By: Jeroen Büscher, Product Manager at VITO/EnergyVille for EIT Professional Learning
We are currently witnessing a surge of new battery supported applications in the marketplace. Prompted by the quest for application optimisation, among other improvements, high performing battery technologies are being developed with ever increasing energy and power densities. The lithium ion (Li-ion) battery technology family has provided an answer to many of the requirements demanded by emerging mobile and stationary applications. Even though Li-ion technology has performed magnificently and improved over the last decade, we know that the chemistry inside the battery is very susceptible to certain risks such as overheating, over-voltage, deep discharge, over-current and pressure or mechanical stress. For this reason, these batteries should be operated inside a safe and well-defined operating window.
To prevent battery failure and mitigate potential hazardous situations, there is a need for a supervising system that ensures that batteries function properly in the final application. This supervising system is referred to as a Battery Management System (BMS).
Battery Management Systems enhance safety and efficiency
Generally, a Battery Management System is an analogue and/or digital electronic hardware device complemented with specific software, that is added to a battery system. The primary function of a BMS is to fulfil safety requirements. But there's more to it. Objectives related to the more efficient usage of battery cells and a prolongation of their lifetime are also being increasingly integrated into the design of BMS.
Minimal requirements for a Battery Management System
While there is no unique definition of a BMS, the world does seem to agree that it should be designed with a minimal set of requirements.
- It must measure individual cell voltages
- It must measure temperatures at different points as close as possible to the battery
- It must measure currents flowing through it
- It should communicate information to control units and undertake action to ensure the battery will be operated within safety limits
- It should balance battery cells passively or actively
- It should provide thermal management
- It should be able to detect and isolate faults
- It should protect against short circuits
State of Charge and the State of Health
Of course, there is also a need to interface with other systems and subsystems in an application or even the outside world. For example, a BMS can provide feedback to the end-user regarding the energy and power available in the battery, or inform a maintenance technician about unusual events or errors. An accurate estimation of available energy in a battery is always highly appreciated. A driver of an electric vehicle wants to know how much further they can drive. A building’s energy management system needs to have an idea of how much energy from its solar panels on the roof can still be transferred to the battery. So, the estimation of energy and power limits, based on the measurement data within the battery, is a very important feature of a BMS. The more accurate the estimation, the more efficiently a battery can be operated.
Next to the estimation of State of Charge (SoC), there is an increasing interest in obtaining more ‘state’ functions of a battery. For example, the State of Health (SoH) of the battery. Reduced capacity or increased internal resistance can limit the functionality of a battery, and hence the end product as well. A BMS offering this insight is more and more valued for applications like electric vehicles, where the batteries still have potential post-removal for use in a second life application such as a stationary energy storage solution.
No single best design for a BMS
Looking at these functions and requirements and considering the various applications of batteries, it becomes immediately clear that there is no single best design of a BMS—both in terms of hardware and software. There is a need to further investigate exactly how such functions can be established, and we can do this by taking a closer look at the different possible hardware and software components of a Battery Management System.
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