Analysis and Improvement of the Effect of Distributed Parasitic Capacitance on High-Frequency High-Density Three-Phase Buck Rectifier

For high-density three-phase buck rectifier (3ph-BR), such as a standard full-brick size 3ph-BR, there exist obvious parasitic capacitances distributed between its dc-link output and the system ground, which lead to low-frequency distortion of input currents, and thus, serious deterioration of the input current total harmonics distortion (THD). The effect of the distributed parasitic capacitances becomes more obvious for the 3ph-BR under light load conditions. To improve the input current quality of the high-density 3ph-BR, a modified 3ph-BR is introduced in this article. The modified 3ph-BR has one low-frequency current path which realizes power transfer from ac input to dc output, and two high-frequency current paths which provide low-impedance path for high-frequency currents. The high-frequency current caused by the parasitic capacitance distributed between the dc-link output and the system ground circulates internally, rather than flow to the ac input side. Thus, input current THD of the modified 3ph-BR can be reduced. A 1-kW experimental prototype of the modified 3ph-BR with 200 kHz switching frequency and standard full-brick size is built to verify the analysis results.