Tech Briefs Magazine - December 2022 - BET17

SOC and temperature. Typically, the BMS
in the Li-ion battery calculates the allowable
regen current in the battery
pack and broadcasts this information
over the supported digital communication
interface. Anytime a battery cannot
accept the regen current generated by
the motor, multiple issues can occur. One
of them is that the system voltage can
spike causing damage to the components
connected in the system power
bus, including the battery. It also impacts
the breaking power.
The battery installed in the vehicle
needs to be capable of absorbing the
generated regen current under all operating
conditions. The battery or the system
can add additional regen absorption
components, such as a bleeding resistor,
and sink the additional regen current that
the battery pack cannot absorb. This requires
precise monitoring of the regeneration
current generated by the motor and
the regen current absorption capability
calculated by the BMS. Switches can be
used to control the flow of the regen
current and ensure smooth functioning
of the braking and regeneration system.
User Interface
LEVs have a battery gauge installed in
the vehicle dashboard that displays the
battery voltage or SOC. If displaying the
SOC, it is typically calculated from the
measured battery voltage. This works
well for a lead-acid battery, but not very
well for a Li-ion battery. The impedance
of the Li-ion cells along with the impedance
of BMS components impact the accuracy
of SOC calculated by such gauges.
One of the main functions of a BMS in
the Li-ion batteries is accurate gauging
of SOC and measuring of the battery pack
voltage. These values are available over a
digital communication interface and can
be read and displayed by gauges that
have the capability to communicate with
the battery packs.
A gauge with digital communication is
typically referred to as a 'smart gauge'. In
addition, battery parameters such as timeto-empty,
temperature, current, battery errors
etc. are also available from the BMS,
and can be displayed in the smart gauge.
Figure 1: A smart gauge digitally communicating
battery parameters such as SOC,
voltage, and time-to-empty. (Image:
Inventus Power)
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Battery & Electrification Technology, December 2022
17
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Tech Briefs Magazine - December 2022

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