The Research And Design Of The Battery Monitoring System And The Key Module-Sigma-Delta ADC

The research and development of Battery Management System is an importantbasis to improve the level of power battery. In order to reach a certain voltage, power,and energy level as well as enhance the lifecycle of the whole battery, it is necessaryto overcome the discrepancies which may caused by manufacture, the initial capacity,the voltage, resistance and temperature of each cell of the electric vehicle seriesbattery. To reduce the impact of these discrepancies on the lithium-ion battery pack, itis also necessary to use the balanced circuit in the process of charging and dischargingthe battery pack. This system uses high-voltage signal acquisition and intelligentcommunication calculation on one chip, which will get higher reliability with lowercost. It is required to achieve high-voltage signal acquisition by the analog signals andintelligent communication and on-chip inter-cascade control by the digital signals.The key technology in this procedure is to connect a high-precision analog-to-digitalconverter between the sample and control signals.This paper is to analyze the overall function of the equalization system, focusingon the completion of the design of the internal analog-to-digital converter.Sigma-Delta ADC is a high-precision, high linearity A/D converter, which is easy tobe integrated in a system-on-chip. With multiple-sampling techniques, gettingmultiple samples and converting into an average value to achieve A/D converter,Sigma-Delta ADC can suppress the ambient noise very effectively. Besides, adischarge branch with equalization control needs to be parallel with the battery beingmeasured, which will cause high-voltage MOS switch control then the high-frequencynoise. This will exist in the whole measurement process but can be eliminatedeffectively also by the digital decimation low-pass filter of Sigma-Delta ADC.Therefore, Sigma-Delta ADC is the best choice for the battery equalization system.The Sigma-Delta ADC designed in this paper consists of a single two order feedbackmodulator and the digital decimation filters in which a comb filter is directlyconnected to a two-stage half band filter. This structure is quite simple and stable, andcan achieve the accuracy of12bit. On the basis above, the optimization of the zerosand adaptive modulator structure is designed according to the large dynamic range and the high precision requirement of Sigma-Delta ADC, with the simulation resultsat behavioral level.With the combination of discrete component board level system test, internal keymodule Simulink behavioral level modeling and integrated system circuit design, thetop-down circuit design can be actualized. With the pre-simulation of the circuitdesign of key module and post-simulation of the parasitic parameters of extractionlayout, Sigma-Delta ADC can finally achieve the requirements of12-digit accuracy,simulation verification of integrated system functions and real-time voltageconversion and A/D quantization.