A novel strategy for three-phase/switch/level (Vienna) rectifier under severe unbalanced grids

Unbalanced grids introduce performance deterioration for the Vienna rectifier topology by producing twice fundamental frequency ripple in the dc-link voltage and input active/reactive power. A traditional control strategy is the input current tracking scheme, which can work under any unbalanced conditions, but it cannot eliminate the input power ripple and the output dc-link voltage ripple. Another class of control strategy for the purpose of eliminating the input power ripple can maintain constant input power and eliminate the dc-link voltage ripple, however, it will fail under severe unbalanced grids. This paper first analyzes the theoretical limits of constant power control method, and based on which a novel control method that injects a small amount of power ripple is proposed to make a compromise between the working area and the output dc voltage ripple. Finally, the experiment results using constant power control method are given and validate the performance of the proposed control method.