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Design of a 24 V, 1 MHz, 5 kW Partial Power Processing Converter and High Frequency Transformer for 80 C Ambient Using Flex PCB Technology

Year: 2023 | Author: Minh Ngo | Paper: H3.5
Hardware prototype picture
Fig.1 Rigid and Flexible PCB Transformer Boards.
  Printed circuit board (PCB) transformers are desirable for future high-density power converter applications due to their well-established manufacturing process, which reduces transformer parameter variation, labor, and system cost. While 1 -- 3 MHz PCB transformers have been demonstrated commercially, the power -- and consequently, current rating -- is low, typically below 300W. In the literature, > 500kHz PCB transformers have been shown, but with little information offered about their thermal performance, which remains the bottleneck for high-density magnetics. This paper analyzes flexible PCB technology with its naturally thin dielectric as a way to enable low-leakage-inductance, high-density PCB transformers with acceptable thermal margins. Ten-layer, 1 MHz, 69A rms flex and FR4 PCB transformers were constructed; the flex PCB showed a 15 -- 20°C peak temperature reduction.

  The PCB transformers constructed in this work are implemented in a 5kW, 1MHz, 360 -- 400Vin to 24Vout partial power processing converter. The majority of the power flows through a fixed-gain CLLC resonant converter that always operates at the resonant frequency, enabling zero-voltage switching (ZVS) and high efficiency to be achieved over the entire load range. A two-phase interleaved buck converter in series with the variable input is used to realize constant 24V output. Because a buck converter is used to set the input to the fixed-gain CLLC resonant converter, the converter uses simple proportional-integral (PI) control instead of complicated pulse-frequency modulation (PFM) control, which simplifies the design process and converter implementation. With ZVS occurring over the entire load range, the partial power processing topology shows improved EMI performance compared to conventional two-stage solutions. The converter achieves a peak efficiency of 98.5% at full load, 156 W/in3 power density, and is able to successfully operate at full load in an 80° C ambient environment with conductive cooling of the converter to a common chassis.
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