A Novel Low-Loss Modulation Strategy for High-Power Bidirectional Buck ${\bm +}$ Boost Converters

TLDR

The paper proposes a low‑loss, constant‑frequency ZVS modulation strategy for bidirectional buck‑boost converters in hybrid and fuel‑cell vehicles, aiming to outperform existing converters and soft‑switching methods. The strategy achieves ZVS by selecting the buck‑plus‑boost inductance and gating the switches so the inductor current has a negative offset at pulse edges, allowing MOSFETs to turn on while the body diode conducts, and is validated analytically and via simulation. The software‑only approach incurs no extra component cost, delivers excellent efficiency across the operating range, higher power density, and experimental tests on 12 kW and 17.4 kW/L prototypes confirm a maximum efficiency of 98.3 %.

Abstract

A novel, low-loss, constant-frequency, zero-voltage-switching (ZVS) modulation strategy for bidirectional, cascaded, buck-boost DC-DC converters, used in hybrid electrical vehicles or fuel cell vehicles (FCVs), is presented and its benefits over state-of-the-art converters and soft-switching solutions are discussed in a comparative evaluation. To obtain ZVS with the proposed modulation strategy, the buck+boost inductance is selected and the switches are gated in a way that the inductor current has a negative offset current at the beginning and the end of each pulse period. This allows the MOSFET switches to turn on when the antiparallel body diode is conducting. As the novel modulation strategy is a software-only solution, there are no additional expenses for the active or passive components compared to conventional modulation implementations. Furthermore, an analytical and simulation investigation predicts an excellent efficiency over the complete operating range and a higher power density for a nonisolated multiphase converter equipped with the low-loss modulation. Experimental measurements performed with 12 kW, 17.4 kW/L prototypes in stand-alone and multiphase configuration verify the low-loss operation over a wide output power range and a maximum efficiency of 98.3% is achieved.