Research And Simulation Of Modulation Methods For High Voltage Variable Frequency Devices

High-voltage frequency control technology is widely used in various types of high-power AC motor load energy-saving and speed,which is cutting-edge technology in the field of power electronics.The high voltage frequency changer is different from the low voltage frequency changer which has mature topology,its main topology is the H bridge cascade multilevel inverter.Because it has many advantages,such as the modular engineering design,using the low voltage component to realize the inverter high voltage output,easy-to-check-fault-redundancy inverter design and so on.As the H-bridge cascade inverter requires real-time control and a large number of power switching devices,so its modulation methods have also been difficult and hot researches.In this paper,a multicarrier PWM control method is studied in detail,and a hybrid multicarrier PWM modulation method is proposed in combination with carrier vertical PWM modulation method and carrier phase shift PWM modulation method.The simulation results show that the inverter circuit with the multi-carrier PWM method has the advantages of the output waveform closer to sine wave and the lowest total harmonic distortion.In addition,for the domestic multi-level PWM control mode of research status,this paper presents a method of using a single carrier signal and a plurality of modulated signal symmetrical sampling PWM.At the same time,the discrete fourier analysis of the simulation waveforms of various modulation methods is carried out,and the corresponding spectrum characteristics are obtained.By analyzing and comparing,the general rules of the output voltage waveform harmonics of cascaded multilevel PWM methods and their characteristics.In the single-carrier PWM modulation mode,drive the motor load to start,run the simulation.Simulation results show that the output-voltage,current harmonic content and torque ripple of the inverter are very small in the single-carrier PWM control mode,which fully shows the superior performance of the cascade high-voltage inverter.