## 4 Simulation and Experiment of Suspension System
### PEMS Platform Suspension Experiment  
In order to verify the stability control effect of the Fuzzy-LADRC controller on the PEMS system, experiments were carried out on the PEMS platform, shown in Figure 10.  
Figure 9: Response curves of three control methods under the influence of noise. Due to certain simplification made to the system during modeling, there will be some differences between the simulation and the real model, resulting in the controller parameters of the simulation and experiment that are not completely consistent. It is necessary to adjust and optimize the real system control parameters considering the simulation parameters. See Table 4 for the experimental parameters of each suspension unit controller. The following experimental scheme is designed: (1) Levitation experiment: in the initial state, the distance between each control unit and the guide rail is the permanent magnetic levitation distance. After the platform is powered on, the given levitation air gap is 18 mm, and the variation of the levitation air gap of each unit is recorded; (2) Immunity experiment: when the PEMS platform is stably suspended at a given air gap, the step interference of 5 V control amount is added and decreased to the system, and the change in the suspended air gap of each unit is recorded; (3) Robustness experiment: when the PEMS platform is stably suspended at a given air gap, an object weighing 2 kg will fall freely from 0.5 m above the external interference experiment point of the platform, and the weight will be removed after 4 s, and the change of the suspended air gap of each unit will be recorded; (4) Adaptability experiment: when the PEMS platform is stably suspended at a given air gap, make the platform move back and forth and record the change of the suspended air gap of each unit. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Controller** & **Parameter** & **Control Unit 1** & **Control Unit 2** & **Control Unit 3** & **Control Unit 4** \\ \hline \multirow{3}{*}{PID} & \(K_{\text{P}}\) & 50,000 & 45,000 & 47,000 & 52,000 \\  & \(K_{\text{i}}\) & 200,000 & 160,000 & 185,000 & 220,000 \\  & \(K_{\text{d}  
1. Suspension experiment  
In the initial state, the suspension air gap of each suspension unit is shown in Figure 11a. After the system is powered on, the given levitation air gap is 18 mm. Under three control methods, the according air gap changes of each levitation control unit are shown in Figure 11b-d. It can be seen from Figure 11 that in the initial state, the distance between each suspension knowable unit and the guide rail is 17.53 mm, 17.68 mm, 17.35 mm and 17.38 mm respectively; after the suspension air gap is given, each suspension control unit starts to adjust under the control of different controllers. Under the control of PID, the air gap of suspension units 1-4 can be stabilized at about 18 mm after suspension, with a steady-state error of 0.062 mm. Under LADRC, because LSEF adopts a principle similar to PD control, the controlled object cannot be simplified into an integral series system, so there is a certain error between the air gap of each suspension unit and the reference air gap, resulting in a certain tilt of the platform during suspension. Under the effect of Fuzzy-LADRC with an integrator, the levitation air gap of each levitation unit is 18 mm and the steady-state error is 0.051 mm; the steady-state accuracy of LADRC is improved, which is about 17.74% lower than PID control. 1. Anti-interference experiment  
Given that the suspension air gap of PEMS platform is 18 mm, on the basis of the stable suspension of the platform, when t = 4 s, a step interference of 5 V is suddenly added to the  
Figure 11: Platform suspension experiment results with given air gap. (**a**) Air gap of each suspension unit in initial state; (**b**) Air gap of each suspension unit under PID control; (**c**) Air gap of each suspension unit under LADRC control; (**d**) Air gap of each suspension unit under Fuzzy-LADRC control. system and when t = 6 s, the interference is removed.