Design and Application of Intelligent Battery Systems

Many new technologies have increased system performance while also increasing power consumption. For chemical companies that produce batteries, substantial progress in battery production technology is difficult, time-consuming, and costly. Therefore, optimizing energy conservation methods is crucial. The intelligent battery system (SBS) is one of the most promising technologies that can significantly improve the performance of battery packs.

In the computer industry, lithium-ion batteries are both admired and feared. Early accidents with lithium-ion batteries left lasting impressions on companies involved, teaching them a critical lesson: under no circumstances should the rated parameters of lithium-ion batteries be exceeded, as doing so can lead to explosions or fires.

Beyond the chemical composition of the battery or electrode parameters, there are several critical parameters for lithium-ion batteries. Exceeding these parameters can cause the battery to enter an uncontrollable state. In the graphs explaining these parameters (referencing lithium-ion battery parameter charts), any point outside the threshold curve indicates an uncontrollable state. As battery voltage increases, the temperature threshold decreases. Any action that causes the battery voltage to exceed its design value will lead to overheating.

Precautions Against Hazards from Chargers
Battery pack manufacturers set multiple layers of protection in the battery and packaging to prevent dangerous overheating. However, one component that can cause these protective measures to fail is the charger.

There are three ways a charger can cause harm to lithium-ion batteries:

The battery voltage becomes too high (the most dangerous scenario).
The charging current is too high (leading to lithium plating, which generates heat).
The charging process is not terminated correctly or charging is attempted at too low a temperature.
To avoid exceeding these parameters, designers of lithium-ion battery chargers take additional preventive measures to ensure that the system operates within safe ranges.

For example, smart battery chargers typically allow for a -9% voltage deviation but ensure that the positive deviation does not exceed 1%, guaranteeing compliance with smart battery safety standards. However, in actual design, the voltage deviation is random. Therefore, designs that meet these specifications often set the target voltage around -4% of the rated value.

Due to charging voltage inaccuracies (whether -4% or -9%), the battery is always undercharged. This potential danger of lithium-ion batteries results in very low capacity utilization. Industry experts suggest that even a minor drop of 0.05% from the rated value can result in a 15% decrease in capacity.

The Integration of a Small Computer in the Battery
The concept of smart battery technology is simple: a small computer is built into the battery to monitor and analyze all battery data, accurately predicting the remaining battery capacity. The remaining battery capacity can be directly converted into the remaining working time of portable computers. Compared to the original capacity measurement methods based solely on voltage monitoring, this can immediately extend working time by 35%.

Unfortunately, smart battery technology only goes so far. Unless the battery can communicate with the charger circuit, it cannot determine its operating environment or control the charging process.

In the “smart battery system” (SBS) environment, under specific voltage and current conditions, the battery requests the smart charger to charge it. The smart charger is then responsible for charging the battery based on the requested voltage and current parameters.

The charger adjusts its output based on its internal voltage and current references to match the values requested by the smart battery. Due to the potential inaccuracies in these references (up to -9%), the charging process may end prematurely, leaving the battery only partially charged.

A better understanding of the charging environment can reveal additional issues that affect the charging efficiency of lithium-ion batteries. Even in ideal situations, assuming a 100% accurate charger, resistance elements in the charging path between the charger and battery introduce additional voltage drops, particularly during the constant current charging phase. These voltage drops cause the charging process to prematurely switch from constant current to constant voltage mode.

Since the voltage drop caused by resistance weakens as the current decreases, the charger eventually completes the charging process, but charging time is extended. The energy transfer efficiency during constant current charging is higher.

Eliminating Voltage Drop from Resistance
The ideal situation would be for the charger output to precisely eliminate the effect of the resistance voltage drop. Some may propose a solution where, during all stages of charging, the smart charger uses the monitoring circuit data inside the smart battery to monitor and correct its output. This is feasible for single battery systems but not ideal for systems with two or more batteries.

In a dual-battery system, it is better to charge and discharge both batteries simultaneously. While charging is parallel, a typical charger with only one SMBUS port cannot handle this task. If the charger or other SMBUS devices only have one port, they can only communicate with one battery at a time. Therefore, an ideal system should provide two or more SMBUS ports so that both batteries can communicate with the charger simultaneously.

SBS Manager for Smart Battery Systems
In addition to providing multiple SMBUS ports, SBS manager technology can significantly enhance the performance of lithium-ion smart batteries. The SBS manager, as part of SBS, is defined by the SBS 1.1 specification and replaces the previous version’s “SmartSelector.”

The SBS manager interfaces with the driver and boost system at one end and manages the smart batteries and chargers at the other. The driver can read and request information related to the battery, charger, and the manager itself. The specification defines the interface for this information transmission. In a multi-battery system, the SBS manager selects the system power source and decides which battery to charge or discharge at any given moment. In short, the SBS manager determines which battery to charge, which to discharge, and when to do so.

A well-implemented SBS manager has several advantages: more complete and faster charging processes, simultaneous efficient charging and discharging, and the ability to detect and respond quickly to dangerous situations (such as potential voltage over-limit).

The SBS manager, which can monitor the voltage of the battery itself, can charge the battery to its true capacity. It can avoid undercharging caused by inaccurate monitoring of voltage by smart chargers (as mentioned earlier, typically -4% to -9%). This process does not require extremely accurate reference voltages (which are expensive).

Conclusion
The SBS manager enables charging efficiency improvements and enhances the overall performance of battery systems. It ensures that lithium-ion batteries are safely charged, that the charging process is optimized, and that the system can respond dynamically to different charging conditions. With such advancements, battery systems can meet the increasing power demands of modern devices, providing smarter power management solutions.