Average-Value Model for a Modular Multilevel Converter With Embedded Storage

This article proposes an average-value model for a modular multilevel converter with sub-module level battery energy storage. The developed model is a computationally efficient representative of the converter in system-level studies; it is also shown to be useful in analytical characterization of circulating currents and sub-module capacitor voltage ripple both with and without circulating current suppression control. The model is then used to investigate the sizing of converter components under different operating regimes. The accuracy of the developed model is verified against detailed EMT models as well as against experimental results on a converter prototype.