## 4 Current Research Status of Energy Management Techniques
### Real-Time Optimal Control Strategy
\begin{table}
\begin{tabular}{c c c c c} \hline \hline
**No.** & **Powertrain Structure** & **Control Strategy** & **Major Findings** & **Ref.** \\ \hline
1 & Power-split hydraulic hybrid vehicle & Deterministic rule-based strategy & Improve the fuel economy by over 24\%. & [118] \\ \hline
2 & Series hydraulic hybrid vehicle & Rule-based tunable energy management & Has a fuel saving of up to 18.9\% in the short loading cycle. & [120] \\ \hline
3 & Parallel hydraulic hybrid vehicle & Control strategy based on fuzzy logic & Yield an energy saving of 15.5\% and 22.5\% for fixed and variable displacement of the hydraulic elements, respectively. & [121] \\ \hline
4 & Parallel hydraulic electric & Global optimization based on the & Improve the economic performance and energy consumption after genetic algorithm & [125] \\  & hybrid vehicle & genetic algorithm & optimization by 36.51\% and 43.65\%, respectively. & \\ \hline
5 & Series hydraulic hybrid vehicle & Hierarchical model predictive control & Improve by 7.3\% and 5.9\% in simulation and experiment, respectively. & [129] \\ \hline
6 & Series-parallel hydraulic & \multirow{2}{*}{Real-time global optimization strategy} & \multirow{2}{*}{Have an energy saving of 32.14\% more than original vehicle.} & [130] \\  & electric vehicle & & & \\ \hline
7 & Parallel hydraulic electric & Novel intelligent controller & Make the optimal energy consumption of & \\  & hybrid vehicle & Novel intelligent controller & 3732 kJ, while the SF is 3835 kJ and the & [89] \\  & & OFLC strategy is 3800 kJ. & \\ \hline
8 & Parallel hydraulic electric hybrid & Intelligent robust hierarchical hybrid & Optimize the lowest energy consumption of & \\  & controller strategy & 43,223 kJ, while the HCSF is 5180 kJ and the & [40] \\  & & FBS strategy is 47,115 kJ. & \\ \hline
9 & Parallel hydraulic electric hybrid & Fuzzy logic and optimal control & Achieve energy saving of about 8.7\% (UDC) and 7.6\% (FP-75). & [90] \\ \hline
10 & Series–parallel hybrid & \multirow{2}{*}{Taguchi method optimization} & Reduce motor and hydraulic torque. Improve & [132] \\  & electric vehicle & & the battery SOC. & \\ \hline
11 & Series–parallel hybrid & \multirow{2}{*}{Fuzzy logic method} & Acquire a 9.57\% reduction in the ratio of & [133] \\  & electric vehicle & & driveline cost to driving range. & [133] \\ \hline
12 & Series–parallel hybrid vehicle & Optimum fuzzy logic controller & \multirow{2}{*}{Reduce by 13.07\% \(IC\) and by 10.58\% C with 35.67\% fuel savings.} & [134] \\  & & & & \\ \hline
13 & Series–parallel hybrid & \multirow{2}{*}{Rule-based and thinking fuzzy logic} & Decrease the energy & \\  & electric vehicle & optimization strategy & consumption rate by 24.42\%. & [135] \\ \hline
14 & Series–parallel hybrid vehicle & Dynamic programming strategy & Save fuel by 11.84\% and 5.96\% compared to that & \\  & with improved rules & & of traditional contemporary with single and & [136] \\  & & compound accumulators, respectively. & \\ \hline
15 & Series–parallel hybrid & \multirow{2}{*}{Rule-based dynamic strategy} & Reduce the battery power consumption to 85.3\%. & \\  & electric vehicle & & Boost the energy recuperation rate of the & [137] \\ \hline
16 & Series–parallel hybrid & \multirow{2}{*}{Entropy-based torque strategy} & Integrate entropy and \(Z\)-score with & [138] \\  & electric vehicle & & torque control firstly. & \\ \hline \hline \end{tabular}
\end{table} 
Table 7: Summary of control approaches used for mechanical–electric-hydraulic hybrid energy storage systems in typical vehicles. Thirdly, more advanced control methods require more advanced hardware support, which therefore tends to increase costs. So, it is not the case that more advanced control methods mean that the control is more effective. Last but not least, the suitability of an energy management method is judged by the application scenario of the control object. There is no best method, but only the most suitable energy management method, which is the best overall.