Yuchen Yang

Design and evaluation of GaN-based dual-phase interleaved MHz critical mode PFC converter

This paper presents the design consideration and performance evaluation of gallium nitride (GaN) high electron mobility transistor (HEMT) based dual-phase interleaved MHz critical conduction mode (CRM) power factor correction (PFC) converter. A 1.2kW 1-3MHz interleaved boost PFC converter prototype is built with 97.9% peak efficiency and 120W/in3 power density. The significant impact of MHz frequency is demonstrated as dramatically size reduction of boost inductor and electro-magnetic interference (EMI) filter. Several inductor designs are discussed. The corner frequency of EMI filter is pushed to several hundreds of kHz. Finally, the limitation of conventional boost PFC converter is discussed as high conduction loss on diode rectifier bridge and high switching loss caused by valley switching, which is negligible in other low frequency PFC converter but significant in MHz PFC converter. The totem-pole bridgeless PFC converter is introduced to further improve the efficiency with no rectifier bridge and zero-voltage switching (ZVS) extension strategy.

Design of GaN-based MHz totem-pole PFC rectifier

Totem-pole bridgeless power factor correction (PFC) rectifier is recently recognized as a promising front end candidate for applications like server and telecommunication power supply. In this paper the advantage, enabled by emerging high-voltage gallium-nitride (GaN) devices, of totem-pole PFC rectifier comparing to traditional PFC rectifier is discussed in the beginning. Critical mode operation is used by the totem-pole PFC rectifier in order to achieve both high frequency and high efficiency. Then several high frequency issues and detailed design considerations are introduced including zero-voltage-switching (ZVS) extension for entire line-cycle ZVS operation; variable on-time strategy for zero-crossing distortion suppression; and interleaving control for ripple current cancellation. The volume reduction of differential-mode (DM) electro-magnetic interference (EMI) filter significantly benefited from MHz high frequency operation and multi-phase interleaving is also presented. Finally, a 1.2kW GaN-based MHz totem-pole PFC rectifier is demonstrated with 99% peak efficiency and 200W/in3 power density.

Design of GaN-Based MHz Totem-Pole PFC Rectifier

The totem-pole bridgeless power factor correction (PFC) rectifier has recently been recognized as a promising front-end candidate for applications like servers and telecommunication power supplies. This paper begins with a discussion of the advantages of using emerging high-voltage gallium-nitride (GaN) devices in totem-pole PFC rectifiers rather than traditional PFC rectifiers. The critical-mode operation is used in the totem-pole PFC rectifier in order to achieve both high frequency and high efficiency. Then, several high-frequency issues and detailed design considerations are introduced, including extending zero-voltage-switching operation for the entire line-cycle, a variable on-time strategy for zero-crossing distortion suppression, and interleaving control for ripple current cancellation. The volume reduction of differential-mode electromagnetic interference filters is also presented, which benefits greatly from MHz high-frequency operation and multiphase interleaving. Finally, a dual-phase interleaved GaN-based MHz totem-pole PFC rectifier is demonstrated with 99% peak efficiency and 220 W/in

Transformer shielding technique for common mode noise reduction in isolated converters

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Analysis and filter design of differential mode EMI noise for GaN-based interleaved MHz critical mode PFC converter

power density.

Analysis and reduction of common mode EMI noise for resonant converters

In isolated converter, transformer is a main path of common mode current. Methods of how to reduce the noise through transformer have been widely studied. One effective technique is using shield between primary and secondary winding. In this paper, EMI noise transferring path and EMI model for typical isolated converters are analyzed. And the survey about different methods of shielding is discussed. Their pros and cons are analyzed. Then the balance concept is introduced and our proposed double shielding using balance concept for wire winding transformer is raised. It can control the parasitic capacitance accurately and is easy to manufacturing. Next, a newly proposed single layer shielding for PCB winding transformer is discussed. The experiment results are provided to verify the methods.

Common mode EMI reduction technique for interleaved MHz critical mode PFC converter with coupled inductor

Power factor correction (PFC) converter consumes a large part of volume of power supply. Typical switching frequency of commercial PFC converter is usually not higher than several hundred kHz. Increasing the switching frequency of PFC converter to MHz by using GaN devices can greatly reduce the size and increase power density of power supply. In order to eliminate the high turn-on loss of cascode GaN device, critical conduction mode (CRM) is applied. However, when operating on CRM, PFC converter has large inductor current ripple and variable switching frequency. This makes the differential mode (DM) noise a serious issue for CRM PFC converter. This paper provides a more accurate model to calculate the switching frequency and DM noise of MHz CRM PFC converter. Based on the model and experiment result, interleaving impact of DM noise for MHz CRM PFC converter is analyzed. DM noise filter is designed and it demonstrates that increasing the switching frequency of PFC converter to MHz can greatly increase the corner frequency of DM filter and reduce the filter size significantly.

Conducted EMI analysis and filter design for MHz active clamp flyback front-end converter

In this paper, the common mode (CM) EMI noise characteristic of three popular topologies of resonant converter (LLC, CLL and LCL) is analyzed. The comparison of their EMI performance is provided. A state-of-art LLC resonant converter with matrix transformer is used as an example to further illustrate the CM noise problem of resonant converters. The CM noise model of LLC resonant converter is provided. A novel method of shielding is provided for matrix transformer to reduce common mode noise. The CM noise of LLC converter has a significantly reduction with shielding. The loss of shielding is analyzed by finite element analysis (FEA) tool. Then the method to reduce the loss of shielding is discussed. There is very little efficiency sacrifice for LLC converter with shielding according to the experiment result.

Shielding Technique for Planar Matrix Transformers to Suppress Common-Mode EMI Noise and Improve Efficiency

Coupled inductor has been widely adopted in VR applications for many years because of its benefits such as reducing current ripple and improving transient performance. In this presentation, coupled inductor concept is applied to interleaved MHz totem-pole CRM PFC converter with GaN devices. The coupled inductor in CRM PFC converter can reduce switching frequency variation, help achieving ZVS and reduce circulating energy. Therefore the coupled inductor can improve the efficiency of PFC converter. In addition, balance technique is applied to help minimize CM noise. This paper will introduce how to achieve balance with coupled inductor. The novel PCB winding inductor design will be provided. The PCB winding coupled inductor will have similar loss with litz wire inductor but much less labor in manufacture.

Multi-phase coupled and integrated inductors for critical conduction mode totem-pole PFC converter

High frequency is the major catalyst for size reduction in the advancement of power conversion technology. It is essential to understand the EMI characteristic of high frequency converter since the EMI filter typically occupies one third of total system volume. This paper presents an insight view of CM/DM noise transformation in Flyback converter for low power adapter applications. The so-called mixed-mode noise is DM noise transformed from CM noise due to unbalanced impedance when the diode-bridge is off. The transformer shielding technique can effectively reduce the CM noise, and therefore it can significantly reduce the magnitude of CM transformed noise. A 65W (19V/3.3A) prototype of active clamp flyback front-end converter operating around 1MHz with GaN devices is developed to verify the analysis. A single stage EMI filter is designed accordingly with much smaller size compared with industry practice.