An Internal Model Direct Power Control With Improved Voltage Balancing Strategy for Single-Phase Cascaded H-Bridge Rectifiers

Single-phase cascaded H-bridge rectifiers (CHBR) are widely studied for vehicular power electronic transformers. In this article, an internal model direct power control (IM-DPC) with a voltage balancing strategy is proposed to improve the control performance of CHBR. First, a modified power control structure is built by the relationship of coordinate transformation. On this basis, the IM-DPC method is presented to obtain a straightforward design for the inner-loop. This approach can be implemented without phase-locked loop, and coordinate transformation is not necessary as well. Then, a first-order transfer function between the difference of dc-side voltage square and that of power is constructed. Further, a novel calculation structure for the compensation duty cycle is proposed. Through the proposed voltage balancing control scheme, the dynamic performance of the dc-side voltage is improved when load unbalancing occurs. The coupling effect between the overall control for the CHBR is also eliminated. Finally, experimental prototype tests are conducted to verify the effectiveness of the proposed method.