## 4 Multi-Objective Optimization and Experimental Verification
### Analysis of Optimized Final Selection Results  
According to the principle of maximum reduction ratio, the design variable under 60% load is selected as the initial value of the second optimization, and NSGA-II is used for the second optimization under 30-90% load. By setting the weight and scale factor, the optimal values of the key parameters under different loads are selected with Equation (13), as shown in Table 6. The optimal values obtained under different load conditions are compared by simulation experiments under different loads to find the key parameter setting values that are suitable for full-load condition optimization. Taking the simulation experiment of the optimal values obtained under 40% load, under 80%, 60%, and 40% working conditions, as an example, as shown in Figure 13, the following conclusions are drawn:  
1. Figure 13a,b show the valve plate and unloader speeds, respectively. The unloader of the control system not only reduced the valve plate withdrawal speed but also suppressed the vibration of the valve plate, thus reducing the fatigue damage and impact damage of the valve plate. 2. The valve plate withdrawal speed decreased with the different optimization parameters. The 60% and 40% loads decreased by almost the same amount and were greater than the 80% load. Similarly, the unloader ejection and withdrawal speeds exhibited the same downward trend. 3. The change in the movement characteristics of the valve plate caused changes in other flow characteristics, which subsequently changed the thermodynamic parameters of the compressor. As the speed decreased, the system moved into an advanced state; Figure 13d shows that the compression and exhaust processes occurred earlier, resulting in increases in both the adjustment displacement error and work deviation. However, owing to the small proportion of lead time, the deviation was small and the values were less than 5%. As Figure 13a,b show, the withdrawal endpoints of the discs and unloaders did not lag under the optimized parameters but instead advanced. This was because, during the withdrawal of the unloaders, they were combined by the spring force of the power source and the hydraulic force of the resistance source owing to two points:  
1. Because the stiffness of the reset spring decreased by a small proportion of the optimization parameters, the reset spring force was basically the same as the initial spring force, indicating that the power source was basically the same. 2. The inlet pressure decreased significantly, resulting in a low initial hydraulic pressure. Additionally, the hydraulic oil outflow speed was slow, owing to the backpressure, which indicated that the initial resistance source was low, and the descent rate was \begin{table}
\begin{tabular}{c c c} \hline \hline
**Design Variable** & **Weight Factor** & **Scale Factor** \\ \hline \(Error\_V\) & 1 & 0.001 \\ \(Error\_W\) & 1 & 0.001 \\ \(v_{min}^{gt}\) & 1 & 0.1 \\ \(v_{min}^{gt}\) & 1 & 0.1 \\ \hline \multicolumn{3}{c}{**Second optimization result**} \\ \hline
**Load** & \(K_{min}\)**(N/m)** & \(p_{in}\)**(bar)** & \(p_{bf}\)**(bar)** \\ \hline
90\% & 77,002 & 60 & 11 \\
80\% & 74,680 & 60 & 11 \\
70\% & 74,988 & 61 & 10 \\
60\% & 74,941 & 62 & 12 \\
50\% & 74,631 & 62 & 11 \\
40\% & 74,715 & 62 & 12 \\
30\% & 74,633 & 62 & 12 \\ \hline \hline \end{tabular}
\end{table} 
Table 6: Second optimization results. slow. Together, the initial acceleration of the unloader withdrawal under the optimized parameters was large and well-advanced. However, the maximum acceleration was less than the initial parameter acceleration (Figure 13c), which also resulted in a more substantial and earlier start of the unloader withdrawal speed. However, the final speed was less than the initial parameter, and the disc withdrawal was controlled by the unloader for the same reason.