1 Overview Batteries are often used as backup power sources in power supply systems. In the event of problems with the AC power loss or other accident conditions, the battery system will face defects, resulting in equipment outages and other major operational accidents. In recent years, with the widespread use of valve-regulated sealed lead-acid batteries (hereinafter referred to as valve-controlled batteries), coupled with poor use of the environment and conditions, accidents caused by early failure of the battery have occurred. Due to the special valve-controlled sealing structure, valve-regulated batteries make it impossible for us to accurately grasp the health status of the battery. This “maintenance-free†advantage has become the shortcomings and difficulties in battery operation management, and it is extremely easy to mislead users. While improving battery performance and reducing maintenance workload, how to quickly and effectively detect early failure batteries and predict battery performance trends has become a new issue in battery operation management. In addition to routine maintenance testing methods such as checking for discharges and voltage inspections, some new detection methods have emerged with the development of technology. The new detection technology for battery on-line monitoring has gradually been used [1].
Beijing Laim Electronics is a wholly-owned subsidiary of LEM. The Sentinel module developed by Switzerland and produced in Beijing is a battery sensor specifically tailored for on-line battery monitoring. The sensor is only the size of a matchbox. Each module monitors a battery. The module uses a four-wire design. It is connected to the positive and negative poles of the battery to achieve power supply and measurement. Then it is connected to 254 modules through the RJ11 interface (phone line interface). , Through the open serial protocol communication to achieve the monitoring of the entire battery pack. The sensor can directly measure the impedance, voltage and surface temperature of the monomer battery (the module is attached to the surface of the battery), and the connection and installation are convenient. At the same time, the warranty period of the module is five years, completely spans the failure cycle of the battery, so it is very easy to construct the battery. Online monitoring system.
2 On-line battery monitoring hardware platform composition The battery on-line monitoring system needs to complete the human-computer interaction of battery parameters in industrial sites such as substations, data centers and other occasions, so that users can observe the overall battery voltage, current, and individual battery cells in the field. Impedance, voltage and temperature; on the other hand, it is necessary to provide a network interface, so that the user can understand the situation at the remote site such as the central control room; finally need to increase the GSM interface, in the event of a failure, you can text or call the way Notice to duty officer. Therefore, it is necessary to design a site monitoring host to complete the above functions and match the Sentinel module to construct the entire battery on-line monitoring system, as shown below:
It is worth noting that:
1) As can be seen from the above figure, due to the unique design of the sentinel module, it is possible to directly test the battery impedance, so the system does not need to install a separate discharge module.
2) Since the sentinel module needs to be identified by an address, the address is 8 bits, and the connection above can achieve a maximum of 254 battery connections.
3) Theoretically, the sbus communication line indicated by the dotted line in the figure does not need to be connected, but considering the complexity of the industrial site, if the communication line between the two modules is destroyed, some modules will not be in the line. Therefore, for the sake of redundancy design, as far as the field allows, try to arrange the cable.
4) The current transducer in the figure is generally used for the host to measure the charge-discharge current and sense the state of the battery. It is very necessary. Considering the convenience of on-site construction, try to use an external current transducer instead of the transmitter. Placed in the host, otherwise the battery charging and discharging cable (usually a very thick cable) needs to pass around the host, which is not economical or safe.
5) When using the GSM antenna, it is necessary to measure the local signal strength on the spot. Some computer room signals are severely shielded. At this time, you may consider moving the antenna outdoors to achieve smooth signal transmission.
From the above analysis, the requirements for on-site monitoring include at least human-computer interaction functions, network functions, GSM transmission functions, sbus bus communication functions, and A/D conversion interfaces.
3 ARM9-based battery on-line monitoring host host is essentially an embedded system with human-computer interaction interface. In order to complete the construction of the embedded platform and facilitate the communication of the network protocol, the ARM9+ operating system is adopted. Taking into account the industrial-grade operating temperature and the convenience of the LCD interface, AT91SAM9261 of ATMEL Corporation is selected as the main control CPU of the system.
In order to facilitate the use of the core board + expansion board, a minimum ARM9 system is placed on the core board, all the interfaces are brought out, and the function part is arranged on the expansion board.
3.1 Core Board Design The design diagram of the core board is as follows:
Explanation:
1) Because the AT91SAM9261 uses Dataflash to start up, it can only work in the range of temperature higher than 0°C and lower than 70°C. Once the temperature is lower than 0°C, it will not start. In order to solve this problem, only ARM can use the external start-up method called NORFLASH. Therefore, it is necessary to select the start-up mode as external start (BMS = 0) to meet the temperature requirements of the industrial site.
