Challenges and Trends in Magnetics

Transcription

1 Challenges and Trends in Magnetics Prof. W. G. Hurley Power Electronics Research Centre National University of Ireland, Galway IEEE Distinguished Lecture The University of Hong Kong 27 May 2016

2 Outline Introduction Magnetics Materials Research and Design Challenges High Frequency Effects Fringing in Inductors Leakage Inductance Packaging Gapped Transformer Design (e.g. LLC) Trends and Applications Planar Magnetics Integrated Magnetics Power Supply on Chip (PwrSoC) Wireless Power Transfer Solar Generation Consumer Electronics Power Electronics Research Centre, NUI Galway 2

3 Magnetic Materials Power Electronics Research Centre, NUI Galway 3

4 Soft Magnetic Materials The magnetic and operating properties of some soft magnetic materials Materials Ferrites Nanocrystalline Amorphous Si Iron Ni-Fe (Permalloy) Powdered iron Model TDK P40 VIROPERM METGLAS AK Oriented 500F 2605 M-4 MAGNETICS PERMALLOY 80 MICROMET -ALS 35μ Permeability, 10,000-5, μ i 150, , , B peak,t ρ, μωm Curie temp. T c, C P loss 60 mw/ cm 3 at 0.1T/50kHz 588 mw/cm 3 at 0.3T/100kHz 72 m W/cm 3 at 0.2T/25kHz mW/cm at 0.2T/5kHz 30.6mW/cm 3 at 1.5T/50Hz 315mW/cm 3 at 0.1T/10kHz Power Electronics Research Centre, NUI Galway 4

5 Core Loss Density vs Frequency [1] Qiang Li, Low-Profile Magnetic Integration for High-Frequency Point-of-Load of Converter, Ph.D. Dissertation, Virginia Polytechnic Institute and State University, Blacksburg, Virginia, Power Electronics Research Centre, NUI Galway 5

6 Core Loss Density vs Frequency A P decreases with increasing frequency Slide provided by T. Merkin Power Electronics Research Centre, NUI Galway 6

7 Losses in Magnetic Components Core losses Hysteresis loss Eddy current loss Fringing loss Skin effect loss Copper losses Proximity effect loss Power Electronics Research Centre, NUI Galway 7

8 Research and Design Challenges Power Electronics Research Centre, NUI Galway 8

9 High Frequency Effects High frequency effects Windings optimization Skin effect Proximity effect Thickness optimization Windings arrangement Core optimization Eddy current Power Electronics Research Centre, NUI Galway 9

10 Design Issues for High Frequency 2r I I I I Core J z Core Eddy currents r Eddy current Gap Ohm loss H 0 Primary H 1 Secondary Skin effect Proximity effect Fringing effect High frequency winding loss Core loss: Steinmetz equation, igse. Parasitic parameters: leakage inductance, stray capacitance Power Electronics Research Centre, NUI Galway 10

11 Skin Effect Factor i k i φ r O (f = 1 khz for 2.5 mm. diam. Cu wire) δ = I B(r) Eddy currents B(r) i r J J Z O r O 1.89 (f = 10 khz for 2.5 mm. diam. δ = r O Cu wire) O 5.99 (f = 100 khz for 2.5 mm. δ = diam. Cu wire) B(r) r O 18.9 (f = 1 MHz for 2.5 mm. δ = diam. Cu wire) r o r Current distribution Outer radius Wire axis ( α) Outer radius Eddy currents in a circular conductor Current distribution in a circular conductor Power Electronics Research Centre, NUI Galway 11

12 Skin Effect Rac R dc r0 Ratio of Radius to Depht of Penetration δ Current distribution in a circular conductor R ac /R dc due to the skin effect δ = 1 π f μσ The ac resistance is proportional to the square root of frequency at very high frequencies. Power Electronics Research Centre, NUI Galway 12

13 Proximity Effect Transformer cross-section with current density distribution Proximity effect factor for sinusoidal excitation As the number of layers increase there is a substantial increase in the ac resistance for a given layer thickness and frequency. Power Electronics Research Centre, NUI Galway 13

14 Proximity Effect R ac R dc p=10 p=8 p=6 p=4 p=3 p=2 p= Δ Transformer cross-section with current density distribution Proximity effect factor for sinusoidal excitation =Δ + where cosh 2 cos 2 3 cosh cos Δ= Δ Δ Δ+ Δ δ 0 2 R sinh2 Δ + sin 2 Δ 2( p 1) sinh Δ sin Δ d ac R dc As the number of layers increase there is a substantial increase in the ac resistance for a given layer thickness and frequency. Power Electronics Research Centre, NUI Galway 14

15 Optimum Thickness di di Reff Ψ R 4 dt eff 1 Ψ rms 3 dt rms = 1 + Δ ; = + Δ R 3 3 dc ωirms R Δ I δ ω rms The optimum value of 2 2 where Δ = opt 4 1 ωi rms Ψ di dt R rms 2 2 I = I + I rms dc n n= 1 R eff R δ di dt rms = ni ω n n= 1 Ψ= 2 5p 1 15 Finally Reff 1 Δ 1 R = + dc 3 Δ opt 4 Δ Plot of R eff /R δ versus Δ for various numbers of layers Power Electronics Research Centre, NUI Galway 15

