17-02-2011, 10:58 AM
In this paper, fuzzy logic control is put forward in a parallel hybrid hydraulic excavator for the purposes ofbetter energy distribution and higher fuel economy. A mathematical model of parallel hybrid hydraulicexcavator is presented in detail, and the parameters of components and overall system are listed andanalyzed. The fuzzy logic controller is then designed to cope with energy distribution and management. Toachieve better equivalent fuel consumption, genetic algorithm is implemented to fine-tune the membershipfunctions. The control effects are compared between different control strategies, e.g. rule-based control andfine-tuned fuzzy logic control. The results indicate that hybrids with the proposed strategy can improve fueleconomy for the excavator without sacrificing any system performance
Introduction
Currently institutes, colleges and companies around the world areworking in the field of energy saving and emissions reduction so as tofind efficient solutions to increase fuel economy for excavators. Untilnow, several potential ways have been developed in the field, e.g.constant power control, all power control, cross sensing control,negative flux control, load sensing control, load-pump powermatching control et al., while it is still necessary to find some otherways to meet higher standard emission criterion and more economicalfuel consumption for excavators.Hybrid technology might be one of the possible ways to get a betterfuel economy in excavators. After all, the successful implement invehicle (so called hybrid electric vehicle) showed that the hybridswould be capable of increasing fuel economy and diminishing emissionsfor a new generation of vehicles. So to study a hybrid hydraulicexcavator should be a promising and encouraged direction in the nearfuture. The differences between vehicles and excavators excludingdifferent system configurations are listed below.
(1) The pattern ofworking conditions is quite different; moreover an excavator's workingcondition is heavy, repeatedly changeable and regularly periodicwhile avehicle's is comparatively stable.
(2) The amount ofworking duration istotally different, and especially for excavators usually it would beoperated for at least 20 h per day, so it has a stronger fuel economyimpact on the hybrid hydraulic excavator compared to the hybridelectric vehicle.
Similarly,we could classify hybrid excavators into threemain types in terms of different systemconfigurations:
(1) series hybridexcavators,
(2) parallel hybrid excavators and
(3) power-split hybridexcavators.
In essential, all types of hybrid excavators are supposed to have three key components in their powertrain architectures. One isexisting power source, and it used to be one internal combustion engine(ICE), e.g. gasoline engine (DI) and diesel engine (CI).The other one iscalled added power source. Usually one or two motors are introduced tocooperatewith the engine to drive the final shaft, and themotor(s) haveboth motor and generation functions. The remaining one is energystorage unit (ESU) that is used to receive excessive energy from theengine in charge mode or drive the motor in discharge mode.Studies on hybrid hydraulic excavators could be traced back to theearly 21st. K.K. Yoshiyu et al. introduced hybrid conception intoconstruction machinery in order to increase system efficiency in 2001[1]. Matsubara M developed one hybrid system for constructionmachine in 2001 and also a series of patents in the related field wereregistered during the period of 2001–2004 in U.S.A., Japan and Europe[2–6]. In 2003M. Kagoshima et al. gave a description about thedevelopment of hybrid excavators [7] and N. Takao et al. developed apower simulation model for a series hybrid excavator that showed 40%fuel reduction in comparisonswith conventional excavators in 2004 [8].Q.F. Wang et al. did simulation research and evaluated energy savingeffect in parallel hybrid excavators in 2005, and also presented the wayto recover potential energy from excavators [9,11,12]. In 2008, rulebasedcontrol strategy for parallel hybrid hydraulic excavators was putforward by Q. Xiao et al. that chose required torque at the pumps andstate of charge (SOC) of the battery as the signals to switch engine'sworking points [14]. D.Y.Wang et Al. presented performance analysis ofhydraulic excavator powertrain hybridization that showed that thesystemcould take the advantage of hybrid configuration in terms of cost,fuel economy and performance [10,13]. Despite the aforementionedefforts in the field, few papers concentrate on advanced control inhybrid excavators although control strategy and energy distribution arethe primary concern here. Compared with the rule-based control inPHHE, i.e. singleworking point control, dynamicalworkingpoint control with/without load sensing functionality, the newly proposed controllerwith GA-tuned fuzzy logic has the advantage of stronger robust, lowerfuel cost and higher efficiency. More details regarding the comparisonswill be demonstrated below.The objective of this paper is to study the feasibility to implementfuzzy logic control into a hybrid hydraulic excavator, and to optimizethe membership functions of the fuzzy logic controller for the parallelhybrid hydraulic excavator using genetic algorithm (GA).The structure of the paper is as follows. Section 2 mainly describesone plant model for the parallel hybrid hydraulic excavator (PHHE), aswell as system configuration and components' parameters. Section 3devotes to demonstrating the design process of fuzzy logic control forPHHE. In Section 4, the optimal control problem is addressed and GAalgorithm is introduced to help find a set of optimum parameters inthe fuzzy logic controller. The results with the fine-tuning process areproposed in Section 5, in which the control effects with theoptimization process are analyzed and the comparisons betweenthe rule-based control (RBC) and the fine-tuned fuzzy logic control(FLC-GA) have been made. Finally, Section 6 provides a summary anda discussion of some extensions of this paper
