The hybrid excavator has two kinds of power mixing: oil-electric mixing and oil-liquid mixing. The oil-electric hybrid power provides power for generators and batteries (or super capacitors), and the oil-liquid hybrid power takes engine and accumulator as the power source. According to the energy recovery mode, it can be divided into two types: energy recovery type and no energy recovery type, in which energy recovery type is mainly to recover the energy of rotary motor. Whether it is electric recovery or hydraulic recovery, the recovered energy is the energy of rotary motor braking, but the prototype of potential energy recovery in the falling process of arm and bucket rod has not been found.
At present, the hybrid power generally adopts the solution of oil-electric mixing. With the help of storage battery, super capacitor and other energy storage elements, the diesel engine drives the generator to the energy storage element under small load conditions, and then releases the stored energy to drive the motor under large load conditions. In this way, the diesel engine can be selected according to the average load power in the design, driven by a diesel engine with less power, and the operating condition of the diesel engine is stable and always in an efficient operating state, so the fuel efficiency can be greatly improved.
At present, the structure of hybrid power system used in excavator is mainly composed of parallel, series and mixed power assembly through different structures of engine, generator and motor.
The series hybrid power system is driven by the engine to generate electricity. The electric energy is transmitted to the motor cargo battery through the controller and frequency converter. The motor provides the torque needed for the hydraulic pump to work. This system structure and control strategy is simple and easy to implement, and the output of the engine is not affected by the workload, and the motor is used to deal with the load change, so the engine can keep working in a high efficiency state, which is helpful to reduce fuel consumption, improve emission quality and prolong engine working life. But the mechanical energy output by the engine must first be converted into electric energy by the generator, and then converted into mechanical energy by the motor. Because of the limitation of technology, the overall efficiency of this energy conversion is not high, the energy saving effect is not obvious, and the power requirement of generator, motor and battery is large, so the application range is not wide.
The parallel hybrid power system is composed of engine and motor. According to the change of load, it can be driven separately and jointly. The main energy of the system is provided by the engine, and the motor plays an auxiliary role in stabilizing the power of the engine. When the output power of the engine is greater than that required by the system, the motor, as a generator, absorbs the excess output of the engine and converts it into electric energy to be stored in the battery. When the output power of the engine is lower than that of the system, the motor recharges the insufficient energy of the engine for the system, which balances the load on the engine and works in the high efficiency area. Compared with the series system, the overall efficiency of the parallel system is higher, the energy saving effect is obvious, and the motor and battery only play an auxiliary role as the engine, so the installed power is not large. However, the load of parallel system is obviously affected, the arrangement is not flexible, and the control strategy is complex.
The hybrid hybrid power system is the sum of parallel and series systems. Part of the power output of the engine is the motor driving load together, and part is used to drive the generator into electric energy and store it in the battery. The energy distribution can be controlled by controlling the clutch. The system has flexible control and high comprehensive performance, but it has many components, difficult installation and layout, and complex control strategy.