16 Optimum Winding Thickness: Pushpull Optimum layer 8 t 2 t (8)(0.025) r r 2 D (0.025) (0025) 4 3 T π T 4 3 π Δ = = = opt 2 2 (5 p 1)15 [(5)(6) 1] /15 Skin depth δ = = = mm 0 3 f (50 10 ) Optimum layer thickness d =Δ δ (0.3342)(0.295) 295) 0.1mm opt opt o = = Effective ac resistance R eff 4 = R 3 AC resistance of round conductor k s r (05) o = (0.5) (05)( (0.5)( ) δ = = 0 dc Round versus foil conductor Power Electronics Research Centre, NUI Galway 16

17 Litz Wire Litz wire reduces the window utilisation factor, core may be 30% larger for same temperature rise Use strands with diameter less than δ/4 Proximity effect occurs at strand level when wire is twisted Twisting cancels proximity effect at bundle level Sullivan C. R., Zhang R. Y., Analytical Model for Effects of Twisting on Litz-wire Losses, IEEE 15th Workshop on Control and Modelling for Power Electronics, (COMPEL), pp Power Electronics Research Centre, NUI Galway 17

18 Litz Wire: skin effect Skin effect acts like a solid conductor at the bundle level Use strands with diameter less than δ/4 Acero J., Lope I., Burdio J.M., Carretero C., Alonso R., Loss Analysis of Multistranded Twisted Wires by Usinf 3D-FEA Simulation, IEEE 15th Workshop on Control and Modelling for Power Electronics, (COMPEL), pp. 1-6, 2014 Power Electronics Research Centre, NUI Galway 18

19 Litz Wire: proximity effect Proximity effect occurs at strand level when wire is twisted Twisting cancels proximity effect at bundle level Acero J., Lope I., Burdio J.M., Carretero C., Alonso R., Loss Analysis of Multistranded Twisted Wires by Usinf 3D-FEA Simulation, IEEE 15th Workshop on Control and Modelling for Power Electronics, (COMPEL), pp. 1-6, 2014 Power Electronics Research Centre, NUI Galway 19

20 Interleaving the Windings Current density distribution before interleaving in FEA J Current density distribution before interleaving Current density distribution after interleaving Current density distribution after interleaving in FEA Power Electronics Research Centre, NUI Galway 20

21 Interleaving the Windings W m = ½ μ0 volume 2 H dv W m μ N = ½ 2 MLT b I 3w 0 p 2 p H H J Current density distribution before interleaving -H 0 J J 0 0 -J J Current density distribution after interleaving A reduction in losses can be achieved by a factor of more than three in the proximity effect losses. Proximity effect reduces the leakage inductance. Interleaving also reduces leakage inductance. Power Electronics Research Centre, NUI Galway 21

22 Fringing (Magnetic Field) Frequency: 100kHz Core: Magnetics port core Gap in the centre leg Gap in the outer leg Power Electronics Research Centre, NUI Galway 22

23 Fringing (Different Frequencies) Magnetic Flux Frequency 1kHz Frequency 100kHz Power Electronics Research Centre, NUI Galway 23

24 Packaging and Thermal Management Power Electronics Research Centre, NUI Galway 24

25 3D Printing Components Power Electronics Research Centre, NUI Galway 25

26 Review of Resonant Converters 4 38kW 20kW 30kW High Power for Battery Charges LCC LLC LCC SRC PRC 3.5 Power / kw LLC Frequency / khz Wide band gap devices no longer limit switching frequency. Power Electronics Research Centre, NUI Galway 26

27 Review of Capacitor Technologies Slide provided by W. Grimm High voltage and high energy uses Al and film caps, ceramic caps for low power Higher operating temperatures envisaged Power Electronics Research Centre, NUI Galway 27

28 Various Energy-Storage Devices Ragone Chart for Various Energy-Storage Devices

29 Battery and Ultra-capacitor Comparison Between VRLA Battery and Ultra-capacitor Lead Acid Battery Li-ion Battery Ultra-capacitor Specific Energy Density (Wh/kg) Specific Power Density (W/kg) ,000 Cycle Life 1, > 500,000 Charge/Discharge Efficiency 70 85% 80 90% 85 98% Fast Charge Time 1 5hr hr sec Discharge Time 0.3 3hr sec 29

30 Trends and Applications Power Electronics Research Centre, NUI Galway 30

31 Planar Magnetics Low profile planar magnetic components have a lower profile than their wire wound counterparts due to the fabrication process; Automation it is difficult to automate the winding of conventional inductors and transformers, the processes used in planar magnetics are based on advanced computer aided manufacturing techniques. Suitable for SMT High power densities planar inductors and transformers are spread out and this gives them a bigger surface-to-volume ratio than conventional components, this enhances the thermal performance; Predictable parasitics with planar magnetics, the windings are precise and consistent, yielding magnetic designs with highly controllable and predictable characteristic parameters. Power Electronics Research Centre, NUI Galway 31

