In high-voltage direct current(HVDC)systems with power electronics,there is a risk of failure in traditional second-order harmonic recognition criteria during the no-load closing of the converter transformer.To address this issue,this paper proposes an inrush current identification method based on the U-I sampling value quadrant space distribution characteristics.This method introduces voltage and current sampling sequences to construct the U-I sampling value quadrant space distribution and analyzes the U-I quadrant space distribution characteristics of the converter transformer under normal operation,no-load closing,and closing during faults.Based on the symmetry degree and shape differences in the quadrant space distribution,an inrush current identification criterion is proposed,which relies on the symmetry error of the U-I sampling value quadrant space distribution.Using the PSCAD/EMTDC electromagnetic transient simulation platform to construct the converter transformer no-load closing model,simulations are conducted under different operating conditions of the converter transformer to verify the proposed method.The results show that the proposed recognition method is accurate and reliable,effectively identifying inrush current and preventing maloperation of differential protection,ensuring the safe operation of a new-type power system is of significant engineering value.