Spurious power and its elimination in modular multilevel converter models

Abstract

This paper demonstrates the presence of spurious power generation or losses in two commonly used Modular Multilevel Converter (MMC) models: the Arm Equivalent Model (AEM) and the Average Value Model (AVM). Such power does not represent any physical phenomenon and appears due to numerical effects. It is demonstrated that spurious power is present when the model equations are not solved simultaneously with the surrounding electrical circuit equations, which is the case when the AEM and AVM are implemented using control system blocks. Depending on operating conditions and simulation parameters, such power can represent a significant part of the total converter station losses or even surpass them, thus making simulation results inaccurate. Several solutions to eliminate the spurious power are proposed for the AEM and AVM. Their effects are demonstrated in steady-state and transient conditions on a point-to-point MMC-HVDC simulation test case.