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SOC Estimation

The State Of Charge (SOC) estimation for rechargeable batteries is very important, which reflects the battery performance, so accurate estimation of SOC helps battery protection, prevent overcharge or discharge, and improve the battery life, also let the application make rationally control strategies to achieve the purpose of saving energy.


                 

A battery is a chemical energy storage source, its non-linear and cannot be directly accessed, the SOC is not directly related to any of the external measurement like voltage and impedance, on the contrast it is depending on lot of parametric uncertainties, therefore SOC estimation is a fundamental challenge for many lithium battery designers, many examples of poor accuracy and reliability of the estimation of the SOC are found in practice.

 

BMTPow had overcome this problem by rich battery parameters collected in past 14 years, also by applying the latest current integration technique (or so called Coulumb Counting) and self compensated algorithm, a high speed and high precision sigma-delta ADC is found in every BMS platform to carry out the Coulomb Counting function.


Over Current Protection Profiles

Instead of providing single, flat level over current protection, the BMTPow BMS supports the multi-level Over Current Protection Profiles, which allow the battery to be functioned normally during system startup, stall condition, (motor) regeneration and under high capacitive / inductive environments, the following example explain how the protection profile works,


Application example: E-bike battery

Over Current Protection

Situation

Magnitude

Detection

Delay

Release Delay

MOSFET 
Control

Remark

Cycling uphill

13A

Pass

Normal condition that
should let it pass

1st Level

Over current

18A

>5 Sec

30 Sec

Break off

Over current and last
too long, should stop it

2nd Level

Bike stalled

30A

>500 mSec

5 Sec

Break off

During stalling, current
will goes higher, which is
normal, but if over 30A for
300 mSec, BMS should stop it

3rd Level

Ignition

100

>25 mSec

15 Sec

Break off

During vehicle ignition,
the current will goes very
high, say 80A for 35 mSec
or 130A for 5 mSec, which
is normal and should let it
goes, however for
magnitude higher than
100A for over 25 mSec,
BMS should stop it

4th Level

Short circuit

180A

>180 Sec

30 Sec

Break off


Dry Contact Outputs

An open collector output to signal the host when an extraordinary event is occurred.


Communication Interfaces
Communication Interfaces like SMBus, RS232, RS485, CAN Bus, Bluetooth or GPRS are used for the host controller to read the varies kind of battery parameters, SOH & SOC data, also may let the host controller to control the ON and OFF of the battery charging and battery discharging, with this communication function, applications like E-bike, Scooter, Consumer Drone may also allow the negotiation between the host controller and the BMS to arbitrate which side to control the ON/OFF of the discharging, purpose of such arbitration allows reasonable operation control in the system yet keep the battery safe.


Adaptive Loading

Different applications may have different kinds of loading condition, for example a 3KW solar inverter may have very large capacitive loading say 14,000F, a water pump in contrast may have very large inductive load too, lithium batteries designed for these application are needed to be adaptive, so that under varies operating conditions like cold start, full load discharge, motor breaking, reverse the batteries will keep normal function.


Parallel Connection

Unlike Lead Acid batteries, without special handling, connecting two or more pieces of lithium batteries in parallel are strictly prohibited due to safety concern, even the batteries are pre-matched in voltage and capacity, still it is highly dangerous as the battery or the protection board may be damaged by the very large mutual charge current.


BMTPow proudly released the parallel cascadable lithium battery protection boards in 2008, lithium batteries equipped with these protection boards may be able to connected in parallel, without worrying the mutual charge current.


Lead Acid Charger Compliance

In some projects where need to upgrade the lead acid battery to lithium battery while hoping to use the original lead acid battery charger, normally the output voltage of a lead acid charger may be able to adjusted to fit the lithium battery, but the output current will normally out of range, also a lead acid battery charger is not able to charge the lithium battery to full.

 

BMTPow had resolved this problem by introducing Lead Acid Charger Compliant batteries in 2009, user may charge this series of batteries with a lead acid battery charger or even a DC power supply.


Series Connection

Again, unlike Lead Acid batteries, without special handling, connecting two or more pieces of lithium batteries in series are strictly prohibited due to safety concern, protection board interface may be damaged by high voltage.

 

BMTPow had successfully overcome such barrier in 2009 by introducing high voltage battery system, for example a 96V75Ah LiFePO4 battery system which is formed by two 48V75Ah batteries connected in series.


Battery Authentication

Application such as Laptop computer, E-bike, Medical equipments always need to authenticate a genuine battery in order to avoid the product be damaged by using fake and unqualified batteries, another purpose of such authentication need is to protect the profit of battery selling, BMTPow may implement battery authentication by SMBus communication together with varies level of security.




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