Design and Control of an Energy-Efficient Speed Regulating Method for Pump-Controlled Motor System under Negative Loads

Pump-controlled motor hydrostatic system (PCMH) is widely applied for rotary driving in heavy industry and construction machinery due to its high-power density and efficient speed regulation performance. However, the contradiction of the PCMH system between energy saving and speed control appears when it deals with negative loads. To address this contradiction, an energy-efficient speed regulating method based on electro-proportional counterbalance valves (EPCBVs) is designed, along with the corresponding controller. The working principle of the proposed scheme is that under a negative-load operation mode, determined by the supervisory controller according to system states and reference inputs, the speed of the hydraulic motor is controlled by a velocity controller through adjustment of the control signal of the EPCBV, and that the inlet pressure of the hydraulic motor is maintained at a defined low point by a pressure controller through pump displacement control. Comparative experiments between the EPCBV and T-CBV (a PCMH system based on a typical CBV) systems are conducted to verify the superiority of the proposed scheme in energy-efficient speed regulation under negative loads. The results show that, in most of the working conditions, the EPCBV system shows better adaption than the T-CBV system to varying negative loads and maintains higher stability than the T-CBV. Moreover, the speed accuracy of the EPCBV system can be maintained above 95%, which is greater than that of the T-CBV system, varying from 48% to 90%. Furthermore, the maximum power consumption is only about 4 Kw and is far less than that of the T-CBV system, which is about 13.79 Kw. The power-saving ratio changes from 20% to 82%, but it goes beyond 50% in most of the working conditions. The proposed method is easy to implement in practical application and is of great significance to the PCMH system for energy-efficient speed control under negative loads.