Influence Of Wind Power Integration On Power System Transient Stability

Large scale of wind power integration into power systems will definitely berealized some day since wind power has already played an important role inelectricity supply nowadays. However, transient processes of power systemsintegrated with wind power after faults have not been clearly revealed at presentas wind power generation sets are more complicated in structure and controlcompared to synchronous generators. This has been a great challenge forguaranteeing and improving transient stability of power systems integrated withwind power. It is still unknown how much wind power would be accepted bytraditional power grids without damaging their transient stability. This thesisaims to explore how different operation conditions, especially wind powerpenetration level, will influence power system transient stability.Firstly a DFIG s structure and its components mathematical models andcontrol strategies are explained. Based on this, a DFIG simulation model, whichis equipped with crowbar and able to ride through low voltages, has beenestablished in DIgSILENT PowerFactory.Secondly, the DFIG model is integrated with an equivalent outer powersystem DFIG s dynamic behavior after faults is analyzed and compared with asynchronous generator. How electrical and mechanical parameters changeduring faults is described in detail. Besides, influence of different fault types onthe DFIG s dynamic behavior is clarified Also influence of the DFIG s electricalparameters on power system transient stability is discussed. Results reveal:○1ADFIG imposes weaker disturbance to power grids after faults compared to asynchronous generator considering integration bus voltage, active power andreactive power while it gives less support in reactive power compensation andvoltage recovery.○2Three-phase short-circuit has the worst influence to a DFIG,followed by two-phase grounding, two-phase short-circuit and single-phaseshort-circuit, for most electrical and mechanical indexes, like mechanical torque,generator speed, blade angle, rotor current and reactive power when faults take place, reactive power when faults are cleared, integration bus voltage andelectromagnetic torque and active power during faults.○3Two-phaseshort-circuit disturbs a DFIG most considering active power and electromagnetictorque when faults are cleared; while for rotor current when faults are cleared, itwill increase under three-phase short-circuits while decrease under other faulttypes.Last but not the least, an aggregated model of a wind farm with thirty DFIGsis integrated with the WECC three generator nine bus power grid model. Influenceof wind power penetration level, wind farm power factor and different integrationconditions on power system transient stability are discussed. Results reveal:○1Transient stability of one power system is better when active powers of unstablegenerators under a certain fault are decreased because of wind power integrationthan that when active powers of stable generators are decreased. Besides, the moreactive power is decreased, the better transient stability is.○2Transient stability ofone power system will get worse if rated capacities of unstable generators under acertain fault are decreased; however, transient stability will not worsen if theseunstable generators’ active powers are reduced at the same time. Besides,transient stability will either not worsen if rated capacities of stable generators arereduced.