Active cell balancing system using an isolated share bus for Li-Ion battery management: Focusing on satellite applications

Commercial and military satellites rely on high performance battery systems to supplement power provided by solar panels. Lithium Ion (Li-Ion) batteries have a higher power density and can operate at a higher state of charge (SOC) than the Nickel Hydrogen (NiH₂) batteries commonly used on communications satellites. The higher energy density and SOC of Li-Ion allows designers to utilize a smaller and lighter battery for a given space mission requirement. This reduces the launch mass and volume of the satellite electrical power system (EPS), allowing more to be allocated to payload. Li-Ion batteries require specialized management, monitoring and control to maintain the safe operation of the power system with mission critical reliability in space flight. Improper charging, balancing or discharge can cause a battery to operate unsafely. It can permanently degrade battery cell performance, or in the worst case, cause catastrophic cell failure. With proper cell charging and balancing, a high state of charge (SOC) can be maintained, and longer battery life achieved. This paper describes an autonomous, active Li-Ion battery cell balancing methodology for GEO (geosynchronous orbit) and LEO (low earth orbit) satellites that employs innovative design and circuit features. The BEU (Battery Electronics Unit) described herein incorporates an isolated “share bus” architecture with resonant magnetic coupling in a synchronous, floating voltage balancing system. It also includes individual cell voltage monitoring, telemetry data, and cell bypass drivers. The authors explain the need for such balancing systems and how they interoperate with charging mechanisms currently in use on satellites today. The advantages of the active BEU balancing methods compared to the alternative passive resistor-shunt method are discussed in the context of the extreme environments and conditions of a GEO/LEO space vehicle. Applications for cell balancing and management in utilit- - y grade Li-Ion battery energy storage as well as electric and PHEV vehicles (Plug in Hybrid Electric Vehicles) are also considered.