EV Hybrid Battery With Integrated Multilevel Neutral-Point-Clamped Interfacing and Lossless Intermodule State-of-Charge Balancing

Abstract

The battery is at the heart of the electric vehicle and determines many of its key performance features. Therefore, an optimized design of the battery is critical. On the one hand, the design of batteries based on a single battery cell leads in many cases to oversized batteries in terms of energy or power, due to the diversity of requirements of the different electric vehicles. On the other hand, the use of a custom cell for each vehicle, optimized for its particular requirements, is not economically viable. Instead, hybrid batteries, combining only two battery cell chemistries, with distinct particular strengths, such as high specific energy or high specific power, offer an opportunity to cover a wide range of vehicle battery specifications while avoiding oversizing and dispersion in the cells to be employed. This work introduces a novel hybrid battery configuration, where the interfacing between the two sets of cells is accomplished through a bidirectional multilevel neutral-point-clamped dc–dc converter. The novel topology is presented, and a suitable power converter modulation and control strategy is developed. The feasibility and benefits of such configuration are demonstrated and illustrated. Particularly, the proposed battery system allows the balancing of the State-of-Charge (SoC) of the battery modules within both the sets of battery banks, which is achieved without introducing additional power losses. The SoC balancing is simply accomplished through the regulation of the power to be extracted/delivered from/to each battery module by the power converter during regular battery discharging and charging operations. The converter features enough regulation margin to correct substantial SoC imbalances. Overall, the proposed approach enables a modular and scalable design of the energy storage system for a wide range of electric vehicles, from only two different standard battery modules and a standard power semiconductor device, while optimizing the battery size for any given battery power and energy specification. Simulation and experimental results are provided in the case of a three-level internal battery interfacing to verify the good performance of the proposed novel hybrid battery configuration, modulation, and control.

Keywords

• Hybrid battery
• modulation
• multilevel
• neutral point clamped (NPC)
• State-of-Charge (SoC) balancing