Research On Drive Control Of High-speed Electric Wheel System

Compared to the conventional internal combustion engine car, vehicles driven byelectric wheel have multiple independent and controlled driving sources, which makethem easy to realize their differential speed or differential force and precise control. Butthis also makes the relevant control technology more complicated. As a result, how tocontrol driving motor and driving force of the electric wheel needs more analysis. Thispaper takes the control technology of electric wheel system as a research object,focusing on driving motor control and driving force control including acceleration slipregulation control and vehicle control.In this paper, the mathematic models of PMSM in different coordinate systems arebuilt and analyzed. Because of the torque equation is related to the rotor position andchanges with time in the three-phase coordinate, it is difficult to control the motortorque precisely. But the torque equation has nothing to do with rotor position in therectangular coordinate. On this basis, combining with the structural characters of motorand the analysis of electric-wheel’s working conditions, this paper adopts the controlmethod that the direct axis current is zero (id=0) as motor’s control policy. Furthermore,the realization of the PMSM vector control system is studied.By analyzing the PMSM vector control system, the current loop and the speed loopare changed into a typical I system and a typical II system. And also the formulas aboutthe parameter calculation of the current loop and the speed loop are derived in this paper.Then the simulations for PMSM vector control system are carried out on this basis,which shows that both the speed control and the torque control can acquire bettercontrol effects, and also the response time of the torque control is much less than that ofthe speed control. Next, the PMSM performance is tested on a test bench, from whichthe torque speed characteristic figures are derived. Combing the results of simulationand experiment with the working conditions of the electric wheel and the analysis offour-wheel velocity coupling relationship, the torque of the in-wheel motor is taken asits control objective.Two kinds of anti-skid control methods for electric wheel including modelfollowing control (MFC) and sliding mode variable structure control (SMVSC) arestudied and also an algorithm identifying road based on piece linear interpolation is putforward in this paper. The simulation results of a quarter vehicle model show that the slip rate can be controlled with wheel speed alone by using MFC and the changes inroad adhesion can be identified with piece linear interpolation accurately, which alsoindicate the SMVSC of electric wheel based on road identification can keep the actualslip rate follow the optimal slip rate.The models of a seven degree of freedom (DOF) vehicle, tires and the motor arebuilt. Then, this paper puts forward a vehicle dynamics control based on hierarchicalcontrol structure, which consists of the upper vehicle motion controller and the lowerforce allocation controller. On the basis of analyzing the ideal vehicle movement, thispaper takes yaw rate and longitudinal acceleration as objective control variables of thevehicle motion controller, of which the controller output is calculated with proportionalintegral controller. The lower force allocation controller takes minimizing the tire withthe biggest vertical load as optimization goal, and adopts the control strategy usingweighted least squares method. Finally, the simulation results of seven DOF vehiclemodel show that the vehicle dynamics control method proposed by this paper can havethe vehicle motion state follow changes of the ideal model and eliminate the impactproduced from the difference between four driving motors. Furthermore, a driving forcecontrol integrated by vehicle dynamics control and MFC can ensure safe driving on lowadhesion road.