Extendable Bidirectional DC-DC Converter With Improved Voltage Transfer Ratio and Reduced Switch Count

Bidirectional dc-dc converter (BDC) plays an important role in battery-based applications. This article presents an extendable BDC using 8+5n components, including 3+n mosfets, where n is the number of stages. The detailed analysis of single stage of the proposed converter is discussed. The voltage transfer ratio (VTR) of the converter during the step-up and step-down modes is derived. The effect of parasitic elements on the VTR and the efficiency is discussed. The state-space model is derived, and the open-loop transfer functions, v(H)/d(H) and v(L)/d(L) for both modes are obtained. These transfer functions are validated using circuit-level simulation. The operating modes of the converter are validated using a 300 W, 650 V, and 50 kHz prototype, and the experimental results are presented. Using the derived transfer functions, the PI controllers are designed using Ziegler-Nichols method for step-up and step-down modes. Using the Xilinx system generator, the designed controllers are implemented, and the experimental closed-loop results are presented. The performance comparison shows that the VTR of the single-stage converter using four mosfets is significantly improved compared to the other converters which achieve the quadratic VTR. Each extended stage requires a single mosfet along with four passive components.