μ -Synthesis-Based Robust Power Control for Single-Phase Cascaded H-Bridge Rectifier in Power Electronic Traction Transformer

Abstract

Single-phase cascaded H-bridge rectifiers (CHBRs) are widely studied for power electronic traction transformers (PETTs). However, dynamic uncertainties, such as parameter perturbations, control delays, and external disturbances, may result in significant dc-link voltage fluctuations, degrade the quality of ac current, and even lead to system instability. Accordingly, this article proposes a $\mu $ -synthesis-based robust power control strategy to improve the control performance and robust stability (RS) of the CHBR system. First, a modified dynamic power model of the CHBR is established in the stationary reference frame, enabling direct and independent regulation of powers while eliminating phase-locked loop (PLL) links. Subsequently, the $\mu $ -synthesis-based direct power control ( $\mu $ -DPC) design methodology is presented, in which the structured parameter uncertainties, delay uncertainties, and external disturbance are all considered. In addition, a desired closed-loop transfer function is incorporated into the suggested power control structure to reflect the time-domain specification. With the proposed $\mu $ -DPC, the required time-domain performance, system RS, and robust performance (RP) can be achieved directly via a $\mu $ -synthesis framework. Finally, comparative simulation and experimental tests are conducted to verify the effectiveness of the proposed scheme.