In the “Outline for the Development of Smart Urban Rail Transit in China”, it is proposed to establish an intelligent operation and maintenance system for power supply and distribution systems, communication systems, and other systems, improve the level of intelligent maintenance of urban rail equipment, improve operation and maintenance efficiency, reduce the workload of maintenance personnel, and form intelligent urban rail equipment. At present, the communication and signal specialties of urban rail transit mostly use an independent power supply system with lead-acid batteries as backup energy storage, which is installed in a decentralized manner using UPS cabinets, distribution cabinets, and battery cabinets (racks). There is a large demand for batteries, which is not environmentally friendly, covers a large area, and has high requirements for the temperature and humidity of the computer room environment. There are problems such as high maintenance workload, high failure rate, and relatively high maintenance costs in the later stage. To this end, the design of the integrated centralized power supply system for lithium iron phosphate battery energy storage is clarified and its feasibility is analyzed, in order to promote the transformation of traditional power systems and complete the application of a lithium iron phosphate battery system that integrates high-voltage boxes (BMS management), battery modules, CAN communication, etc., as well as an integrated system that integrates cabinets, power distribution, UPS, batteries, precision air conditioning, monitoring, and fire protection in communication and signal power supply rooms, Realize centralized power supply and intelligent operation and maintenance of communication and signal power systems.
1.Advantages of integrated centralized power supply system for lithium iron phosphate battery energy storage
1.1 Advantages of lithium iron phosphate battery energy storage
(1) Intelligent BMS management. Real time monitoring of voltage, current, temperature and other information of battery modules, predicting the operating status of lithium batteries, and playing a control and protection role in the battery system.
(2) High security. Adopting lithium iron phosphate positive electrode material with high safety and long cycle life, even if the battery is damaged internally or externally, the battery will not burn, explode, and have good safety; Good performance at high temperatures, lithium iron phosphate batteries can still operate normally at an external temperature of 55 ℃.
(3) More energy-efficient and environmentally friendly. Lithium batteries have a low self discharge rate and are more energy-efficient. Lithium batteries do not contain toxic substances such as lead, mercury, or other harmful heavy metal elements to the human body.
(4) Good durability. Compared to traditional lead-acid colloidal batteries, lithium iron phosphate batteries have a significant advantage in service life by using 1C charging and discharging cycles up to 2000 times; At the same time, lithium batteries have strong durability, slow consumption, and no memory effect.
(5) High cost-effectiveness. The service life of lithium iron phosphate is basically synchronized with that of UPS (10-12 years). Traditional lead-acid batteries have a service life of about 6-8 years. Considering the need for modification and replacement of lead-acid batteries during use, the longer service life has a higher annualized cost-effectiveness.
(6) Easy installation and maintenance. The volume of lithium iron phosphate batteries with the same specification and capacity is 2/3 of that of lead-acid batteries, and the weight is 1/3 of that of lead-acid batteries. The standard rack design is convenient and fast for installation, with high installation density and space utilization rate, which does not occupy additional computer room area and is easy to maintain.
1.2 Advantages of Integrated Design System
(1) Small footprint and small renovation workload. The lithium iron phosphate battery system can be installed in the existing equipment room, which is more convenient for installation and wiring, reduces pollution and noise caused by the construction process, and reduces the impact on existing equipment. At the same time, for new lines, a smaller footprint can also effectively reduce civil engineering costs.
(2) High safety and stability. Adopting a lithium iron phosphate battery module and BMS intelligent management, the lithium battery itself has better high-temperature resistance and durability. The BMS management system can also monitor the battery in real-time, predict the operating status of the lithium battery, and play a control and protection role in the battery system.
(3) Strong environmental adaptability. After the renovation, while improving the stability of the power system, the dual cabinet system seals the lithium battery system with a cold channel and internal circulation, making it more adaptable to the external environment; Reduce dust intrusion in the computer room while achieving better precision cooling effect, reducing the overall equipment failure rate; In addition, it is equipped with a condensate evaporation device to avoid the troubles of air conditioning refrigeration and drainage problems. For new lines, adopting an integrated cold channel closure design can effectively reduce external dust intrusion during construction and effectively reduce potential faults caused by dust and humidity.
