’s energy crisis. Among all kinds of wind power technology, direct-drive wind power technology is the focus of the current wind power technology research. Direct-drive wind turbine connects to the grid by full-power converter, and the system can decouple grid and generator by inverter control, it can adapt to the power grid fluctuations compared with the double-fed. The direct-drive wind turbine run in the grid failure still exist many problems, which are direct drive wind power technology research focus, in particular, the problem of asymmetric grid fault is the difficult point in study. This paper makes direct-drive wind power system grid side converter as an object of study, and it carries out the research work for the grid side converter control strategy on grid fault condition.First, this paper describes the current development of wind power technology, compares several frequency control solutions, analyzes the research status of direct drive wind systems found in the grid failure, then it presents the main elements of the study.Secondly, on the grid failure case the grid side converter control requires detection of the grid voltage and current signals, so this paper research how to detect grid voltage signal on the grid failure case. Then it analyzes the deficiency of traditional PLL detection methods which based on synchronous rotating coordinate transformation. On this basis, this paper uses the symmetrical components to improve it, and builds the PLL detection methods based on double synchronous rotating coordinate transformation. Simulation results confirm that the proposed method is correct.Besides, this paper analyzes the grid side converter circuit topology and control strategy under normal circumstances, introduces the space vector pulse width modulation (SVPWM) working principle and algorithm implementation process, and gives the software simulation models. Then on this basis,it analyzes the impact of grid fault to run for direct drive wind power generation system, and build the mathematical model of the grid side converter. Then it proposes the control strategy of the negative sequence current feedforward, and analyzes the deficiency of the control strategy, by introducing a proportional-integral resonant controller to improve its short.This paper uses Matlab software simulation to confirm the performance and effectiveness about grid side converter control strategy.Lastly, On the basis of the simulation, This paper designs experimental hardware circuit, and focuses on several parts of the detailed design process. Then it designs the grid side converter digital control program using the chip of TMS320F2812 made by TI’S, and gives the main program flow.