Design of Powder Core Inductors
Håkan Skarrie 
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 equations. 
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.