Lithium battery application scenarios can be divided into consumption, power and energy storage. The earliest applications are consumer products such as mobile phones, notebook computers, digital cameras, etc. Currently, they account for about half of the global lithium battery shipments. The demand for energy vehicles has increased, and the proportion of power lithium batteries has increased year by year. At present, it accounts 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 power batteries is less than 80%. New energy vehicles, and the requirements of ordinary energy storage batteries are not so high. After the power battery is retired, it can be used in energy storage systems. Energy storage lithium batteries are gradually gaining importance as an emerging application scenario. Energy storage is to solve new energy sources. Wind power, photovoltaic intermittent volatility, one of the important means to achieve the function of 'cutting peaks and valleys'.
At present, the mainstream energy storage lithium battery has two kinds of ternary lithium and lithium iron phosphate, and the power density is much higher than that of the lead carbon battery. Relatively speaking, the ternary lithium is higher than the lithium iron phosphate.
In the energy storage system, lithium batteries and lead carbon batteries, lead-acid batteries are all stored in electrical energy, there is no essential difference, battery capacity, charge and discharge current design is the same. Compared with lead-acid batteries, lithium battery energy storage is new Things, there is no standard product at present, unlike lead-acid batteries, there are many kinds of specifications and models. Generally, manufacturers are set according to the amount of electricity. The biggest difference between lithium batteries and lead-acid batteries is that lithium batteries must be equipped with a battery management system.
BMS Battery Management System
Lithium batteries have the advantages of light weight, large energy storage capacity, high power, no pollution, long life, etc. However, lithium batteries are sensitive to overcurrent and overvoltage, and large-capacity batteries are made up of many small-capacity single cells (such as 18650), through a large number of series and parallel connection, more batteries in parallel, easy to cause imbalance of the current of each branch, so it must be introduced into the battery management system to join the control. Lead-acid batteries have many advantages, such as high current characteristics, from Low discharge, stable performance, safe and clean. At present, the routine maintenance of lead-acid batteries is mainly done manually, mainly for troubleshooting the connection status and terminal voltage of the battery. No BMS battery management system is required.
The Battery Management System (BMS) is a device consisting of microcomputer technology, detection technology, etc. It dynamically monitors the operating status of the battery pack and battery unit, accurately measures the remaining battery capacity, and simultaneously protects the battery from charge and discharge. The battery is operated in an optimal state to extend its service life and reduce operating costs, further improving the reliability of the battery pack. The electric vehicle battery management system must implement the following functions:
1---Accurately estimate the state of charge (SOC) of the power battery pack
That is, the remaining battery capacity, to ensure that the SOC is maintained within a reasonable range, to prevent damage to the battery due to overcharge or overdischarge, so as to predict at any time how much energy or energy storage state of the energy storage battery remains in the hybrid vehicle energy storage battery.
2---Dynamic monitoring of the working status of the power battery pack
To ensure the safety of the battery, during the charging and discharging process of the battery, the terminal voltage and temperature of each battery in the battery pack of the electric vehicle, the charging and discharging current and the total voltage of the battery pack are collected in real time to prevent the battery from being overcharged or overdischarged.
3---Equilibrium between single cells
That is, the single battery is balanced and charged, so that each battery in the battery pack reaches a state of equilibrium. The equalization technology is the key technology of a battery energy management system that the world is currently researching and developing.
Lithium battery selection and design
The energy storage system includes a bidirectional converter and a battery system, such as a set of 21kW/42kWh energy storage, indicating that the power of the bidirectional converter is 21kW, and the battery system stores 42kWh. The lithium battery system includes the battery core and the BMS battery management system. , provided by the manufacturer. Pay attention to the following points when designing:
1 The energy storage lithium battery has a BMS system, and needs to communicate with the inverter or the bidirectional energy storage converter PCS. It is necessary to select a device with a lithium battery function and a corresponding communication interface function. 2 Energy storage lithium battery and lead acid battery phase Compared, the charge and discharge current is not the same, special attention should be paid during design. 3 Lithium batteries do not have uniform specifications at present. The specifications of each manufacturer are different, and the BMS communication protocol is different. It should be customized according to the specific requirements of the project.
