ANSYS ADVANTAGE Volume VIII | Issue 3 | 2014 © 2014 ANSYS, INC. 1

ACADEMIC

BRINGING DOWN THE VOLUMEThe University of Pittsburgh and Carnegie Mellon University have teamed up with the Advanced Research Project Agency - Energy and others to develop novel high-frequency, magnetic nanocomposite materials for power applications with material performance proven by ANSYS simulation.

By Brandon Grainger, Student; Oreste Scioscia, Student; and Gregory Reed, Director, Electric Power Initiative, University of Pittsburgh, U.S.A.

W ith any modern technology, the key to success is to make the prod-uct smaller, faster, simpler and more

cost efficient. Engineers need to find a way to integrate renewable energy (wind and solar primarily) into the existing grid while considering these design goals. Engineers at the University of Pittsburgh (Pitt) and Carnegie Mellon University (CMU) are working with patented nanocomposites (HTX-012B) that are designed to com-pete with ferrites used in modern power transformers. The Advanced Research Projects Agency -Energy (ARPA-E) — part of the U.S. Department of Energy (DOE) — advances high-potential, high-impact energy tech-nologies that are too early for private- sector investment. The agency exists to help fund energy research and technology developments that break through techno-logical and scientific barriers and accel-erate technology to market. Awardees of ARPA-E funds are developing entirely new approaches and methods for solving exist-ing energy challenges. ARPA-E focuses on transformational energy projects by pro-viding funding, technical assistance and aid in preparing products for the market. In conjunction with ARPA-E, the Magnetics Division of Spang & Company and Los Alamos National Laboratory (LANL) are helping to transform the power electronics industry. Spang special-izes in research, design and production of a broad range of powder, ferrite and strip-wound magnetic cores for such applica-tions as transformers, inductors and power supply components. Spang is developing novel manufacturing techniques for the

HTX-012B core materials. LANL is a fed-erally funded research and development center, which aligns its strategic plan with priorities set by the DOE and other energy administrations. LANL uses the HTX-012B-based transformer core to develop next-generation power electronics systems that convert DC solar power into readily avail-able power for distribution to end users. Power electronics system design is a multiphysics application, and ANSYS soft-ware plays a critical role. Engineers at Pitt are using ANSYS PExprt and ANSYS RMxprt

With any modern technology, the key to success is to make the product smaller, faster, simpler and more cost-efficient.

Switches2nd Priority

HardMagnets High-flux

softmagnets

Highvoltage,

High energydensity,

High speed

>10 W, >95%Single-Chip

Single ChipAC

IntegratedWBG

>13kV WBG

UnipolarSiC

Si

HighEfficiency

1st Priority

3rd Priority

Magnetics

Convertors Capacitors

�Areas and priorities for power electronics improvements determined by ARPA-E in 2010

Primarycoil Secondary

coil

Magnetic flux

Iron core

�Diagram of a transformer

ANSYS ADVANTAGE Volume VIII | Issue 3 | 2014 © 2014 ANSYS, INC. 2

to compare the performance of the mate-rials developed by CMU in the ARPA-E program to ferrites in various applica-tions, including electric machines and transformers. PExprt is a tool for design, modeling, and analysis of transformers and induc-tors. Using a combination of classical and finite element analysis techniques, PExprt determines the core size and shape, air gaps and winding strategy for a given power converter topology. RMxprt is a tem-plate-based design tool used to calculate machine performance, to make initial siz-ing decisions and to perform hundreds of “what if” analyses. RMxprt can then auto-matically set up the ANSYS Maxwell project (2-D/3-D) including geometry, materials, boundary conditions (plus appropriate symmetries) and excitations with coupling circuit topology for rigorous electromag-netic transient analysis.

