Unified Modeling and Double-Loop Controller Design of Three-Level Boost Converter

A new small-signal modeling of a three-level boost (TLB) converter, as well as the design methodology for a double-loop controller, are presented in this paper. Unlike the conventional modeling of the TLB converter, which involves three state variables, the suggested modeling is based on two state variables; hence, simple transfer functions can be obtained. The proposed method is operable at a full duty ratio using unified modeling approaches, regardless of the mode changes. The analysis shows that the transfer functions of the two operation modes are identical. This suggests that the small-signal modeling of the TLB converter is identical to that of a conventional single-level boost converter. Hence, this implies that a linear feedback controller is applicable for all operational ranges. The method to design a double-loop controller using a proportional-integral controller is shown in a stepwise sequence. In addition, a capacitor voltage unbalancing controller is described. Simulations and experimental verifications are conducted to verify the effectiveness of the small-signal analysis and control system design.