Researchers at the University of Birmingham have developed a modular electric vehicle (EV) battery architecture that uses solid-state switches to selectively connect or bypass individual battery modules.
The approach is designed to address two challenges within the electric drivetrain: voltage and state-of-charge imbalance between battery modules, and power losses associated with supplying the traction inverter from a fixed dc-link voltage.
The proposed modular battery pack uses a bypass topology to provide a variable dc-link voltage to the traction inverter while balancing battery modules. (Image: Ashraf et al., Journal of Energy Storage, CC BY | ScienceDirect)
In the proposed architecture, each battery module uses two MOSFETs. One connects the module during normal operation, while the second bypasses it. The battery management system determines how many modules are required based on the voltage demand from the traction motor.
At lower motor speeds, modules that are not needed can be bypassed, reducing the dc-link voltage supplied to the traction inverter. The researchers say this allows the system to vary the dc-link voltage without requiring an additional dc/dc converter.
Key findings from the research include:
- A voltage-based balancing controller reduced an initial 30% state-of-charge imbalance to a residual imbalance of less than 1%.
- The controller uses measured module voltage rather than requiring precise state-of-charge calculations for each module.
- Selective module bypassing provides a variable dc-link voltage without an additional dc/dc converter.
- Testing using the WLTP-3 driving cycle showed an approximately 40% reduction in overall system power loss compared with the fixed dc-link configuration.
- Traction inverter efficiency increased from 96.5% to 98.0% under the tested conditions.
- The architecture was validated using a hardware-in-the-loop setup with a real microcontroller.
The voltage-based balancing strategy also reduces the need for separate active or passive balancing circuitry. Rather than transferring energy between modules or dissipating excess energy through resistors, the controller selects modules according to their voltage while meeting the traction system’s requested dc-link voltage.
The researchers identified limitations to the approach. Voltage alone becomes a less reliable indicator of state of charge for battery chemistries with extended flat voltage regions. Balancing capability is also reduced above the motor’s base speed because all of the battery modules must be connected in series to provide the higher dc-link voltage required by the traction system.
The research was conducted by Adnan Ashraf, Basit Ali, Mothanna S.A. Alsunjury, Paul Weston and Pietro Tricoli from the University of Birmingham’s Department of Electronic, Electrical and Systems Engineering. The study was published in the Journal of Energy Storage.
Resource
Ashraf, A., et al. “EV battery management system with integrated bypass switching matrix for voltage/SOC balancing and traction inverter loss minimisation.” Journal of Energy Storage, 2026. sciencedirect.com/science/article/pii/S2352152X26023479
Filed Under: Batteries, Power Electronics, Technology News