Three-Phase AC-side voltage-doubling high power density voltage source converter with intrinsic buck-boost cell and common-mode voltage suppression

The three-phase two-level voltage source converter (VSC) is widely employed in power conversions between ac and dc for its four-quadrant operation and control flexibility. However, it suffers from the low output voltage range with a peak value of half dc-link per phase, which necessitates the use of either high dc-link voltage or bulky step-up transformer to enable the medium voltage operation. Additionally, the high common-mode (CM) voltage between ac loads neutral points and ground may reduce the service life and reliability of electric machinery. In this paper, a three-phase ac-side voltage-doubling VSC topology with intrinsic buck-boost cell is analyzed. By this configuration, the ac-side voltage is doubled with the phase peak value equal to dc link. That is, only half of the dc-side capacitor bank is needed to generate the same output voltage. The proposed converter uses its buck-boost cell as a virtual voltage source to synthesize negative half of the output voltage by modulating its output ac phase voltage around the negative bus (which is the real zero when grounded). This permits the average CM voltage to be suppressed to zero, and loads connected to converter ac side not to withstand any dc voltage stress (reducing the insulation requirement). Modeling and control design for both rectifier and inverter modes of this converter in synchronous reference frame have been investigated to ensure a four-quadrant three-phase back-to-back system. Experimental results have verified the feasibility and the effectiveness of the proposed configuration and the designed control strategies.