Battery Management System (BMS)

Why are battery management systems (BMS) needed and how do they work?

Battery management systems (BMS) are electronic control circuits that monitor and regulate the charging and discharge of batteries. The battery characteristics to be monitored include the detection of battery type, voltages, temperature, capacity, state of charge, power consumption, remaining operating time, charging cycles, and some more characteristics.

Tasks of smart battery management systems (BMS)

The task of battery management systems is to ensure the optimal use of the residual energy present in a battery. In order to avoid loading the batteries, BMS systems protect the batteries from deep discharge, from over-voltage, which are results of extreme fast charge and extreme high discharge current. In the case of multi-cell batteries, the battery management system also provides for cell balancing function, to manage that different battery cells have the same charging and discharging requirements.

The TLE9012AQU is a multi-channel battery monitoring and balancing system IC designed for Li-Ion battery packs used in automotive, industrial, and consumer applications. TLE9012AQU fulfills four main functions: cell voltage measurement, temperature measurement, cell balancing, and isolated communication to the main battery controller. In addition, TLE9012AQU provides the necessary diagnostic tools to ensure the proper function of the controlled battery.

Main benefits:

› Robust communication without the need for transformers or common-mode chokes

› Best in class voltage measurement accuracy even after soldering due to stress sensor technology

› Integrated diagnosis capability eases customer battery module functional safety design

› Integrated UART communication for systems with a microcontroller on local ground

For a powerful combination, system designers can use  TLE9015QU. It is a battery monitoring transceiver IC designed for the connection of several TLE9012AQU devices in a daisy chain inside a Li-Ion battery. By means of its two isoUART interface pairs, it can support ring communication, therefore improving the availability of the system at a low cost.

It also enables bidirectional information flow by including an error management unit with several inputs and outputs that are programmable on each TLE9012AQU.

The battery charging system is built to recharge the high voltage battery from the AC grid. The system in cars is the on-board charging unit.  By increasing the battery capacity and the energy efficiency of the electric components, battery pack voltage tends to become standardized at approx. 450 V with a trend towards higher voltages. This supports a faster charging time and enables lighter cabling within the vehicle. The trend towards fast charging also impacts the power range demanded, therefore new system designs trend towards 11 kW or even up to 22 kW. Today typically the use case is a unidirectional power flow from the grid to the battery, but there is also a bidirectional use case like a battery to load or battery to grid.

Check our recommended products and design solutions for the on-board charger and power conversion in energy storage systems.

One of the basic tasks in the battery charger is the regulation of battery voltage and current without exceeding the temperature limits. This requires a control loop that involves measurement of the battery parameters (voltage, current, and temperature) and controlling the PWM duty cycle that drives the external power network. PSoC with its precision ADC (max 14 bits) - implemented using its analog blocks, PWM - implemented using its digital blocks and a processor core forms such a control loop required for regulation. Other algorithms like cell balancing and fuel gauge can be implemented using a firmware logic.

The advantage of using PSoC lies in the implementation of a custom protocol for charging the battery and integration of other functions like CapSense, segment LCD drive, etc which is not possible when using dedicated battery charger ICs.

Besides current/voltage and temperature measurements, advanced analytics are performed on pack-level with respect to thermal, electrical, and mechanical strain. Highly accurate pressure sensing allows observing the possible extension of cell housing as a result of overload/charge condition or detection of mechanical impacts on the battery pack‘s mechanical structure. Sensing evaporated CO2 from the cell’s electrolyte as a result of cell aging or overstress could be used as a vital indicator for battery health. Combining and analyzing the values of the different condition sensors allows the detection of unauthorized pack manipulations, e.g., for modification or replacement of cells by measuring variations of pressure or 3D magnetic structures.

Check our pressure sensor portfolio, 3D position sensing, and CO₂ sensing (commercial/industrial qualified version currently only).

AURIX™ microcontrollers from Infineon secure communication between the off-board charger and the BEV or PHEV being charged. They also protect the in-vehicle communication network. These advanced microcontrollers provide all the safety and security features required for OBC applications. Infineon’s AURIX™ 32-bit microcontroller family (SAK-TC275TP-64F200N DC, SAK-TC265D-40F200N BC, SAK-TC234LP-32F200N AC and SAK-TC224L-16F133N AC) provides a scalable portfolio that supports automotive safety standard ISO 26262. The embedded hardware security model (HSM) enables secure communications. AURIX™ includes an optimized peripheral set with ADC & timers for electromobility applications.

Isolation monitoring is key for high-voltage batteries. In combination with short circuit and overload current measurements, the voltage of the high-voltage DC+/- lines are continuously measured against the pack’s mechanical housing and the surrounding chassis. The availability of high-performance current sensors also allows for additional use of precise current measurements in the context of Coulomb counting, state-of-charge, the depth-of-discharge calculation in battery monitoring, or advanced impedance spectroscopy in battery diagnostics.

