Environmental pollution and energy shortages have led to the development of new energy sources. In order to use new energy sources reasonably and efficiently, battery storage energy has been applied. The Battery Management System (BMS) is a guarantee for energy storage battery applications, monitoring battery voltage, estimating battery charge status, and giving battery runtime recommendations.
The early BMS was mainly composed of distributed components, and its function was relatively simple. It mainly completed the monitoring of the voltage and current of the whole battery, and the monitoring accuracy was not high, and the over-voltage and over-current protection of the whole battery was completed [1]. The circuit is complex and has poor scalability and cannot be applied to large-scale energy storage systems. The article uses the LTC6804 as the core to design an energy storage battery BMS with balanced, battery condition monitoring and fault alarm functions.
1. Introduction to LTC6804 functionLTC6804 is the third generation multi-cell battery monitoring chip of Linear Technology, which can measure 12 series connected battery packs online at the same time (can also measure series connected battery packs with less than 12 batteries, the serial battery voltage sum is greater than 11V), single The maximum voltage of the battery is 8V, the series voltage is up to 75V, the maximum measurement error is 1.5mV, and all batteries can be measured in 290 microseconds.
The LTC6804 has an isoSPI communication interface, and multiple LTC6804s can be connected to the control chip via isoSPI serial communication. It is also possible to individually address each LTC6804 and manage multiple LTC6804s in parallel. When using twisted pair communication, the communication distance is up to 100 meters.
The LTC6804 integrates an equalization circuit to directly control the external switch to discharge the battery. It has five universal digital input and output interfaces, which can be used as the input of the sensor or as a communication interface. The LTC6804 consumes only 4uA of current during sleep.
The LTC6804 integrates a 16-bit delta-sigma ADC with a frequency-programmable third-order noise filter to measure battery voltage. In addition, the LTC6804 also integrates an auxiliary ADC internally, and the general-purpose input and output pins can be configured as auxiliary input pins for the ADC. Temperature measurement can be done by inputting the amount of voltage from the thermistor input to the ADC port. The battery current is measured by connecting the input of the Hall current sensor to the ADC port.
2, LTC6804 peripheral circuit designThe peripheral circuit of LTC6804 mainly includes power supply circuit, ADC reference circuit, communication circuit, general-purpose input and output circuit, watchdog circuit and voltage measurement circuit, etc. The hardware structure diagram is shown in Figure 1. The LTC6804 power supply is taken from both ends of the battery pack to avoid the design of a separate power supply.
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