Research On Bi-directional DC-DC Converter For Motor Driver Control Strategy In Electric Vehicles

Aiming at the permanent magnet synchronous motor control system used inelectric vehicle, must to meet the requirements of large starting torque, starting,climbing, and the motor system also must has the wide speed range. In order to meetthe requirements of high torque at low speed, the motor maybe has a large torquecoefficient. However, because the vehicle’s transmission system does not need a clutchand gearbox, the speed is controlled by the controller, the back EMF of the motor willbe increased by the large coefficient, when the voltage of the battery is certain, themotor’s high speed performance will be greatly affected by the increasing of the speed.How to balance the two important performance indexes that the large torque and widespeed range is the key technical problem of the development of electric vehicle.The traditional voltage source inverter before joining bi-directional DC/DCconverter is studied in the paper, the DC/DC converter is worked in boost mode whenthe motor needs to enlarge the speed, improve the DC side voltage, which increases theinverter voltage capacity, so that the motor in the whole operating process are workingin the constant torque, the maximum torque current control strategy can be adopted.Because the traditional maximum torque current control method requires a prescriptionand arcsine operation, in practical engineering applications for very difficult, moreover,it is strictly dependent on the inductance of the motor and permanent magnet fluxlinkage parameters. Aiming at the shortcomings of the traditional method, an improvedMTPA control algorithm is proposed, the IPMSM torque angle complex formulasusing polynomial fitting, using the fitting polynomial approximation to calculate thetorque angle, and the angle of torque as the initial value of variable step searching,searching optimal torque angle, to achieve maximum torque current ratio controleffect.In this paper, according to the requirements of the system, design of bi-directionalDC/DC electrical parameters, according to its small signal model for the analysis of thestability of the system, and a transformer compensator design. The vehicle motorvector control strategy simulation model is established by MATLAB/Simulink toolbox,and it’s proved that the proposed algorithm is feasible.On the basis of analysis and simulation based on TMS320F2812has beendesigned with bi-directional DC/DC converter of permanent magnet synchronous motor control system hardware circuit and software structure design. Finally, withbi-directional DC/DC converter for permanent magnet motor of the electric vehiclecontrol and drive system for the test bench, the results show that, the control systemcan basically realize the control target, the proposed method is validated the accuracyand feasibility, for motor control system provides certain theory basis for engineering,the practical application has laid a good foundation.