A New Type Of Asymmetric Three-phase Four-leg Quasi-four-level Inverter And SVPWM Algorithm

400Hz intermediate frequency inverter power supplies are widely used in important occasions such as aerospace systems,ship systems,and radar systems.Compared with industrial frequency inverter power supplies,the increase in frequency will cause the quality of the output waveform to decrease under the same switching frequency.In order to maintain a lower switching frequency,reduce switching losses,and meet the requirements of non-linear and unbalanced load of the intermediate frequency inverter power supply,this article focuses on the characteristics of the intermediate frequency inverter power supply,through the structure and operation of the existing hybrid multi-level inverter Based on the in-depth analysis of the principle,starting from the topology,an asymmetric three-phase four-leg quasi-four-level topology is proposed.This topology is based on the three-phase four-leg three-level topology without adding any power devices.Only adjust the ratio of the DC side voltage divider capacitance from 1:1 to 1:2,increase the number of output levels from the original three-level to four-level,increase the number of output levels,the output waveform distortion rate is lower,the switching frequency and The switching loss is also lower.The space voltage vector of the proposed asymmetric three-phase four-leg quasi-four-level topology is partially missing compared to the traditional four-leg four-level topology,which makes it difficult to synthesize the reference voltage vector.To solve this problem,an improved Based on the three-dimensional space vector modulation algorithm in the abc coordinate system,the complexity of the conventional four-level space vector modulation algorithm is reduced.Aiming at the voltage equalization problem of the DC side capacitor of the hybrid multilevel inverter,a hardware auxiliary circuit capacitor voltage control method is adopted to suppress the midpoint potential shift of the DC side voltage divider capacitor and realize the control of the capacitor voltage.MATLAB simulation and experimental results show that the inverter can still output three-phase symmetrical voltage waveform under unbalanced load,the THD of the simulated output voltage can be controlled to 0.78%,the THD of the experimental output voltage waveform can be controlled to 4.904%,and the switching frequency is also It has been effectively reduced,and the switching loss is reduced by about 2%.