Control Strategy And Parameter Matching Of Hybrid System In Hydraulic Excavator

Energy is consuming up and pollution is more and more serious nowadays, so research on energy saving of hydraulic excavators has great significance because of their large application quantities, high energy consumption and bad exhaust. As hydraulic excavator is one typical construction machinery, such research can also provide solutions for other construction machines which have the same characteristics to achieve energy saving.In one hydraulic excavator, all exhaust and most components which have low energy conversion efficiency are in the power system. So the research on energy saving and exhaust reduction of hydraulic excavators should concentrate in the power system. Generally, the main factors affecting the efficiency and exhaust of the power system are the structure, parameter matching and control strategy.In this dissertation, the corresponding energy saving methods are proposed and the structure of hybrid system is presented based on the analyses of energy consumption of hydraulic excavators. The corresponding control strategy of the hybrid system is developed according to the working condition of hydraulic excavators. And parameter matching of this hybrid system is studied. Then a design method of hybrid system in hydraulic excavators is proposed based on the above research. This dissertation can provide some theoretical and experimental references for the further research on energy saving of power system in hydraulic excavators.The chapters of this dissertation are organized as follows.In Chapter 1, the significance of the research on parameter matching and control strategy of the power system in hydraulic excavators under the circumstance that energy is consuming up and pollution is more and more serious is discussed. The development of parameter matching and control strategy of the power system in hydraulic excavators is introduced. The characteristics of different parameter matching method and control strategy are analyzed and compared. Then a driving program in which hybrid system is used to drive hydraulic excavator is proposed. The state of the art of parameter matching and control strategy of hybrid system in hydraulic excavators is presented. Finally, the primary research contents of this dissertation are provided.In Chapter 2, the structure of hydraulic excavators is analyzed and simulation model is built. The typical working condition of hydraulic excavators is analyzed based on the simulation model and the measured working data. Then a hybrid driving structure of hydraulic excavators is proposed according to the above analyses. In this structure, parallel hybrid system is chosen by comparing the merits and demerits of different hybrid systems; as there is a lot of energy can be regenerated when hydraulic excavators are working, one set of hydraulic motor-generator is used to recovery energy; capacitor is chosen as the accumulator of the hybrid system according to the characteristic of the working condition of hydraulic excavators. This hybrid driving structure is analyzed by simulation study on the built model.In Chapter 3, the hybrid system applied in hydraulic excavator, which is proposed in Chapter 2, is modeled and analyzed. The power system is devided into two parts: engine system and capacitor. The models of engine, hydraulic pump, electric motor, inverter, generator and capacitor are built. The characteristics of the two parts in power system are analyzed. The analyses provide rules for the control strategy parameter matching of hybrid system applied in hydraulic excavator.In Chapter 4, Control strategies of the hybrid system applied in hydraulic excavator is studied based on the modeling and analyses in Chapter 3. Some control strategies of the hybrid system applied in hydraulic excavator were proposed in former study and are analyzed in this chapter. According to the characteristic of the hybrid system applied in hydraulic excavator, a control strategy named engine self-determined multi-phase multi-point and a control strategy named engine dynamic working points are developed and studied through simulation and experiments.In Chapter 5, a parameter matching method, which is based on genetic algorithm uses efficiency of power system as optimal target functions and uses drving desire of load and minimum machine power as restraint condition functions, is proposed to optimize the hybrid system in hydraulic excavators. According to the structure, working condition and control strategy of the hybrid system, this method, which is based on genetic algorithm and satisfies optimization target functions and constraint condition functions, is developed. The parameters of the main components, such as engine, electric motor, generator and capacitor, of the power system were matched using this method. The matching results were analyzed using the built hybrid hydraulic excavator model. The results show the system efficiency is improved significantly.In Chapter 6, design rules of hybrid system in hydraulic excavator are presented systematically based on the above study. In these design rules, the structure of the hybrid system is first determined according to the analyses of the design object. Then the corresponding control strategy is developed. Finally, the components of the hybrid system are parameter matched. A hybrid system in 7-ton hydraulic excavator is designed using these rules. And the designed hybrid system is simulated in the built model. The results show this hybrid system has good energy saving effect, which indicates the feasibility of the design rules.The main conclusions and achievements are summarized in Chapter 7, and the further research work is put forward.