Batteries play an increasingly significant role in our electrical systems but they need to be always healthy, safe, efficient, and above all, they should be able to interact with other smart devices effectively. Central to achieving all these is a Battery Management System (BMS), which does all the technical stuff for you in the background.
Reading this piece will arm you with all the crucial concepts about Battery Management Systems, including their types, components, functions, operation, design considerations, applications in real life, and potential future trends. Now let's proceed step-by-step while shedding light on all the important details.
What Makes Up a Battery Management System?
To better understand everything else about a BMS, it's vital you first familiarize yourself with all its key components. Therefore, regardless of the brand or type, a complete Battery Management System should have a battery monitoring unit, control unit, and power management unit as we've described in the subsequent sections.
The Battery Monitoring Unit (BMU)
Just as the name suggests, the battery monitoring unit collects data that is vital for monitoring the status of your batteries. For example, we cannot tell the amount of charge your battery has already accumulated without the BMU, and neither can we know whether it's time to get a new battery pack or not. For a more straightforward understanding, we've gotten deeper into the various parts of the BMU as below.
The Voltage Sensors
Battery Management Systems can't perform their role of showing you the various performance parameters of your battery if they don't know the voltage coming from the battery pack, and that's where the voltage sensors kick in.
The voltage sensors detect the voltage characteristics of your battery pack and send the information to the control unit for processing, interpretation, and decision-making by the BMS. With the help of the voltage sensors, the monitoring unit can determine things like the charge on each cell and send a signal to the control unit to take the appropriate corrective measures.
The Current Sensors
The amount of current flowing through a given electrical system is an important consideration. So, by knowing the amount of current flowing from or to the batteries, a Battery Management System figures out if it's within the permitted range or not.
Interestingly, a BMS can't do anything without the current sensors because they're the devices that pick up the data on electrical current characteristics. Then like voltage sensors, current sensors send the data to the control unit for processing and execution of the most appropriate actions.
The Temperature Sensors
To acknowledge the importance of temperature sensors in a BMS, you need to know that various battery chemistries perform best in different temperature conditions. Some batteries, for instance, Lead-acid accumulators, exhibit optimal performance at moderate temperatures.
However, modern technologies such as Lithium Iron Phosphate batteries can maintain top-notch performances even under extreme temperature conditions. Therefore, the thermosensors ensure that the control unit is always aware of the surrounding temperatures so that it can adjust accordingly. In other words, the temperature sensors ensure your battery is safe from damage and lasts long.
The Control Unit (CU)
The control unit is another vital component of a Battery Management System. It is where all the necessary decision-making processes occur. However, the CU cannot know what decisions to make if it doesn't receive the signals from the sensors in the battery monitoring unit. For simplicity and better comprehension, let's dig deeper into the specific components of the CU using an example.
How The CU Works
As the BMS operates, the battery monitoring unit collects data about the voltage, temperature, and current that's flowing through the system. This information is sent to the control unit via the appropriate communication interfaces. The CU then checks if the temperature is within the optimum range for the given battery technology. Additionally, the CU confirms the appropriateness of the two other parameters, voltage and current.
If there are any abnormalities with the current flow, voltage amplitude, or temperature, the CU sends signals to the microcontroller. It's the microcontroller that then performs the actual adjustment of the irregular parameters by communicating with the appropriate hardware. This could result in lowering or raising the temperature of the battery, or adjusting the current and voltage as necessary.
The Two Main Components of The Control Unit
In the control unit of a BMS, you'll find two components, which include:
- The Microcontroller - A microcontroller is the actual mechanism, usually hardware, that initiates an adjustment action to the battery parameters depending on the signal it receives from the control unit. So, basically, the CU does the data processing and interpretation while the microcontroller does the actual execution.
- Communication Interfaces - The communication interfaces are mechanisms through which the various BMS components interact with each other. Moreover, the interfaces facilitate the communication between the BMS and external systems. These can be a car control or energy management system in electrical vehicles (EVs) or solar power units, respectively.
Modern Battery Management Systems use three different types of communication interfaces. The first one is the Control Area Network (CAN) Bus, which the BMS uses to communicate with external systems, especially in EVs.
