Spurious power losses in modular multilevel converter arm equivalent model

This paper demonstrates the presence of spurious power losses or generation in the Arm Equivalent Model (AEM) of Modular Multilevel Converters. Such power losses can occur if model equations are not solved simultaneously with surrounding power circuit equations, which is the case when the AEM is implemented using control system blocks in electromagnetic transient simulation software. Depending on operating conditions and simulation parameters, these additional losses can represent a significant part of the total converter station losses or even surpass them, thus making simulation results inaccurate. Analytical demonstration of the losses is presented, and several models that eliminate the losses are proposed. Based on simulation studies, only the variable resistance model and equivalent voltage source model can give accurate simulation results without significantly increasing simulation time and generating or consuming spurious power.