Impact of the arm resistance and inductance on the PQ diagram of a modular multilevel converter

In this article we discuss the PQ diagrams for the modular multilevel converter. Firstly, we compare two models associated with PQ diagram construction: the conventional model and the steady-state time-invariant model. We show that the former model is less accurate than the latter model, since it is based on various hypotheses such as a zero arm resistance and an ideal modulated voltage behavior. Secondly, we study the impact of the arm resistance and arm inductance on the operating area of the converter using the steady-state time-invariant model. We show that the arm resistance is responsible for the asymmetry of the operating area leading to different maximal power transfers in the two directions. Further, we show that a reduction of the inductance expands the operating area, potentially leading to a better exploitation of the converter.