Reconfigurable Cascaded Multilevel Converter: A New Topology For EV Powertrain

Abstract

This paper presents a novel cascaded multilevel converter topology with reconfigurable battery modules able to merge the power conversion and the battery management functionalities for electric powertrain application. In the proposed topology, each battery cell can be individually connected or bypassed according to the required voltage and current levels. Both the charging and discharging processes can be controlled to avoid voltage imbalances between the cells and to enhance fault tolerance, battery life, and safety. Converter switching and conduction losses are evaluated and used as key parameters for the optimization of the proposed architecture. Furthermore, an efficiency comparison between a conventional three-phase IGBT-based inverter and the proposed topology is carried out. The two topologies are evaluated according to the WLTP Class 3 driving cycles, showing their average efficiency in each cycle. The comparison results show that the performance achieved with the proposed topology is extremely promising to combine state-of-the-art functionalities with the new paradigm of battery management.

Reconfigurable Cascaded Multilevel Converter design for Battery Energy System Storage

“…Several submodules are serially connected; each of them is characterized by the serial connection of RBMs connected to a H-Bridge converter, used to invert the output voltage and to bypass the submodules . Each RBM includes three battery cells -a larger number would create short circuits between the cells [7].…”

“…The structure of the RCMC can be decided according to customizable requirements. In this paper, the configuration with 3 RBMs per each submodule is chosen [7]. On the other hand, the peak voltage installed within one phase is designed according to the voltage ratings of the AC grid to which the BESS will be connected.…”

“…The control strategy requested for a converter used in BESS application should implement a power control which operates on top level, to supply the power fluctuations of the grid, and on local level, to guarantee the state of charge (SOC) balancing of the battery cells. Indeed, particular working conditions may affect the capacity of the battery units and it is important to compensate the differences between them through an accurate control [7]. Therefore, a power control loop is combined with a sorting strategy in order to provide or absorb power keeping the system balanced.…”

“…The power control is implemented by modulating the converter with the Nearest Level Modulation. Indeed, the high number of levels of the RCMC, equal to 235 [7], permits to have a negligible harmonic content in the output current even with low values filter inductance. Further details will be given in the next section.…”

“…This paper presents a Reconfigurable Cascaded Multilevel (RCMC) converter for BESS application. The RCMC structure resembles the multilevel converter but permits the full control of each battery cell, thanks to the Reconfigurable battery modules (RBMs) [7]. This topology enhances all the potential advantages described above.…”