Comparison of energy-saving effects of hybrid excavators
The energy-saving effect of a hybrid excavator is one of the key indicators to measure its performance. The prototype system, series system and parallel system all use the heavy-duty excavation load spectrum as the load input. The fuel consumption simulation results are shown in Figure 11. From the figure, it can be seen that during the running time, the common system fuel consumption is 540g, the series system fuel consumption is 362g, parallel The fuel consumption of the system is 330g, which is 36.1% and 40.7% higher than that of the ordinary system. However, it should be noted that the fuel consumption model in the simulation model of the series and parallel hybrid excavators does not include the equivalent engine fuel consumption due to the change of the battery SOC. From the SOC fluctuation curve of the series and parallel system in Figure 14, the fuel consumption statistics can be obtained for 300s time The SOC of the battery pack of the internal series system has changed from 0.6 to 0.65, while the SOC of the battery pack of the parallel system has changed from 0.6 to 0.64. The calculation method of the equivalent fuel consumption is as shown in formula (5):
In the formula, malsoe is the equivalent fuel consumption; ASOC is the battery SOC conversion amount; Qaur is the battery pack capacity, the series system is 2.52kwh, the parallel system is 1.96kwh: 7a is the fuel consumption rate, which can be combined with the engine operating point distribution of Figure 13 and Figure 50,000 The characteristic curve is obtained, the series system takes 230g / kwh, and the parallel system takes 240g / kwh. Finally, consider the comprehensive fuel consumption of battery soc fluctuations as shown in Table 3.
Figure 12 is a characteristic curve diagram of the hydraulic pump. Before the hydraulic pump enters the regulation pressure P1, the power absorbed by the hydraulic pump changes with the speed fluctuation, and the load fluctuation directly affects the engine speed and power output. The ordinary power system engine directly drives the load hydraulic pump (constant power variable pump), so the engine operating point fluctuates frequently, the fuel efficiency map rate is very low, and the fuel consumption curve shows a curve with a large slope fluctuation. In the series system, because there is no direct mechanical hard connection between the power source and the load, the fluctuation of the load cannot directly affect the working point of the engine, so the working point can be relatively easily controlled on the economic fuel consumption curve. The final system has low fuel consumption, stable operation, and low consumption. The oil curve appears as a straight line with a substantially stable slope. There is no fuel consumption at the beginning of this linear simulation because the load is low and the SOC of the battery is high, so it is driven by the motor alone.
Parallel system, the energy-saving effect is between the above two situations, the peak-shaving and valley-filling effect of the auxiliary power source makes the engine operating point fluctuate, but it is always around the economic fuel consumption point. In addition, the reason why the hybrid power system can improve the fuel efficiency of the excavator can also be verified from the improvement of the engine operating point. Figure 13 is the fluctuation of the engine operating point of the three-power system collected by the test bench. Significant improvement. The fuel consumption curve reflects that the series system consumes more fuel than the parallel system, because all the energy in the series system has undergone the energy conversion link of the generator and the battery, and the increased energy conversion link reduces the overall fuel efficiency.
