Design and control of batteries integrated CHB converters for reliability and power density

Eltaief, Abdurrhman 2025. Design and control of batteries integrated CHB converters for reliability and power density. PhD Thesis, Cardiff University. Item availability restricted.

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Abstract

High penetration of renewable energy sources such as wind and solar in distribution networks creates operational challenges for Distribution Network Operators (DNOs), including intermittency, reverse power flow, and voltage rise. An existing solution is to deploy a Static Synchronous Compensator (STATCOM) for reactive power support alongside a Battery Energy Storage System (BESS) for active power support. The STATCOM is typically based on a Cascaded H-Bridge (CHB) converter, which connects directly to the grid without bulky transformers or harmonic filters. However, CHB converters rely on large electrolytic capacitors, which have a short lifetime, increase volume, reduce power density, and contribute nearly 30% of the total converter cost. In addition, a BESS requires a dedicated converter, transformer, battery management system, and filters, making the overall solution bulky and costly. This thesis proposes an integrated approach that integrates Toshiba lithium-ion batteries directly to the CHB converter, leveraging its modularity. This configuration eliminates the need for a separate BESS converter, transformer, and filters, while also reducing the system’s capacitance requirements, thereby enabling the replacement of electrolytic capacitors with more reliable film capacitors. The modular structure of the CHB further allows distributed and independent battery operation with inherent state-of charge (SoC) balancing capability, removing the need for additional balancing circuits. A CHB converter with integrated Toshiba batteries is designed for the UK 11kV distribution network. The batteries are modelled using an existing electrical model parameterised using laboratory data provided by Toshiba. The interaction between the battery and the DC capacitor is analysed. Reducing the DC capacitance increases the batteries’ exposure to current ripple, which may accelerate battery capacity degradation. The effects of reduced DC capacitance on current ripple, and their implications for battery lifetime, are reviewed with particular emphasis on the 100Hz component. Finally, a fault tolerant method is developed to account for battery faults to ensure reliable and continuous operation throughout the converter. Simulation results demonstrate the successful operation of a CHB converter with integrated Toshiba batteries. The effectiveness of the SoC balancing strategy is verified by initialising the batteries with random state of charge values, which converge after several charging and discharging cycles. Published studies indicate that the 100 Hz ripple component has minimal impact on lithium-ion battery capacity degradation. A formulation is established to quantify the reduction in DC voltage ripple resulting from the coupled behaviour of the capacitor and the battery. Finally, the proposed fault tolerant strategy is evaluated using an N = 3 converter under three simulation scenarios. In all cases, the converter tolerates module disconnection while maintaining balanced line to line voltages and phase currents, together with balanced average power sharing among the remaining modules. The case involving one bypassed module in each of two different phases is further implemented and validated in real time using the Real Time Digital Simulator. The close agreement between the RTDS and PLECS results confirms the effectiveness of the proposed strategy and provides further confidence in the simulation results obtained for the other fault cases considered in this thesis.

Item Type:	Thesis (PhD)
Date Type:	Completion
Status:	Unpublished
Schools:	Schools > Engineering
Uncontrolled Keywords:	1. Battery Integrated Cascaded H-Bridge Converter 2. E-STATCOM 3. Lithium-Ion Battery Modelling 4. State of Charge Balancing 5. DC link Capacitor Sizing 6. Fault Tolerant Control
Date of First Compliant Deposit:	4 September 2026
Last Modified:	07 Sep 2026 08:31
URI:	https://orca.cardiff.ac.uk/id/eprint/189176

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