REDUCING MATERIALSUsing advanced magnetic materials that operate at a high switching frequency will result in significant reduction of materi-als for components. HTX-012B is a novel nanocomposite magnetic material with chemistry optimized to operate at high temperatures (above 200 C), high switch-ing frequency, tunable permeability that depends on the desired application, and a design applicable to high-power appli-cations (kW to MW scale magnetic core designs). If the material volume is min-imized, the result is a weight reduction in magnetic-based components with observed power density improvements. In addition, space restrictions may no longer apply when installing equipment — all benefits for electric ship design, as one example.

TAKING TURNSThe bidirectional DC/DC power converter interests engineers because it can trans-form DC voltages in shipboard power systems, accommodate electric vehi-

ACADEMIC

l1

l3

l2

b

a d

2h

cle design and be used for other power engineering applications. The convert-ers use high-frequency transformers in their design.

�Illustration of the framework used to provide analytical results for optimizing the transformer volume

Carnegie Mellon University Explores Other MaterialsIn another study, CMU colleagues ex-plored a new class of Fe-Co-based ma-terials in permanent magnet machine applications. Cobalt-rich compositions offer an alternative to iron-rich alloys for high-frequency operation when material strength is critical. With ANSYS simula-tion, 10 kW-rated machines showed a 70 percent size reduction when using HTX-005C (Fe-Co nanocomposite material) in place of non-oriented silicon steel.

80000

70000

60000

50000

40000

30000

20000

10000

0

Volu

me

(mm

3 )

Solution Volumes

Optimal Manufacturer Core Volume Solutions

24510 24510 39621 39621 43050 50416 50416 51152 51152 68265

1 2 3 4 5 6 7 8 9 10

�Optimal manufacturer core volume solutions of the top ten ferrite core solutions shown below.

Core Volume Turns Temperature Parallel Power Name (mm3) (°C) Turns Losses (W) ETD49 24,510 72 58.91 2 5.2485 ETD49 24,510 72 74.55 1 8.3685 EC70 39,621 55 42.84 2 4.6319 EC70 39,621 55 51.26 1 7.2212 EE45528 43,050 44 50.03 2 5.4129 EE47228 50,416 42 45.32 2 5.0993 EE47228 50,416 42 54.36 1 7.7417 ETD59 51,152 42 42.92 2 4.7803 ETD59 51,152 42 50.65 1 7.3051 EE48020 68,265 42 43.71 2 6.1329

Top ten ferrite core solutions rated for 1 kW

�ANSYS PExprt solutions for a ferrite-based core that can be improved by adopting the HTX-012B core.

ANSYS ADVANTAGE Volume VIII | Issue 3 | 2014 © 2014 ANSYS, INC. 3

When designing a 300 V, 20 kHz, 1 kW-rated transformer for a bidirec-tional DC/DC converter, PExprt opti-mizes the magnetics by minimizing the total system loss associated with the core and windings. The software also provides the top ten off-the-shelf fer-rite-core solutions that ANSYS users can purchase to use in their designs and prototypes. Engineers compared optimized solu-tions for a transformer core designed with traditional ferrites and the designed nanocomposite magnetic material. By operating at higher switch-ing frequency, component volume can be reduced, resulting in improved power density. This is one of the key milestones of the ARPA-E program. Hence, the core volume, total loss and number of wire turns on the core are parameters of interest in this analysis, with core vol-ume as the highest priority. Before the nanocomposite material could be evaluated in a charger applica-tion, the team needed to experimentally obtain loss characteristics of various cores as a function of frequency and induction level. Once engineers obtained the ferrite core parameters, they evalu-ated Steinmetz coefficients and used them as inputs into PExprt for HTX-012B. Six circular cores of HTX-012B were manufactured, annealed, impreg-nated and tested by technicians at Spang to determine loss characteristics. The material properties from the tested HTX-012B cores were obtained, provided to PExprt, and a similar analysis was con-ducted as previously described.

