This paper focuses on the study of the high frequency transformer incorporated in solid- state transformers, specifically on the development of the steps that enable the design of an optimized high frequency transformer and its equivalent model based on the desired characteristics. The impact of operating a transformer at high frequency and the respective solutions that allow this impact to be reduced are analyzed, alongside the numerous advantages that the utilization of these transformers has over traditional 50/60 Hz transformers. Furthermore, the power scheme of the solid-state transformer is outlined, focusing on the power converters, which are immediately before and after the high frequency transformer (HFT). We also investigate a control technique that allows for correct operation and the existence of power bidirectionality. In a novel approach, this paper demonstrates the systematic steps for designing an HFT according to the desired specifications of each given project, helping students and engineers achieve their objectives in power-electronic applications. Moreover, this paper aims at increasing the knowledge of this area of power electronics and facilitating the development of new topologies with high power density, which are very important to the integration of renewable power sources and other applications. Finally, a simulation is presented to validate a high frequency transformer and its control technique.

This paper presents the sliding mode control (SMC) of unified power quality conditioners (UPQC) intended to compensate power quality issues in three-phase four-wires systems. The SMC UPQC can be applied in electrical grids or isolated grids to mitigate power quality problems at the consumer facilities and also to minimize issues for the grid supplier. The UPQC is configured as a shunt-series filter. The shunt Active Power Filter (APF) uses a three-phase rectifier with SMC to enforce sinusoidal mains currents. The series APF uses three single-phase H-bridge inverters and SMC to improve the voltage quality at the point of common coupling. SMC design, analysis and simulation results are presented and discussed.

In recent years, there has been a desire to improve electricity generation and consumption, to reach sustainability. Technological solutions today allow a rational use of electricity with good overall performance. Traditionally, from production to distribution, electrical energy is AC-supported for compatibility reasons and easy voltage level transformation. However, nowadays most electric loads need DC power to work properly. A single high-efficiency central AC-DC power converter may be advantageous in eliminating several less efficient AC-DC embedded converters, distributed all over a residential area. This paper presents a new single-phase AC-DC converter using one active bridge (most isolated topologies are based on the dual active bridge concept) and a high-frequency isolation transformer with low-value non-electrolytic capacitors, together with its control system design. The converter can be introduced into future low-voltage DC microgrids for residential buildings, as an alternative to several embedded AC-DC converters. Non-linear control techniques (sliding mode control and the Lyapunov direct method) are employed to guarantee stability in the output DC low voltage with near unity power factor compensation in the AC grid. The designed converter and controllers were simulated using Matlab/Simulink and tested in a lab experimental prototype using digital signal processing (DSP) to evaluate system performance.

This paper presents a high–voltage (HV) inverter to generate bipolar voltages with variable duty-cycle and frequency for HV pulsed power or HV electrical network applications. Each one of the four HV inverter switches is built with a series stack of semiconductor devices, derived from the Marx generator concept, using small capacitors to equally share the voltage among the individual series stacked semiconductors. A sliding mode control is used to control the output voltage and a delay technique is used to reduce dU/dt at the HV inverter output and to balance the capacitor voltages. The design and structure of the HV inverter switches is described together with the delay technique. Steady-state and dynamic behavior is evaluated. Simulation results are presented (using MATLAB/Simulink software) and discussed.