Research on background harmonic evaluation of UHV DC access considering mutual impedance of external nodes of power grid

摘要

At present, the background harmonic evaluation of the UHV DC integration into receiving power grid needs to consider the equivalence of the external power grid. The existing methods are independent equivalence of single point of the external power grid. When there are many external nodes, multiple single-point equivalence are needed. Node superposition will cause the model to have a large deviation from the actual, and ultimately affect the accuracy of the method. This paper proposes an external grid equivalent strategy that takes into account the mutual impedance of multiple external nodes. The external grid equivalent is the self-impedance of a single node and the mutual impedance of any two nodes. The self-impedance can be equivalent to the short-circuit capacity of a single node. The mutual impedance is equivalent to the connection relationship between the two nodes. A UHV DC integration was carried out to carry out background harmonic evaluation, and the actual measurement of the 220kV side and 500kV outlet of the six 500kV substations was carried out. Based on the measured data, ETAP software was used to establish six 500kV substations and 9 external grid nodes. The background harmonic evaluation model verifies the agreement between the model and the measured data. The model is used to evaluate the background harmonic level of the UHV DC project, which provides a technical basis for the filter design.