Due to the complexity of measurement and control, integrated multichannel ICs that incorporate battery balancing as well as voltage and temperature measurements represent a cost-effective and optimized solution. An example of such a monitoring and balancing device is STMicroelectronics' L9963 chip, which supports up to 14 batteries per chip and up to 7 NTC temperature sensor inputs.
An L9963 chip provides the functionality required to implement 14 Cell Management Units (CMUs) and Module Management Units (MMUs). The battery monitoring and protection chip provides a high-precision battery voltage measurement path that synchronizes battery voltage and stack current readings, thereby indicating the state of charge of the entire stack cell by cell.
A combination of one or more such devices with a suitable microcontroller—to implement a battery pack management unit (PMU)—provides a complete battery pack solution.
For each connected battery, the CMU acquires the battery voltage and temperature and transmits this data to the main processing unit via an electrically isolated interface. The CMU directly impacts the overall battery's KPI parameters. The more accurately it determines the battery voltage, the better it can utilize the available battery capacity, and the more precisely it can derive other higher-level application parameters, such as state of charge.
To achieve effective charge balance among the batteries, a passive balancing method can be applied. A switchable load is placed in parallel with each battery, so that during the charging phase, the charge level of each battery can remain constant or decrease slightly when the switch is on. This balances the charge level of the entire battery pack, as batteries with a non-conductive "balancing bypass" continue to increase their charge level.
Here, the L9963 battery protection chip simplifies this passive balancing process by providing an integrated balancing MOSFET that requires only an external balancing load. Furthermore, the device offers a variety of configuration options to facilitate autonomous and simplified control of the balancing process.
The acquired sensor data and diagnostic information must then be transmitted to the processing unit using an electrically isolated interface to properly isolate the high-voltage battery domain from the conventional vehicle bus system and power supply. The L9963 chip supports transformer-based and capacitor-based coupling to create the electrically isolated interface.
High-speed communication is key, and the L9963 allows data rates up to 2.66 Mbps, meaning an update interval of less than 4 ms for a complete 400 V battery. In this example, the battery consists of 96 cells connected in series, containing 7 L9963 devices, each managing a group of 14 cells. All L9963 devices communicate via a single daisy-chain communication interface.
All of these aspects—sensor data acquisition, measurement integrity testing, sampling data transmission, and permanent battery monitoring—are critical to the safety of vehicle operation and occupants. Appropriate battery management devices, such as the L9963 developed according to ISO 26262 standards, are designed to meet ASIL D safety requirements, and safety functions are implemented.
Lithium-ion battery chemistry offers excellent power density and specific power, characteristics key to maximizing vehicle range per charge. This article highlights the importance of the Battery Management Unit (BMU) to ensure the battery delivers expected performance and maximizes battery life while meeting safety requirements. At the component level, this means signal paths must provide high accuracy over a wide temperature range, along with appropriate controls to manage the battery.
Nevertheless, the battery pack and BMU are only one part of the overall energy transfer and storage system associated with an EV. In addition to charging equipment installed in the owner's garage, EV service equipment (EVSEs) are becoming increasingly prevalent as electric vehicle sales continue to grow. EVSEs connect to onboard chargers and convert input power from the grid into high-voltage direct current (HVDC). Some chargers directly provide HVDC at very high currents, capable of charging a vehicle to over 70% in 20 to 30 minutes.
Battery electric vehicles (BEVs) and hybrid electric vehicles (HEVs) have the potential to deliver on their promise to reduce the carbon footprint of transportation. By adopting appropriate and suitable battery charging technologies, consumers have found they can do so without compromising vehicle performance and convenience.
