Design of Powder Core Inductors
External reviewer: Prof. Tore Undeland,
Dep. of Electrical Power Engineering, NTNU, Trondheim, Norway
In this work an inductor design program
is developed. For evaluation of the program two iron powder core inductors
with different core materials have been designed. The resulting designs
have been manufactured and the inductance and total loss of the inductors
are determined by a resonant measurement system and compared to corresponding
figures estimated by the program.
In the design program different core materials,
core geometries and winding configurations, can be selected from three
databases included in the program. Before making a design also the electrical
specifications, thermal restrictions etc. are settled. Within defined restrictions
the program calculates the optimum design based on the specified parameters
and the selected object function.
The expressions used in the program for
estimating core and winding losses are thoroughly presented together with
the physical background of the different loss parts. For the estimation
of hysteresis loss the Preisach model is used. An extension to the model
is also suggested to improve the accuracy. The expressions for eddy current
and anomalous loss use coefficients determined by loss separation. Skin
and proximity effects in the winding becomes apparent at an increasing
frequency, these eddy current effects are included in the winding loss
Two iron powder core inductors with different
core materials have been designed. Both materials are based on the iron
powder Somaloy 500, manufactured by Höganäs AB, Sweden, but with
a difference in mixes and heat treatment they experience diverse magnetic
and electric properties. The inductors are designed for use as line side
filter inductors in a battery charger for charging of electrical vehicles.
The inductors are manufactured and tested
in a developed resonant measurement system. The system uses the damped
oscillation originating when a charged capacitor, with known parameters,
is discharged over an 'unknown' inductor for determining the inductor parameters,
inductance and series resistance. By determining the resistance and measuring
the current in the LCR-circuit the total loss of the inductor can be estimated.
By changing the size of the capacitor the parameters can be determined
at different frequencies.
Comparisons between inductance and total
loss calculated by the design program respectively measured by the resonant
system for the two inductors are presented. The maximum error in the inductance
is 3% while the error in the total loss is within 12%. Calculated and measured
losses as a function of the current are also compared at some different
frequencies. A slight increase in the discrepancy with increasing frequency
is observed for the LB1-inductor, i.e. the frequency dependence is somewhat
overestimated in the employed loss expression.
Approximate calculations are performed
on a laminated core inductor with thick laminates, 0.5 mm. Comparison with
the powder core inductors indicate the possibility of reduce inductor size
and weight when using a laminated core in the low frequency application
investigated in this thesis.