During recent years, Lithium battery got a remarkable position and becomes the most important battery to work with the hybrid inverter to form the energy storage system. This document will give you a deep understanding and let you learn more about battery storage system protection. It also gives you deep insight into the Growatt hybrid inverter and its support to avoid your lithium battery system to get fully drained during the sleep mode.

The lithium battery system always works with the BMS (Battery Management System) irrespective of a low or high voltage battery system. The BMS can provide support regarding full inspection and protection for the battery system including current, voltage, and temperature which further guarantee the safety, reliability, and endurance of the battery system.

How to Avoid Over-discharging of Lithium Battery under Sleep Mode

p o w e r i n g t o m o r r o w

Lithium Battery System Protection

Inspection

Temperature

Voltage

Current

SOC

Protection

Over Temperature

Low Temperature

Over Voltage

Low Voltage

Over Current

Short Circuit

Inspection and protection of Lithium battery system

Protection of the lithium battery system always required to set up the low voltage and overvoltage values of the battery cell and the system voltage in the battery management system. In most cases, the overvoltage and low voltage value of the cell is closed to 3.65V and 3V. It also enables easy control and keeps the DOD (depth of discharge) at 90% and provides support with longer lifecycles.

Encountered problem with low voltage protection

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0.9

0.8

0.7

0.6

0.5

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0.1

0.0

4.4

4.2

4.0

3.8

3.6

3.4

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3.0

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0 10 20 30 40 50 60 70 80 90 100

State of Charge(%)

Battery

volta

ge

(v)

Charg

ing

curr

ent (

C-r

ate

)

Battery voltage

Charging currentLow Voltage Protection

Over Voltage Protection

The low-voltage protection delivers backing for the lithium battery system to protect itself from over-discharging. However, when the battery voltage of the lithium battery system reaches the low-voltage point, it will lead the system into the sleep mode and cut off its power output. In that case, most of the battery system requires human intervention to reboot the battery system but if it fails to reboot the battery system early enough. The self-consumption of the BMS will use the energy from the battery until the battery system drained out. In this situation, the battery system may get damaged and cannot reboot again, which requires the function of a hybrid inverter automatically to avoid the battery system going into sleep mode and evade battery from complete damage.

Growatt SPA/SPH Storage Inverter

SPH hybrid inverter series SPA AC battery inverter series

Growatt Hybrid Inverter divided into SPA and SPH series, SPA hybrid inverter series is designed for the AC-Coupled system mainly used to provide support for the already installed solar system and require to upgrade by adding battery into the system. Whereas, SPH hybrid inverter series is designed for the DC-Coupled system and primarily used for the system which requires to install the solar and battery system at the same time. The above two series of hybrid inverter is designed with the intelligent charge strategy to help and avoid battery from complete drain out.

Growatt Solution Strategy

GROWATT SPH Series Hybrid Inverter GROWATT SPA Series Hybrid Inverter

SOC 100%SOC 100%

SOC 12%

SOC 9%

SOC 5%

SOC 15%

SOC 13%

SOC 8%

Nominal Charging/ Discharging

Battery Charging, Avoid Discharging

Mandatory Charging, Avoid Discharging

The SOC (state of charge) is the way to show the capacity of the battery system. When the SOC is closed to 0%, it also means that the battery system will attach the low voltage protection sooner or later. In order to avoid the battery system going into the sleep mode, Growatt SPH/SPA series hybrid inverter adopts the intelligent charging strategy.

1.When SOC of the battery system is in the green part, the hybrid inverter can charge the battery and discharge to the loads normally.2.When SOC of the battery system is in the yellow part, the hybrid inverter only permits to charge the battery, but stop discharging to the loads.

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3. When the SOC of the battery system is in the red part, the hybrid Inverter will adopt mandatory charge strategy with 10% of the rated power to charge the battery until the SOC reaches the grey line.

Conclusion

The running strategy of the Growatt Hybrid Inverter is designed based on the operation of the lithium battery system. With this intelligent charge strategy, it provides support regarding running out of all the energy of the battery system. The intelligent charge strategy of the hybrid inverter can help to build the no human intervention system and form the second-level protection for the battery system.