Energy Balancing Strategy in a Modular Multilevel Converter With Unequal Active Power Sharing for Grid Scale PV-BESS Application

This article proposes the use of a modular multilevel converter (MMC) to connect two different rated distributed energy resources (DER) with photovoltaic (PV) and battery energy storage system (BESS) in different arms. In DER-MMC, power mismatch due to unequal power in different arms is a reported challenge that can send unbalanced power into the ac grid. The unequal power generation in PV connected arms may happen due to partial shading, dust, different rated PV panels, and different state of charges in batteries, which may lead to unequal active power in the distributed PV-BESS system. The existing circulating current (CC) control approach ensures power balancing control despite unequal arm powers; however, it increases additional loss and overcurrent issues in the converter. In contrast, this article proposes a control solution to connect two different rated systems, eliminating the differential power circulating current (DPCC) in the system. With the proposed technique, significant power loss and overcurrent issues caused by DPCC can be reduced. The proposed technique gives a solution for operating an arm in bidirectional power mode without CC. A time domain MATLAB simulation and a scale down experimental prototype is developed to verify the proposed work.