Three Phase Buck Type Three-level AC/AC Converter

The voltage stress of power electronics devices is an important factor that affects the converter to handle higher voltage and higher power.And the multi-level technology is an effective way to solve this problem.To this end,the topology of three-phase Buck type three-level AC/AC converter is presented in this paper,and its working principle and control strategy are studied in detail.Voltage stress of each switch is half of the three-phase Buck type two-level AC/AC converter.At each stage of operation,the three-phase Buck type AC/AC converter can be equivalent to two single-phase Buck type AC/AC converters.Based on the topology of the single-phase Buck type three-level AC/AC converter and three-phase Buck type two-level AC/AC converter,the topology of the three-phase Buck type three-level AC/AC converter is proposed.Three kind voltage levels can be obtained at the front end of the filter inductor because of the flying capacitor clamped.The charging and discharging circuit of the flying capacitor is analyzed,and it is proved that the three-phase Buck three level AC/AC converter can regulate the output voltage and the flying capacitor voltage simultaneously.After a detailed study of the working principle of the converter,the control strategy of the three-phase Buck-type three-level AC/AC converter is proposed:using the flying capacitor voltage error signal to modify the duty ratios of the switches realizing double closed loop of output voltage and flying capacitor voltage.The principle of the three phase Buck type three-level AC/AC converter is simulated by Saber simulation software.Aiming at the distortion of flying capacitor voltage waveform and the wave forms at the front end of the filter inductor,the causes is detailed studied.At the same time,the limitation of the three-phase Buck type three-level AC/AC converter for the full duty cycle regulation of output voltage is explained in detail.A prototype of the three-phase Buck three level AC/AC converter is developed,and the experimental research is carried out.The experimental results show the correctness and feasibility of the topology and control strategy of the three-phase Buck type three level AC/AC converter.