Robust Single-Loop Control Strategy for Four-Level Flying-Capacitor Converter Based on Switched System Theory

Abstract

For the four-level flying capacitor converter (FFCC), it is required to simultaneously control the output voltage and balance the flying-capacitor voltages. Existing control methods for the FFCC always employ multiple control loops, where for every controlled voltage variable an independent control loop is to be designed. However, such a control structure of multiple loops leads to a complex coupling effect among these loops. Due to the coupling, it is difficult to achieve a coordinated design of a large number of control parameters and demonstrate the control system stability. To simplify the control design and the implementation, this article proposes a single-loop control strategy by using the switched system theory. All the voltages are driven towards their desired values with a single control loop, instead of using several individual controllers. Thus, the issue of devoting efforts to dealing with the couplings among multiple control loops is bypassed. Moreover, the system's large-signal stability is ensured in a straightforward manner, thereby simplifying the stability analysis. In the design process, the system parameter uncertainties are also considered. Comparative experiments demonstrate the good transient performance and the strong robustness of the proposed control strategy.