# Research on Constant Power Control Strategy of Pure Electric Excavator
## 6 Experimental Research  
Further experimental research on the proposed control strategy was carried out. The test platform is shown in Figure 10. The temperature of the EM and its driver was collected by a positive temperature coefficient (PTC) thermistor interface. The operation state of the power battery, including the maximum allowable discharge power, was collected by a CAN communication network through EM, EM inverter, and BMS. The relief valve was used for load simulation. The state information of each component was transmitted to the controller of the whole machine. After calculation, the proportional coefficient \(k\) between the system pressure difference and the pilot pressure was obtained. Finally, combined with the pressure drop control, the piecewise constant power control was realized when the current required power of the hydraulic pump exceeded its maximum allowable output power. Figure 9: Simulation results. During the test, the ambient temperature was 23 C. Because of the short test time, the battery temperature was unchanged. Firstly, the SOC of power battery was discharged to 10%, 30%, and 80%, respectively. The load was simulated by the proportional relief valve. In order to study the change of the system pressure drop conveniently, the pilot pressure was set as fixed. Combined with Equation (3), the output of the power train system for different SOC are shown in Figures 11-13. The pressure-flow curves and output power curves of the hydraulic pump were obtained when the residual battery power is 10%, 30%, and 80%, respectively. From the test results, it can be seen that when the discharge power of the power battery does not reach the maximum power at different stages of power supply, the output power increases with the increase of the load pressure, because the pressure drop and flow rate remain unchanged. When the discharge power of the battery reaches the maximum allowable discharge power, namely, the output power of the hydraulic pump reaches the maximum allowable output power, the output power of the hydraulic pump no longer increases and remains constant. With the increase of the maximum load pressure, the flow rate of the hydraulic pump decreases and the pressure difference of the system decreases, and the output power of the hydraulic pump can be stabilized near the maximum allowable output power, so that the discharge power of the battery does not exceed the maximum allowable output power. From the test results in Figure 12b, it can be seen that when SOC of the battery pack is more than 30% at room temperature, the latter half of the EM works in overload mode. Because the cooling effect of the water cooling system of the EM and its driver is superior, the temperature of the EM and its driver can hardly exceed the allowable working range, so the maximum power at this time is still the maximum power of the battery. The feasibility of piecewise constant power control can be further verified by the above experiments. Compared with the constant power control of a single operation point, that is, the rated power of the li-ion battery is taken as the constant power, the piecewise constant power control strategy proposed in this paper can effectively ensure that the li-ion battery can avoid over discharge and  
Figure 13: Test curve at 30% SOC. improve the service life of the power battery. In addition, it can also avoid that when the li-ion battery has a low SOC value, due to the insufficient power of battery can be provided for EM, the EM is stalled. The single working point constant power control of s traditional electric excavator uses s lead-acid battery for power supply, without corresponding BMS. In this study, the power battery is a lithium-ion battery, which is equipped with a corresponding BMS unit. In the process of the constant power control experiment with a single operating point, when the battery SOC is low, the overload operation will cause the BMS to alarm continuously and then shut down.