The other communication mechanism is the Universal Asynchronous Receiver/Transmitter (UART), which is essential for efficient communication between various BMS components. The third one we have the Serial Peripheral Interface (SPI), which picks up the signals from the peripheral components such as the sensors we've mentioned up there.
The Power Management Unit (PMU)
Like the BMU, the power management unit plays three crucial and distinct roles that are somehow the heart of your Battery Management System. Without the PMU, your BMS will not protect your batteries against many potential dangers. The power management unit performs the following three functions.
Prevents Overcharging of The Batteries
Your battery has a maximum amount of charge it can hold, and it would immediately undergo damages if you exceeded the upper limit. So, how does your BMS know that the battery has hit the maximum possible voltage? Well, this takes us back to the battery monitoring unit.
The PMU constantly sends data about the total voltage that has accumulated in your battery to the control unit. The CU then determines if the voltage is still within the range or not. If the total voltage is higher than the upper limit, the CU signals the microcontroller, which further signals the charge control to stop charging. This way, your battery cannot get overcharged and remains safe at all times.
Prevents Excessive Discharge
When a battery is supplying current to an external circuit or just any load, it undergoes discharging, which by the way, is just fine. The problem kicks in only when the discharge is too much. The maximum depth of discharge (DoD) varies with battery chemistry and capacity.
Generally, high DoDs shorten the battery's lifespan and increase maintenance costs significantly. So, the power management unit protects your battery by implementing a maximum depth of discharge beyond which the power supply to an external circuit automatically stops. This happens in coordination with a very critical component called the discharge control.
Balancing Power In the Cells
The amount of charge each cell holds is always not the same, and that causes an imbalance that's not good for the health and performance of your battery. Fortunately, the power management unit of a BMS has a balancing circuit that ensures an even distribution of charge on the battery's cells.
There are two mechanisms Battery Management Systems use to balance the charge. The first one is the less efficient passive balancing. This balancing mechanism converts the extra charge on some cells into heat energy, which is then released to the environment. We don't prefer passive balancing because it's wasteful and can cause problems to your batteries if there isn't a robust cooling mechanism in place.
Besides passive balancing, the power management unit of a BMS can also employ the more efficient active balancing mechanism. In the case of active balancing, all the excess charge is distributed equally to all cells, thereby preventing any possible loss of energy. Therefore, BMS units with active balancing are ideal in the 21st century where energy conservation has become a global goal.
What Are The Types of Battery Management Systems?
This is one of the most common questions we receive from people almost daily. So, to clear any rumours you might have heard, there are currently three types of Battery Management Systems.
Centralized
A centralized BMS has all its components on the same motherboard, a configuration that simplifies the wiring work for smaller projects. However, when the project in question is on a large scale, working with a centralized Battery Management System becomes pretty cumbersome. Luckily, there are other BMS options that are optimized for larger projects.
Distributed
In distributed Battery Management Systems, there's no single module in charge of all the battery cells. Instead, cells have been grouped into subsets, which are managed using multiple modules. A distributed BMS is ideal if you want to achieve excellent thermal management and high scalability for ease of maintenance and upgrades. This is because dividing the BMS into multiple units makes the wiring simple.
Modular
If you're looking for a blend of both centralized and distributed then the modular BMS units might interest you. Modular Battery Management Systems comprise several modules that you can control independently using their respective management systems. While there are multiple modules, each sends relevant signals to the main management system for integrated and seamless monitoring. They exhibit moderate complexity and scalability.
Verdict
Our alternative power systems like UPS backups are reliable because of robust Battery Management Systems. A BMS monitors our battery and informs us about their State of Health and Charge. Additionally, BMS units protect batteries against things like overcharging, excess discharge, and short circuits, thereby lengthening their lifespans.
Battery Management Systems also monitor the power distribution on individual cells and initiate the appropriate balancing processes. Importantly, a BMS can detect if the environmental temperatures are too high or too low for your batteries and adjust accordingly. Before you purchase a BMS, read and learn more about the three types available.
