Research On Power System Design And Control Strategy Of Hybrid Wheel Loader

Wheel loader is important earthwork construction equipment, and widely used inconstruction field. Its fuel consumption, emissions problem has been concerned by allinterested parties. Hybrid technology is the main way of energy saving and reducingemissions for mobile equipment, and also is one of the most important developmentdirections of wheel loader.This thesis depends on the key project of national "863" plan—Application Re-search of Hybrid System and Energy-saving Technology of Construction Machinery.Based on a6t domestic loader, a coaxial parallel electric-hybrid loader was thorough-ly studied. The research of whole machine performances was applied on the founda-tion of key parts researches, and research links includes hybrid theory, configurationdesign, parameter matching, virtual prototyping simulation, control strategies and soon, idiographic researches are as follow:(1) Hybrid Theory and ApplicationThe basic hybrid theory after of development is already matured now. Throughthe cooperation between engine and electric motor, the working area of engine wasadjusted to high efficient status, and then fuel can be saved. At present, the applicationon wheel loader is still in its infancy, most prototypes in development have adoptedcoaxial parallel style, except for the Kawasaki65ZHybrid which adopted a planetarygear power coupling device.(2) Configuration DesignConfiguration design is related to parts selection intimately and also is the mostimportant foundation for system development. Series, parallel and series-parallel hy-brid form all have been used in auto category successfully. Series style is intrinsicallya pure electric drive system with self-generating device, so it has relatively the highestrequirement for motor power. As series-parallel style owns the highest technical re-quirement, parallel is most suit to medium-sized wheel loader.(3) Study of Key PartsThe hybrid system is achieved by add a set of electric drive device to traditionalpower system. So the characteristics of motors, batteries, super capacitors, power in- verter, coupling device and other key parts must be studied exhaustively. Comparisonsbetween different kinds of key parts were conducted in research of this paper.(4) Analysis of Working ConditionAs specialized equipment, wheel loader often acts in cycle. Different workingstates have different power requirements. By analysis the working condition, maxi-mum traction, maximum speed and other parameters can be obtain, and the founda-tion for parameter matching and control strategy design was laid.(5) Parameter Matching of Power SystemThe common method for parameters matching of hybrid system is implementingequalization on power flow of whole machine. Key parts can be selected out based onthe mean power, power variation of working condition, the working voltage range ofelectric motor and super capacitor and so on.(6) Virtual Prototype SimulationBased on the graphical simulation platform–AMESim, virtual prototype modelsthat designed after parameters match was established from parts to entirety, both tra-ditional and hybrid. Besides, co-simulations were conducted with the control pro-grams which programmed in Simulink.(7) Control StrategiesAfter the comparison of different control theories that ever used in hybrid system,basic logic threshold control, SOC maximization control, motor assistant minimiza-tion control and real-time optimal control that combined with logic threshold partitionwere laid out. Then combined with the simulation results, the four control strategieswere analyzed in detail.