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Low Loss Integrated Inductor and Transformer Structure and Application in Regulated LLC Converter for 48V Bus Converter

Year: 2020 | Author: Ahmed Nabih | Paper: T3.10
Converter schematic
Fig. 1. Single stage LLC DC/DC converter with matrix transformer
  Intermediate bus architectures employing 48 V bus converters are widely used in telecom power supply applications. With the rapid increase of demanded power by these loads, higher efficiency and power density are driving for better performance power management solutions.
  In this work, a single stage LLC converter with integrated mag- netics is proposed for 48 V/12 V-1 kW bus converters that can provide both regulation and isolation. The current practice for dc-dc-bus converters is to operate at low switching frequencies, 100-200 KHz, with power density below 400 W/in3. For higher power density, this converter will operate at a 10-times higher frequency than indus- try practice. The LLC converter is most suitable for high-frequency operation due to its soft switching properties for all devices so that higher efficiency and power density can be realized. For high output current and low voltage dc-dc converters, the matrix converter has proven to be a perfect candidate as it distributes the secondary cur- rent among different outputs to reduce the total conduction>  In this work, two matrix transformers, each with two transformer outputs, is used to deliver a 1 kW output power. The two transformers are connected in parallel from both primary and secondary windings as shown in Fig. 1; the primary windings are arranged in a way to integrate the parallel transformers with one core structure.
  To achieve output voltage regulation, the resonant inductor needs to be designed to a specific value to have the required regulation capabilities. A novel magnetic structure is proposed where the transformer primary windings are extended with the addition of a magnetic core to achieve a controllable leakage inductance to achieve the regulation capabilities. The shared winding will result in lower losses of the resonant inductor. The proposed PCB winding arrange- ment is shown in Fig. 2. A prototype has been developed for the pro- posed converter, achieving a power density of 800 W/in3 with an es- timated efficiency > 97% higher than all available industry practices.
Matrix transformer and inductor
Fig. 2. Integrate matrix transformer and inductor PCB winding arrangements

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