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Building a high-efficiency battery management system

assuming you have accepted a task to design a monitor circuit for a new and battery based power system, what strategies will you adopt to optimize the cost and manufacturability of the design? The initial consideration will be to determine the preferred structure of the system and the location of batteries and related electronic components. After the basic structure is clear, the next problem that must be considered is the trade-off and coordination of circuit topology, for example, how to optimize the communication and interconnection of the final product

the overall dimension of the battery will have a significant impact on the structure of the power supply system. Do you want to use a large number of small batteries to fit complex battery modules (or battery packs)? Or do you want to use batteries with large overall dimensions, which leads to restrictions on the number of batteries or other dimensional restrictions due to weight problems? This is perhaps the most variable part of the design, because the batteries with novel shapes are constantly on the market, and people are also making continuous efforts to ensure that the battery module or battery pack integrated into the product will be more consistent with the whole product concept. For example, in the case of automobile design, the battery may eventually be scattered in some spaces on the vehicle. If the battery is not placed in these spaces, the utilization efficiency is very low

another consideration is the interconnection of test signals and/or telemetry signals between batteries (or modular battery packs), battery management systems (or their subsystems), and final application interfaces. In most cases, a shell can be made to integrate some data acquisition circuits in the battery module or battery pack, so that if it needs to be replaced, important information such as production ID, calibration, use specification can be taken away with the replaceable components. This kind of information may be useful for battery management system (BMS) or maintenance equipment, and minimizes the number of high voltage rated wires required in the harness

next, for a given mechanical conceptual design, the monitoring hardware topology is determined by the precisely defined number of batteries that need to be supported. In automotive applications, there are generally not more than 100 battery measurement points in waste plastic recycling plants, and the modularity of the system will determine how many batteries a given circuit system measures. The most common case is to divide all batteries into at least two subgroups by safely disconnecting the "maintenance plug". By keeping the voltage below 200V in case of fault, this method can minimize the risk of electric shock that maintenance personnel may encounter. The larger battery pack means that two sets of isolated data acquisition systems are used, each of which may support 50 battery taps. In some cases, all electronic components are on an affordable printed circuit board, but this requires a lot of interconnection, as shown in Figure 1 (a). Alternatively, electronic components can also be placed separately and more closely integrated in the battery module, but this requires the use of telemetry link method. In order to achieve reliable data integrity, the remote measurement function circuit built into the vehicle harness must adopt a solid protocol, such as the widely used can bus. Although the real can bus interface involves several network layers, the PHY layer can be easily used to form the BMS LAN structure to efficiently communicate within the module. This kind of distributed structure is shown in Figure 1 (b). This topology allows the calculation workload to be distributed among several small processors, thereby reducing the required data transmission rate and alleviating the EMI problems that may be caused by LAN methods. The final BMS application interface is likely to be a CAN bus connection to a main system management processor, and will need to define (or specify at the beginning) specific information transactions

other factors may also affect the physical structure and monitoring circuit. For lithium-ion batteries, battery capacity balance is required, which leads to additional heat management problems (heat removal), and if active balance is required, power conversion circuit is also required. Temperature probes are often distributed over the entire module to provide a way to correlate voltage readings with the state of charge, requiring some support circuits and connection schemes. An often overlooked consideration in design is that when the product is idle or stored on the shelf before installation, the battery leakage should be the lowest. In some cases, additional control wiring is necessary

among these structures implemented above, there is a common measurement function component, which includes a multi-channel ADC, a safety isolation barrier and a certain degree of local processing capacity. The circuit in Figure 2 shows an extensible design platform for data acquisition. In this figure, the core component to realize the function is the ltc6803 battery pack monitor IC of linglilte. At the same time, it also shows an SPI data isolator and some optional special-purpose circuits. The circuit includes input filter and passive balance function, forming a complete 12 battery data acquisition solution. If necessary, such circuits can be simply copied to support more battery measurement schemes, while sharing the local SPI port of the main microcontroller, which in turn provides the external. At the same time, the polishing damage layer will not affect the final inspection of the construction of CAN bus or other LAN type data links

Figure 2: complete 12 cell isolated BMS measurement function

compared with the previous generation of monitor devices, the main improvement of ltc6803 is to support power shutdown and/or separate power supply from the battery pack. When the power supply is removed from the v+ pin, the battery load will drop to zero (only Na level semiconductor leakage). The working power supply can be provided by the connected battery pack voltage, or from a separate power supply to v+, as long as the voltage is always at least as high as the battery pack. For simplicity, the ltc6803 can also obtain power directly from the battery pack, in which case the lowest power state (i.e. standby) will consume only 12ua of current. The development trend of ltm28 "replacing steel with plastic" and "replacing wood with plastic" provides a broad market space for the development of the plastic industry. 83 the data isolator supplies power from the main processor through an internally isolated DC-DC converter, so the device will automatically power off together with the main processor. A very useful function of ltm2883 is that it can also provide a large amount of power from the host to isolated electronic components (i.e. battery end). This is how a small boost power functional component (LT in Figure 2) is driven to independently power the ltc6803 so that the battery only provides ADC measurement input current (i.e. average value at effective conversion

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