Research On Beat-less Control With Multi-Mode PWM Method

Using the single phase four-quadrant rectifier, high speed train traction system will produce the frequency twice as high as that of AC supplied voltage in the DC-link,thereby triggered beat phenomenon which can affect system stability and ride comfort. In EMUs traction system, in order to meet the control requirements of low switching frequencies, usually using multi-mode PWM method, namely to take a different modulation methods in different frequency bands, and in different modulation methods, the beat-less control methods are different.Firstly, this paper analyzes the causes of double frequency ripple voltage in the DC-link of traction system and the several factors affecting the size of the ripple component; compares two different ways taking care of the voltage ripple in the DC-link of the existing four typical EMUs. Secondly, introduces a special pulsewidth modulation Selective Harmonic Elimination Pulse Width Modulation which is widely used at middle fundamental frequency, analyzes the principle and method for solving switching angles, and uses a new SHEPWM algorithms to simplify the calculation. Thirdly, for different frequencies corresponding to different PWM modes of CRH5 EMUs, the use of different beat-less control methods, suppressing the impact caused by the DC voltage ripple. And proposes an improved beat-less control method at middle fundamental frequency, it is not only ensure its effect on the elimination of harmonics, but also on the harmonics generated by the DC voltage ripple, and it was verified by Simulink modeling simulation. Finally,5.5kW induction motor experiment platform is built, the traction system based on DSP hardware and software platform is designed, completed the multi-mode PWM control experiments for induction motor, and in the presence of double frequency ripple voltage in the DC-link, beat-less control method for SHEPWM is verified.