TEMPERATURE PREDICTION

AND THERMAL MANAGEMENT

FOR COMPOSITE MAGNETIC

CONTROLLERS OF INDUCTION

COILS

V. Nemkov, R. Goldstein, J. Jackowski, N. Vyshinskaya, C. Yakey

Fluxtrol, Inc., 1388 Atlantic Blvd, Auburn Hills, Michigan 48326,

USA

Overview

• Composite Magnetic Controllers for

Induction Coils

• Specialty Material Fluxtrol 75

• Temperature Prediction via Computer

Simulation

• Methods of Temperature Control

• Examples of Application

• Conclusions

Composite Materials for Magnetic

Controllers

Fluxtrol magnetic composites are premium materials widely

used in induction devices due to excellent machinability, ability

to work in 3D field and at any frequency (even at 13.56 MHz)

Temperature prediction and management are very important

for reliable performance of inductors

Controller temperature depends upon its geometry,

magnetic losses, material thermal conductivity and

boundary conditions

New specialty material Fluxtrol 75 with high thermal

conductivity was recently developed in addition to three

main materials (Fluxtrol A, Fluxtrol 50 and Ferrotron 559)

4

Specialty Material Fluxtrol 75

Formulated for middle to high frequencies (30-400

kHz), it has maximum permeability of 75 and saturation

flux density 1.5 T. Due to high permeability and thermal

conductivity (λ = 0.16 W/cmK) it can be effectively used

for heavy loaded HF applications

0

2000

4000

6000

8000

10000

0 20 40 60 80 100 120 140

H, A/cm

B,

Gs

0

10

20

30

40

50

60

70

80

0 2000 4000 6000 8000 10000

B, Gs

μ

Composite Material Anisotropy

Fluxtrol A: λ ᅩ = 0.2 W/cmK λ ॥ = 0.06 W/cmK

Pressing

direction

All pressed composites have certain anisotropy!

B A C

Orientation C is optimal due to lower

losses and higher heat transfer

Particle deformation and

orientation during pressing

Thermal Management

Methods of thermal control:

- Favourable coil design

- Optimal material selection

- Material orientation

- Gluing technology

- Cooling plates

- Internal cooling

Controller temperature prediction and

management are very important for reliable

performance of inductors

Prediction of Magnetic Controller

Temperature in 2D Case

25.4

I1

I1

I1

I2

I2

I3 Glue

In Flux 2D:

Step1: EM simulation and mapping magnetic field distribution

Step2: Controller area discretization for subdomains with appr.

constant B and extracting of Bavg vector

I1 – I3 - boundary conditions

Prediction of Magnetic

Controller Temperature

Pv = c Ba fb c – coefficient specific for material

a and b – values of flux density and frequency

dependencies a = 2-2.2, b = 1-1.25

Pv = (c1B1a + c2B2

a) fb

Step 3: Calculation of a vector of magnetic loss power

density Pv

If magnetic field has two components, the coefficients c1

and c2 can characterize the anisotropy in the calculation of

the vector of magnetic loss power density Pv

Prediction of Magnetic

Controller Temperature

Step 4: insertion of magnetic

losses into Flux 2D and

calculation of temperature

distribution with account of proper

boundary conditions In

Max T = 90 C

Temperature in coil copper and

Fluxtrol A concentrator at 20 kHz; the

part power is 80 kW per half meter

In Flux 3D:

Formulae for losses Pv vs. B

and f can be inputted directly

into the program

Max T = 193 C Max T = 127 C

III

Prediction of Magnetic

Controller Temperature

Temperature distribution in coil copper and Fluxtrol 75

concentrator at 200 kHz; part power is 80 kW per half meter

Optimal orientation (C) Non-optimal orientation (A)

Frequency (kHz)

Orientation

Ppart (kW)

Pcu (kW)

Pconc (kW)

Ptotal (kW)

Tconc

max

U (V)

I (A)

20 C 80 23 1.7 104 90 0C 183 4000

200 C 80 24.7 4.2 108 127 0C 878 2190

200 A 80 25 5.8 109 193 0C 877 2200

Induction Coil Parameters

• Orientation of the concentrator material influences its

temperature without notable influence on coil parameters

• Relative losses in concentrator grow significantly with

frequency

Coil length is half meter

Induction Coil with Cooling Plates

Cooling

plate

Extended

Cross

Legs

Rated coil parameters: Frequency 150 kHz, Bm = 400 Gs

U = 660 V, I = 3500 A, S = 2300 kVA, Q = 90

Controllers with Internal Cooling

Sandwich of two plates with cooling channels (left)

and a single plate with water connector (right)

Magnetic Bridge with Internal

Cooling

Bridge with cooling channel Illustration of Bridge setup for

welding with multi-turn inductor

Magnetic Bridge improves welding quality and allows to

increase welding speed 25-30%

Summary

• Composite magnetic materials may be effectively

used in the most challenging applications

• Computer simulation can predict the controller

temperature with good accuracy

• Several methods of thermal management may be

used to prevent controller overheating

• Internal cooling is one of the most effective

methods

• More information about composite magnetic

materials may be found @ www.fluxtrol.com