## 4 Speed Segmented Variable Constant Power Control Strategy
### Electric Motor Speed Segmented Control Strategy  
The maximum flow coefficient of each actuator is calculated by multiplying the total pressure of each handle by the maximum demand flow coefficient of each actuator. Suppose the total flow of each actuator in real time is the system target flow \(Q_{\text{T}}\).  
When the target flow of the hydraulic system \(Q_{\text{T}}\) is equal to zero, it is in the minimum displacement in the idle stage. The idle speed of the electric motor is set as \(n_{\text{min}}\). When the handle starts to act, the target demand flow will increase. Meanwhile, the target speed of electric motor \(n_{\text{T}}\) can be calculated as Equation (22). Moreover, due to the limitation of the allowable speed of hydraulic pump, the upper speed of the electric motor is limited to \(n_{\text{max}}\). When the hydraulic system does not enter the constant power condition, the constant power valve and the pressure cut-off valve do not work. The pump outlet pressure is always higher than the maximum load by a load sensing differential pressure \(P_{\text{LS}}\) through the action of LS valve, and the pump operates at the maximum displacement \(V_{\text{max}}\).  
\[n_{\text{T}}=\frac{Q_{\text{T}}}{V_{\text{max}}} \tag{22}\]  
where \(n_{\text{T}}\) is the target speed of electric motor in real time. \(Q_{\text{T}}\) is the target flow of system in real time. \(V_{\text{max}}\) is the maximum displacement of pump.  
When the motor is within the allowable speed range, the actual electric motor speed \(n\) is determined according to the electric motor target speed \(n_{\text{T}}\). To satisfy the needs of different operations, the electric motor speed is classified into four grades according to the different actuators operation requirements. The first grade is idle stage. \(n_{\text{T}}\) is equal to \(n_{\text{min}}\), the actual electric motor speed \(n\) is equal to \(n_{\text{min}}\) as well. The second stage is fine  
Figure 5: Schematic diagram of speed segmented variable constant power control.  
motion of different actuator, the \(n_{\rm T}\) is distributed between \(n_{\rm min}\) and \(n_{1}\), where \(n_{1}\) is the upper limitation of electric motor speed in the fine motion. To improve the action response, combined with the displacement adaptive control of the hydraulic pump, the actual electric motor speed \(n\) is equal to \(n_{1}\). The third stage is normal motion of different actuator, the \(n_{\rm T}\) is distributed in \(n_{1}\) and \(n_{2}\), where \(n_{2}\) is the upper limitation of electric motor speed in the normal motion. To improve the action response, combined with the displacement adaptive control of the hydraulic pump, the actual electric motor speed \(n\) is equal to \(n_{2}\). The fourth stage is fast motion of different actuator, the \(n_{\rm T}\) is distributed between \(n_{2}\) and \(n_{\rm max}\). To improve the action response, combined with the displacement adaptive control of the hydraulic pump, the actual electric motor speed \(n\) is equal to \(n_{\rm max}\). Therefore, the actual electric motor speed \(n\) can be expressed as  
\[n=\left\{\begin{array}{l}n_{\rm min},n_{\rm T}=n_{\rm min}\\ n_{1},n_{\rm min}<n_{\rm T}\leq n_{1}\\ n_{2},n_{1}<n_{\rm T}\leq n_{2}\\ n_{\rm max},n_{2}<n_{\rm T}\leq n_{\rm max}\end{array}\right. \tag{23}\]  
where \(n\) is the actual electric motor speed. \(n_{\rm min}\) is the speed of the electric motor in the idle stage. \(n_{\rm T}\) is the target speed of the electric motor. \(n_{1}\) is the upper limitation of electric motor speed in fine motion. \(n_{2}\) is the upper limitation of electric motor speed in normal motion. \(n_{\rm max}\) is the maximum allowable speed of the hydraulic pump.