A battery management system (BMS) is an electronic system that manages a rechargeable battery (cell or battery pack), by monitoring its state, controlling its load environment, and charge-balancing the system.
Ridgetop has experience in the physics-of-failure for various chemistries of batteries and fuel cells, and can apply domain knowledge in advanced diagnostics and prognostics to create a tightly managed and optimized BMS.
Battery Packs and Cell Balancing
The battery packs incorporated into a BMS will improve the charging efficiency, extend the useful life, and increase overall capacity of rechargeable Li-Ion battery packs through a principle known as cell balancing. Among a stack of Li-Ion cells, each battery will be slightly different in its State-of-Charge (SOC) and Capacity-to-Energy (C/E) mismatch. Under conventional charging methods, all cells are charged (and discharged) at the same current, and the battery pack is limited by its weakest cell.
In contrast, Ridgetop has designed systems that are capable of measuring the individual cell voltages of an 8-cell series-connected battery pack. This system is based on a System Control ASIC, a Solar cell subsystem, and a Li-Ion battery subsystem. A simplified diagram of Ridgetop's Satellite Power Supply System architecture is shown in Figure 1.
Figure 1. Satellite Power Supply System
In addition to the battery interface electronics, Ridgetop can provide a complete solar cell/battery power subsystems that are very efficient and flexible and will operate in the following modes:
- Satellite power coming from the solar cells
- Charge the batteries
- Satellite power coming from the batteries
- Combination of power coming from the batteries and the solar cells
- Charge the batteries while the rest of the satellite is receiving power from the solar cells
- Monitor Battery level of charge, charge leveling between batteries, and state of health
A protection system is self-contained within the BMS and all power lines distributed to various loads should be adequately protected. For spacecraft applications interfaces and protections are critical. Ground commands which can override or disable critical protection and reconfiguration circuitry should be included in a design as a safeguard against failures.
Figure 2 below shows a block diagram of a combined solar/battery BMS solution.
Figure 2. Top Level Block Diagram
The diagram depicts the satellite power system being composed of three subsystems, the solar cell subsystem which contains the solar cell array, the Li-Ion battery subsystem which contains the batteries and the control ASIC which is the "brains" of the system. It maintains the state-of-health of the batteries, the current output of the solar cells and the 28v system power. It can pull all of the power from the solar cells and charge the batteries at the same time if there is enough capacity or just supply the main power or supplement the solar cells with battery power or use the batteries to supply all of the main power to the system.
Relevant BMS Programs from Ridgetop
- NAVSEA MH-60 NiCd Power System for Sonobuoy power — In this case, Ridgetop designed a unique variable addressing scheme for charging and isolating battery strings.
- NAVAIR Program — Ridgetop designed a BMS system for a military program.
- NASA Fuel Cell Program — Ridgetop designed a 48 channel IC for individual cell monitoring. This IC is also suitable for monitoring the cell voltages of battery cells and using the measured data to control the charging and discharging. Ridgetop also designed the embedded controller to control the mixture of chemicals to support PEM fuel cell.
- Commercial Electric Vehicle (EV) BMS — Working with Automotive partner, Ridgetop designed advanced diagnostic and prognostic capabilities into a complex BMS for an automobile.
