The student Manez Aizpurua Alberdi obtained an outstanding grade with 'CUM LAUDE' and 'INTERNATIONAL DOCTOR' mentions
The student Manez Aizpurua Alberdi obtained an outstanding grade with 'CUM LAUDE' and 'INTERNATIONAL DOCTOR' mentions
The student Manez Aizpurua Alberdi obtained an outstanding grade with 'CUM LAUDE' and 'INTERNATIONAL DOCTOR' mentions
- Thesis title: Development of a Modular and Scalable Battery Energy Storage System
Court:
- Presidency: Giorgio Spiazzi (Padova University)
- Vocal: Erick Matheus Da Silveira Brito (Federal University of Viçosa)
- Secretary: Eneko Unamuno Ruiz (Mondragon Unibertsitatea)
Abstract:
Lithium-ion batteries are widely used in many applications, ranging from small-scale batteries with low cell counts to large-scale systems that require thousands of interconnected cells. The intrinsic inhomogeneities and operational differences that exist between cells limit the usable energy of the pack, and result in accelerated system ageing. To mitigate these effects, this thesis focuses on the development of a modular and scalable battery energy storage system (BESS). Instead of utilising a centralised power converter, the proposed BESS features multiple submodules with dedicated converters to enable module-level control and replacement capabilities.
The design and sizing of modular BESSs entail a significant challenge related to increased complexity and cost, which should be justified by the long-term benefits. In this regard, long-duration storage applications are seen as particularly suitable. The high battery costs predominantly dictate the total system cost, reducing the impact of increasing power conversion system (PCS) related expenses. Furthermore, the system architecture directly influences the extent to which these benefits can be exploited. Focusing on DC conversion, a parallel connection between converters provides the highest flexibility and reliability. For this reason, it is prioritised over the series configuration, even though a series interconnection remains necessary to scale the system voltage. Thus, both interconnection modes can be combined to balance system controllability and scalability, enabling a single design to be utilised across applications with different requirements.
A laboratory-scale, modular and scalable BESS prototype is built to validate different functionalities. The developed low-level control strategy enables differential-power processing for an arbitrary number of parallel- and series-connected controllable battery modules (CBMs), combining input current and bus voltage regulation capabilities. Its fault-tolerant operation is also demonstrated. At a higher level, a self-diagnostic testing approach is proposed to facilitate battery prognostics. By leveraging system redundancy, periodic tests are performed on specific CBMs without interrupting system operation. This approach effectively tackles the state estimation challenges of lithium iron phosphate (LFP) batteries coming from their flat open-circuit voltage and large hysteresis; by physically forcing battery observability, it ensures robust estimation updates using standard algorithms.