Balancing control actions for cascaded H-bridge converters with integrated battery energy storage

This paper investigates the ways to handle active power components for control and balancing purposes in three-phase Cascaded H-Bridge converters with embedded battery energy storage systems. The split storage elements are interfaced to the converter modules through a non-isolated DC/DC stage, in order to eliminate the inherent second-order harmonic of the module output current. Both the cases of star and delta converter configurations are analyzed. The topology-specific degrees of freedom are exploited, control algorithms are developed and limitations are established. Potential grid asymmetries are taken into consideration through the utilization of symmetrical components. Several modes of operation are studied, such as independent load feeding, State of Charge balancing as well as converter operation under grid faults.