# Research on an Energy Recovery Strategy for Fuel Cell Commercial Vehicles Based on Slope Estimation
## 5 Experimental Simulation and Conclusions
### Braking Energy Recovery
#### 5.4.2 Simulation Verification of C-WTVC Operating Condition  
The C-WTVC operating condition is a driving cycle designed based on the Worldwide Transient Vehicle Cycle (WTVC) for heavy-duty commercial vehicles. It consists of three driving conditions: urban cycle (900 s), highway cycle (468 s), and high-speed cycle (432 s). This driving condition includes numerous acceleration and deceleration segments. The speed statistics of the driving cycle are shown in Table 4, and the speed profile of the driving condition is illustrated in Figure 14.  
Under the C-WTVC condition, when the slope angles are 0\({}^{\circ}\) and 5\({}^{\circ}\), a comparison was made between the case without slope detection and brake force allocation strategy, and the case with slope detection and brake force optimization strategy. Energy recovered from power batteries is shown in Figure 15a,b.  
\begin{table}
\begin{tabular}{c c c c} \hline \hline \multirow{2}{*}{**Vehicle Speed**} & \multicolumn{4}{c}{**Speed Segment Statistics**} \\ \cline{2-4}  & **Urban** & **Highway** & **High-Speed** \\ \hline
0 \(<\) v \(\leq\) 10 & 66 & 14 & 0 \\
10 \(<\) v \(\leq\) 20 & 76 & 16 & 0 \\
0 \(<\) v \(\leq\) 30 & 89 & 21 & 0 \\
0 \(<\) v \(\leq\) 40 & 95 & 34 & 0 \\
0 \(<\) v \(\leq\) 50 & 69 & 55 & 4 \\
0 \(<\) v \(\leq\) 60 & 23 & 4 & 23 \\ v \(>\) 60 & 16 & 68 & 192 \\ \hline \hline \end{tabular}
\end{table}
Table 4: Vehicle speed statistics.  
Figure 14: C-WTVC speed curve.  
In the C-WTVC scenario, due to the presence of multiple deceleration sections, the regenerative braking control strategy is frequently activated. As shown in Figure 15a, the vehicle is driving on a flat road. Initially, the vehicle is in an accelerating state, resulting in the power battery has not been recycled. From 300 s to 1150 s, the power battery recycling capacity is increasing significantly, this is because the vehicle encounters numerous deceleration conditions during operation, leading to the activation of the regenerative braking strategy and entering the energy recovery mode. As depicted in Figure 15b, the vehicle is traveling on a 5\({}^{\circ}\) slope. From 100 s to 350 s, the recycling capacity of power batteries will increase as the vehicle encounters frequent deceleration conditions on the slope. From 1150 s to 1750 s, due to the vehicle operating under high-speed and uphill conditions during this period, during this period, the vehicle frequently brakes, the regenerative braking strategy is activated, and the power battery recovery capacity increases, indicating the effectiveness of the regenerative braking strategy.  
Table 5 presents the different results under various strategies for two different scenarios. Figure 16a represents the improvement rate of energy recovery from power batteries for the CHTC-HT scenario, while Figure 16b represents improvement rate of energy recovery from power batteries results for the C-WTVC scenario.  
\begin{table}
\begin{tabular}{c c c c} \hline
**Duty** & **Program** & **Energy (KJ)** & **Boost Level (\%)** \\ \hline \multirow{2}{*}{CHTC-HT (0\({}^{\circ}\))} & Series braking & 3593 & \multirow{2}{*}{7.24} \\  & Optimize braking & 3853 & \\ \hline \multirow{2}{*}{CHTC-HT (5\({}^{\circ}\))} & Series braking & 7124 & \multirow{2}{*}{4.99} \\  & Optimize braking & 7480 & \\ \hline \multirow{2}{*}{C-WTVC (0\({}^{\circ}\))} & Series braking & 5761 & \multirow{2}{*}{6.42} \\  & Optimize braking & 6131 & \\ \hline \multirow{2}{*}{C-WTVC (5\({}^{\circ}\))} & Series braking & 10,350 & \multirow{2}{*}{1.73} \\  & Optimize braking & 10,530 & \\ \hline \end{tabular}
\end{table}
Table 5: Results.  
Figure 15: Energy recovered from power batteries at the slope angle of 0\({}^{\circ}\) and 5\({}^{\circ}\) under the C-WTVC condition: (**a**) the energy recovered by the power battery at a slope angle of 0\({}^{\circ}\); (**b**) the energy recovered by the power battery at a slope angle of 5\({}^{\circ}\).