Completely Decentralized Active and Reactive Power Control of Grid-connected Cascaded H-Bridge Inverters with Integrated Battery Storage

AC-DC converters with cascaded units are gaining popularity for medium voltage level grid connection however, as the number of cascaded stages increase, their widespread application are limited by existing centralized and distributed control schemes. In this article, a completely decentralized control scheme has been proposed for cascaded-type ac-dc converters with integrated energy storage. The proposed control method is capable of locally controlling both the active and reactive power processed by an individual unit and thereby achieve State-of-Charge (SOC) balancing of the energy storage units integrated with each converter. In this framework, the reactive power control loops achieve voltage synchronization among the converters and the grid, and the active power control loops modulate the terminal voltage amplitudes that influence power delivery. The proposed control is inspired from conventional droop control used for parallel connected converters, however, it has been modified by incorporating state feedback of voltage angle in order to facilitate stable bidirectional power flow in series connected systems. The stability analysis and simulation results have been presented along with relevant experimental results.