## 3 Results and Discussion
### Comparison of Estimated Battery Charge  
Table 4 summarizes changes in charge level due to the SOC signal from the OBD of the vehicle and current measured directly from the battery for hybrid to the PicoScope. Error value, the difference between the previous two values, is shown, and charge amount is also calculated for the SOC 65% condition in the same method.  
From error results shown in Tables 4 and 5, current error measured in the PicoScope is larger than SOC fluctuation obtained through the OBD.  
As a result of performing the experiment three times, error occurs in the result obtained with OBD and the PicoScope. After displaying measured charge in the repeated experiment according to each SOC condition, the difference between the OBD and the PicoScope was indicated. Although there  
\begin{table}
\begin{tabular}{c c} \hline \hline \multicolumn{2}{c}{**Parameter Specification**} \\ \hline Driving cycle & IM 240 Driving mode \\ Ambient temp. & \(24\pm 3\) (\({}^{\circ}\)C) \\ Fan speed & Fan speed \\ Eco-mode & On \\ Test procedure & Confirm RBS \(\rightarrow\) Vehicle running state (speed, SOC) in IM240 \\  & \(\rightarrow\) GDS data processing \(\rightarrow\) Analysis and comparison \\ \hline \hline \end{tabular}
\end{table}
Table 3: Experimental Conditions.  
is no consistent error in the specific measurement method, the difference according to the SOC reveals a larger error in the state of low charge (SOC 35%).  
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**SOC 35\%** & \multicolumn{3}{c}{**1 st Test**} & \multicolumn{3}{c}{**2 nd Test**} & \multicolumn{3}{c}{**3 rd Test**} \\ \hline  & **SOC (OBD)** & **SOC (PicoScope)** & **SOC (OBD)** & **SOC (PicoScope)** & **SOC (OBD)** & **SOC (PicoScope)** \\ \hline Section A & 1.62 & 2.00 & 1.46 & 1.00 & 1.80 & 2.00 \\ Section B & 3.29 & 3.24 & 3.49 & 4.00 & 3.26 & 3.97 \\ \hline
**Error** & \multicolumn{3}{c}{**1 st test**} & \multicolumn{3}{c}{**2 nd test**} & \multicolumn{3}{c}{**3 rd test**} \\ \hline Section A & 0.38 & \multicolumn{3}{c}{0.46} & \multicolumn{3}{c}{0.20} \\ Section B & 0.05 & \multicolumn{3}{c}{0.50} & \multicolumn{3}{c}{0.71} \\ \hline \hline \end{tabular}
\end{table}
Table 4: Comparing Electric Charging Variation between SOC and PicoScope at SOC 35%.  
Figure 5: Charge–discharge current and regenerative braking characteristics.  
Figure 6 shows the error of each condition by linear fit, and absolute value of the slope was analyzed. Each case represents a total of three experiments with the hybrid vehicle under the same conditions. The slope of error between zone A and zone B is approximately 3.67 times under SOC 35% condition and 2.75 times under 65% condition. SOC error increased because charging is performed more frequently in low-SOC condition. The amount of recovered electric energy in the high-speed Section B is large, influencing increase of the charge amount error. So, algorithms and applications for SOC estimation with higher accuracy are needed.  
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**SOC 65\%** & \multirow{2}{*}{**1 st Test**} & \multirow{2}{*}{**2 nd Test**} & \multirow{2}{*}{**3 rd Test**} \\
**Condition** & & & & & & \\ \hline  & **SOC (OBD)** & **SOC (PicoScope)** & **SOC (OBD)** & **SOC (PicoScope)** & **SOC (OBD)** & **SOC (PicoScope)** \\ \hline Section A & 0.65 & 0.00 & 0.84 & 1.00 & 0.81 & 0.00 \\ Section B & 2.28 & 2.00 & 1.65 & 2.00 & 2.61 & 1.89 \\ \hline
**Error** & \multirow{2}{*}{**1 st test**} & \multirow{2}{*}{**2 nd test**} & \multirow{2}{*}{**3 rd test**} \\
**(SOC 65\%)** & & & & & & \\ \hline Section A & 0.65 & & 0.16 & & 0.81 \\ Section B & 0.28 & & 0.35 & & 0.72 \\ \hline \hline \end{tabular}
\end{table}
Table 5: Comparing Electric Charging Variation between SOC and PicoScope at SOC 65%.  
Figure 6: Linear fitting of error values between OBD data and PicoScope data.