Application to the Italian AC/DC EHV Network of the Paduan Three-phase Power Flow (PFPD_3P)

The HVDC tie lines represent a growing solution for the transmission system operators in order to dispatch the renewable source plant production on long distances. In the Italian transmission network, there are currently five HVDC links and other two are planned (i.e., Tyrrhenian Link and Adriatic Link). In this paper the matrix algorithm PFPD_3P is generalized in order to assess the power quality of real and large AC/DC transmission networks. The method is applied to study the voltage unbalance in two case studies: a 76-busbar network, and the Italian AC/DC HV/EHV network. In order to validate the method, solution comparisons with the commercial software DIgSILENT PowerFactoy are performed for both case studies showing a good agreement. The HVDC-VSC/LCC links are modelled as PV/PQ constraints at the positive sequence, which represent both the AC and DC behavior of the HVDC links. Since three-phase power flow is fundamental to compute network power quality, converter zero/negative sequence circuit is considered for both VSC and LCC.