Design of a 400kHz High-Frequency PCB Winding Transformer Based Dual Active Bridge Converter

Abstract

This paper presents a new design method for high-frequency printed circuit board (PCB) wound transformers and analyzes the selection method of magnetic cores and design considerations. This method differs significantly in structure from the traditional LITZ wire magnetization technique. The PCB wound transformer enables the transformer to have a broader frequency range and a smaller size, and the PCB manufacturing technology ensures highly consistent inter-turn and inter-layer spacing. By arranging the transformer windings appropriately, it can effectively operate at high frequencies up to 400 kHz. To optimize the transformer, the finite element analysis was conducted. By adjusting the length of the magnetic core air gap, the desired inductance value can be controlled. In addition, a comprehensive analysis of the transformer design stage, including losses, temperature, and insulation, was conducted using modeling and simulation functionalities in ANSYS, such as Maxwell and HFSS. The purchased PC95 magnetic cores are precision-cut in manufacturing, obtaining the dimensions that meet the simulation requirements based on the optimized design results. Simultaneously, the final design of the PCB winding is performed using Altium Designer to ensure compatibility with the magnetic cores. For the simulation modeling and control of the DAB converter, a simulation model was constructed using PLECS. The control scheme is based on the PI Energy Control energy controller, which adjusts the power by charging and discharging the energy of the DC-link capacitors on the load side. The DAB converter control system was improved based on the SPSM modulation method, which controls the direction and magnitude of power transmission by controlling the phase difference of the output voltage of the primary/secondary side full-bridge converter. In this paper, the voltage ratio between the two DC-link voltages is set at 1:1, and the winding ratio of the high-frequency transformer is designed as 4:4 based on a series of simulation designs, ensuring zero-voltage switching (ZVS) operation of the designed DAB converter throughout its operating range. Finally, the advantages of achieving high efficiency through single-phase shift modulation (SPSM) are validated, and implementation code that works in conjunction with TI's MCU is developed. This study conducted experiments on a 5.0 kW 400 kHz transformer based on the DAB converter prototype under 100 kHz conditions, demonstrating a high transformer efficiency of up to 98.91%. The results also confirmed that in the design process of the transformer, placing the PCB winding in the middle position of the magnetic core results in the lowest winding resistance. Therefore, the transformer exhibits the lowest losses and highest efficiency at this position.