Large battery arrays can be used as backup and continuously powered energy storage systems. This usage is gaining more and more attention. The domestic and commercial Powerwall systems recently launched by Tesla Motors have proved this. The battery in this type of system is continuously charged by the power grid or other energy source, and then the AC power is supplied to the user through the DC/AC inverter.

Using a battery as backup power is not new. There are already many battery backup power systems, such as the basic 120/240V AC and hundreds of watts of desktop PC short-term backup power supply system, ship, hybrid car or all-electric type The use of several thousand watts of special car and boat backup power systems for automobiles, grid-level hundreds of kilowatts of backup power systems used in telecommunication systems and data centers (see Figure 1)...etc. Although advances in battery chemistry and battery technology have generated a great deal of attention, there is an equally important part of a viable and battery-based backup system, which is the battery management system (BMS).

The backup power supply according to the battery is very suitable for fixed and mobile use from several kilowatts to hundreds of kilowatts of power and can reliably and efficiently supply power for a variety of uses.

There are many challenges to complete the battery management system for energy storage use, and its solution is by no means simply “expanded” from the management system of small, low-capacity battery packs. Instead, new, more sophisticated strategies and critical support components are needed.

The starting point for the battle is to require high accuracy and reliability in the measurement of many critical battery parameters. In addition, the planning of the sub-systems must be modular in order to be able to customize the configuration according to the specific needs of use, but also to consider possible extension requirements, overall management issues, and necessary maintenance.

The working environment of larger storage arrays also brings other major challenges. In situations where the inverter voltage is very high/current is large and therefore current spikes occur, the BMS must also supply accurate, common data in a noisy electrical environment and often a very high temperature environment. In addition, the BMS must also provide extensive “fine” data for internal module and system temperature measurements, rather than a limited number of rough totals because these data are critical for charging, monitoring, and discharging.

Because of the important role of these power systems, their operational reliability is inherently important. To make this easy-to-interpret goal into reality, BMS must ensure data accuracy and completeness and continuous health assessments so that BMS can continue to take the required actions. Completing robust planning and reliable security is a multi-level process. The BMS must anticipate possible problems for all sub-systems, perform self-tests and provide fault detection, and then select appropriate actions in standby mode and work mode. The last requirement is that BMS must meet many strict regulatory standards because of high voltage, high current, and high power.

System planning turns concepts into real-world results

Although supervising the rechargeable battery is conceptually simple, it is sufficient to place the voltage and current measurement circuits at the terminals of the battery. However, the actual BMS is very different and much more complicated.

Robust planning begins with the overall supervision of the batteries, which puts forward some important requirements for mimicking the function of the circuit. Battery readings require millivolt and milliamp accuracy, and voltage and current measurements must be synchronized to account for power. The BMS must evaluate the effectiveness of each measurement because it needs to maximize data integrity and the BMS must also identify erroneous or problematic readings. The BMS cannot ignore unusual readings, because such readings may indicate potential problems, but at the same time, the BMS cannot act on the basis of erroneous data.