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The presence of renewable energy resources in LV distribution networks may lead to a distribution transformer, also known as a Smart Transformer (ST), experiencing the bidirectional power flow. Therefore, the ST must have the capability to operate in both directions. However, the reverse power is less as compared to the forward power, thus the design of ST with the same capacity in both directions increases the hardware cost and decreases the system efficiency. This paper proposes a Hybrid-modular-ST (H-ST), composed of a mixed use of single active bridge-based series resonant converter and dual active bridge instead of complete use of uni-or bi-directional converter adopted in the conventional solid-state-transformer. Based on the proposed H-ST, the impacts of power imbalance among cascaded modules in reverse operation mode are analyzed and then an effective solution based on reactive power compensation combined with the characteristics of the proposed architecture is adopted. The simulation and experimental results clearly validate the effectiveness and feasibility of the theoretical analyses.

Smart solid-state transformers (STs) have been proposed to modernize the distributed renewable resources dominated distribution system and facilitate the integration of different subsystems/resources as an energy hub/router. A solid power deliver amongst these integrated subsystems is critical to maintain the power balance and to ensure the ST stable operation, while the research on ST loadability analysis is insufficient. Generally, the ST is composed of three-stage offering medium voltage alternative current (MVAC), medium voltage direct current (MVDC), low voltage direct current (LVDC) and low voltage alternative current (LVAC) connectivity. Although the voltage at each port is independently controlled, the power conversion among these ports is electrically coupled and constrained by the maximum deliverable power of each stage. This paper analyzes the operating points of the ST stage by stage with respect to its loadbility and defines the stable operational region of the ST considering the interactions amongst these stages. Moreover, effects of the current limits, voltage regulation and reactive power compensation on the ST loadability and stability enhancement are considered. RT-Lab platform serves to verify the stable operation region of the ST and the efficiency of the above loadability enhancement methods.

Power Line Communication (PLC) and Simultaneous Wireless Information and Power Transfer (SWIPT) are popular examples of applications, where power and information are transmitted simultaneously. In most cases, different devices have been used to generate the power and communication signals independently. Usually, the information is superimposed onto the power signal using an external modulator. Recently, power converters have been used to generate pulses not just for power conversion but also for information transfer simultaneously. This approach represents a fundamental difference because it exploits the signal processing potential of Pulse Width Modulation (PWM), where for power conversion only the average pulse width is used, while the information is represented by the harmonics instead of being filtered out, as typically done in power electronics. The concept of embedding information into the switching ripple generated by a switched-mode power converter has recently been dubbed Talkative Power (TP), in this paper referred as Talkative Power Conversion (TPC). TPC technologies are reviewed in non-isolated and isolated converters in this paper. Potential applications include visible light communications, battery management systems, switching reluctance generators/motors, microgrids, and wireless electric vehicle charging stations. Finally, trending topics are identified.

Abstract As one of the most representative series active compensators, dynamic voltage restorer (DVR) can solve voltage‐related power quality uses effectively. The in‐phase voltage control and energy‐optimised control are the two typical control strategies of DVR. However, the in‐phase voltage control results in a large amount of active power exchange between the main grid and the dc link of DVR, and hence high capacity of storage system is needed in the dc link while the energy‐optimised strategy requires high injected voltage, resulting in oversizing of the DVR inverter. Thus, in order to avoid the aforementioned drawbacks, this study proposes a modified DVR, which connects an external capacitor in series with the LC filter (LCC) of DVR (LCC‐DVR). Based on the operational principles of the LCC‐DVR, an updated procedure of reference voltage is proposed to avoid overmodulation of DVR caused by load variations, ensuring the continuous operation capability of the LCC‐DVR. The overall control scheme of the LCC‐DVR and the comparative analysis among the proposed strategy and traditional strategies are also presented. The effectiveness of the proposed topology and method is clearly validated by the simulation and experimental results.

Renewable Energy Systems have been in the spotlight of the academic and industrial research for more than two decades, thanks to the development of several fields related to the Electrical Engineering. More recently, with the increasing complexity of the individual renewable energy systems and the interconnection to the grid, the scientific panorama has been witnessing to a convergence of different topics, which span across several IEEE-IES thematic areas: power electronics, electrical machines, smart grids, energy storage, transportation electrification and aerospace. After a brief overview of the renewable energy technologies, this work deals with how the convergence of multiple technologies developed to provide marginal support to the grid has evolved into the foundation of the future utility grid and expanded to transportation sector. It will be shown how the design of a renewable energy system cannot prescind anymore from the electrical grid and from the ancillary services that are requested. Example of convergence are given for a smart transformer application and for a transportation application.