32 PCB Embedded Power Magnetics Air-core / Ferrite Cores / Thin Film Cores PCB Air-core Power Inductors in Haswell Processor Package 32

33 Thin film Magnetic Materials 10 mm Suitable for MHz eg e.g. GaN Converters Suitable Tyndall for Wire-wound MHz Inductor with Thin Film Laminated Core 40% reduction in volume 25% Magnetic core loss reduction 33

34 Planar Transformer Power Electronics Research Centre, NUI Galway 34

35 Technologies Comparison Technology Frequency Power Inductance Size (Typical) (Typical) (Typical) (Typical) PCB 100 mm 20 KHz ~ 2 MHz 1 W ~ 5 kw 10 µh ~ 10 mh 2 ~ magnetics 100 s cm 2 Thick Film < 10 MHz < 10 W 1µH~ 1mH < 1cm 2 LTCC 200 KHz ~ 10 MHz < 10W 1 µh ~ 1 mh < 1cm 2 Thin Film MHz < 1W 10 s ~ 100 s nh < 1mm 2 Power Electronics Research Centre, NUI Galway 35

36 Integrated Magnetics Integrated process, in which discrete magnetic devices are processed together with other components in an ultra-low profile, being compatible with integrated t circuit it (IC) technology. Power supply on chip Hybrid modules Micro-processed magnetic devices LTCC (Low Temperature Co-fired Ceramics) Power Electronics Research Centre, NUI Galway 36

37 PwrSoC: Silicon Integrated Micro-inductor Silicon integrated microinductor: (a) Top view. Reproduced with permission from [1]. Copyright 2008 IEEE, (b) Cross-section. Reproduced with permission from [2]. Copyright 2005 IEEE [1] W. Ningning, T. O'Donnell, R. Meere, F. M. F. Rhen, S. Roy, and S. C. O'Mathuna, 'Thin-Film-Integrated Power Inductor on Si and Its Performance in an 8-MHz Buck Converter,' IEEE Transactions on Magnetics, vol. 44(11), pp , [2] S. C. O. Mathuna, T. O'Donnell, W. Ningning, and K. Rinne, 'Magnetics on silicon: an enabling technology for power supply on chip,' IEEE Transactions on Power Electronics, vol. 20(3), pp , [3] CF Feeney, NW Wang, CO'M O'Mathuna, MD Duffy, A 20MHz 1.8 W DC-DC Converter with Parallel l Microinductorsi and dimproved Light-Load Efficiency, IEEE Transactions on Power Electronics, Power Electronics Research Centre, NUI Galway 37

38 Micromagnetics on Silicon for PwrSoc Killer Applications: Granular Power Management for Multi-core Microprocessors Isolated Power Micro-Transformers 38

39 Deploy & Forget - Powering the Smart Things in the Internet of Things (IoT) - < 1mWatt Wireless Sensor Node (WSN) Data Energy Storage Micro batteries Supercapacitors Energy Harvester Energy Source Vibration, Temp. Difference, Biofuel, Wireless Power 39

40 Wireless Power Transfer: Biomedical Implant Receiver Transmitter Receiver Wireless Power Transfer AC Source Load Transmitter Power levels constrained by EMI regulations Power Electronics Research Centre, NUI Galway 40

41 Wireless Power Transfer: Charger Power Electronics Research Centre, NUI Galway 41

42 Induction Heating Pot Vitroceramic glass Inductor Control electronics EMI filter Power electronics Power Electronics Research Centre, NUI Galway 42

43 Electric Vehicles Mobile charging Inductor of the DC-DC converter in 2010 Toyota Prius hybrid electric vehicle Power Electronics Research Centre, NUI Galway 43

44 Semiconductor Switches Slide provided by W. Grimm Power (W) Thyristor 100M 10M 1M 100K IGBT 10K MOSFET SiC,GaN 1K K 10K 100K 1M 10M Frequency (Hz) New devices allow for higher frequencies Power Electronics Research Centre, NUI Galway 44

45 GaN Switching Devices in LLC 1 Faster switching Higher frequency Smaller gap length Less fringing loss 2 Reduced output capacitance Larger magnetizing inductance Less conduction loss 3 No recovery in body-diode at light load Faster switching, smaller output capacitance and no recovery in the body diode at light load condition can be achieved. The reduced output capacitance of GaN will result in the possibility of applying larger magnetizing inductance which means lower fringing loss. Power Electronics Research Centre, NUI Galway 45

46 Research Directions Failure mechanisms in discretes Improved efficiency vs. power density High temperature operation Integration of passives and sensors Reliability/life time vs. redundancy New materials for magnetics e.g. nanocrystalline New materials for capacitors e.g. ceramics, nanotubes, graphene DC link capacitors Power Electronics Research Centre, NUI Galway 46

47 Acknowledgements Tyndall Institute Delft University of Technology Stanford University Technical University of Denmark Universidad de Zaragoza Zhejiang University Power Electronics Research Centre, NUI Galway 47