Research On The Control Strategies Of The Parallel Hybrid Power System Of The Hydraulic Excavator

It's an important research area in the field of hydraulic excavators to utilize hybrid technology so as to realize high efficiency, energy saving and low emission. Some of the famous excavator producers abroad have already started to make pre-industrial prototype for hybrid hydraulic excavator, while few domestic counterparts cooperate with colleges to do researches using hybrid technologies. General speaking, the overall research level is still at the initial stage,and some key techonologies in terms of parameter matching, control strategies et al. should be further studied. The paper mainly involves academic and experimental research including structure design, parameters matching, control strategies et.al, and finally gains some progresses listed below.1. Based on hybrid theory, the parallel hybrid hydraulic excavator system is depicted.And the off-line static optimization processes are developed under both pure electric mode and parallel drive mode while the off-line dynamic optimization of the system is performed based on the particle swarm optimization algorithm. All of the above optimization research would lead to good control strategies.2. The engine on/off control method is proposed in parallel hybrid hydraulic excavators, moreover the engine on/off switch rule and triggering condition are carefully designed. Two modes including pure electric drive mode and parallel drive mode are realized, which could greatly optimize the fuel economy of the system and also make good use of the working capacity of the motor and the battery.3. Two control strategies with engine on/off control are put forward. The rule-based control strategy:the working mode identification block is introduced, initially analyze the working condition and battery SOC, and later control engine on/off. When engine is on, the engine throttle is altered in real-time so the power matching between engine output power and external required power is achieved. The fuzzy logic control strategy:the fuzzy logic controller adopts pump average required power and battery SOC as inputs which could adapt to the changeable working condition. Futheremore, based on the genetic algorithm the off-line optimization process for membership functions of the fuzzy controller is performed, and the fuel economy of the system is increased.