2.Design of an integrated centralized power supply system for lithium iron phosphate battery energy storage
2.1 Overall System Structure
(1) System composition
The main body can be divided into a lithium iron phosphate battery energy storage system and an integrated power system. UPS modules, lithium battery modules, power distribution modules, fire protection modules, refrigeration modules, dynamic environment monitoring, etc. are deployed through a fully enclosed dual cabinet combination method, achieving dual channel cold circulation inside the cabinet to ensure long-term safe and stable operation of the equipment, and also ensuring that the system has no excessive requirements for the installation environment; Through BMS intelligent management, real-time monitoring of voltage, current, temperature and other information of battery modules can be achieved, and the operating status of lithium batteries can be estimated, playing a control and protection role in the battery system. Significantly improve the technical level of operation and maintenance, significantly reduce daily inspection workload, reduce equipment failure rate and maintenance costs. The integrated centralized power supply system diagram of lithium iron phosphate battery energy storage.
(2) System Design
① Integrated cabinet part. Adopting a dual cabinet parallel cabinet system, the cabinets are deployed with cold and hot channels: a sealed cold channel is located at the front end of the IDU, with a channel width of approximately 175 (185) mm; The closed hot channel is located at the rear end of the IDU, with a channel width of approximately 175 (165) mm.
② UPS section. Adopting a modular N+1 redundant deployment method, one set of 30KVA modular UPS is selected. Switch to battery inverter power supply during power outage; When the device malfunctions, it automatically switches to the bypass AC power supply.
③ Power distribution selection design. Adopting a rack mounted precision air conditioning integrated distribution cabinet mode, deploying ATS dual switch to monitor real-time voltage and current data of each branch.
④ Refrigeration section. Adopting a rack mounted air conditioner deployment method, one rack mounted integrated precision air conditioner with self evaporative design is selected to achieve a closed cold channel.
⑤ Monitoring section. Manage real-time data, equipment status, and real-time alarms of UPS, power distribution, air conditioning, temperature and humidity, fire protection, video, access control, water leakage, and other equipment within the system. The IDU power environment monitoring system can provide real-time data, views, and reports for system operation.
⑥ Fire protection part. Equipped with 1 set of rack mounted fire extinguisher, using heptafluoropropane (HFC-227ea/FM200) as the extinguishing agent. It is colorless, odorless, low toxic, non-conductive, non polluting, and will not cause damage to precision facilities.
⑦ Lithium phosphate electric energy storage system. Configure one high-voltage box and a 512V, 50Ah lithium battery module. The high-voltage box has intelligent BMS management function for each battery module, has multiple communication methods, and has communication function with UPS and monitoring devices; Capable of real-time monitoring of voltage, current, temperature and other information of battery modules, predicting the operating status of lithium batteries, and playing a control and protection role in the battery system.
2.2 Key Technologies
(1) BMS intelligent management
① High precision monitoring function for battery analog quantity. Real time voltage detection for battery packs, charging and discharging current detection for battery packs, single battery terminal voltage detection, multi-point temperature detection and leakage monitoring for battery packs.
② Battery system operation alarm, display, and reporting functions. For battery system overvoltage alarm, battery system undervoltage alarm, battery system overcurrent alarm, battery system high temperature alarm, battery system low temperature alarm, battery system leakage alarm, battery management system communication abnormality alarm, and battery management system internal abnormality alarm.
③ The protection function of the battery system throughout its entire life cycle. The battery management system will isolate faults when analog quantities such as voltage, current, and temperature exceed the safety protection threshold in the battery system. The faulty battery string will be removed from operation, and protection information will be reported and displayed locally.
④ Balancing function. This battery management system has a passive balancing function, which can effectively maintain the consistency of the battery pack through an efficient balancing strategy.
(2) Lithium iron phosphate battery energy storage
① Material safety. Lithium iron phosphate battery is a lithium-ion battery that uses lithium iron phosphate (LiFePO4) as the positive electrode material and carbon as the negative electrode material. Lithium iron phosphate batteries do not contain any heavy metal elements and are a safe, non-toxic, and environmentally friendly energy storage medium.
