應用於電動車電池管理系統計算電池即時功率之線性電壓-電流轉換電路設計

Abstract

因應環境保護需求，近年來車廠製造各式電動車與混合動力車；計算電池剩餘電量(Stage Of Charge, SOC)，是其電池管理系統(Battery Management system, BMS)之重要技術。目前電動車/混合動力車的電池管理系統，多是以庫侖電量累積法來估算SOC；本論文先設計一結構簡單且可調整輸出電流量之高線性電壓-電流轉換電路，再以此電路設計一鋰鐵電池組即時充放電功率計算電路，其輸出之電壓可供電池管理系統作電池SOC估算。 所設計之線性電壓-電流轉換電路，只由3個MOSFET組成，具有輸入電壓範圍大、輸出電流線性區寬廣與可調整範圍大等優點，使用HSPICE以0.25um CMOS製程進行模擬，輸出電流之線性度誤差在0.1%以內，THD約為-60dB，電路消耗功率最小僅約為10uW；電路以外加PMOS來輸出線性電流，以達成各電流量等級，電路特性近似一固定電阻值，若用於取代積體電路內建電阻，可大幅降低多晶矽需求面積；而將2組電路並聯輸出，即可對輸出之線性電流量進行迴授控制，使此高線性度電壓-電流轉換電路更符合實際應用之需求。將本論文所提出之線性電壓-電流轉換電路，結合線性電壓-電阻轉換電路後，再設計一電池充放電判斷電路與時序電路，以對電容充放電方式，組成高電壓電池組充放電即時功率值計算電路，微處理器或DSP可直接使用此電壓值，進行電池組充放總功率積分計算電池SOC，不必再經過多次的取樣、A/D轉換與乘法運算，此將可減輕微處理器或DSP之負擔。電路中之外接調整式精密電阻，能修正因製程差異造成之輸出電壓誤差；使用0.25um CMOS製程進行電池組即時充放電功率值輸出模擬，在電池組最常充放電流範圍下，代表功率之電壓值與正確值差異在2.5%以內。

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.