Research Projects

This proposal includes research work on high-voltage battery energy storage systems. The research work begins with the procedure to understand the cell characteristics used in a battery pack. This objectives include the development of the hardware setup for characterizing the cell under various operating conditions, encompassing both static and dynamic test setups. After understanding the battery characteristics, a circuit-based cell model is developed that can incorporate most of the cell behaviour. Also, an algorithm that can predict the state of charge of the cell for any given operating condition is also incorporated. The research work will further focus on the issue of balancing the cells in a high-voltage battery pack, which can improve the life of the battery pack and also provide efficient utilization of the battery capacity. Battery Characterization and Modelling To develop an experimental setup to characterize the battery. This mainly includes two set ups. Static test setup: This includes a constant current charging/ discharging circuit at very low C-rate and a dither circuit. This hardware should be able to conduct the static test on at least 5 cells independently for different charge/discharge current rates. Dynamic test setup: The test setup requires a bidirectional converter that can handle a current of 3C rate, sensors to measure voltage, current, and temperature, a data logger, and a protection chamber. Cell model: A cell-level equivalent circuit-based model that includes the OCV vs SoC relationship, the effects of internal ohmic resistance, the changes in the terminal voltage with the diffusion of ions, and the variations with variations in the cell capacity. This cell-level model needs to be scaled up to represent an entire battery pack. Active balancing schemes for multi-cell in a large voltage battery pack The voltage levels of series-connected cells in a high-voltage battery pack may vary within the pack due to variations in the chemical composition, operating conditions, manufacturing tolerance, and aging effects. This can lead to the underutilization of the entire battery pack's capacity, with some cells being overcharged and some undercharged. A voltage equalizer circuit can help maintain the charge balance of each cell, thereby improving the battery pack's lifespan, enhancing safety, and optimizing the efficient utilization of the battery pack's capacity. Modularizing the voltage equalizer enhances scalability for high-voltage battery packs without the need for a redesign. A modular multi-cell to multi-cell balancing circuit with intra-modular and inter-modular balancing current control is proposed in this document. Phase shift modulation method with a constant phase delay angle is utilized in this modular topology. It is planned to implement this scheme for a 400V battery pack, with 8 modules, each module having 16 cells in series. This scheme help in better utilization of battery capacity and cell lifecycle.

Cell characterization, Cell Circuit Modelling, Active Cell Balancing, Intra-module equalization, inter-module equalization, State of charge estimation