Operation Control Of A Permanent Magnet Brushless DC Motor System Driven By A Single-phase To Three-phase Converter

With simple mechanical structure,high power density and large output torque,Permanent Magnet Brushless DC Motors(PMBLDCM)have been widely used in electric vehicles and household appliances.For the PMBLDCM system driven by single-phase to three-phase converter,the DC-link of traditional topology is usually connected with a large electrolytic capacitor in parallel,which enlarges the volume and weight of the system.The phase currents of PMBLDCM system without DC-link capacitor will fluctuate greatly or even become discontinuous.Since the two problems mentioned above can be avoided in PMBLDCM system with small DC-link capacitor,it has received extensive attention all over the world.The small DC-link capacitor topology will be investigated closely in this thesis,aiming at improving the power density and converter efficiency of motor system.In this thesis,the stable operation condition of the PMBLDCM was derived,and the operating principle of the converter was analyz ed.Then,based on these analyses,the motor operation of the large-capacitor,capacitor-less and small-capacitor single-phase to three-phase converter drive system were introduced.By analyzing two traditional control strategies,the shortcoming that DC-link capacitance and converter efficiency can not be balanced at the same time was revealed,and an improved control strategy was proposed based on the traditional control strategies.When the output voltage of the rectifier can not meet the requirement of the motor operation,the rectifier output and the capacitor alternately supply energy to the motor via the DC-link switch chopping,while the inverter switches are only used for commutation,rather than participation in motor speed regulation.The improved control strategy can effectively reduce the capacitance and the converter switching frequency at the same time,and the converter efficiency can be improved as a result.In addition,the proposed control strategy uses hysteresis controller as current controller and thus the converter switching frequency can be further reduced.In this thesis,the minimum capacitance that meets the requirements of motor operation was designed under rated operating conditions,and the experimental system was built with the designed capacitance.The DC-link voltage,the switching frequency and the converter efficiency of the two traditional control strategies and the improved control strategy are compared by simulations and experiments,and the results demonstrate that the improved control strategy can improve the converter efficiency while reducing the capacitance of the DC-link.