Formation and research of low voltage modules of batteries and supercapacitors for autonomous power supply systems

In modern autonomous electric power supply systems, in particular, for electric vehicles (EV), rechargeable batteries (B) are often used as energy sources and supercapacitor (SC) modules are often used as power sources. To ensure the necessary level of on-board voltage, these devices consist of a large number of low-voltage cells, the work of which is accompanied by complex electronic energy management systems (EMS). Simplifying the operation of such systems, reducing their cost, as well as providing a number of other advantages of powertrain systems for EV can be achieved by applying a modular approach to both the design of electric motors with appropriate control systems and their electrical power supply. The work presents the results of the formation and research of low-voltage (12–16 V) Li-Ion B modules and SC modules for the construction of modular electric power supply systems for EVs. The work began with the measurement of the main parameters – a capacity and an internal resistance – for a sufficiently large number of Li-Ion and SC cells of the same type. Because of further selection (screening) of cells with similar parameters, appropriate low-voltage modules were created, the operation of which was studied in charging/discharging cycles at constant current values. At the same time, the voltages on series-connected elements or groups of parallel-connected elements were compared, both with and without the use of special EMS electronic boards, as well as for the purposeful screening of cells with similar parameters and their arbitrary selection. Conducted studies of low-voltage Li-Ion B modules showed that in the case of using a special EMS board, selection of element parameters for their parallel- serial connection is not required. However, screening of Li-Ion cells of similar basic parameters for low- voltage modules gives similar results even without the use of EMS. In SC modules, the function of passive charge balancing of SC cells is well performed by a simple protective electronic board, but only when the cells are fully charged. For active balancing, more complex and expensive EMSs are required. However, in the case of a low-voltage SC-module with selected SC-cells of similar parameters, the process of self- leveling of voltages of six series-connected SC-groups with two parallel-connected SC-cells in each group was noted. Thus, energy cell screening is an effective approach to create simpler and cheaper low-voltage Li-Ion Bs and SC modules.