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Creators/Authors contains: "Shafei, Ahmad El"

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  1. High frequency modular power converters are increasingly becoming popular due to their small size and weight. Targeting the input-series and output-parallel (ISOP) dual active bridge (DAB) DC-DC converters, this paper proposes a control scheme based on optimal triple phase-shift (TPS) control for both power sharing control and RMS current minimization. This achieves balanced power transmission, even under mismatched leakage inductance of a DAB module of the ISOP. In order to obtain the optimal zones of operation for the converter, the RMS current was minimized using the Lagrange multiplier method to obtain the optimal duty cycles. The power balancing was added to compensate unbalanced power sharing for variations in model parameters or module shutdown. Analyses and simulation results through MATLAB/Simulink are presented to validate the proposed controller.
  2. The cascaded H-bridge multilevel active rectifier is a prominent converter configuration. It presents compelling advantages, including high adjustability for a number of applications, such as in solid-state transformers, traction applications, medium and high power motor drives and battery chargers. However, when the H-bridge is operating under an unbalanced load and asymmetrical voltage conditions, it becomes important to design advanced control strategies to maintain the stability of the system. In this study, a Lyapunov-function based control method is proposed for controlling the single-phase cascaded H-bridge active rectifier to achieve global asymptotic stability. A capacitor voltage feedback is added to the conventional Lyapunov-function based stabilizing control method to minimize the resonance of the LCL filter. Additionally, a Proportional-Resonant (PR) control approach is adopted to obtain the reference current signal. This increases the robustness of the current control scheme. A DC voltage balancing control procedure is also employed to prevent the unbalanced DC voltage conditions among the H-bridges. The DC voltage is controlled via a PI controller. The capability of the control approach is verified with simulation and experimental studies.
  3. In this study, design of a 330kW single-phase transformer (corresponding to 1MW three-phase) operating at 50kHz is presented. Possible core materials and their performances are investigated under high switching frequency operation. Core volume, area, configuration, and market availability are studied to achieve the optimal compact and cost-effective transformer model. Next, transformer winding type, size, placement, and cost are analyzed. These steps will result in a complete transformer electromagnetic design and modelling. Afterwards, a 3D transformer model is created and simulated using a Finite Element Analysis (FEA) tool. ANSYS Maxwell-3D is used to simulate the magnetics, electrostatics, and transients of the designed transformer. This model is integrated with a power electronics circuit in ANSYS Simplorer to make a co-simulation for the entire system. Results obtained will include core maximum flux density, core/copper losses, leakage/magnetizing inductances, windings parasitic capacitances, and input/output voltage, current, and power values. Finally, the systems' overall efficiency is calculated and presented.
  4. In this study, a four-port solid-state transformer (SST) with decoupled control scheme to control the power flow and the output voltage is proposed. The proposed decoupled control scheme controls all of the four ports' powers independently. In addition, the design of the four-port transformer including core material selection and winding placement is investigated. The designed transformer is modeled in ANSYS-Maxwell and also co-simulated with ANSYS-Simplorer. The operating frequency of the system is designed for 100 kHz; therefore, a very compact size is obtained for the entire multi-port converter. The performance of the proposed system is validated throughout MATLAB/Simulink simulation and experimental studies carried out for a 10kW/port SST prototype. The obtained results show that the four-port SST provides an interface for four-different power supplies or loads. It is seen that the proposed decoupled control scheme can control the output voltage at the desired value and track the reference power signals for each port. It provides as well a good steady state and dynamic performance.