How to structure a battery management system

June 23, 2011 // By Jon Munson
Jon Munson from Linear Technology explains in detail how to design a management system for batteries - considering in particular the boundary conditions of vehicle requirements.

So you've been tasked to design the monitor circuitry for a new battery-based power system. What strategies will you employ to optimize the design for cost and manufacturability? The initial considerations will be to determine the preferred structure of the system and the location of the cells and electronics involved. When the basic structure is understood, then one must consider the tradeoffs in the circuit topology such as, how to optimize communications and interconnection within the final product.

The form factor of the cells being considered will have a significant influence on the structure of the power system. Will there be a large number of small cells to fashion complex-shaped modules (or pack), or will large format units be used that impose weight limitations on cell count or other dimensional constraints? This is perhaps the biggest area of design flux, as new cell formats enter the market and efforts are made to more organically integrate the module or pack structures into an overall product concept. In the case of vehicle design, for example, batteries may well end up being distributed over the vehicle in otherwise inefficiently utilized spaces.

Another consideration is the interconnection of test signals and/or telemetry between the cells (or their modularized groupings), BMS (or sub-sections thereof), and final application interface. In most situations, a case can be made for integrating some of the data acquisition circuitry within the module or pack so that if interchanged, important information like production ID, calibrations, usage metrics, etc. can travel with the replaceable elements. This information can be useful for the BMS or service equipment, and it minimizes the number of high-voltage-rated wires required in the harness.

Figure 1. Different Battery Monitoring Topologies. For full resolution, click here .

The topology of the monitoring hardware is then driven by the refined definition of the cell-count to be supported for a given mechanical concept. In a vehicular application, it is typical to

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