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Energy management system of energy storage systems

Author: Source: Datetime: 2016-11-22 11:28:40

In the energy storage power station, the solar power battery is usually composed of dozens of strings or even hundreds of strings. Because the battery in the production process and use process, inconsistencies will cause the battery internal resistance, voltage, capacity and other parameters. This difference shows that the battery pack is filled with or placed in the series between the battery voltage is not the same, or the energy is not the same. This situation may cause overcharge, and battery voltage during discharge may be too low, so that the discrete cell group increased significantly, the use of more prone to overcharge and overdischarge phenomenon, a sharp decline in overall capacity, capacity of the battery performance out of batteries battery capacity in the worst performance, eventually lead to battery failure in advance. Therefore, for the lithium iron phosphate battery pack, the balanced protection circuit is necessary. Of course, the battery management system of lithium battery is not only the balance protection of the battery, but also has more requirements to ensure the stable and reliable operation of the lithium battery energy storage system.

 energy storage

1 monomer battery voltage balance function

 

This function is to discrete voltage, correction in series battery due to their differences in cell technology or energy, avoid individual monomer battery due to overcharge or overdischarge due to poor battery performance or even damage occurs, so that all the individual differences are the voltage of the battery in a reasonable scope. Requires that the error between the battery is less than + + 30mv. (electric cars just break through this bottleneck,)

 

2 battery pack protection function

 

Single battery over-voltage, under voltage, over temperature alarm, battery pack over charge, over discharge, over current alarm protection, cut off and so on.

 

3 data collected mainly:

 

The single battery voltage, battery temperature (the actual temperature for each battery module), terminal voltage, charge and discharge current, calculate the internal resistance of battery.

 

Communication interface: the use of digital communication protocol IEC61850. In the system of energy storage power station, it is required to communicate with the dispatching and monitoring system.


4 diagnostic function

 

BMS analysis of diagnostic function with lifepo4 battery pack performance, according to the real-time measurement of battery module voltage, charge and discharge current, temperature and battery voltage, calculated the internal resistance of the battery and other parameters, through the analysis of the diagnostic model, single cell current capacity or residual capacity (SOC) diagnosis, single battery state of Health (SOH) diagnosis, battery state assessment, and the estimated sustainable discharge time under the current status at the time of discharge. According to the requirements of the relevant standards "electric vehicle lithium ion battery assembly" General requirements (currently Bess no standards), the remaining capacity of the (SOC) diagnostic accuracy of 5% (SOH), the health state of the diagnostic accuracy of 8%.

 

5 heat management

 

Lithium battery module in the charging process, will produce a lot of heat, so that the entire battery module temperature rise, thus, BMS should have the function of thermal management.

 

6 fault diagnosis and fault tolerance

 

In case of abnormal, the BMS should give the alarm signal by monitoring fault diagnosis, network is sent to the upper control system. The storage battery for each series of battery real-time monitoring, monitoring and analysis of the parameters such as voltage and current, resistance and voltage change calculation rate, and relative temperature integrated approach, whether there is some bad can't use Instant Check in the battery or may soon be bad battery, battery fault give the alarm signal, and positioning, and take appropriate measures to deal with these batteries. When the fault is accumulated to a certain extent, may appear or start serious accidents, given a warning signal output, and cut off the charging and discharging circuit of busbar or branch cell stack, so as to avoid accidents. The fault tolerant technology of energy storage battery, such as battery bypass or energy transfer, is used to avoid the impact on the entire battery operation when a single battery failure occurs.

 

 

The management system has self checking function to the system's own software and hardware, even if the device is damaged, it will not affect the safety of the battery. To ensure that the failure of the storage system can not be caused by the fault of the management system, and even lead to the battery damage or the occurrence of vicious accident.

 

7 other protection technologies

 

For the battery voltage, under voltage, over current and other fault conditions, to take the way to cut off the loop protection. The flow state of instantaneous short circuit, over-current protection delay time is generally at least hundreds of microseconds to milliseconds, and short circuit protection delay time is microsecond, almost instantly cut off the short circuit, can avoid the huge damage to the battery caused by short circuit. Fast fuse is used in bus circuit, and high speed power electronic device is used to quickly cut off.


 solar storage

8 battery online capacity evaluation SOC

 

In the measurement of dynamic resistance and the true value of voltage on the basis of using the corresponding relationship between the charging characteristics and discharge characteristics, using a variety of pattern segmentation approach, mathematical analysis and diagnosis model, to measure the residual capacity of SOC. Discharge characteristic analysis of lithium battery and method using dynamic updating of battery based on the consideration of the phenomenon of self discharge of battery, online measurement of current and voltage, the discharge time of the battery; residual capacity prediction and calculation of the battery at different discharge conditions, and according to the using time of the battery and the ambient temperature correction to forecast electricity and predict the remaining power value of SOC.

 

In order to solve the battery effects on measurement, methods can be dynamically updated battery, using a power released by the discharge of electricity as a benchmark, such as the battery, the battery decreases reflects the base power decreases; while the base power also need corresponding correction according to the changing environment temperature.

 

Four. Recommendations

 

Solar backup generator system, micro grid system investment is very large, the cost of the battery is very high. Usually a plant with energy storage system (at night from the power grid to take the peak energy storage, peak daytime release) peak valley electricity price gap to reach 0.5-0.7 yuan lithium battery energy storage to achieve profit. Energy storage system technology is complex, non professional design institute can not be designed, to each device manufacturers closely.

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