EV battery management system with integrated bypass switching matrix for voltage/SOC balancing and traction inverter loss minimisation

The battery pack of an electric vehicle consists of several modules in series, and each module consists of several cells connected both in series and parallel. The major issue of battery packs is the imbalance between modules and/or cells, as it reduces the usable capacity and leads to faster cell degradation. The second important aspect is that battery packs have to provide a constant DC-link voltage to the traction motor to employ standard control techniques based on the torque and speed demand. However, this leads to high power losses at low speeds due to the high DC-link voltage. To address the aforementioned problems, this paper proposes a new modular battery pack using solid-state switches to selectively bypass individual modules. Depending on the voltage level required by the motor, only the necessary modules are connected, while the others are bypassed. The modules are selected by an advanced balancing control that ensures that the imbalance is minimised. Accurately estimating the state of charge of individual modules poses a significant challenge in any balancing algorithm. This paper has shown that adopting a voltage-based controller architecture offers an effective alternative to methods based on state-of-charge calculations. A comprehensive numerical analysis of power loss at the electrical drive level, confirmed by experimental results on a hardware-in-the-loop simulator, shows that variable DC link voltage substantially reduces power losses in the traction inverter compared to fixed DC link voltage configurations. • An optimal controller design based on voltage measurement to achieve nearly zero residual voltage/SOC imbalance. • It provides a variable DC link for the traction inverter to reduce power loss without an external DC-DC converter. • A real-world driving condition using the WLTP-3 driving cycle is used to validate the proposed topology.