In-depth Discussion of Battery Management Systems for Lithium Ion Batteries
Objective: Globally over 90% of newly installed energy storage systems are paired with Lithium Ion battery. Unlike the traditional lead acid batteries, Lithium batteries need Battery Management System (BMS) to operate safely and efficiently. If the system is not properly designed and programmed, it could cause the BMS to shut the system off, or even damage the battery cells. Thus, it’s important to understand how it works. Methods/
Results: There are two main types of BMS that are used for energy storage applications; Mosfet-based and Relay-based. BMS act as the brain of the lithium battery, as it controls and monitors the voltage, amperage and temperature levels to protect the battery cells. It’s important to know the differences and how they operate. The Mosfet-based BMS is relative in-expensive and it’s more compact. The potential risk is the unexpected large charging and discharging current could hit-through the Mosfet and creates a short circuit between inverter and the battery cells, which could lead to thermal run-away or even firing. While Relay-based BMS can not only handle much larger charging and discharging power, it will disconnect the battery cells from the inverter, once the battery operates outside of its specifications. The communication link between Lithium battery and hybrid inverter can be either close-loop or open-loop. Under close-loop systems, the BMS will report voltage, state of charge, amperage and temperature to the inverter. In open-loop system, this communication protocol is not available therefore it’s crucial to program battery parameters properly in the hybrid inverter, to avoid any system failures. When sizing up the battery bank system, it’s important to understand the load and duration requirements, which will determine the size of the battery. Furthermore, making sure the BMS can handle the inverter’s full load capacity and surge capacity, for seamless operation is critical. It’s also important to note that there are different types of lithium ion batteries are available on the market. Each type has its own strengthens and weaknesses.
Conclusion: As a result, a relay-based BMS with close-loop communication provides much higher safety reliability, and much better system performance. It’s critical for Solar + Storage developers and installers to obtain proper training to make sure the systems are well designed.