| Recent years, the new energy power generation is experiencing a global surge, and the percentage of wind power increases continuously, so wind power system and grid are mutually influential to each other more and more. It will lead adverse effect to the grid, if the wind power system is off-grid during the fault of grid. Therefore, wind power system should have the LVRT capability in order to keep connecting to the grid during the fault period. This paper do a research on LVRT to the direct-drive permanent magnetic wind power system, and to lay special emphasis on analysis and comparison of main LVRT technologies in depth, and some main of them are verified to effective by simulation.Firstly, to summarizes and analyze the background and present development situation of wind power worldwide, and come to have a overview of the adverse effects caused by grid voltage sags to the connected-grid wind power system, which is the major way to exploiting wind energy, and then get quantitative requirements combined the relevant regulations of LVRT.Secondly, the major components of PMSG direct-drive wind power system are researched carefully, including wind turbine,Dual-PWM converter and Permanent magnet generator;on this basis, the simulation model with proper control policy of them are constructed: grid-side converter uses voltage-oriented vector control strategy and the controller of motor-side converter uses the rotor flux-oriented vector control strategy , which provides most simulation platform support for the next step.Thirdly, dynamic response characteristics of direct-drive wind power system are analyzed and summarized in detail under balanced fault of three-phase grid voltage, and then verifying the conclusion correct by simulation. Based on the DC-link and grid-side converter,getting the damage to DC bus capacitor and power electronic devices from over-current and over-voltage caused by the grid fault, and this adverse impact is closely bound up with the key factors, such as the duration and extent of the grid fault, and the summing up the control purposes to achieve LVRT.At last, the main LVRT technologies are summarized, analyzed and compared, getting the Advantages and disadvantage of them from some aspects. The DC-link crowbar protections are preferable to solve the problem of over-current and over-voltage, and using the simulation platform to prove the effectiveness of them. Further, comparing and analyzing from two aspects: the different DC-link crowbar, and the different dissipative crowbar combined different control means. To getting the better solution to do a further validation to make wind power system ride though the grid fault. |
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