## 5 Simulation Research
### Speed Segmented Variable Constant Power Control Simulation  
Under the constant power condition, the pump is at a constant speed, and the pump outlet flow changes with the pump outlet pressure. Therefore, the variable constant power control function of the hydraulic pump is realized by making the electric motor at a certain speed level through the speed segmented control strategy. To verify the reliability of the speed segmented variable constant power control system, the electric motor speed stages of 1000 and 2000 rpm are simulated, respectively. The working condition switching is set from medium load to heavy load mode. Set the starting pressure of the medium load constant power valve to 5.1 MPa and that of the heavy load constant power valve to 9.9 MPa. The  
Figure 12: Pump displacement, electric motor speed, and system flow curve. (a) Curve of pump displacement; (b) curve of electric motor speed; (c) curve of system flow. purpose of this experiment is mainly to verify the function of variable constant power, so the test can be carried out with the movement of a single actuator. The maximum flow of the actuator is 160 L/min. The proportional overflow valve is used to load the oil circuit. The simulation results of test 1 and test 2 are given in Figures 13 and 14, which are the main parameter curves of variable constant power control in the 1000 rpm speed stage and variable power control in the 2000 rpm speed stage, respectively. As can be seen, the speed segmented control strategy can realize the variable constant power operation in a certain speed range. The time when the two groups of simulation test electric motors reach the fixed speed range is the same. Moreover, the load application is the same. The simulation of variable constant power control under the condition of speed classification is analyzed. During 0-2 s, the ratio of target flow to the maximum flow of the pilot handle is kept at 0. The pump displacement is the minimum, and the electric motor is kept at an idle speed of 500 rpm. The system is in the minimum flow overflow stage. During 2-4 s, the ratio of target flow to the maximum flow of the pilot handle increases from 0 to 0.25. The pump displacement increases to 80 mL/r, the motor operates at 500 rpm, the system is in the variable displacement flow control stage, the hydraulic oil flows into the actuator, and the pump outlet pressure decreases. During 4-6 s, the ratio of target flow to the maximum flow of test I (1000 rpm) and test II (2000 rpm) handle increases from 0.25 to 0.5 and 1, respectively. The pump displacement remains at the maximum value of 80 mL/r. The system is in the variable speed flow control stage. Through the speed segmented control strategy, the system increases to 1000 and 2000 rpm, respectively. The system flow increases to 80 L/min and 160 L/min, respectively. Figure 14: Simulation curve of variable constant power control of electric motor at 2000 rpm. (**a**) Curve of handle signal and load; (**b**) curve of pump displacement and electric motor speed; (**c**) curve of outlet flow and pressure of the pump and current of electro proportional reducing valve. Figure 13: Simulation curve of variable constant power control of electric motor at 1000 rpm. (**a**) Curve of handle signal and load; (**b**) curve of pump displacement and electric motor speed; (**c**) curve of outlet flow and pressure of the pump and current of electro proportional reducing valve. During 6-9 s, the ratio of target flow to the maximum flow of the handle remains unchanged. Test 1 and test 2 maintain electric motor speed and system flow unchanged; the load gradually increases from 8 s, and the pump outlet pressure also increases. At this time, by monitoring the pump outlet pressure, it is recognized that the working condition is under medium load condition, and the control current of the electric proportional reducing valve is 405 mA. When the outlet pressure of the pump exceeds the constant load at 15 s, the outlet pressure of the pump increases, and the displacement of the pump decreases.