## 5 Experimental Study
### Positive Flow System Test  
To verify the performance of the designed controller, the variable speed, constant speed, loading and unloading tests are carried out during the cylinder extension and retraction process, shown in Figure 29. The AB and JL are the static stages of the cylinder, the pump outlet pressure is about 0 MPa, and the cylinder displacement is about 0 mm. At the time of B, the directional control valve is switched to the left position, the cylinder begins to extend without load. The target speed of the BC section is 700 r/min, and the pump outlet pressure is about 0.5 MPa. At the time of C, the electric motor speed changes to 1280 r/min. At this time, the pump outlet flow becomes larger, and the operating speed of the cylinder becomes larger too. The slope of the displacement curve corresponding to the CD segment becomes larger than that of the BC segment. At the time of D, the electric motor speed changes to 1000 r/min. At the time of E, the cylinder moves to the maximum stroke, until the directional control valve is switched to the right position at time G when the cylinder starts to retract. The EF section indicates that the cylinder is at the maximum stroke, the pump outlet hydraulic oil overflows through the main relief valve to the oil tank, and the pump outlet pressure is the relief valve which pressure is 2.7 MPa. The FG section is the directional control valve working in the neutral position. Pump outlet oil  
Figure 28: Comparison curve of \(I_{d}\) change under constant speed loading.  
Figure 27: Comparison curve of \(I_{d}\) change under constant speed loading.  
directly flows back to the oil tank through the check valve, and the pressure is close to 0 MPa. At the time of H, the relief valve on the side of the rodless cavity is adopted to load, the pump outlet pressure changes from 1.4 MPa to 2.4 MPa. At the time of I, the relief valve is unloaded, the cylinder is retracted without load, and the pump outlet pressure returns to 1.4 MPa. At the time of J, the cylinder is retracted to the minimum stroke, the pump outlet oil overflows from the main relief valve back to the tank. At this time the pump outlet pressure is the relief valve pressure which is 2.7 MPa.  
Seen from Figure 29, when the motor speed changes, the slope of the cylinder displacement curve changes accordingly, and the responsiveness and following performance are superior. When the electric motor speed is constant, the displacement curve is stable, and the slope is consistent. The cylinder runs smoothly with no pressure shock.  
A partial enlarged curve diagram of the loading and unloading process is provided in Figure 30. When the load fluctuates, the electric motor speed fluctuates to a certain extent. When loading and unloading, the load power is about 50% of the motor power, and the electric motor speed fluctuates within 1% of the target value. At the time of F and K when the pressure changes, the load power is about 70% of the motor power, and the electric motor speed fluctuates within 3.5% of the target value. When the load is stable, the electric motor speed is relatively stable, and the steady-state error is about 0.3%.  
According to test results of the positive flow system, when the vector control system based on fuzzy PI is used, not only the motor has good responsiveness, stable rotation speed, and good load disturbance resistance, but also the pressure shock caused by the hydraulic system can be reduced. When the load fluctuates severely, the electric motor speed  
Figure 30: The partial amplification curve of positive flow system test.  
Figure 29: The test curve of positive flow system.  
fluctuation is small, the stability is fine, and the system has better maneuverability. The test results show that the vector control system based on fuzzy PI has better responsiveness, stability, and anti-load disturbance ability. It can better apply to electric CM under severe load fluctuations.