Abstract
Asymmetric Cascaded H-bridge (ACHB) level inverters can output more voltage waveforms with fewer cascaded units while ensuring the quality of output voltage waveforms, so they have attracted more and more attention. Taking the topology of Type-III asymmetric CHB multilevel inverters as the research object, a Modified Hybrid Frequency Pulse Width Modulation (MHF-PWM) strategy is proposed in this paper. This modulation strategy overcomes the local overshoot of low-voltage unit in the presence of traditional Hybrid Frequency Pulse Width Modulation (HF-PWM), thus completely eliminating the low frequency harmonics in the output voltage waveform of Type-III ACHB nine-level inverters, and the Total Harmonic Distortion (THD) of output line voltage of the modulation strategy is lower than that of PS-PWM strategy in the whole modulation degree, which effectively improves the quality waveform of the output line voltage. At the same time, the strategy can also improve the problems of current backflow and energy feedback caused by the high-voltage unit pouring current to the low-voltage unit, thereby reducing the imbalance of the output power of the high-voltage and low-voltage units. Finally, the Matlab/Simulink simulation model and experimental platform are established to verify the validity and practicality of the modulation strategy.
Highlights
The Cascaded H-bridge (CHB) multilevel inverter is one of the most common multilevel inverter topologies, and has been widely used in medium voltage high-power inverters and AsymmetricCascaded (AC) drive industry
In order to verify the effect of Modified Hybrid Frequency Pulse Width Modulation (MHF-pulse width modulation (PWM)) strategy in the Type-III Asymmetric Cascaded H-bridge (ACHB) Inverter, the simulation model was built in the Matlab simulation environment for the Hybrid Frequency Pulse Width Modulation (HF-PWM) strategy and the MHF-PWM
An MHF-PWM strategy is proposed, and the following conclusions are obtained through simulation and experimental results: (1)
Summary
The Cascaded H-bridge (CHB) multilevel inverter is one of the most common multilevel inverter topologies, and has been widely used in medium voltage high-power inverters and Asymmetric. A hybrid multilevel modulation strategy was proposed for the 11-level hybrid multilevel inverter mentioned above, using stepped waveform synthesis in higher power cells in conjunction with high-frequency pulse width modulation (PWM) in the lowest power unit This strategy uses a novel logic combination method to increase the number of output levels, the phenomenon of back-filling energy will occur during the modulation process, which will lead to poor output voltage waveform quality. Based on the above research contents, a modified hybrid frequency modulation strategy is proposed solve the problem of local overshoot of the low-voltage unit in traditional hybrid frequency for the characteristics of the Type-III ACHB inverter topology. Effectiveness of the proposed method are verified by simulation and experiment
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