PCM-controlled superbuck converter with super performance and surprises

The paper investigates the dynamics associated to the fourth-order converter known as two-inductor buck, current-sourced buck or superbuck converter under peak-current-mode control. In late 1970s, the optimality of a converter was considered based on the continuity of the input current and the output current supplying the output capacitor. As a consequence, the converter named as Cuk converter according to its inventor was qualified as an optimal converter. The continuity of input and output currents does not suffice anymore but the properties such as input and output invariance, nonexistence of control anomalies, and the order of control dynamics have to be considered. The paper investigates the dynamic properties of the superbuck converter under peak-current-mode control. The investigations show that the superbuck converter contains all the desired features but it may also incorporate resonant right-half-plane (RHP) zeros and poles, which can destroy the optimality. The appearance of the RHP zeros and poles can be controlled by careful power-stage design. Practical evidence is provided based on two high-frequency converters.