Dialogue Session I: EMI and Magnetics

Monday, April 10, 2017


D1.1 2 W Gate Drive Power Supply Design with PCB-Embedded Transformer Substrate

Bingyao Sun
Rolando Burgos
Dushan Boroyevich

Abstract
As silicon carbide (SiC) and gallium nitride (GaN) devices become commercially available nowadays, high switching frequency operation becomes a popular way to increase the power converter efficiency and power density. A key trade-off of these gains is the increasing electromagnetic inference (EMI) noise. In order to attenuate the EMI noise from the power loop into the auxiliary sources, the isolation capacitance in the isolated gate drive power supply is expected to be as small as possible. To this end, a gate drive power supply dedicated to driving two 650 V GaN devices in a phase leg is presented with a PCB-embedded transformer as substrate, achieving an ultra-low intercapacitance 1.6 pF, high efficiency 83% and high power density 72 W/in3. The power supply uses active-clamp flyback topology, switching at 1 MHz with soft-switching technique, and owns two isolated outputs, generating 1 W each. A PCB-embedded transformer is proposed, whose toroidal core and three windings are fully embedded into PCB, using standard lamination process, in favor of high-integration converter design.

Video Nugget


D1.2. Active dv/dt Control of 600V GaN Transistors

Bingyao Sun
Rolando Burgos
Xuning Zhang
Dushan Boroyevich

Abstract
With the fast-switching devices like GaN HEMT applying in power converters, the converters achieve higher switching frequency, higher efficiency and higher power density. As a result of the fast switching edge and high commutation speed, the issues like electromagnetic interference (EMI), overvoltage, gate protection become daunting tasks. The active gate control technique has been verified on the Si device to be an effective tool to relieve the challenges above, especially to reduce EMI noise by slowing down dv/dt with less penalty of switching loss. The paper proposes a new active dv/dt control circuit with fast response to change the 600 V GaN HEMT turn-off and turn-on dv/dt slew rate freely and independently, while the converter is running. To achieve this, simulations are first performed to verify the circuit function, considering all the possible parasitics distributed on the experimental setup, and a detailed circuit design is followed. Experimental results obtained on the 300V dc 15 A load current double pulse tester, composed by a GaN HEMT phase leg, validates the proposed method by varying turn-on dv/dt slew rate from 27.1 V/ns to 8.8 V/ns, turn-off dv/dt from 34.6 V/ns to 7.6 V/ns. Finally comparison with different gate resistors is provided, showing the proposed method has a smaller switching loss underthe same dv/dt condition than using a large gate resistor.


D1.3. Very High Frequency IVR for Small Portable Electronics with High-Current Multi-phase 3D Integrated Magnetics

Dongbin Hou
Fred C. Lee
Qiang Li

Abstract
As today’s small portable electronics (smartphones, tablets, e-readers, etc.) becomes lighter, thinner, quicker, and smarter, the voltage regulator for the processor is expected to be efficient, miniaturized, integrated, and placed closer to the processor. In this paper, a concept of a very high frequency (tens of MHz) 3D integrated voltage regulator (IVR) for small portable electronics is proposed. The magnetic characterization technique at tens of MHz is investigated, and the issues of and solutions for permeability and loss measurement are demonstrated. The LTCC and NEC flake materials are characterized and compared for the IVR inductor development. Both single-phase and five-phase integrated inductors are designed, fabricated and experimentally tested at 20MHz, featuring a simple single-via winding structure, small size, ultra-low profile, ultra-low DCR, high currenthandling ability, air-gap-free magnetics, multi-phase integration within one magnetic core, and lateral non-uniform flux distribution.


D1.4. Over-Molded Inductor (OMI) – Feasibility Demonstration in a dc-dc Converter

Ting Ge
Yi Yan
Guo-Quan Lu
Khai Ngo

Abstract
A significant fraction of the volume of a dc-dc power module is often occupied by the filter inductor and by the molding compound padding the unused space. This letter presents a method to fabricate an inductor in which the core is realized by molding a magnetic mixture over the circuit board. Permeability above 20 was achieved using a curing temperature not exceeding 250 °C, and no applied pressure. A power converter with input of 12 V, output of 1.2 V at 5 A, and switching frequency of 500 kHz was constructed to check the operation with a 1.1 μH OMI. The over-molded magnetic material did not adversely interfere with converter operation, e.g., switching noise was low. The maximum temperature of 48.3 °C and full-load efficiency of 82% are similar to those of the same circuit using a discrete inductor.


D1.5. Two Core Implementation of Coupled Inductor for Parallel Three-phase Power Converters

Sunjae Ohn
Xuning Zhang
Rolando Burgos
Dushan Boroyevich

Abstract
Coupled inductors are widely used for parallel operation of three-phase converters. By adding one coupled inductor for each phase, the circulating current between two converters can be effectively suppressed. The conventional structure of the coupled inductor is originated from DC-DC conversion and does not employ any characteristics of 3-phase system. In this paper, an integrated structure of coupled inductors is proposed for 3-phase ac-dc power conversion. According to the differential-mode and common-mode, three coupled inductors can be integrated into two; one for suppressing differential-mode circulating current, the other for common-mode circulating current. The proposed integrated coupled inductors can easily be built with standard shape cores. The validity of proposed integration is verified by an experiment with 2kW paralleled converters. With proposed integration, the total weight of the coupled inductors could be reduced by 30%.


