Operations of multilevel converters such as the Alternate Arm Converter (AAC) mainly depend on voltage availability provided by charged Sub-Module (SM) capacitors. To ensure proper operations, these capacitors must be sized enough to limit voltage fluctuations caused the instantaneous power that flows through the converter arm and hence, through the SM capacitors. This paper details an analytical modelling of the AAC instantaneous arm power. The proposed model takes into account most of the AAC operations and considers different control strategies such as the AAC with a short or an extended overlap period. Thus, the impact of each control strategy on the stored energy requirement is highlighted.