Analysis and design of printed windings of power transformers using partial inductance method

Abstract

It is a common occurrence that hand-wound or machine-wound transformers have the problem of wide variation in parameter values - inductance and leakage inductance, etc. - in a lot of sample. These are partly due to the tolerance of ferrite core but more importantly it is the result of inconsistent spacings between loosely packed windings as inductance and leakage are geometric shape dependent. The method of printed windings of transformer-windings are printed on a printed circuit board (PCB) and all windings are embedded in a stack of these PCBs - is a promising way in controlling the windings' shape and air spacing in a fixed pattern. While it eliminates the parameter variations in a great deal. However, traditional analytical methods of inductance calculations are based on a lot of assumptions. The complicated geometric constructions of transformer also hinder the accuracy of calculations. The partial inductance method gives an easy and accurate approach to calculate loop inductance by the generalised partial inductance, which is derived from dividing the whole loop into finite length of elements. Self and mutual inductance are then the summation of inductance contributed from individual elements. This is useful in predicting the leakage inductance which has been the most undesirable parameter in PWM converter. And this method can also be applied to transformers in resonant converters in which inductances have to be accurately controlled.