Lithium battery application scenarios can be divided into consumption, power and energy storage. The earliest applications were in consumer products such as mobile phones, laptops, and digital cameras. At present, it accounts for about half of the global lithium battery shipments. With the increase in the demand for new energy vehicles worldwide, the proportion of power lithium batteries has increased year by year, currently accounting for more than 40%. The future of power batteries will become the main application scenario of lithium batteries. According to the standard, the capacity of the power battery is less than 80% and can no longer be applied to new energy vehicles. The requirements for ordinary energy storage batteries are not so high. After the power battery is decommissioned, it can be modified slightly and can also be used in the energy storage system. As an emerging application scenario, energy storage lithium batteries are gradually gaining importance. Energy storage is one of the important means to solve the problem of new energy wind power and photovoltaic intermittent volatility and realize the function of “cutting peaks and flats”.
At present, the mainstream energy storage lithium battery has two kinds of ternary lithium battery and lithium iron phosphate battery, and the power density is much higher than that of the lead carbon battery. Relatively speaking, the ternary lithium battery is higher than the lithium iron phosphate battery.
Lithium iron phosphate battery
Ternary lithium battery
Lead carbon battery
In the energy storage system, lithium batteries, lead carbon batteries, and lead-acid batteries are all storing electrical energy. There is no essential difference, and the battery capacity and charge and discharge current are designed and selected. Compared with lead-acid batteries, lithium-ion battery storage is a new thing. There are no standard products at present. Unlike lead-acid batteries, there are many types of specifications. Generally, manufacturers are regulated according to the amount of electricity. The biggest difference between a lithium battery and a lead acid battery is that the lithium battery must be equipped with a battery management system.
Lithium batteries have the advantages of light weight, large energy storage capacity, high power, pollution-free, long life, etc. But lithium batteries are very sensitive to overcurrent and overvoltage. Large-capacity batteries are composed of many small-capacity monolithic batteries (such as 18650), through a large number of series-parallel connected batteries, more parallel batteries, easy to cause uneven current in each branch. Heng, so the battery management system must be introduced into the control. Lead-acid batteries have many advantages, such as high current characteristics, small self-discharge, stable performance, safe and clean. At present, the daily maintenance of lead-acid batteries, mainly through manual completion, mainly on the battery connection status, terminal voltage fault detection, do not need battery management system.
Battery Management System is a device composed of micro-computer technology, detection technology, etc. It monitors the running state of battery pack and battery cell dynamically, accurately measures the remaining power of battery, protects the battery from charging and discharging, and makes the battery work in the best state to extend its operation. The purpose of service life and operation cost is to further improve the reliability of battery pack.
Selection and design of lithium battery
The energy storage system includes bidirectional converter and battery system, such as a set of 21 kW / 42 kWh energy storage, indicating that the power of bidirectional converter is 21 kW, battery system storage of 42 kWh. The lithium battery system includes the core and battery management system, which is provided by the manufacturer. We should pay attention to the following points in design.
1. Lithium-ion battery has battery management system. It needs to communicate with inverter or bidirectional energy storage converter PCS. The equipment with lithium-ion battery function and corresponding communication interface function should be selected.
2. Compared with lead-acid batteries, the charging and discharging current is different.
3. At present, there is no uniform specifications for lithium batteries. Each manufacturer has different specifications and BMS communication protocols. It should be customized according to the specific requirements of the project.
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