Analysis of the second harmonic of circulating currents in low-voltage bipolar DC ring networks and improved detection methods

The safety protection of bipolar low-voltage direct current (LVDC) systems is of paramount importance for their development in conventional applications, especially in civil buildings. This paper analyzes the circulating current and its second harmo nic in bipolar LVDC ring networks, derives the expressions of the second harmonic in the circulating current under the conditions of asymmetrical neutral and pole lines with constant impedance load (CIL) and constant power loads (CPL), and discusses in depth the influence of asymmetrical positions and load characteristics on the second harmonic in the circulating current. In addition, this paper introduces a new type of sensor to reduce the interference of the second harmonic on the residual curren t detection. Simulation verification has proved the effectiveness of the sensor, significantly improving the accuracy of residu al current detection, enhancing the safety and reliability of the bipolar DC system, and providing a reference with practical engineering significance for future development.