At present, the stabilization of power peaks and valleys, the safety and reliability of power grids, the development of power quality, the development of renewable energy, and the development of smart grid technologies all place high demands on large-scale energy storage technologies, among many energy storage technologies. With its superior performance, sodium-sulfur batteries have attracted the attention of researchers in various countries. The research and development of sodium-sulfur batteries mainly includes the development of battery manufacturing technology and battery management technology. These two technologies are also the biggest technical bottlenecks in the practical application of sodium-sulfur batteries.
In the management technology of sodium-sulfur batteries, the detection of the cell voltage is an indispensable part, which has a very important impact on the safe and stable operation of the entire battery module. According to the detected cell voltage, balance management and alarm analysis are performed. The single-cell voltage alarm usually adopts two-stage gradient: alarm and blocking (or called cut-off), which generally includes: single-voltage over-voltage alarm, single-voltage over-voltage lockout , single undervoltage alarm, single undervoltage lockout, single voltage negative rate of change alarm, single voltage negative rate of change blocking, and some will increase the monomer voltage imbalance alarm and blocking. Sodium-sulfur battery modules usually contain many single-cell batteries. For example, a 5 kW battery module contains 48 single-cell batteries. Because of the large number of monomers, it is important to find a practical detection scheme.
There are many methods for detecting the single-cell voltage. Commonly used measurement methods include common mode measurement and switch switching. The common mode measurement method is that the voltage of each measurement point is attenuated by a precision resistor in proportion to the same reference point, and then the voltages of the respective cells are sequentially subtracted. The circuit of the method is relatively simple, and the disadvantage is that there is a cumulative error, thereby reducing the measurement accuracy. . The switch switching method is adopted in the reference, but each module is equipped with two switches, which increases the cost, volume and power consumption of the system. Based on this, an improved scheme is implemented. For the detection of the cell voltage, this solution can effectively reduce the number of switches and the volume of the entire detection system.
1 single voltage inspection system design
The research object of this paper is a sodium-sulfur battery module containing 48 monomers. When measuring, 48 monomers are divided into 4 groups: the first group is the monomer numbered 01~12, and the second group is the monomer numbered 13~24. The third group is a monomer numbered 25-36, and the fourth group is a monomer numbered 37-48. Parallel measurement of the four groups, that is, the first round of the measurement number 01, 13, 25, 37 of the single, the second round of the measurement number of 02, 14, 26, 38 of the monomer, and so on, the twelfth The rounds measure the cells numbered 12, 24, 36, 48, and all the cell voltages of the entire battery module are detected.
Taking the first set of measurements as an example, the measurement schematic is shown in Figure 1, where IN+ and IN- are connected to the A/D chip via the signal conditioning circuit. When the cell 1 with the number 1 is measured, the switches S1, S2, O1, and O2 are closed, and the positive terminal of cell1 is connected to IN+ and the negative terminal is connected to IN-. When the cell 2 with the number 2 is measured, the switches S2, S3, E1, and E2 are closed, the positive terminal of the cell 2 is connected to the IN+, and the negative terminal is connected to the IN-, and the relationship between the measured cell and the switch that needs to be closed is as follows. As shown in Table 1, it is not difficult to find that when measuring odd-numbered cells, the switches O1 and O2 are closed. When the even-numbered cells are measured, the switches E1 and E2 are closed. Therefore, in order to reduce the switches O1, O2, E1, and E2, The number of actions and the loss caused by the frequent operation of the switch, and the efficiency of the voltage inspection. The odd-numbered cells are measured separately from the even-numbered cells, that is, the odd-numbered cells are measured first, and then the even-numbered cells are detected. .
In terms of device selection, the TMS320F28335 is used as the main controller of the battery module management unit (BMU), and the field programmable gate array (FPGA) EP2C8Q208C8N is used as the auxiliary control of the BMU in accordance with the principle of meeting the system requirements and having a certain amount of upgrade margin. In this way, the TMS320F28335's off-the-shelf interface, such as SPI interface, CAN interface, etc., can be utilized, and a large number of discrete logic devices can be avoided, so that the circuit is small in size and low in power consumption.
The switch in Figure 1 uses the Panasonic PhotoMOS type optocoupler relay AQW214EH. The five GPIO ports of the TMS320F28335 are used to control the EP2C8Q208C8N output 17-channel control signals, respectively controlling the 17 switches in Figure 1.
One AQW214EH can be used as two switches. Figure 2 shows the specific implementation of switches S1 and S2. The implementation principles of the other switches are exactly the same. In Figure 2, cell1+ indicates that it is connected to the positive terminal of cell1 in Figure 1, and cell2+ indicates that it is connected to cell2 in Figure 1. The positive poles, S1 and S2 are respectively connected to the corresponding IO ports of the FPGA. When the IO port of the FPGA outputs a low level, the corresponding switch is closed, and vice versa, the switch is turned off.
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