Two Independent Single-Loop Voltage Mode Control Method for 3-Level Buck Converter

Compared to a basic buck converter, the 3-level buck converter operates with the output inductor at twice the switching frequency. Additionally, the voltage across its flying capacitor contributes to reducing the slope of the inductor current. These factors can result in a reduction in the maximum output current ripple by up to four times, enabling the use of a smaller output inductor. Moreover, the voltage stress on the switches is only half of the input voltage. Therefore, the 3-level buck converter is advantageous for achieving high efficiency and high power density. To maintain these advantages, the voltage across the flying capacitor must be kept at half of the input voltage. Conventionally, this condition is usually ensured by using peak or valley current mode control methods. However, these methods have complex control circuits or algorithms and are vulnerable to noise interference because their operation is based on instantaneous peak or valley current sensing. Additionally, different control configurations must be employed for $M \lt 0.5$ and $M \gt 0.5$ , where M is the input-to-output voltage conversion ratio. In this paper, we propose a two independent single-loop voltage mode control method that can guarantee the flying capacitor voltage remains at half of the input voltage. The proposed control method is simple to implement and does not require current sensing or complex control algorithms, allowing the use of simple and low-cost digital or analog controllers. The method is also robust to noise interference because it only operates based on the output and flying capacitor voltage. Furthermore, this method ensures normal operation across all values of M without changing the control configuration. The experimental results from a 500 W-rated prototype confirmed the validity of the proposed control method.