2) The Norflash memory chip selects AMD's AM29LV160DB with a capacity of 4M*16bit for storing BOOT programs, small operating systems and small application programs. Word alignment is used during design, that is, the A0 address line of the chip corresponds to the A1 address line of the ARM chip. In addition, since the SAM-BA programmer provided by ATMEL only supports Dataflash and Nandflash, it is necessary to modify the script file of SAM-BA to realize the programming of Norflash. 3) The Nandflash memory chip selects K9F1208U0B from Samsung. Its storage capacity is Storage capacity: 64M*16bit,
When using Wince or Linux operating system, the operating system and application programs are stored in the chip; if a small operating system such as ucos is used, the chip can be omitted from welding, and the system and BOOT programs can be stored in Norflash.
4) Sdram chip uses MT48LC16M16A2TG-75IT: D, each piece of capacity is 16M*16bit, this system uses two pieces of SDRAM to constitute 32 data buses. Since the SDRAM chip is the memory of the entire embedded platform, it needs frequent data exchange with the CPU. In order to achieve better signal integrity, a 22 ohm balanced resistor is connected in series to the address and control bus near the ARM to absorb signal reflections. When a small operating system is used, the operating system can run in ARM's internal SRAM. Sdram can be omitted from soldering.
5) The expansion interface extends all available interfaces of the ARM chip for connection with the expansion board.
6) Because of the signal intensive and the need to bring all interfaces out and ensure good electromagnetic compatibility, the PCB adopts a six-layer PCB design method and uses a signal layer - stratum - signal layer - power layer - stratum - signal The layer way.
To ensure the effect of high-frequency operation, consider designing the buses of the two SDRAMs to be equal in length and adopting two-sided layout and serpentine routing.
3.2 Expansion Board Design The design block diagram of the expansion board is as follows:
Explanation:
1) The SPIflash chip is used to store the data collected by the battery sensor. Here, the write protection pin of the chip is managed by an I/O port of the ARM to prevent the on-chip data from being modified during power-on or power-down.
2) The GSM module adopts Siemens TC35i module and communicates with the expansion interface (connects to the new ARM chip) through the serial port. In addition, an I/O port of ARM is used to control the IGT pin to activate the module. In order to ensure normal communication between the module and the SIM card, the distance between them should be as short as possible.
3) The network interface chip adopts DM9000, and the data packet is transmitted to Ethernet through it until the upper computer software. At the same time using the network protocol can achieve remote firmware upgrades to ensure that the host runs the latest application software.
4) Sbus is the protocol of lem company. The protocol can be converted to serial port protocol. The conversion circuit is open. The circuit is designed on the expansion board to realize the communication between the main control board and the sentinel module.
5) Since the AT91SAM9261 provides a liquid crystal data interface, it can be directly connected to the LCD.
6) The touch screen interface chip is implemented with a dedicated chip ADS7843.
4 Whole-unit adjustment We conducted experiments on this system in the substation, using 2 sets of batteries, each with 54 sections of 2v300Ah batteries, as shown below:
Write the test program to run in the system, take each battery module once every half hour and then print out the information through the debug serial port. The following is the result of a fetch:
#1battery:2.28v24.29404.9uohm #2battery:2.24v24.08362.1uohm
#3battery:2.22v24.29426.1uohm #4battery:2.29v24.29350.1uohm
#5battery:2.25v24.29381.8uohm #6battery:2.28v24.29392.6uohm
#7battery:2.28v24.29359.0uohm #8battery:2.31v24.29373.2uohm
The above parameters for each battery are voltage, temperature, and impedance. In the practical application in the future, the comprehensive analysis of these parameters can be used to know the health status of each battery. At the same time, this experiment also verified that the platform can be applied to battery on-line monitoring.
In addition, a basic test was performed on the display function and network communication function of the platform, and the performance was completely normal. Further development of upper management software, using this hardware platform to build a complete battery online monitoring system is the focus of follow-up work.
5 Outlook The battery on-line monitoring hardware platform based on ARM9 and LEM sensors can be used not only for the study of battery failure models, monitoring algorithms, and even battery activation technologies, but also if the supporting monitoring software can be applied to various practical occasions that need to monitor the battery, such as electricity. The on-line monitoring of the DC power system and UPS system in the telecommunication, communications, petroleum, chemical, railway, and coal industries has truly provided insurance for the weak link of the battery and escorted the country's safe electricity use.
references:
[1] Application of battery on-line monitoring technology in substations Shen Mengtian Chen Hong China Power Communication Network [2] Why maintain and monitor prepared VRLA batteries Beijing Laim Electronics Co., Ltd. [3] AT91SAM9261-EKEvaluationBoardUserGuide