Rutronik News

Alles, was man für ein Batteriemanagementsystem braucht

Erstellt von Ralf Hickl, Product Sales Manager Automotive Business Unit, Rutronik |

Das Batteriemanagementsystem (BMS) übernimmt zahlreiche unverzichtbare Aufgaben. Hierfür ist eine ganze Reihe verschiedener Bauelemente erforderlich. Ein Überblick.

Den typischen Aufbau eines Batteriezellenmanagementsysems zeigt das Bild: Die Energiezellen sind hier in einer Reihenschaltung angeordnet. Für das Balancing ist jeder Zelle ein Widerstand mit Schalttransistor parallel geschaltet. Die Ansteuerung dieser Schalter übernehmen Balancing-ICs, die über eine serielle Schnittstelle miteinander kommunizieren. Übergeordnet überwacht und steuert ein Mikrocontroller die Funktionen des Zellenmanagements.
Eine bidirektionale elektronische Sicherung regelt auf Anforderung oder im Fehlerfall auch die Trennung der Batterie von der Last oder vom Ladegerät. Links oben findet sich die Stromsensorik, hier als Shuntwiderstand mit Signalaufbereitung ausgeführt, alternativ können auch Magnetfeld-empfindliche Sensor-ICs diese Aufgabe übernehmen.

Energiezellen
Der Energiespeicher selbst kann mit Li-Ionen-Zellen oder Ultrakondensatoren, auch Electric Double Layer Capacitors (EDLC) genannt, ausgeführt sein. Bei Lithium (Li)-Ionen-Zellen ist Samsung SDI einer der Weltmarktführer, vor allem im Bereich automobiler Anwendungen, wie Elektro- und Niedrig-Emissions-Fahrzeuge (Low Emission Vehicles, LEV). Die Rundzellen in der gängigen Bauform 18650 (18mm Durchmesser, 65mm Länge) bieten höchste Energiedichten, mechanische Stabilität und effiziente Assemblierungsoptionen. Zukünftig wird das neue Format 21700 (21mm Durchmesser, 70mm Länge )eine entscheidende Rolle im Markt spielen.
Die Ultrakondensatoren des chinesisch-schweizerischen Herstellers Sech SA zeichnen sich durch eine nominale Zellenspannung von 3,0V aus. Die Energiedichte gipfelt bei 8Wh/kg. Dank ihrer niedrigen inneren Wirkwiderstände kommen sie in den meisten Fällen ohne aktive Kühlung aus. Laut Hersteller erfüllen sie die Normen ISO 16750-3 und SAE 2464.

Energy cells

Manufacturer

Type

Series

Description/Properties

Samsung SDI

Li-ion cell

INR18650-29E EV

High energy cell of 18650 design with 2.5 Ah @ cut-off 4.125V, discharge current 1C and 80% nom. cap. after 1000 cycles

Sech SA

Ultracapacitor

CxxW

cylindrical or pouch, 3.0V, up to 3200 F

Current and voltage sensor technology
Current and voltage sensor technology forms the basis for all higher-level functions such as undervoltage and overvoltage monitoring, energy meters, calculating the residual battery capacity, measuring the level of power, short-circuit monitoring, and measuring the charging current.

Current sensor technology
Current measurement can be achieved with the aid of shunts or magnetic field sensors. They must be bidirectional in order to cover both motor and regenerative operation of the drive unit (recuperation) as well as external charging from a measurement perspective.

Current measurement using a shunt is characterized by the following features:

  • Power dissipation in the shunt increases quadratically with the current according to Ptot = R I².
  • In order to cope with the power dissipation, the shunt requires a certain mechanical size. It ensures heat dissipation and a minimum of thermal capacity.
  • It is robust against magnetic interference fields.
  • The measurement is non-isolated, which in many cases requires galvanic isolation for the further signal sequence.
  • It enables broadband measurements.
  • The measuring accuracy is basically determined by the properties of the shunt, above all by its tolerances and temperature coefficients.
  • Calibration is simple.

Current measurement using magnetic field sensor technology offers the following features:

  • It has low power dissipation.
  • System-dependent galvanic isolation is available.
  • The development effort is greater than with shunts, since mechanical and magnetic integration of the magnetic field sensor is incorporated into the overall performance of the measuring system.
  • It requires production and assembly skills; a magnetic field simulation saves experimental resources.
  • Depending on the actual structure, a sensitivity to magnetic stray fields is exhibited.

