Independent Voltage Mode Control for 3-Level Buck Converter

A 3-level buck converter has half the switch voltage stress compared with a conventional buck converter. In addition, the operating frequency of the output inductor is not only twice the switching frequency, but also the flying capacitor voltage can reduce the slope of the inductor current, resulting in a smaller output inductor size. As a result, a 3-level buck converter can achieve high efficiency and power density, provided that the flying capacitor voltage is maintained at half of the input voltage. Most conventional control methods for ensuring the voltage balance of the flying capacitor adopt peak or valley current mode control techniques, which require real-time current sensing. Therefore, these control methods not only require high-performance and expensive digital controllers to implement their complex control algorithms but are also susceptible to noise. This paper proposes an independent 2-loop voltage mode control technique that can ensure that the flying capacitor voltage is half of the input voltage. The proposed control technique is simple to implement and does not require current detection or complex control algorithms, allowing the use of a simple and low-cost microcontroller. Experimental results from a 500-W prototype confirm the validity of the proposed control technique.