| In the continuous development and application of wind power technology,Double Fed Induction Generator(DFIG)has become the mainstream model of wind power generation.When the grid voltage drops,the stator and rotor windings of the DFIG will induce inrush current.The stator short-circuit current will endanger the stable operation of the distribution network.The rotor short-circuit current will damage the back-to-back converter and even cause the turbine to be disconnected.In a commercial DFIG unit,a crowbar resistor(Crowbar)is connected between the rotor winding and the Rotor Side Converter.When the DFIG stator voltage drops deeply or the rotor current oscillates at high frequency,the crowbar resistor acts so that When the rotor?side converter exits operation,the long-term operation of the rotor-side converter will result in loss of DFIG reactive power and absorption of grid reactive power,affecting the power quality of the grid.In order to prevent DFIG output short-circuit current from impacting on the distribution network,a bridge-type fault current limiter(BTFCL)is often on the stator side of the DFIG,but the inductor element is connected to the stator circuit in the BTFCL to cause a stator voltage.Spikes are generated and result in severe stator flux and electromagnetic torque oscillations,which may reduce the useful life of the turbine shaft.According to the equivalent model of DFIG,the short-circuit current when DFIG is distributed into the distribution network with distributed power supply will be affected by the operation status of the distribution network,the location of the fault,etc.,combined with the normal operation and exit operation of the DFIG rotor-side converter.The different forms of DFIG fault current(stator current)characteristics were analyzed.The relative positions of the fault point and the grid point will affect the DFIG short-circuit current and simulate the DFIG output short-circuit current at different fault points,which provides a theoretical precondition for the suppression of the DFIG stator-side fault current.After the DFIG stator voltage drops,solving the rotor-side converter for a long time to get out of operation to solve the tamper resistance action causes the DFIG to lose excitation control,absorb grid reactive power,and cause electromagnetic torque oscillations.This paper presents a series of dynamic resistance topology of rotor coordination current limiting scheme.By deducing the rotor current expression under different types of faults of the conductive network,a dynamic resistance and crowbar coordinated protection control scheme was designed,and dynamic resistance values were calculated.The simulation results show that the three-phase symmetrical fault,phase-to-phase fault,and phase-to-earth fault are optimized for the dynamic resistance coordination current-limit protection scheme.In addition,the optimization performance of series dynamic resistance and crowbar protection in reactive power and electromagnetic torque is compared through simulation.When using the bridge fault current limiter on the DFIG stator side,in order to eliminate the negative influence of the inductive element in the BTFCL,a BTFCL with a parallel resistor(PR)is proposed in this paper.The PR absorbs most of the current harmonics during normal operation.And eliminate voltage spikes on the stator terminals.And it is verified through simulation analysis that BTFCL-PR significantly reduces the DFIG stator flux linkage and electromagnetic torque oscillation and can also retain the BTFCL automatic current limiting capability without delay.This dissertation focuses on the DFIG rotor short-circuit current and the stator short-circuit current under grid faults,proposes a dynamic resistor topology coordination current limiting scheme,and at the same time designs a stator voltage spike that can improve the DFIG,and can reduce the stator flux linkage and electromagnetic transfer.Moment-oscillating bridge fault current limiter. |
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