Electrical equivalent circuit modeling of active components is one of the most important approaches for modeling high-frequency high-power devices. Amongst the most used microwave devices, AlGaN/GaN HEMTs demonstrated their superior performance, making them highly suitable for 5G, wireless and satellite communications. Despite the remarkable performance of AlGaN/GaN HEMTs, these devices reside on substrates that invoke limitations on the operating-frequency, power-efficiency, and current dispersion phenomenon. Also, there is a limitation in present parameters extraction techniques being not able to consider both the substrate effect (Silicon, Silicon Carbide, and Diamond) and the asymmetrical GaN HEMT structure. In this thesis work, a single extrinsic parameters extraction technique using a single small-signal topology takes into account both the asymmetrical GaN HEMT structure and the different substrate types with their parasitic conduction will be developed and studied for the first time. Moreover, large-signal modeling using Quasi-Physical Zone Division technique has been applied to both GaN/D and GaN/SiC to model the isothermal-trapping free drain current, and combined with a new simple technique for comparing performance between active devices in terms of current-dispersion. The models were verified by simulating the small-signal S-parameters, large-signal IV characteristics, and single-tone load-pull. High accuracy was achieved compared to the measurement data available in the technical literature and obtained from fabricated devices.

In this Thesis a Unified Discrete State-Space Model for power converters in CCM is presented. Two main approaches to arriving at the discrete model are used. The first approach involves an impulse function approximation of the duty cycle modulations of the converter switches , and this approach results in a small signal discrete model. The Second approach is direct and does not involve any approximation of the modulations , this approach yields both a large signal nonlinear discrete model and a linear small signal model. Harmonic analysis of the converter states at steady-state is done for steady-state waveform acquisition , which increases the accuracy of the model especially for finding the control to inductor current frequency response. Finally the Discrete model is verified for the Half-Bridge DC/DC topology for its three main control schemes (Asymmetric , Symmetric , DCS). A GUI platform in MATLAB is presented as a wrapper that utilizes the models and analysis presented in this thesis.

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