D1.6. Synergetic Optimization of Efficiency and Stray Magnetic Field for Planar Coils in Inductive Power Transfer Using Matrix Calculation

Ming Lu
Khai D. T. Ngo

Abstract
Efficiency and stray magnetic field are influenced simultaneously by design of planar coils in inductive power transfer. Their synergetic optimization is lacking in previous literature. Parametric sweep in finite-element simulation is one method for optimization but it’s time-consuming because thousands of simulations are required. A faster method using matrix calculation is described in this paper. Efficiency and magnetic field are calculated with winding vectors, permeance matrices, and current-to-field matrices instead of being simulated. Physical parameters of coils such as inner radii, outer radii, and distribution of turns are represented with winding vectors. Parametric sweep in simulation is replaced by sweeping winding vectors in matrix calculation to derive Pareto fronts which are used to select optimized coils. Comparison between matrix calculation and experimental measurement for an exemplary set of coils shows maximum differences of 4% for inductances, 9% for equivalent series resistances, and 12.5% for stray magnetic field.


D1.7. Equivalent Circuit for Gapped Coupled-Inductors from Flux Distribution

Han Cui
Khai D. T. Ngo

Abstract
An equivalent circuit for coupled windings is developed for inductors with significant fringing effect. The equivalent circuit is derived from a physical model that captures the flux paths through a leakage inductor and two mutual inductors on the primary and secondary side. Each side has a winding resistor in parallel with one mutual inductor to model winding loss with open circuit and phase-shift impact. Two time-varying resistors are employed to represent the core loss dynamically. The equivalent circuit is verified by both finite-element simulation (FES) and prototypes fabricated with flexible circuit.


D1.8. Additive Manufacturing of Toroid Inductor for Power Electronics Applications

Yi Yan
Jim Moss
Khai D. T. Ngo
Yunhui Mei
Guo-Quan Lu


Please note: This paper will be presented by Lanbing Liu (pictured), as Yi Yan has graduated.

Abstract
A commercial multi-extruder paste-extrusion 3D printer was used to process both metal and magnetic pastes into 3D structures of magnetic components for power electronics circuits. For the magnetic core, we formulated a permalloy powder filled benzocyclobutene composite in the form of paste, termed poly-mag paste, as a feed stock for the printer; while for the conductive winding feed stock, we used a commercial nanosilver paste. A toroid inductor was 3D-printed by using the metal and magnetic pastes, and it was cured at 250 °C for a half hour without any external pressure to form the structure. The inductance of the 3D-printed toroid inductor was measured to be about 110.3nH. The DC resistance of the winding was 0.28Ω. Both the winding and core magnetic properties can be improved by adjusting the feed paste formulations and their flow characteristics and fine-tuning the printer parameters, such as motor speeds, extrusion rate, and nozzle sizes.

Video Nugget


D1.9. Improved Coupled Inductor Design for 6.6kW On Board Battery Charger

Yuchen Yang
Zhengyang Liu
Fred C. Lee
Qiang Li

Abstract
Coupled inductor has been widely adopted in VR applications for many years because of its benefits such as reducing current ripple or improving transient performance. In this paper, the positive coupled inductor concept is applied to interleaved totem-pole CRM PFC converter for 6.6kW on board battery charger. The difference between negative coupling and positive coupling will be discussed. The benefit of positive coupling for battery charger will be presented, such reducing switching frequency range and reducing input DM noise. Hence the positive coupled inductor can improve the performance of PFC converter. In addition, balance technique is applied to help minimize CM noise. Furthermore, the inductor is integrated into PCB winding. With the inductor integration, the converter can avoid labor intensive production and achieve fully automatic manufacture. However, it is noticed that the PCB winding inductor has larger parasitic capacitance. And this parasitic capacitance will introduce spikes and ringing and extra loss. In this paper, an improved PCB winding inductor design is provided to minimize parasitic capacitors and reduce loss.


D1.10. Design of Inductors With Significant AC Flux

Zhemin Zhang
Khai D. T. Ngo
Jeff L. Nilles


Please note: This paper will be presented by Ting Ge (pictured), as Zhemin Zhang has graduated.

Abstract
A design methodology is introduced to select a minimum core volume for an inductor or coupled inductors experiencing appreciable core loss. The geometric constant (Kgac) has been found to be a power function of the core volume for commercial toroidal, ER, and PQ cores, permitting the total loss to be expressed as a direct function of the core volume. The inductor is designed to meet specific loss or thermal constraints. An iterative procedure is described in which 2-D or 3-D proximity effects are first neglected and then subsequently incorporated via finite element simulation. The methodology is demonstrated for coupled inductors in a 5-MHz converter in critical conduction mode. The core loss is verified using rectangular excitation and the winding loss is inferred from thermal measurements.


