Analysis and suppression strategy of DC ripple voltage of single-phase cascaded multilevel converter

TAO Haijun; XIAO Qunxing; ZHANG Jinsheng; ZHENG Zheng; YANG Ming; HUANG Tao

doi:10.16186/j.cnki.1673-9787.2022010084

Abstract：Cascaded H bridge type multilevel converter using phase shift transformer and rectifier power sup-ply with the advantages of high power factor,low harmonic content of output voltage has been widely used in high-power industrial fields.The traditional modulation algorithms are based on the assumption that the DC bus voltage is a constant value.However,the low-frequency ripples appeared on the DC side are modu-lated and transmitted to the load,resulting in the distortion of the output voltage waveform.Objective To ex-plore the problem that a large amount of DC ripple voltage exists on the power supply side of cascade H-bridge unit,resulting in waveform distortion of output load voltage,Methods the DC ripple voltage was firstly analyzed by using the double Fourier theory in this paper,and then a DC ripple feedforward compen-sation strategy was introduced.By measuring the actual input voltage of the DC side of each cascaded H-bridge divided by the voltage reference value and multiplied by the traditional carrier signal,the carrier phase shift modulation was carried out with the modulation voltage.At the same time,the reactive voltage was simulated by FFT transformation with vector control,and faster convergence speed,higher stability and smaller oscillation were obtained.Results The simulation and experimental results verified that the proposed modulation algorithm and control strategy could effectively suppress the low-order harmonics in the load voltage,reduce the waveform distortion of the output voltage,and realize the fast dynamic response and no steady-state error control of the inverter power supply.Conclusion The experimental results verified the fea-sibility and rationality of the modulation strategy and control strategy used above.