1. EET 423 POWER ELECTRONICS -2
Prof R T Kennedy
POWER ELECTRONICS 2

2. ELECTRIC - MAGNETIC ANALOGY
ELECTRIC CIRCUIT
CURRENT I
VOLTAGE
(EMF) V
(E)
RESISTANCE R
CONDUCTANCE G
CONDUCTIVTY
POWER
limits current density P
Ohm’s Law
Prof R T Kennedy
POWER ELECTRONICS 2

3. ELECTRIC - MAGNETIC ANALOGY
MAGNETIC CIRCUIT (N turns)
FLUX
wb (webers)
MMF F
A-T
(ampere turns)
RELUCTANCE R
A-T/wb
PERMEANCE P
PERMEABILITY
FLUX DENSITY
saturation limited
Tesla
Ampere’s Law
FIELD INTENSITY H
A-T/m
Faraday’s Law 
Prof R T Kennedy
POWER ELECTRONICS 2

4. Permeance is comparable to Conductance
(SI system) permeance is the inductance of a single turn
Reluctance is comparable to Resistance
Don’t equating these they’re not the same thing !!!!
Resistance is a power-dissipating element
Reluctance is an energy storage element
Reluctance: convenient way to describe magnetic elements
Prof R T Kennedy
POWER ELECTRONICS 2

5. current contained within circuit elements
circuit conductivity >>conductivity of air
Prof R T Kennedy
POWER ELECTRONICS 2

6. permeance of magnetic circuit only a few orders > air
air frequently forms part of magnetic circuit
flux leaves magnetic circuit (LEAKAGE FLUX)
Prof R T Kennedy
POWER ELECTRONICS 2

7. SMPS MAGNETICS INTENTIONAL: inductors and transformers
UNINTENTIONAL (PARASITIC):
leakage inductance
Prof R T Kennedy
POWER ELECTRONICS 2

8. INDUCTORS and INDUCTANCE
The FUNCTION of the SMPS ‘filter’ inductor is to STORE ENERGY in one interval and return it to the circuit during a later interval; a process that smoothes the current waveform.
Inductance (L), the primary functional parameter of an inductor, is a measure of the magnetic flux linking a coil and is the flux linkage per ampere
Prof R T Kennedy
POWER ELECTRONICS 2

9. core geometry and materials
scaling factor
core geometry and materials
Prof R T Kennedy
POWER ELECTRONICS 2

10. electromagnetic interference (EMI)
AIR CORED INDUCTORS A
low inductance
m = mo = 4 p 10-7
electromagnetic interference (EMI)
Prof R T Kennedy
POWER ELECTRONICS 2

11. due to ease of winding and assembly
MAGNETIC CORES
E I Cores
E Cores
the most common in use
due to ease of winding and assembly
but
are not self shielding
Prof R T Kennedy
POWER ELECTRONICS 2

12. MAGNETIC CORES Pot Cores
almost completely surround the windings thereby reducing EMI
but
difficulty in bringing the winding outside core
Prof R T Kennedy
POWER ELECTRONICS 2

13. MAGNETIC CORES Toroids
high flux density possible  smaller lighter cores
high flux density possible  smaller lighter core
reduced EMI: windings shield core!
Prof R T Kennedy
POWER ELECTRONICS 2

14. mcore  mr= mcore
 L 
Prof R T Kennedy
POWER ELECTRONICS 2

15. ASSEMBLIES
Prof R T Kennedy
POWER ELECTRONICS 2

16. MAGNETICS and ENERGY (J)
LOW ENERGY STORAGE
Prof R T Kennedy
POWER ELECTRONICS 2

17. core material characteristics depend on
sample
temperature
flux level
 inductor design unpredictable
Prof R T Kennedy
POWER ELECTRONICS 2

18. AIR GAPS N I A
F = NI
Prof R T Kennedy
POWER ELECTRONICS 2

19. independent of core material: gap counteracts Dm with current
reduced inductance
larger gap linear inductor
Prof R T Kennedy
POWER ELECTRONICS 2

