The large-scale integration of renewable energy sources (RESs) and the increasing number of energy-storage (ES) systems connected to the grid will create a big challenge for power flow management at the distribution level. In this new scenario, a solid-state transformer (SST) will be a highly efficient key element for providing highly efficient and controllable power flow in distribution grids. SSTs not only mimic the operation of conventional transformers, which scale the voltage level between primary and secondary terminals, but they also control bidirectional power flow, stabilize voltage, facilitate direct integration of ES, and mitigate harmonics and transients, which can cause the power quality of the grid voltage to deteriorate. This article surveys several proposed structures for SSTs in the literature based on different ways of interconnecting power converter topologies.

This paper proposes advanced control of a three-phase three-level neutral-point-clamped pulsewidth-modulated (PWM) converter connecting a permanent-magnet synchronous generator to a grid. The control scheme is mainly based on active and reactive power loops and contains the following additional blocks: virtual flux and filter-capacitor voltage estimators for sensorless operation, active damping (AD) of possible resonances in the LCL filter that connects the converter to the grid, and a PWM modulator with dc-link voltage balancing and minimization of switching losses. It is shown that the proposed control method exhibits several features such as sensorless operation, robust algorithm, minimization of switching losses, and simple tuning procedure of AD. The simulation and experimental results have proven an excellent performance and verified the validity of the proposed system.

Energy storage systems (ESSs) facilitate utility grid operations on various levels, which include power generation, power transmission, and power distribution. The benefits of these systems produce an overall improvement of grid stability, security, and resilience; cost reductions resulting from the need for less expensive reserve equipment; enhanced power quality; and customer satisfaction. In line with the development of the technology, pricing standards, and operator familiarity, ESSs' role in future utility operations will be substantial. This article summarizes ESS applications and control and specific issues related to power electronic converter (PEC) applications.

Growing interest in DC-type Energy Storage Systems (ESS) and DC/DC converters has led to increased power ratings of such devices, which often requires parallel connection. The process of energy efficiency optimization of such modular systems is described in literature mainly in terms of the varying power demand, but the problem is more complex and not analyzed yet in relation to varying ES voltage level and bidirectional energy transfer at the same time. Therefore, this paper considers the Input Parallel Output Parallel (IPOP) connection of two Dual Active Bridge (DAB) modules as a representative modular converter, and to answer a question of: how to improve (maximize) efficiency of such system, at different power demands and varying ESS voltage, only by a turn on/off operation of the module without any circuit and control algorithm changes. The proposed solution defines an operating area (enclosing different ES's voltage levels and loading power conditions) showing where one or two modules should operate to improve the overall efficiency. A curve fitting approach and polynomial approximation of the single module's input/output power curves are utilized for the proposed algorithm based on parametric functions. After simulation study, the method is validated with two 1.4 kW SiC-based DAB converters

Presented in the paper is a novel approach to synchronization of shore and ship power systems, providing a blackout-free supply from the shore. An application of the shore-to-ship synchronization strategy, proposed in the paper, instead of the commonly used ship-to-shore synchronization, enables a fuller exploitation of the high dynamic offered by power electronic converters. Converters are increasingly being used in shore-to-ship supply arrangements in order to ensure the required levels of voltages and frequencies, specified in shore-supply related standards. Simulation results, supported by preliminary tests in small-scale experimental arrangements, have confirmed that shore-to-ship applications might significantly improve the dynamics of the synchronization as well as the parameters of the load transferring process, especially under distorted ship voltage conditions.

This paper proposes improvements to the control method based on the complete dynamical model published by Kömürcügil and Kükrer, which is very simple by operation in the stationary reference frame and lacks ac-line-current sensors. Nevertheless, the basic control method is very sensitive to variations of the line inductances, which provide difficulties in many industry applications. The modifications proposed in this paper overcome this disadvantage using a fuzzy logic controller to tune parameters and do more robust the basic control in view of line inductance parameters variations. Unfortunately, the new tuning method needs information about the reactive line current; therefore, ac-line-current reconstruction algorithm based on the dc-link current measurement has been included to keep the same number of sensors as the basic solution. Simulation and experimental results have proved the correct system operation at wide variations of the line inductance.