Switching Angle Based Synchronized SVPWM Strategy Used In Traction Inverter

In the traction drive system,Pulse Width Modulation is the fundamental technol-ogy used to control the traction inverter,making it able to convert the electric energy to feed the motor.This paper focuses on the PWM technique,the author proposes a switch-ing angle based synchronized Space Vector PWM(SVPWM)strategy.With theoretical analysis,simulations and experiments,its validity and correctness has been verified.The conventional synchronized SVPWM strategy is based on space vector synthesis,which places a number of sampling points with fixed position in a fundamental period to synthesize the reference voltage vectors,so the carrier ratio is changeless due to the fixed number of sampling points.Nevertheless,carrier ratio will change in a transition with different sampling points,this will cause a sudden variation on modulation delay and out-put voltage phase,resulting a degradation of traction motor's closed loop control perfor-mance.Targeting at this problem,by analyzing the waveform of synchronized SVPWM strategies and adopting the concept of switching angle from optimal synchronous mod-ulation,the author proposes an enhanced switching angle based synchronized strategy with high flexibility to change the carrier ratio.The principle of conventional synchronized SVPWM overmodulation algorithm is moving the voltage vector to the hexagon vertices by modifying its phase angle and am-plitude.For some typical synchronized SVPWM strategies with special switching se-quence,it is incapable to enter six-step mode.This paper presents a switching angle based overmodulation scheme,its principle is more intuitive and clear.Making the adja-cent switching angles coincide and re-dividing the subcycles,the narrow pulses are easily eliminated,and six-step operation is possibly achieved.The carrier ratio remains unchanged during a PWM mode transition after re-dividing the subcycles,but selecting proper transition point is still an inescapable problem.Aiming at this problem,the author claims that the transition guideline is to ensure a continuous fundamental voltage phase and stator flux trajectory after analyzing this two quantities.Applying this guideline,appropriate transition points are easily selected.