Research On Fault Ride Through Capability Of Direct-driven Permanent Magnent Synchronous Wind Generation System

With the increasing demand for energy, the traditional energy will be in danger of drying up and the environmental problem will be increasingly serious. The nations of the world have joined the ranks of developping the wind technique, which increasing the proportion of wind power in grid.When the fault occurs, large scale of wind field will be off the grid without any measurements,which will affect the voltage and frequency of the grid.Therefore, many states put forword LVRT(Low Voltage Ride Throuth) rules.Direct-drive wind turbine with permanent magnet synchronous generator(PMSG) has been rapidly applied for its omitted gearbox, no brush and slip ring. This paper mainly discussed the LVRT technology of PMSG.First, the mathematical model of permanent magnet direct-drive wind power generation system and the control strategy have been analyzed in detailed. Second, the fluctuation mechanism in the system of PMSG is analyzed when the grid voltage symmetrically drops, the Crowbar protection circuit and the static reactive compensation control are applied to solve the problem of over-voltage of DC bus and to support the point of common coupling(PCC), which are verified by simulation. Then, the fluctuation mechanism in the DC bus of PMSG is analyzed when the grid voltage occurs unbalanced drop. Two kinds of control strategy are studied, which depend on the degree of unbalanced voltage sags of power grid. Grid synchronization is one of the key techniques for the integration of PMSG wind power generation system into grid, and its accuracy of detection impacts on the operating results of the PMSG wind power system control strategy directly. A decoupled double synchronous reference frame phase-locked loop(DDSRF–PLL) was analyzed in detail, and was applied in the detection of the voltage positive and negative sequences under unbalanced grid voltage conditions. Finally, the hardware circuit design of the grid-side converter is introduced in detail, The experiment platform of grid-connected converter has been built, which based on the TMS320F2812, experimental studies have been conducted to verify the effectiveness of control strategy under balanced and unbalanced grid voltage conditions.