Impact of Converter Control on Differential Protection Under Symmetrical Fault and Optimization Strategy
The strongly controlled fault characteristics of converter brings severe challenges to the relay protection of AC systems.The control response of grid-following converter when a symmetrical fault occurs on the connection line between the converter and the grid is analyzed.From the point of view that the current control targets of the converter cannot automatically match the power demand of the fault circuit during the fault,the jump and rotation characteristics of the voltage phase angle on the grid side are analyzed and derived.Restricted by the impedance of the fault circuit,the phase angle of current at the converter terminal changes synchronously with the grid-side voltage,resulting in serious degradation of the differential protection performance of the connection line.Based on the change mechanism of grid-side voltage phase angle,considering the protection demand and power supply demand,an optimization strategy is proposed by adjusting the current control targets and the phase locked loop(PLL)control.The simulation results show that the proposed strategy can effectively inhibit the current phase difference between the two sides of connection line under symmetrical faults and significantly improve the operation performance of differential protection.
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