# Research on Constant Power Control Strategy of Pure Electric Excavator
## 5 Simulation Research  
To verify the feasibility of the control method, simulation research was carried out. Based on the variable speed control of EM and the load sensing hydraulic system, a constant power simulation model of variable pressure differential control was established by using AMESim simulation software platform, as shown in Figure 8. In this system, the hydraulic oil circuit is composed of a main oil circuit and pilot circuit. The main oil circuit drives the quantitative pump to supply oil through variable speed control of EM. On this basis, a load sensing system was constructed. The load simulation was carried out by the relief valve, which connects with the outlet of the control valve. The pilot oil circuit is controlled by the movement of the spool.  
The parameters of the components in the simulation model are given in Table 4.  
The simulation model verifies that when the required power of the hydraulic pump is greater than its maximum allowable output power, the system pressure will be reduced, so as to make the pressure drop of the throttle valve change according to the outlet pressure of multi-way valves, the pilot pressure, and the maximum allowable output power of the hydraulic pump, which control the current output power of the hydraulic pump equal to its maximum allowable output power.  
In the simulation model, the maximum allowable output power of the hydraulic pump is 20 kW and the simulation time is 20 s. The simulation curve of constant power control is given in Figure 9. The maximum load sensing pressure (LS pressure) and pilot pressure are set artificially. In the first  
\begin{table}
\begin{tabular}{c c} \hline \hline
**Components** & **Value** \\ \hline Battery & Quantity of electricity: 117 kW-h. Capacity: 202 Ah \\ EM & Rated power: 49 kW. Rated torque: 260 N-m \\ EM driver & Voltage: 420-750 V. Maximum power: 63 kW \\ Hydraulic pump & Displacement: 100 mL/r. Pressure: 35 MPa \\ Controller & TTC60 \\ Valve & Load sensing multi-way valve \\ Pilot pump & Displacement:10 mL/r. Pressure: 35 MPa \\ Pilot EM & Rated power: 2.5 kW \\ Auxiliary driver & Rated power: 5.5 kW. Output voltage: 380 V/24 V \\ \hline \hline \end{tabular}
\end{table}
Table 4: Parameters of components in the system.  
Figure 8: AMESim simulation model of constant power control.  
10 s, when the required power of the hydraulic pump does not reach the maximum allowable output power, the hydraulic pump outputs the power according to the load required power and maintains the pressure drop between the maximum load pressure and pump outlet pressure as the initial control target value. At this time, the pilot pressure and the ratio coefficient \(k\) are not limited by the maximum system power. In this paper, the initial set value of the \(k\) is 2:  
\[\Delta p=kp_{i},k=2. \tag{21}\]  
While, after 10 s of simulation, the current required power of the hydraulic pump reaches the maximum allowable output power. At this time, with the increase of the pump outlet pressure, the outlet flow of the hydraulic pump decreases, and the output power of the hydraulic pump equals the maximum allowable output power.  
When the constant power point is reached, the pressure drop between the pump outlet pressure and the maximum load pressure, the pilot pressure, and the relationship between the ratio coefficient \(k\) no longer conform to Equation (20). The pilot pressure, the maximum load pressure, and the maximum allowable output power of the hydraulic pump are taken as the input values. The ratio coefficient is modified to change the differential drop of the system, so that the output power of the hydraulic pump is equal to the maximum allowable output power, which will not exceed the maximum allowable working range.