An Expanded Lyapunov-Function Based Control Strategy for Cascaded H-Bridge Multilevel Active Front-End Converters

Cascaded H-bridge multilevel (CHBML) active front-end (AFE) converters exhibit some enticing benefits, comprising high adaptability for numerous applications, such as tractions, solid-state transformers, electric vehicle charging stations, and medium and high power electric drives. Yet, when the CHBML-AFE is operating under an unbalanced load condition, it is crucial to utilize an advanced control technique to maintain system stability. In this research, a Lyapunov Function (LF)-based control approach is utilized for regulating a single-phase CHBML-AFE with LCL filter to achieve global asymptotic stability. A capacitor voltage feedback is introduced and added to the traditional LF-based control strategy to reduce the resonance of the LCL filter. Furthermore, the proportional-resonant (PR) control procedure is utilized to derive the grid current reference, offering improvement to the robustness of the current control design. A balanced DC voltage control method is also employed to suppress the unbalanced DC voltage conditions among CHBML-AFE cells. In addition, the transfer function of the reference grid current and the actual grid current is evaluated for the CHBML-AFE with LCL filter parameters and their eventual variations in the employed control technique. The effectiveness of this control strategy is validated utilizing simulation and experimental studies.