• Enables  controlled emergency disconnect in case of over-charging, short-circuit and thermal run-away
• Drives system-level benefits for solid-state based implementation like
  • Pre-charging of DC bus @ main inverter(s) for traction motor(s) w/o additional components
  • Active limitation of fault currents
  • Extended lifetime due to the higher number of switching cycles
  • Reduced wiring diameters because of by orders of magnitude faster disconnect in case of detected overload / short-circuit
  • Programmable switching characteristic
  • Fastest possible crash protection
  • More than 40% reduction of electrical losses for solid-state based implementation compared to electromechanical relays

Recommended products:

• High-voltage super junction MOSFET switches for low-frequency switching applications—600V CoolMOS™ S7
• Isolated single-channel driver for high voltage applications 1EDI2002AS
• Isolated single-channel booster 1EBN1001AE

Find more details on battery protection topologies here.

In battery management systems (BMS), a compact and reliable solution that powers the entire system is required. Several components can be integrated, extreme battery voltage fluctuations are managed and requirements of the latest network interfaces and automotive security are met with Infineon‘s portfolio of Power Management Ics (PMICs).

The PMICs support comprehensive power supplies with a small form factor footprint for system solutions using  Traveo™, AURIX^TM, and PSoC MCU families. Boost function integrated into the PMICs avoids system blackout under extreme battery voltage fluctuations. The low quiescent current of the PMICs reduces the standby current of always-on functions. The PMICs comply with AEC-Q100, and extensive system safety functions help to comply with modern vehicle ECU requirements.

Recommended PMIC for BMS:

• S6BP20x series (S6BP201A, S6BP202A, and S6BP203A) PMICs are one-channel buck-boost DC/DC converters for automotive and industrial applications.
• S6BP501A and S6BP502A PMICs are 3-channel output power management ICs (PMICs). They come with a buck controller and a buck converter, as well as a boost converter, offering a single chip 5.0V, 3.3V, and 1.2V power source. These PMICs have quiescent current as low as 15μA
• S6BP401A PMIC is a single-chip power management solution that has 6-channel power output. It includes a 4-channel DC/DC converter and 2-channel LDO. Integrating output impedance setting and phase compensation circuits internally for all channels, the S6BP401A reduces the PCB size and bill of materials
• OPTIREG™ PMIC products are providing integrated, multi-rail power supply solutions. The family is offering high efficient voltage regulation including pre-and post-regulator architectures with DCDC-, linear, and tracking regulators. Besides the power supply, additional monitor- and supervision features and functions are integrated. Check the OPTIREG^TM switcher simulation tool to calculate efficiency and stability!

The TLF35584 is a multiple output system supply for safety-relevant applications supplying 3.3V-μC, transceivers, and sensors by an efficient and flexible pre-/post-regulator concept over a wide input voltage range. The wide switching frequency range allows optimization in respect of efficiency and usage of small filter components. A dedicated reference-regulator supplies the ADC independent from μC-load steps and acts as a tracking-source for the 2 independent sensor-supplies. 

Active thermal control is a key element within modern Li-Ion battery packs as cell temperature for charging has to be kept between 0 to 45°C and for discharging between -20 to 60°C; operation outside these ranges results in accelerated aging, reduced capacity, or even full damage of the battery.

• embedded motor controllers enable efficient motor control with inbuilt diagnostic functions for the efficient operation of internally controlled fans, pumps, or valves for thermal control purposes of the pack. The smallest package form factor and a minimum number of external components are essential for integration close to the motor.
• On a single die the 32-bit microcontroller, the non-volatile flash memory, the analog, and mixed-signal peripherals, the communication interfaces along the driving stages are integrated.
• DC and BLDC motors are operated via optional interfaces for half-, H- or 3-phase bridging circuit

Battery charger demoboard

LVD scalable power demoboard

In this training you will:

• Identify the aspects covered by the battery management systems (BMS), their main components and their function
• Recognize Infineon’s main components for battery management applications and the key features and benefits of Infineon battery management devices

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Getting the most out of batteries. By the end of this decade, the majority of new cars sold around the world is expected to have a partially or fully electric drivetrain. Battery management systems have a great impact on the range, cost and service life of electric vehicles, which makes them a key success factor for this mobility revolution. Furthermore, they play an essential role when it comes to second-life concepts that allow former EV batteries to be used as flexible storage for renewable energy, for example. Dr. Clemens Mueller exclusively explains in-depth market trends and challenges, provides details on Infineon products and solutions, and introduces the new BMS-IC TLE9012AQU.

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Training topics:

• Get to know how AURIX^TM is able to answer the needs of the electric vehicle market
• Recognize and explore how AURIX™ TC3xx addresses key electric vehicle challenges, and understand the main features of the AURIX™ TC3xx microcontroller

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In this training you will:

• Understand what a battery management system is
• Recognize the main advantages that Infineon AURIX™ microcontrollers can bring to these systems

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