Master's thesis and Internship : Resonant planar transformer modelling methodology in the application of an X-ray generator

Abstract

Serel enterprise is a major sensor company which utilizes an X-rays generator and receptor (TSP), to measure the density of any textile material driven between both devices. In other words, rough textile roller is led towards the sensors, where X-rays run through it and are then received by the TSP. The TSP computes the X-ray composition after running through the textile and measure its density at a precise point. Allowing to monitor the motor responsible of aligning the textile fibers, in order to have a homogeneous fabric with a constant density. To this end, the generator requires high voltage in order to generate X-ray. Therefore, high voltage must be precisely generated, to do so, a conventional transformer with high transformation ratio is utilized, combined with a multiplier. Noticing how high the voltage is required to be, the resonance frequency is experimentally determined after its manufacture and is exploited. In this instance, conventional transformers are hardly accurate due to many factors such as the specific spire ratio and spacing, making it difficult to predict their intrinsic resonance frequencies. In this regard, planar transformers are a promising technology allowing their intrinsic characteristics to be rigorously predicted. To predict the fundamental electro-magnetic planar transformer’s behaviour, analytical and FEM analysis are concurrently undertaken, under a same simplified T model. Indeed, an analytical analysis details the geometrical limitations such as the amount of PCB layers and copper track dimensioning, leading to a first approximation of physical parameters such as track resistance, magnetizing inductance, core loss and intrinsic capacitive effects. FEM analysis is then performed with GetDP solver and Gmsh software to enhance the accuracy of the computed parameters and to compute the more complex ones such as the leakage inductance. Combining both analysis, results in a high precision resonance resolution and specifies the required modifications to perform in order to match given nominal requirements. Eventually, this only input of this approach is the nominal conditions such as transformation ratio, input voltage and magnetic core specifications, and outputs a fully designed planar transformer. The strength of this methodology is the planar transformer itself, making transformers precisely reproducible in large-scale manufacturing. Therefore, this thesis marks a significant accomplishment in the design of resonant planar transformers allowing to optimize the compactness and performance for any kind of application and more specifically for high voltage. This paper details a simplified methodology which combines efficiency and resonance monitoring for a given nominal frequency. Allowing to build any kind of planar transformers which intrinsic characteristics are tailor-made for a precise purpose.