Engineers compared an estimated analytical solution, the simulated fer-rite core and the simulated HTX-012B core. The analytical result is an approxi-mation, whereas PExprt provides a more finite solution from a larger family of core shapes and sizes that are widely available. By using the HTX-012B mate-rial, the losses are more evenly distrib-uted between the core and windings. The number of turns required to achieve the converter rating is reduced in compari-son to the ferrite design, as is the core’s magnetizing inductance. The ferrite material does not exhibit any noticeable advantage in comparison to HTX-012B from an engineering design perspective. With the power of PExprt and its selection algorithms, the team found that the HTX-012B was a more suitable core structure than the ferrite core.

ACADEMIC

The design of power electronics systems is a multiphysics application and ANSYS software plays a critical role in the project.

NEW MATERIALS FOR INDUCTION MOTORSAlthough HTX-012B is an iron-rich alloy, the intent was to show power density improvements for induction motor appli-cations. Using the ANSYS RMxprt motor library, the researchers selected an exam-ple motor model to observe possible power density improvements for induc-tion motors. By increasing the driving fre-quency of the motor, the motor’s size will be shown to decrease. When increasing the driving frequency without changing any of the motor’s other parameters, the mechanical speed increases proportionally. The team con-sidered two motor models — one motor with two magnetic poles and another with eight poles, both operating at the same mechanical speed. The two-pole and eight-pole machines operated with a

HIGH-PERFORMANCE ELECTRONIC DESIGN: PREDICTING ELECTROMAGNETIC INTERFERENCEansys.com

ELECTRICAL POWER SYSTEM DESIGN, MODELING AND ANALYSIS USING ANSYS SUITE OF TOOLSansys.com/83volume

Transformer Analytical Result Optimized / Optimized / Property (Square Core) Commercial Ferrite Core Commercial Ferrite Core HTX-012B Core

Volume (mm3) 85,376 24,510 24,510

Bmax (T) Core 0.3 0.242 0.355

Loss (W) 1.79 0.924 2.516

Winding Loss (W) 7.02 4.324 2.683

Total Loss (W) 8.81 5.249 5.199

Turns 82 72 49

Core Temperature (C) -- 53.04 52.74

�Comparison of optimized core results

�Hardware of the ETD-49 core which was considered the best option. ANSYS Maxwell simulation shows a cross section of 72 windings configured in two parallel turns around the ferrite core.

ANSYS ADVANTAGE Volume VIII | Issue 3 | 2014 © 2014 ANSYS, INC. 4

�ANSYS RMxprt results show that a 56 percent size reduction and 57 percent weight reduction can be obtained when operating an eight- pole compared to a two-pole machine if HTX-012B is incorporated into the machine stator.

driving frequency of 50 Hz and 200 Hz, respectively. HTX-012B material replaces the stator material but not the rotor mate-rial to maintain mechanical integrity. M600-50A, a high frequency (2 kHz or less) electric steel, is used in the rotors of both machines. RMxprt is able to quickly optimize a motor's geometric parameters includ-ing stator and rotor diameters, and slot dimensions for given system constraints. These factors can be varied so that a decrease in the overall size (volume) of the motor becomes apparent. The team wanted the motor to operate at rated out-put power with efficiency greater than 80 percent and motor power factor above 0.90 while improving its overall power density. For the eight-pole motor, the mag-netic flux has less distance to travel to get from one end of a pole to the other. The width of the return path in the stator core must be wide enough so the motor’s abil-ity to produce torque is not diminished and the magnetizing current increased. If the magnetizing current increases, over-all system losses will increase, the power

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factor will decrease and the output power will not meet rated conditions. ANSYS RMxprt results showed that a 56 percent size reduction and 57 percent weight reduction can be obtained when operating an eight-pole compared to a two-pole machine if HTX-012B is incorpo-rated into the machine stator.

WINDING DOWNUsing ANSYS simulation products, the engineering teams provided numerical proof that smaller may, in fact, be bigger.

Material innovations for power magnet-ics allow those units to operate at higher switching frequency, resulting in drastic volume reductions and improved power density performance. With the help of ANSYS simulation solutions, specifically PExprt and RMxprt, engineers can eval-uate many designs rapidly. These design improvements in bidirectional convert-ers and electric machines could not have been economically determined any other way.