Abstract
Traditional high-voltage battery systems are implemented using multiple battery modules connected in series, with each battery module made up of many series/parallel connected cells, to provide the required voltage and power. In the series-connected battery
systems, typically, separate converters for battery module balancing, bi-directional connection to a load and charging from an external power source are employed. In this thesis, an
integrated reconfigurable converter (IRC) topology for high-voltage series-connected battery storage systems is proposed. The main advantage of the proposed converter is that
it can be reconfigured to operate in a range of operating modes: ‘feeding a load’ from the
battery system, ‘feeding a load from a backup’ power source, ‘regenerative’ mode, ‘battery
module balancing’ mode and ‘charging’ mode. The proposed topology shares semiconductor devices and an inductor among the operating modes which makes it compact. It also
exhibits redundant modes which, together with a backup mode, increase its reliability.
Furthermore, the proposed IRC topology minimises the batteries’ stress during charging
and discharging cycles. Operation of all modes is analysed and explained in detail.
For the state of charge (SOC) ‘battery module balancing’ mode, two advanced strategies are developed. A distributed control strategy provides advantages in terms of reduced
communication requirements and increased modularity, over a centralised battery management system. A load sharing balancing strategy distributes the load between the battery
modules based on their SOC and is useful in applications where simultaneous balancing
and load supply is required.
In the initial IRC configuration, the ‘charging’ mode is implemented using a unidirectional DC/DC buck converter supplied by an external DC source. To further extend the
IRC flexibility, an enhanced IRC configuration with bidirectional energy transfer between
the battery modules and the AC grid is presented.
The IRC topology can be used for hybrid energy storage systems (HESSs) as well. The
proposed integrated reconfigurable configuration for HESSs allows direct energy transfer
between the energy storage systems by using only a single converter and bypassing the DC
link. This reduces stress on the DC link, reduces the DC link capacitor size and improves
overall efficiency.
All proposed IRC configurations and operating modes are experimentally verified.