Simulation And Research On The Improvement Of LVRT Capability Of Doubly-fed Induction Generator Using Superconducting Magnetic Energy Storage (SMES)

With human’s energy crisis becomes more and more serious and environmentalprotection problem is attracting more and more attention，a variety of new energytechnologies such as wind power generation，solar power generation and tidal generationand so forth have made considerable progress. Among these，wind power generationtechnology is at present the most mature one. Wind power is a renewable，clean，andwidely distributed energy. In the past ten years，the installed capacity of wind powerincreased at a remarkable average rate of30%annually. To the end of2010，the world’stotal wind power installed capacity has reached199，520MW，and the total generatingcapacity is more than409.9billion kWh，1.92%of the world’s total generating capacity.Doubly-fed induction generator (DFIG) is now the mainstream type both at homeand abroad，which can be working at variable speed and constant frequency，and itsactive and reactive power can be controlled independently. However，as the stator isdirectly connected to the grid，DFIG is very sensitive to grid fault，resulting in aweakness on dealing with grid fault. Recent years，with the rising proportion of windpower capacity in grid，the latest wind power guidelines demand more on DFIG，requiring a certain low voltage ride through (LVRT) capability in responding to gridfault.In This paper，current development status of wind power industry at home andabroad is outlined firstly，combined with existing problems within wind power industry，the concept of LVRT is brought out. Then，a detailed analysis of the basic characteristicsof DFIG and superconducting magnetic energy storage (SMES) is applied，includingbasic principle，electrical circuit topology and mathematical model and so on. On theplatform of MATLAB/Simulink，related Simulink models are built through which twosimple cases are simulated，that is，SMES is used to stabilizing the output power andimproving the transient stability of wind farm separately. Finally，a method is put forward that connecting SMES with DC bus of DFIG inparallel to maintain the stability of the bus voltage and prevent the rotor overcurrent andovervoltage，and thus improve the LVRT capability of DFIG. Simulation results verifiedthe effectiveness of the proposed method.