A whole control strategy for cascaded H-bridge rectifiers under distorted grid voltage and unbalanced load

Control for single-phase cascaded H-bridge rectifier (CHBR) under distorted grid voltage is seldom discussed in the existing control methods; a modified direct power control (DPC) scheme is therefore proposed in this paper. A simple power control structure with proportional-integral control method is first presented, which can discard phase-locked loop (PLL) and coordinate transformation. Then, an improved fictitious orthogonal algorithm is proposed to provide a better anti-disturbance ability compared with the traditional second-order generalized integrator (SOGI). Since the orthogonal component of the grid current runs concurrently with the power reference, it offers an excellent dynamic performance in inner loop. On the other hand, a voltage balancing control (VBC) model by the relationship between the difference of dc-side voltage square and that of power is established. On this basis, an internal model VBC (IM-VBC) method is provided to reduce the parameter tuning complexity. With this method, the dynamic performance of voltage balancing on the dc side is improved. Finally, several test results on hardware-in-the-loop (HIL) and scale-down platform are demonstrated, which validate the effectiveness and superiority of the proposed control strategy.