20. Inductor Energy –Air Gap
Virtually all of the inductor’s energy is stored in the gap
Prof R T Kennedy
POWER ELECTRONICS 2

21. Prof R T Kennedy
POWER ELECTRONICS 2

22. LEAKAGE FLUX I L Lleakage N F = NI Prof R T Kennedy
POWER ELECTRONICS 2

23. reluctance R is now even lower
Fringing N I
F = NI
reluctance R is now even lower 
increased inductance
Prof R T Kennedy
POWER ELECTRONICS 2

24. minimal external field
large external field
minimal external field
Prof R T Kennedy
POWER ELECTRONICS 2

25. FERROMAGNETIC MATERIALS
magnetisation curve (hysteresis loop)
binternal
bexternal
Prof R T Kennedy
POWER ELECTRONICS 2

26. FERROMAGNETIC MATERIALS
magnetisation curve (hysteresis loop)
bexternal
binternal
Remanence (retentivity)
b when H is zero
Coercivity
H when b is zero
Prof R T Kennedy
POWER ELECTRONICS 2

27. b-H characteristic f-F characteristic b
flux density v magnetic field intensity
slope: permeability F f
f-F characteristic
total flux v magnetomotive force
slope: permeance
characteristic
defines equivalent electrical characteristic
(core + N turns)
slope: inductance
Prof R T Kennedy
POWER ELECTRONICS 2

28. HYSTERESIS CURVE and ENERGY
MAGNETIC SYSTEM ENERGY INPUT
HYSTERESIS LOSS
STORED ENERGY
RETURNED .
Prof R T Kennedy
POWER ELECTRONICS 2

29. HYSTERESIS CURVE and ENERGY
MAGNETIC SYSTEM ENERGY INPUT
HYSTERESIS LOSS
STORED ENERGY
RETURNED .
Prof R T Kennedy
POWER ELECTRONICS 2

30. CORE DATA SHEET + saturation SMPS major loop SMPS minor loop
sinusoidal driven
- saturation
Prof R T Kennedy
POWER ELECTRONICS 2

31. IDEAL MAGNETIC CORE
Prof R T Kennedy
POWER ELECTRONICS 2

32. ‘REAL’ MAGNETIC CORE LOW ENERGY STORAGE HIGH ENERGY LOSS HIGH L
Prof R T Kennedy
POWER ELECTRONICS 2

33. AIR GAPPED CORE HIGHER ENERGY STORAGE reduced L reduced energy loss
characteristic linearised
Prof R T Kennedy
POWER ELECTRONICS 2

34. PARAMETER DESIGN CHOICES
INCREASE FLUX DENSITY ‘b’
increase b  reduced turns N
 reduced winding loss
 increased efficiency
 reduced size
increase b  increased core loss
 increased core temperature
 reduced efficiency
Prof R T Kennedy
POWER ELECTRONICS 2

35. PARAMETER DESIGN CHOICES
INCREASE TURNS ‘N’
increase N  reduced b
 reduced core loss
 increased efficiency
increase N  increased winding loss
 increased winding temperature
 reduced efficiency
increase N  increased size
Prof R T Kennedy
POWER ELECTRONICS 2

36. PARAMETER DESIGN CHOICES
INCREASE AREA ‘A’
increase A  reduced b
 reduced core loss
 increased efficiency
increase A  increased winding length
 increased winding loss
 increased winding temperature
 reduced efficiency
increase A  reduced efficiency
increase A  increased weight
 increased size
Prof R T Kennedy
POWER ELECTRONICS 2

37. PARAMETER DESIGN CHOICES
INCREASE FREQUENCY
increase f  reduced b
 possible reduced core loss
increase f  smaller size due to N /A reduction
Prof R T Kennedy
POWER ELECTRONICS 2