 

Current sensor technology

Manufacturer

Type

Series

Description/Properties

Vishay

Shunt resistor

WSBS

Power Metal Strip®, up to 36W, 50µΩ ... 1mΩ

KOA

Shunt resistor

PSG4

Metal plate power shunt, 10W (0.5mΩ) and 8W (1mΩ)

Panasonic

Shunt resistor

ERJM

Metal plate technology, 0.5mΩ -1Ω, up to 5W

ROHM

Shunt resistor

PSRxxx

up to 5W, 0.2mΩ to 3mΩ

ST

Shunt resistor

TSC201

bidirectional, 300kHz

Melexis

Current sense OpAmp

MLX912xx

bidirectional, DC up to 250kHz

TDK-Micronas

Current sense OpAmp

many variants available

 

Cell balancing for Li-ion cells
Cell balancing levels out production tolerances and the individual aging of the battery cells connected in series. For this purpose, the voltage of each cell is monitored and the charging current is distributed in such a way that all the cells have the same charge state.
With passive balancing, a resistor is temporarily connected in parallel to a cell with a charging lead via a semiconductor switch (e.g. MOSFET). This causes a discharge current to superimpose the charging current until the other cells have caught up. However, this is accompanied by undesired power dissipation in the resistor. The IC ISL78600 from Renesas/Intersil, for example, is suitable for passive balancing.
In more complex active balancing, the excess charge of individual cells is distributed to the other cells with the aid of a DC/DC converter circuit with as little power dissipation as possible.
The new TLE8001 Balancing IC from Infineon supports both passive and active balancing. Also new to the market is the L9963 from ST, which stands out due to the number of its channels.
Balanced switches are either internal MOSFETs or, for higher switching currents, external MOSFETs in a simple design or as a pair in one package.

Cell balancing for ultracapacitors (EDLC)
Ultracapacitors are sensitive to overvoltages, therefore balancing is also recommended for them. A special balancing IC also ensures the even distribution of the total voltage to the individual ultracapacitors.

Cell balancing

Manufacturer

Type

Series

Description/Properties

Renesas/Intersil

Balancing IC

ISL786xx

L9963

Infineon

Balancing IC

TLE8001

Balancing IC for up to 12 Li-ion cells, active or passive balancing possible

ST

Balancing IC

L9963

Balancing IC for up to 14 Li-ion cells

ROHM

Balancing IC

BD14000

Balancing IC for 4-6 EDLC

DIODES

Balancing IC

DMN1xxx/DMN2xxx

Single/Dual N-channel, miniature package

DIODES

Balancing IC

DMPxxxx/DMGxxxx

Single/Dual P-channel, miniature package

Littelfuse

Fuse

885 Nano²®

SMD, up to 500VDC, 1A … 5A

Microcontroller in the control and monitoring device
The control and monitoring device fulfills several functions:

  • It works as an energy meter and calculates the remaining charging time and the residual capacity or range.
  • It increases security by merging data as part of a multi-layered monitoring system and checking it for plausibility. It monitors the functionality of subordinate controls and interrupts the charging process or the energy extraction from the battery, if necessary.
  • It is the diagnostic computer for impedance spectroscopy (DC and AC impedance measurement) and provides information on the state of charge, the temperature, and the general condition of the battery.
  • It hosts the operating system.

Due to the multitude of requirements, including functional safety and data security, only high performance microcontrollers with multiple cores in lock step mode and hardware security modules (HSM) are considered.

Microcontrollers & power/safety companion ICs

Manufacturer

Type

Series

Description/Properties

ST

Microcontroller

SPC56, SPC58

32-bit PowerArchitecture™, safety & security

Infineon

Microcontroller

TC2xx, TC3xx

32-bit AURIX™, safety & security

BOSCH

Microcontroller

CY32x, CS600

ASIL up to D, Q&A WDG

Infineon

Microcontroller

TLF35xxx

ASIL up to D, Q&A WDG

Galvanic isolation via optocouplers or inductive transformers
Optocouplers are suitable for galvanic isolation between signals with high voltage potential and the low-voltage side. The Toshiba models TLX93xx and TLX92xx listed in the table are well established on the market. In early 2018, Vishay also introduced a solution for the automotive market with an initial AEC-Q101 qualified optocoupler with phototransistor at the output (VOMA617A). Due to the dielectric strength of the collector-emitter path of 80V, both are also suitable for use in 48V electrical systems. Inductive transformers from Pulse are another alternative for potential separation at high common mode voltages.

