A Bidirectional Three-Level Converter Control With Shared Control Circuit and Single-Point Sensing for Flying Capacitor Balance

This article presents a novel three-level (TL) converter control integrated circuit (IC) with a flying capacitor control loop, an adaptive constant
on
-time (ACOT) control, and a shared control circuit in bidirectional operation for the battery charger system. To solve the flying capacitor balance issue in TL converters, the flying capacitor control with single-point sensing (SPS) of switching voltage
V_X
is proposed to balance the flying capacitor without a complex control and sensing circuit in an IC implementation. The proposed SPS also minimizes the inductor ripple. Besides, both directions (buck mode or boost mode) share the same control circuits except for the compensator to minimize the controller die area. The proposed scheme is realized with a 1.5 MHz switching frequency bidirectional TL converter IC in the TSMC 0.18
μ
m complementary metal-oxide-semiconductor (CMOS) process. The measurement result verifies that the functions are feasible in both directions, and there are no flying capacitor voltage runaway and mismatch issues. The proposed ACOT design achieves less than 6% switching frequency variation over the load range in boost mode, which is much smaller than conventional ACOT control. The proposed TL buck converter achieves an efficiency of 95.89% at 1-A load. The efficiency of the proposed TL boost converter is up to 96.02% at 0.5-A load.