D1.11. New Tunable Piezoelectric Transformers and Their Application in DC-DC Converters

Mudit Khanna
Qiong Wang
Rolando Burgos
Alfredo Vazquez Carazo
Khai D. T. Ngo

Abstract
This paper introduces a new Tunable Piezoelectric Transformer (TPT) and demonstrates its operation in a dc-dc converter application. Piezoelectric Transformers (PTs) have been conventionally used in high voltage, low power applications such as electronic ballasts. Recently, radial type PTs have been developed for higher power ac-dc and dc-dc step down applications. Based on the latter, a new TPT has been developed featuring an auxiliary secondary terminal to control the voltage gain of the transformer. This results in some exciting characteristics from a dc-dc converter standpoint, like an adjustable frequency response of the TPT, and fixed frequency control of the converter with no-cross talk between the primary and secondary in the control circuit. This paper introduces the design concept behind TPT-based dc-dc converters, and proposes a control scheme for their implementation. Experimental results with a 30 W 220:55 V converter unit are shown to validate these concepts.


D1.12. Resonant Converter with Coupling and Load Independent Resonance for Omnidirectional Wireless Power Transfer Application

Junjie Feng
Minfan Fu
Qiang Li
Fred C. Lee

Abstract
Omnidirectional wireless power transfer (WPT) system has been studied recently due to its better user experience compared with directional WPT system. And this paper focus on resonant converter study in omnidirectional WPT system. At first, three challenges of resonant converter design are identified: I. moving resonant frequency under variable coupling condition; II. voltage controllability under load change; III. complicated system control with coupling between multiple coils. CLCL-LC resonant converter is proposed to solve all the challenges and provide zero voltage switching (ZVS) operation for primary device at resonant frequency. A 6.78MHz CLCL-LC resonant converter for omnidirectional WPT system is built and tested.


D1.13. Very High Frequency Integrated Voltage Regulator for Small Portable Device

Dongbin Hou
Fred C. Lee
Qiang Li

Abstract
As today’s small portable devices (smartphones, tablets, etc.) becomes lighter, thinner, quicker, and smarter, the voltage regulator for the processor is expected to be efficient, miniaturized, integrated, and placed closer to the processor. In this paper, a concept of very high frequency (tens of MHz) 3D integrated voltage regulator for small portable devices is proposed. Both single-phase and 5-phase integrated inductor with NEC flake magnetic material is designed, fabricated and experimentally tested at 20MHz, featuring simple single-via winding structure, small size, ultra-low profile, ultra-low DCR, air-gap-free magnetic core,and lateral non-uniform flux.


D1.14. High-Frequency High-Efficiency GaN-Based Interleaved CRM Bidriectional Buck/Boost Converter with Inverse Coupled Inductor

Xiucheng Huang
Fred C. Lee
Qiang Li
Weijing Du


Please note: This paper will be presented by Yuchen Yang (pictured), as Xiucheng Huang has graduated.

Abstract
This paper presents a high-frequency high-efficiency GaN device-based interleaved critical current mode (CRM) bidirectional buck/boost converter with an inverse coupled inductor. The switching frequency is continually driven to megahertz range with GaN devices due to their small switching loss and driving loss, which greatly reduces the size of the passive components. The coupled inductor further reduces the core volume due to certain dc flux reductions. The equivalent inductance and the impact of the inverse coupled inductor on the CRM buck–boost converter are analyzed in detail. The resonant period in CRM is less with an inverse coupled inductor than with a noncoupled inductor, which is beneficial for the high-frequency operation. The soft-switching range and the circulating energy are both improved using an inverse coupled inductor in CRM. Experimental results validate the theoretical analysis, and the coupled inductor prototype efficiency is 98.5% at 1 MHz, which is 0.3% higher than a prototype with a noncoupled inductor.


D1.15. Omnidirectional Wireless Power Transfer for Portable Devices

Junjie Feng
Qiang Li
Fred C. Lee

Abstract
In this paper, omnidirectional wireless power transfer system proposed by Intel and the University of Hong Kong are evaluated first based on FEA simulation and numerical model. The analysis results show that their systems cannot generate preferred omnidirectional magnetic field. Then, a new transmitter coil structure with preferred omnidirectional magnetic field is proposed. Two modulation methods of the excitation current are also studied and compared. Finally, three 6.78MHz LCL resonant converters are built to drive the transmitter coils and generate omnidirectional magnetic field. Near field probe is used to measure the magnetic field to verify both the proposed transmitter coil structure and modulation methods.

Video Nugget


NP1.1. Development of High Noise Immunity Sensing Architecture for SiC-based Power Electronics

John Noon
Jun Wang
Jianghui Yu
Sungjae Ohn
Rolando Burgos

There is no paper associated with this session number. Click below to view the poster.


NP1.2. EMI Mitigation and Containment Strategy for Full SiC-based UPS

Sungjae Ohn
Paul Rankin
Jianghui Yu
Rolando Burgos
Dushan Boroyevich

There is no paper associated with this session number. Click below to view the poster.