Improving the Performance of Passive Components of the Power Electronics at High Switching Frequency

Abstract

Power converters have an important role in modern electric and electronic systems due to different voltage and power level requirements. Magnetic components are considered to be essential elements of the power converters. Storing the energy, filtering the signal, and transferring the energy are the main tasks of the magnetic components in the power converters. With developing the technology of power switches, the power converter can be operated at high frequencies. However, the magnetic components are suffering from their parasitic capacitance at high frequencies. Modeling the parasitic capacitance of the magnetic components is crucial to design power converters at high frequency. To date, the researches that have been conducted to modeling the parasitic capacitance have mainly targeted the low power applications with very high frequencies and high power with multi-layer transformers. Consequently, there remains a blank in the body of knowledge regarding modeling the parasitic capacitance of a single-layer inductor with a magnetic core at medium power. The relation between the number of turns and the parasitic capacitance of the single-layer inductors with the magnetic core should be considered. Moreover, improving the magnetic components by reducing the parasitic capacitance is essential. By using the technique of reducing the parasitic capacitance, the resonant frequency of the magnetic components can be shifted to a higher frequency besides improving the impedance of the inductor. Therefore, this dissertation contributes in four main parts: (1) Modeling the parasitic capacitance of a single-layer inductor with a magnetic core. (2) Reducing the parasitic capacitance using the technique of magnetic coupling. (3) Selecting the appropriate range of high operating frequency for power converter applications. (4) Estimating the parasitic capacitance of interleaved coupled two-phase inductors. For the first part, a new approach to determining the total parasitic capacitance of a singlelayer inductor with the magnetic core at a medium frequency range that is below the first resonantfrequency is presented in this research. The proposed analytical approach can obtain the parasitic capacitance between the winding and core based on the physical structure of the inductor. The analytical approach depends on approximating the rod wire shape to a square shape. The total equivalent parasitic capacitance is derived. The results are verified by finite element analysis and experimental measurements using impedance network analyzer.The second part of this research presents a technique for improving the performance of an inductor at high frequencies through mitigating effects caused by the parasitic capacitance. This technique adds a small capacitor to the coupled windings of the inductor to reduce the parasitic capacitance of the inductor. The relationship between the parasitic capacitance, magnetic coupling coefficient, and the small capacitor is introduced. The method to size the reduction capacitor is detailed in this research. The results of applying this technique show an improvement in the inductance impedance by 40 dB and shifting the resonant frequency to a higher frequency when 𝑘 = 0.97. The experimental results validated the effectiveness of the proposed technique. Moreover, a new methodology to properly select the highest operating frequency for the magnetic components in power electronics devices is presented in this research. Several parameters of the magnetic components such as the resonant frequency and the losses of the magnetic core are taken under consideration. The results of this methodology prove the maintaining the efficiency with reducing the volume of the magnetic core by 70%. Finally, the parasitic capacitance of the interleaved two-phase coupled-inductors is introduced in this rese