# Temperature Regulation of Hot Vapor Preservation Treatment of Litch Based on PSO-Fuzzy PID
## 5 System Testing and Discussion
### Equipment Load Test  
The PID control method did not perform well in the simulation test. To balance test efficiency and cost, this paper only compared the Fuzzy PID control method before and after PSO optimization in the load test to validate the effectiveness of PSO. The load test was carried out on 16 July 2022, using a total of 160 kg of litchi. Before the test, the measured fruit temperature was 11-15 \({}^{\circ}\)C and the room temperature was 30-31 \({}^{\circ}\)C. To compare the temperature control effects at different treatment temperatures and different treatment times, the treatment temperatures of 80 \({}^{\circ}\)C and 85 \({}^{\circ}\)C were treated for 20 s and 30 s, respectively. The control methods before and after optimization were compared under each treatment parameter combination, namely Fuzzy PID and PSO-Fuzzy PID. The litchi was divided into eight groups of 20 kg each, labeled 1-8, corresponding to the different treatment parameters as shown in Table 5. During the test, the litchi was evenly placed on the inlet end of the conveyor chain of the equipment prototype, as shown in Figure 12. \begin{table}
\begin{tabular}{c c c c} \hline
**Control Method** & **Overshoot/\%** & **Rise Time/s** & **IAT/s** \\ \hline PID & 6.2 & 56 & 150 \\ Fuzzy PID & 0.7 & 104 & 116 \\ PSO-Fuzzy PID & 0.4 & 76 & 81 \\ \hline \end{tabular}
\end{table} 
Table 4: Control performance comparison. Figure 11: Step response curve. \begin{table}
\begin{tabular}{c c c c} \hline
**Test Groups** & **Processing Temperature/\({}^{\circ}\)C** & **Processing Time/s** & **Control Method** \\ \hline a & 85 & 20 & Fuzzy PID \\ b & 85 & 20 & PSO-Fuzzy PID \\ c & 85 & 30 & Fuzzy PID \\ d & 85 & 30 & PSO-Fuzzy PID \\ e & 80 & 20 & Fuzzy PID \\ f & 80 & 20 & PSO-Fuzzy PID \\ g & 80 & 30 & Fuzzy PID \\ h & 80 & 30 & PSO-Fuzzy PID \\ \hline \end{tabular}
\end{table} 
Table 5: Grouping of litchi load test. The paperless recorder was utilized to record temperature data, following the same method as measuring the heating curve. This test aims to compare the effectiveness of different control methods at the same treatment temperature and time. To avoid inconsistency caused by multiple tests, such as varying temperatures of lychee fruit and room temperature, a one-button switching control method was designed on the touch screen, which also enhanced test efficiency. Figure 13 shows the curve obtained from the test, with the temperature curves of 18 measurement points represented by dashed lines and the real-time processing temperature indicated by a solid black line. The maximum temperature difference (MTD) and interference adjustment time (IAT) of each group are analyzed and presented in Table 6 as evaluation indicators of the temperature control system. Smaller values indicate better control performance. The processing time, processing temperature, and control method are the three experimental factors of this test. The MTD and IAT of each factor are averaged and presented in Table 7, allowing for easy comparison of the influence of different experimental factors on the curve. Note: The test group that used a certain treatment parameter or control method is indicated by corresponding serial number inside the parentheses, for example, test groups (a), (b), (c), and (d) at a treatment temperature of 85 \({}^{\circ}\)C, indicated by 85 \({}^{\circ}\)C (a/b/c/d). By analyzing the test curve presented in Figure 13 alongside the data provided in Tables 6 and 7, the following results can be obtained:  
1. The temperature curve of the treatment time of 20 s is more stable than that of 30 s (a/b/e/f compared with c/d/g/h, respectively). From the data, the maximum temperature difference of the former is 1.665 \({}^{\circ}\)C on average, and the interference adjustment time is 48.5 s on average, which is smaller than the latter. This is because with the increase in treatment time, lithci absorbs more heat in the treatment chamber, resulting in a more obvious decrease in vapor temperature and a larger fluctuation range. 2.