② Thermal safety. The positive electrode material of lithium iron phosphate batteries exhibits an ordered olivine structure and excellent stability. Therefore, the thermal decomposition temperature of lithium iron phosphate batteries can reach 480 ℃. Meanwhile, through sintering experiments on lithium iron phosphate materials, it can be determined that during thermal decomposition, lithium iron phosphate materials do not release oxygen like ternary materials, but instead generate solid substances such as iron oxides, iron phosphate compounds, and lithium oxides.
③ Destructive testing. Lithium iron phosphate batteries underwent destructive tests such as compression, short circuit, and overcharging, and the test results showed no ignition or explosion. They also did not explode during combustion tests.
3. Feasibility analysis of integrated centralized power supply system for lithium iron phosphate battery energy storage
3.1 Comparison and Analysis with Traditional Power Systems
In exploring the application and innovation of intelligent and integrated power supply systems based on lithium iron phosphate energy storage media in rail transit communication signal systems, this system innovates in the following aspects compared to traditional power supply systems. The integrated centralized power supply system is compared to traditional power supply systems, as shown in Table .
| Comparison item/name | Integrated centralized power supply system | Traditional power supply system |
| Structure | Adopting a three-layer BMS management architecture, ensuring the safe and reliable operation of lithium batteries with multiple layers | UPS cabinet+distribution cabinet+lead-acid battery pack power supply mode |
| Overall dimensions, weight, cost | Small size, small footprint, and light weight | Large volume, small footprint, and relatively heavy |
| Environmental adaptability | Integrated design of closed cold channels, with strong environmental adaptability and reduced invasion of external dust | High environmental requirements |
| Centralized power supply | Centralized power supply and unified monitoring for communication and signal specialties, saving room space, reducing equipment and operation costs, and reducing potential fault points | One set of power supply system for communication and signal respectively |
| Intelligent operation and maintenance | Realize centralized monitoring of power and environment in the computer room, and real-time detection of fault alarms for individual battery cells | High workload of operation and maintenance |
| UPS module | High frequency modular power module, CAN communication for more precise and efficient management of lithium battery cells, active current sharing technology and intelligent voltage sharing technology support the mixing of old and new batteries, N+1 redundancy design is safer, and supports hot swapping and easy maintenance | Power frequency UPS cabinet with strong impact resistance |
| Battery management | The intelligent BMS management system monitors the voltage, current, temperature and other information of the battery module in real-time, estimates the operating status of the lithium battery, and plays a control and protection role in the battery system | No monitoring, requiring manual periodic charging and discharging tests to test the internal resistance and voltage of a single battery, resulting in a large maintenance workload |
3.2 Comparative analysis of lithium iron phosphate and lead acid
Compared to lead-acid batteries, lithium iron phosphate batteries have many advantages such as high working voltage, small size, light weight, high energy density, strong adaptability to high-temperature environments, no memory effect, small self-discharge, long cycle life, high cost-effectiveness, pollution-free and easy recycling, and are suitable for intelligent operation and maintenance. They can be widely used in various precision equipment and have great development potential.
4.Conclusion
This article briefly analyzes the composition and key technologies of the integrated centralized power supply system using lithium iron phosphate battery energy storage, and discusses the application value of its lithium iron phosphate battery system and IDU integrated system in communication signal power supply systems. A comprehensive comparison and analysis of the performance parameters, equipment and maintenance costs, safety factors, etc. between the integrated centralized power supply system and traditional power supply systems, as well as between lithium iron phosphate batteries and lead-acid batteries, reveals that the integrated centralized power supply system with lithium iron phosphate battery energy storage has a high degree of integration, high level of maintenance intelligence, good performance durability, strong environmental adaptability, and long cycle life, which has a higher cost-effectiveness, It can effectively improve operation and maintenance efficiency, reduce the workload of maintenance labor, and form intelligent urban rail equipment. I believe that with the maturity of technology and increasing cost optimization, integrated centralized power supply systems will replace traditional power supply systems, and lithium iron phosphate batteries will replace lead-acid batteries in communication signal power supply systems.