| Summary: | 碩士 === 國立交通大學 === 電機學院電機與控制學程 === 100 === In recent years, vehicle manufacturers produce many electric vehicles (EV) and hybrid electric vehicles (HEV) for environmental protection. Calculating the State of Charge (SOC) is an important technology in battery management system (BMS). Today, the BMS widely uses coulomb-accumulation method to estimate the SOC. In this thesis, a precise linear voltage-to-current (LVC) converter with an adjust output current function is proposed first. Due to high precision converter, a LiFePO4 battery pack is set up to instantly calculate the charge/discharge power for generating a voltage to the BMS to accurately predict the SOC.
The LVC converter consisting of only three MOSFETs is designed to contain the advantages of wide input voltage and output linear current ranges. Simulation results got by HSPICE in 0.25-μm CMOS process demonstrate the error percentage of the LVC converter is smaller than 0.1% , the Total Harmonic Distortion (THD) achives -60dB, and the minimum power consumption is only about 10μW. The proposed LVC converter outputs linear current in various rates by an additional P-type MOSFET. The function of the LVC is similar to a fix resistance that can substitute internal resistors of integrated circuit, which dramatically reduce the demanding area of polysilicon. The output current can be adjusted by two parallel structures that would be more suitable for real demands.
The proposed LVC converter combines a linear voltage-to-resistance circuit, a battery charge/discharge determined circuit, and a timing circuit to form a battery pack real-time charge/discharge power calculation circuit to output a voltage that represent the battery pack real-time charge/discharge power. The determination power value is directed to the microprocessor or DSP in the BMS to calculate the actual accumulation power in the battery pack without sampling, A/D converter, and multiplication operation, which may increase load of the microprocessor or DSP.
The output voltage error from process differences is able to be corrected by an additional precise resistor. In frequent charge/discharge current range, simulation results of battery pack power in 0.25-μm CMOS process show the prediction error in battery pack power value is smaller than 2.5% compared to the correct value.
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