Research On Space Vector Pulse Width Modulation For Electric Vehicle Motor Controller In Whole Modulation Range

Motor controller,as the central control unit,controls the star,gear,motor speed and so on.While inverter can covert the direct current(DC)into alternating current(AC).The utilization of DC link voltage affect the output speed range and the output power of the controller,which is an important parameter to judge the level of the motor controller.Recently,SVPWM(Space Vector Pulse Width Modulation)is widely used in order to achieve this target.Except for the improvement of utilization of DC link voltage,SVPWM also has other advantage such as wider modulation index and easier to digital realization.Based on the analysis of SVPWM,this paper broad the operation range from linear modulation,over modulation,to rectangular wave modulation based on MI.Achieve the SVPWM in whole voltage range,meanwhile,improve the utilization of DC link voltage.The whole range of voltage range means the amplitude of fundamental voltage can achieve from 0 to the amplitude of the fundamental voltage of rectangular wave,which broad MI from 0 to 1.In this paper,the linear modulation,over modulation,rectangular wave modulation of SPWM are discussed.The simulation and the strategy of rectangular wave modulation is emphasized in this paper.Firstly,the fundamental theory of SVPWM is discussed.The judgement of the section of output voltage,the calculation of the hold time of the basic space vector and three phase PWM duty are analyzed.The simulation model of SVPWM is built and analyzed.Secondly,divide the operation range into three region: linear modulation,over modulation and rectangular wave modulation,and discussed the characteristics of them.Proposed the control strategies of over modulation mode I and over modulation mode II.In over modulation mode I,the phase of the output voltage vector and the reference voltage vector are same,but the amplitude of the output vector has to make some adjustment as it could not over the hexagon.So,calculate the reference angle through formula;then fix the amplitude of the output voltage vector;at last,adjust the hold time of the basic vector.In over modulation mode II,both the phase and the amplitude of the voltage vector need to be fixed.First,calculate the hold angle of the basic vector;then calculate the phase of output voltage vector;and adjust the hold time of the basic vector at last.Simulation model of over modulation I and over modulation mode II are build and analyzed.Lastly,a novel control strategy of rectangular-wave modulation based on current close-loop phase control is proposed for motor controllers in order to get maximum utilization of DC link voltage for electric vehicle in high speed range.The phase of rectangular-wave is regulated by reference current and feedback current.A model of surface mounted permanent magnet synchronous motor is built,which use the phase in the last sample time of over modulation mode as the initial integral value of the current close-loop.The results of simulation and experiment verify that the proposed strategy can realize the smooth and continuous transition from over modulation to rectangular-wave modulation;realize the stability of the phase of rectangular-wave;decrease the switching loss of the inverter;improve the utilization of DC link voltage;broaden the operating speed range of the AC motor.