Reaserch On Optimization Control Strategy For Motor Drives In Electric Vehicle With A Bi-directional DC/DC Converter

To meet the needs of electric vehicle(EV) for starting, climbing and high speedrunning, the permanent magnet synchronous motor(PMSM) used in driving system,should have a large torque coefficient and a wide speed range meanwhile. Consideringthe factors such as cost and volume of the vehicle power battery, the voltage of thedc-bus in traditional driving system is always not very high, which leads to PMSM toadopt flux-weakening control for a higher speed at a relatively low speed. For it is hardto increase the speed of PMSM used in EV with flux-weakening control strategy, thehigh speed running performance of electric vehicle may be affectted.In this master thesis, a permanent magnet synchronous motor driving system inelectric vehicle with a bi-directional DC/DC converter is reserched, and questions howto regulate the voltage of dc-bus and how to enhance the performance of thebi-directional DC/DC converter is really we care about. Meanwhile considering theripple of dc-bus voltage impacting on the driving quality of PMSM, some factors whichmainly affect the ripple of the dc-bus voltage, are also deeply studied. For astricting theripple of dc-bus voltage, some electric parameters of the the bi-directional DC/DCconverter are appropriately selected.The dc-bus voltage requirement of the motor driving system in EV, is veay relatedto the operating condition of PMSM. Based on the analysis of the typical operatingcurve of PMSM, a dc-bus voltage regulating scheme is presented firstly in chapter two,by real-time computing the minimum command value of dc-bus voltage with theinformation such as the speed and command value of d/q axis current of the PMSM,benefits the dc-bus voltage self-adjusting in accordance with the need of motor drivingsystem.The vehicle load composed of the inverter and PMSM in driving system, has thecharacteristics of power load varied in a large range and impact in an instant, meanwhileit has a high requirements on the voltage of dc-bus. An improved control strategy ispresented in chapter three, which makes the load current forward feed and has a varyingproportions part within double loop cascade structure, guarantee a fine dynamicresponse performance of the bi-directional DC/DC converter to control the voltage ofdc-bus quickly and effectively.Finally, a PMSM driving system in EV with bi-directional DC/DC converter is established, using the proposed the improved control strategy in Matlab/Simulinkcondition. And the simulation results show that the dc-bus voltage regulating schemeand improved control strategy of the bi-directional DC/DC converter for EV, presentedin this thesis, can well meet the requirements of the PMSM driving systems in electricvehicle.