An Isolated Modular Multiport Converter for the Integration of Photovoltaic Energy Sources and Battery Storage in MVDC Networks

The intermittent nature of solar photovoltaic (PV) energy sources necessitates the use of energy storage devices, such as batteries, in electrical networks. Typically, each energy resource is integrated into the network through a separate power conversion stage. That is, clusters of PV arrays and batteries are each connected to the grid via separate power conversion stages. This paper, therefore, proposes a novel converter topology based on the dual active bridge (DAB) and modular multilevel converter (MMC) topologies that is capable of integrating both PV arrays and batteries into a medium-voltage dc (MVdc) network through a single stage. Moreover, the converter operates with a modified modulation scheme that reduces the current stress on its transformer in the presence of non-unity dc link voltage ratios. It is also shown that the converter can harvest energy from the PV arrays with maximum-power-point tracking (MPPT) over a wide range of dc voltages. All of the developed mathematical models are verified through simulation studies carried out in the Matlab & Simulink software environment. The results of the simulation are further verified by a 600-W experimental prototype.