Solid-state transformers (SSTs) are an emerging technology that has been developed to improve the stability, reliability, and economic operation of distribution systems. These new transformers are composed of a medium ac voltage (MV) stage, a dc stage, and a low ac voltage (LV) stage. Passive and active dc-links are used to construct the dc stage in SSTs in order offer new functionalities, including hybrid (ac and dc) distribution, reactive power compensation, voltage/frequency regulation, power quality improvement, and distributed generation utilization. On one hand, a distribution SST has its ac stage connected to a MV level, which mandates specific power electronic converter (PEC) topologies, switching element capabilities, and filtering circuits. On the other hand, the dc-link stage has to provide isolation between the MV and LV levels, which requires the employment of isolated dc PECs. Part I of this work provides a review of SST designs and constructions (for deployment in distribution systems), in terms of the required technology, supported functionalities, and construction features.

Solid-state transformers (SSTs) have diverse designs and constructions that make them suitable for various industrial applications, including distributions systems. This new breed of transformers has been developed to support the typical functionals of core-type distribution transformers, along with new functionalities, such as controlling power flows, integrating dc distribution systems, utilizing distributed generation and storage units, supporting load-side voltage/frequency control, and improving the power quality. As SSTs become candidates for distribution systems, their deployment can pose challenges for distribution systems. Such challenges include the cost, protection, size and weight, efficiency, and adequate grounding designs. This paper presents and discusses challenges that can face the deployment of SSTs in distribution systems. Furthermore, this paper provides a comparison between core-type and SST transformers, when deployed in distribution systems.

This paper presents the development and performance evaluation of a compact-converter-based power supply for plasma dielectric barrier discharge (DBD) devices. The developed power supply is designed to meet weight and size requirements for applications in aeronautical systems. Multistage and multilevel switch-mode converters are employed to construct the power supply. The multistage part of the power supply is constructed from multiple dc-dc boost converters that have their inputs fed by rechargeable batteries. The outputs of the dc-dc converters are used to feed different levels of a single phase cascaded H-bridge (CHB) multilevel dc-ac converter. The switching signals for the CHB dc-ac converter are generated to facilitate the adjustments of the magnitude and/or frequency of the output voltage. Such adjustments are set to allow manipulating the generated plasma body force. A prototype for the multistage multilevel power supply is constructed for performance evaluation using a fiberglass DBD device. Performance results show an effective generation and control of plasma body force, which can be achieved by a modular, lightweight, and compact size power supply.

In this study, direct torque control (DTC) of induction motor is evaluated based on space vector modulation (SVM). DTC is a method to control machine with utilizing torque and flux of motor controlled. The torque and current ripple are occurred in the conventional DTC. Reason of undesired torque and current ripple is low number of voltage vectors applied to the motor controlled by the conventional DTC technique. SVM-DTC is a technique to reduce the ripple. SVM techniques have several advantages that are offering better DC bus utilization, lower torque ripple, lower total harmonic distortion in the AC motor current, lower switching loss, and easier to implement in the digital systems. Simulation results from the classical and improved DTC are presented and compared. Result shows that the torque, flux linkage and stator current ripple are decreased with the improved DTC.

Three phase ( $3\phi$ ) power transformers can have their windings configured to create local neutral points that can be grounded. The grounding of a $3\phi$ power transformer is designed to limit ground fault currents and maintain low ground potentials. These constraints can be translated into a resistive grounding that is usually designed based on the system ratings and parameters. The resistive grounding, however, can impact the flow of the harmonic components present in the exciting currents. As a result, undesired harmonic components are induced in primary and secondary voltages. This paper presents the design and performance of a frequency-selective grounding that can meet the constraints for grounding a $3\phi$ power transformer. The developed grounding is designed to provide a resistive path for low frequency currents (faults), while providing a low impedance path for high frequency currents (harmonics). The frequency-selective grounding is experimentally tested for a $3\phi$ power transformer with different primary and secondary winding configurations, different fault types, and source grounding. Test results show that the developed grounding can reduce the ground potential, harmonic distortion in primary and secondary voltages, and ground fault currents with a minimum interference with ground fault protective devices.