Task:

Design the electronics for a Sodium-Ion Battery (SIB) charging and discharging controller

• Develop charging/discharging and protection algorithms for the battery, including safeguards against improper operating conditions (overcharging, deep discharge, overheating), as well as active cell balancing.
  
  Since active cell voltage balancing is planned during both charging and discharging — considering expected variations in cell capacities and internal resistances over time — it is necessary to determine the optimal power rating of the balancing circuit, which significantly affects the system cost.
  
  Based on the defined requirements, design and manufacture a SIB monitoring and active balancing controller.
• Develop the interface between the SIB control system and a hybrid inverter.
  
  This requires an analysis of interface protocols used in hybrid inverters for energy storage systems (e.g., RS485, CAN) and the creation of signal and register data definitions.
  
  Using the existing hybrid inverter command system and based on measured and derived SIB parameters, implement optimal control of the battery’s power circuit using the algorithm defined in the initial phase.
  
  Design, manufacture, and program the interface controller according to the defined requirements.

Uncertainties:

Battery cell charging/discharging control and balancing require detailed monitoring of cell characteristics.
In addition to standard measurements such as cell voltage, temperature, and total battery current, derived parameters are also planned to be used — such as internal resistance (Ω), charging/discharging durations, number of cycles, and cycle characteristics.

Active balancing provides additional benefits over passive systems — such as adjusting imbalances between cell capacities, ensuring optimal usage of each cell, and improving overall storage system performance.
It also adapts to long-term changes in cell properties (e.g., aging or inaccuracies in manufacturer specifications).

When properly utilized, active balancing can significantly extend battery life.
However, it is still unclear which active balancing topology is most suitable for SIB cell systems.
The main topologies are listed in the article Comparative Analysis of Cell Balancing Topologies in Battery Management System and are illustrated below:

Additional material analyzed regarding cell balancing:

The article Comparative Analysis of Cell Balancing Topologies in Battery Management System focuses primarily on comparing passive and capacitor-based active balancing technologies.
Other promising active balancing technologies are described in detail in the following sources:

Active Battery Cell Balancing – A very promising technology based on flyback converters; it also presents an original method where an additional battery is used instead of capacitors for balancing.

Active Cell Balancing in Battery Packs – Describes buck-boost technology, which is less expensive than flyback but features more complex control and sensitivity to uneven cell capacity distribution.

When selecting a technology, in addition to cost and efficiency, it is very important to assess the consequences of component failures.
Since the system is powerful, failures must not lead to critical or irreversible consequences.
Currently, the literature lacks data on the reliability of different active balancing technologies in this context — this analysis will need to be conducted independently.

Furthermore, all the technologies mentioned in the literature have been developed for Li-ion, lead-acid, nickel, or silver-zinc batteries, so their adaptation to Na-ion technology requires additional research.
Finally, as the devices are intended for long-term use, it is essential to ensure maintainability throughout their lifecycle.
This means that during circuit design, the availability of components and their production lifecycle duration must be considered.

Hybrid Inverters

Current hybrid inverters on the market are mainly designed for Li-ion batteries.
Since Na-ion and Li-ion batteries differ in their parameters, it will be necessary to develop an optimal conversion system between the two types.
In some cases, direct control commands may be required.