Research On Multilevel Inverter Circuit Its Moundation Method For Bridge

The traditional H bridge two level inverter circuit can not be applied effectively in the field of high voltage variable frequency speed regulation.Even the two level inverter circuit,which is directly connected by the power device,also has the problem of dynamic and static voltage sharing,and it causes the problem of electromagnetic interference which is difficult to handle.At present,there are stepped wave modulation,harmonic suppression,triangular carrier modulation,space vector modulation and carrier phase shift modulation.Selecting the appropriate control strategy of inverter topology can improve the value of the whole system.The cascaded multilevel inverter circuit of H bridge has the advantages of small switching stress,excellent output waveform,easy encapsulation and expansion.It is widely used in the field of high voltage variable frequency speed regulation.The carrier phase shift modulation(carrier phase shift modulation)technology can achieve high switching frequency at low switching frequency.It has good harmonic characteristics.Carrier phase shift SPWM modulation(PWM)is widely used in cascaded multilevel inverters.Because of its simple principle,easy control mode and cascaded multilevel inverters.Therefore,the cascaded multilevel inverter circuit based on carrier phase shift modulation(carrier phase shift modulation)is studied in the cascade multilevel inverter(H bridge).It solves the contradiction between low voltage withstand and high voltage and power output.Through the superposition of multiple DC power sources,the waveform is closer to the sine wave,the harmonic content is gradually reduced and the output voltage waveform is better,so it is widely used in the field of high voltage variable frequency speed regulation.This thesis focuses on H bridge cascaded nine level inverter circuit.Based on the carrier phase-shift modulation of the H-bridge cascade nine the single-phase and three-phase circuits of the flat inverter circuit are simulated by Matlab/Simulink.By adjusting the parameters in the simulation waveform diagram,the factors that can affect the output waveform quality of the cascaded single-phase and three-phase nine level inverter are analyzed and compared.The harmonic spectrum of five level and seven level different modulation system is simulated.The simulation results show that:1)when the carrier frequency remains constant,the output level of cascaded inverter will increase with the increase of modulation.2)when the modulation system remains unchanged,the output voltage waveform distortion rate THD value increases with the carrier frequency increasing.3)when other parameters are unchanged,the output harmonic content decreases with the number of cascades of H bridge module.