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Battery modeling

Testing a battery management system

Monitoring and controlling larger cell arrays through battery management systems, helps maximize efficiency and battery life. Maplesoft’s battery modeling test system for a battery management system offers CAN communication.

Simulation of the thermal runaway using the Li-Ion model from the Maplesim battery library (Photo: Maplesoft)

THE USE OF RECHARGABLE BATTERIES IN CONSUMER products, business applications, and industrial systems continues to grow. The global market for all batteries will reach almost $74 billion this year, and rechargeable batteries will account for nearly 82 % of that, or $60 billion, according to market researcher Frost and Sullivan.

Growth like this means several things: First, large companies have moved or are moving into the market, designing and offering products ranging from hand-held devices to large power back-up systems. Second, as the systems get larger, battery technologies have to match the technical challenges of increasing cell capacity, thermal stability, life extension, and disposal.

Meeting the technical challenges

Monitoring and controlling larger cell arrays through battery management systems (BMS) helps to minimize charge times and maximize efficiency and battery life. Designing and testing a sophisticated BMS can pose challenges, however, one of the largest producers of electronic products in the world discovered. That’s why they relied upon Maplesoft (Germany) and Control Works (Korea), a real-time testing systems integrator with experience developing BMS test stands. They developed a Hardware-in-the-Loop (HiL) test system for the BMS in one of their energy storage systems (ESS).

A solution to these testing challenges is to use virtual batteries – mathematical models of battery cells that are capable of displaying the same dynamic behavior as real ones – for early-stage testing of the BMS. These models are able to achieve the execution required to deliver real-time performance for batteries containing hundreds of cells on real-time platforms.

The battery modeling technique employed by Maplesoft uses a partial differential equation (PDE) discretization technique to streamline the model to a set of ordinary differential equations (ODE) that can be solved by system-level tools like Maplesim. The model optimization features of Maplesim also allow the resulting code to be capable of running in real-time.

Model calibration and validatio

Maplesoft and Control Works engineers determined the average cell response using the parameter-estimation tool supplied with the Maplesim battery library. This uses optimization techniques to determine the values of cell-response parameters that provide the closest fit to the experimental results. This response was then validated against response data from other cells to ensure close estimation of the resulting model.

The end result was a battery model capable of being configured to represent a stack of up to 144 cells that can be connected in any combination of parallel and series networks. Fault modes were also built-in, such as individual cells shorting or opening, as well as incorporating variations in charge capacity from cell to cell, and degradation of capacity over the life of the cells.

The final BMS test station provides the client’s engineers with the ability to configure the battery model (number of cells, series/parallel, etc.) and apply a range of tests to it. The engineer can go back to the Maplesim model at any time to make necessary changes to the model configuration, and then generate the model for use on the real-time platform.

The Control Works system also integrates a real-time platform, signal processing, fault-insertion tools, and standard communications protocols (CAN for automotive, Modbus for industrial applications), allowing the engineer to run the BMS through a range of tests on the battery model, including Constant Current (CC) and Constant Voltage (CC/CV) charge/discharge cycles, as well as Constant Power (CP) and Constant Resistance (CR) discharge cycles.

“We were pleased to be able to partner with Maplesoft on this project,” said Kenny Lee, PhD, Director of Research Center of Automotive Electronics, Control Works. “The use of battery models in this case proved to be an effective alternative to the use of real batteries,” he added.

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Control Works