Galvanic isolation

Manufacturer

Type

Series

Description/Properties

Toshiba

Optocoupler

TLX93xx

IC output, 1 Mbps up to 20 Mbps, 125 °C

Toshiba

Optocoupler

TLX92xx

Transistor output, 3750Vrms, 80V VCE, 125°C

Vishay

Optocoupler

VOMA617A

Transistor output, 3750Vrms, 80V VCE, SOP-4

Interfaces, interface drivers
CAN transceivers for twisted two-wire lines as the physical layer of the CAN bus are available in a wide variety of models. Infineon offers a particularly broad portfolio of bus transceivers that have been approved by many automotive OEMs. They are characterized by data rates of up to 5Mbps for CAN-FD (Flexible Data Rate) and the support of partial networking. They are available in a small TSON8 package (3mm x 3mm) with and without bus wake-up. Suitable CAN chokes complete the interface and ensure interference-free transmission of signals.

Fuse disconnectors
Conventional fuses, pyrotechnical disconnectors, and semiconductor switches can be used for electrical protection of the battery circuit.
The semiconductor switches consist of power transistors connected in parallel and their gate drivers. An interesting component is Infineon's TLE9180D. Developed as a motor control IC for 3-phase BLDC motors in electrical systems up to 48V, it has three high-side gate drivers as well as analog amplifiers for current measurement via shunts. Originally developed for applications such as electric steering and starter generators, it has protective mechanisms and diagnostic functions, making it ideal for use in functionally safe applications. When applied in a three-channel electronic fuse, its three low-side gate drivers are not used.
Pyrotechnical disconnectors are disposable products. The control unit generates an ignition with a corresponding cause of deployment. The power dissipation of a live heating wire in a squib causes a small propellant to explode, thereby separating a predetermined breaking point inside a conductor. Detailed treatment of the squib drivers goes beyond the scope of this article.

Power transistors for electronic protection (48 V and HV)

Manufacturer

Type

Series

Description/Properties

Infineon

MOSFET

OptiMOS™-5

100 V, N-channel, RDSon up to 1.5mΩ, package: TOLL

Infineon

MOSFET

OptiMOS™-5

80V, N-channel, RDSon up to 1.2mΩ, package: TOLL

ST

MOSFET

STripFET™-F7

80V, 100V, N-channel, PowerFLAT™ package

Toshiba

MOSFET

UMOS8

100V, N-channel

ROHM

IGBT

RGSxxx

650V, 1200V, short-circuit proof up to 8 µs, up to 90A

Infineon

IGBT

TRENCHSTOP™ 5 AUTO

600V, 650V, 1200V, up to 400A

ST

IGBT

STGxx

600V, 650V, 1200V, up to 120A

Gate driver for electronic protection (48 V and HV)

Manufacturer

Type

Series

Description/Properties

Infineon

Gate driver

EiceDRIVER™

HV single/dual channel, isolated with diagnostics

ST

Gate driver

STGAP

HV single channel, isolated with diagnostics

ROHM

Gate driver

BM6xxx

HV single/dual channel, isolated with diagnostics and DC/DC

BOSCH

Fuse ASSP

iFuse

up to 48V, 4 channel, current sense, DC/DC, Vreg

Infineon

BLDC-ASSP

TLE9180D

up to 48V, 3-channel, current sense, diagnostics & safety

Fuses

Manufacturer

Type

Series

Description/Properties

Littelfuse

Fuse

LC-HEV

450V/425V, up to 30A/40 A

Temperature recording
Li-Ion cells are specified for a relatively narrow temperature range. If this is exceeded, the service life of the battery may be shortened or even irreparably damaged, in extreme cases a thermal runaway is created. All the energy stored in the battery is released within milliseconds, so that the cell catches fire or explodes. To avoid this, sensors are needed for recording temperatures that detect a temperature increase quickly. AVX offers temperature-dependent resistors (thermistors) with a negative temperature coefficient (NTC) in various designs. They are available for surface mounting and as wired or unwired panes for customer-specific installation.

Temperature sensors

Manufacturer

Type

Series

Description/Properties

AVX

NTC

NC12, NC20

SMD, sizes 0805, 1206

AVX

NTC

NP30, NJ28, NI24

wired, high accuracy

AVX

NTC

NR, NK20

customer specific pane, plates

Find components at www.rutronik24.com.

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Simplified diagram of cell and battery management (source: Rutronik)
Prinzip-Schaltbild zum Zell- und Batteriemanagement (Quelle: Rutronik)Translate to German:] Simplified diagram of cell and battery management (source: Rutronik)