Solid-state transformer-based smart transformer (ST) can provide the dc connectivity and advanced services to improve the grid performance and to increase the penetration of the power electronics interfaced resources (e.g., distributed generators and electric vehicle charging stations) in modern electricity distribution grids. Since the ST is a new and effective paradigm of the electricity grid evolution to well understand the ST, this paper systematically presents the basic architecture and the typical control schemes of the ST and then the advanced services that ST can provide to improve the electricity grids performances in terms of the power flow control, power quality improvement, active damping and active contribution to improve distribution grid resilience by means of enabling autonomous microgrids operation as well as launching a restoration procedure following a general blackout.

Dynamic voltage restorers (DVRs) are devices that compensate for voltage sags/swells in power distribution systems effectively. However, the performance of DVRs may be easily endangered by large load-circuit currents. This work proposes a dual-functional DVR (DFDVR) that solves multiple problems by controlling the trigger angle of antiparallel thyristors, which are connected between the power converter and output filter. The DFDVR not only compensates for voltage fluctuation in the upstream grid but also limits fault current in the downstream grid. Moreover, the combined application of the DFDVR with a recloser is introduced. The DFDVR flexibly regulates the amplitude of the faulty current to coordinate the recloser. In addition, the coordination sequence diagrams of the DFDVR and the recloser under instantaneous and permanent faults are analyzed in detail. Simulations and experimental results verify the correctness and feasibility of the operations and coordination of the DFDVR and the recloser.

The traditional intelligent algorithms for the selected harmonic elimination pulse-width modulation (SHEPWM) of multilevel converters provide low convergent rate and low accuracy of solutions when solving quarter-wave symmetry nonlinear equations. To obviate this problem and obtain a better modulating performance, an improved imperialist competition algorithm is proposed. The proposed algorithm enhances the global search ability by using moving imperialists. Also, a novel type of particles, named independent countries, are proposed to help the algorithm jump out of the local optimum. These independent countries change their positions using swarm intelligence. Compared with the existing particle swarm algorithm and genetic algorithm, the proposed algorithm has significant advantages by improving the accuracy of solutions and the rate of convergence. Finally, the correctness and effectiveness of the proposed algorithm are verified and evaluated by simulation and experimental results.

For the grid-connected doubly-fed induction generator (DFIG)-based wind turbine, because of the stator connected to the grid directly, the stator flux easily suffers from the effects of grid voltage variations, such as grid disturbances and grid faults. Moreover, since the magnetic field is excited by the rotor current, stator flux is also affected by the rotor current. Therefore this study systematically studies the dynamic performances of stator flux under consecutive grid voltage variations and varying rotor currents, and its influence on the performances of the DFIG during grid faults. The analyses reveal that the stator flux can be accumulated by the consecutive variations of the stator voltage, and the instants of grid voltage variations can lead to different amplitudes of the stator flux. In addition, the conventional vector control strategy and the active damping strategy are compared with the behaviour of the stator flux. Furthermore, the simulation and experiment are carried out to validate the theoretical analyses, and the results have clearly confirmed the correctness and effectiveness of the analyses of the stator flux performances. [ABSTRACT FROM AUTHOR]

In this study, a duty cycle-based space-vector pulse-width modulation (SVPWM) with overmodulation and capacitor voltage balance control for three-phase three-level neutral-point clamped (NPC) inverters is presented. On the basis of simple linear calculations of three-phase reference voltages, the proposed SVPWM can be derived, which avoids the trigonometry operation required by the conventional SVPWM. The modulation region can also be smoothly extended from the linear region to the overmodulation region through re-synthesising the three-phase reference voltages. This avoids the conventional non-linear function and look-up table. The neutral-point voltage balancing control is achieved via changing the duty cycle of the redundant small vectors in each switching period, which can be easily embedded into the proposed duty cycle-based SVPWM. The dynamic and steady-state performances of the proposed SVPWM are eventually verified by both simulation and experimental results. [ABSTRACT FROM AUTHOR]

The modular multilevel converter (MMC) is attractive for medium- or high-power applications because of the advantages of its high modularity, availability, and high power quality. However, reliability is one of the most important issues for MMCs which are made of large number of power electronic submodules (SMs). This paper proposed an effective fault detection and localization method for MMCs. An MMC fault can be detected by comparing the measured state variables and the estimated state variables with a Kalman filter. The fault localization is based on the failure characteristics of the SM in the MMC. The proposed method can be implemented with less computational intensity and complexity, even in case that multiple SM faults occur in a short time interval. The proposed method is not only implemented in simulations with professional tool PSCAD/EMTDC, but also verified with a down-scale MMC prototype controlled by a real-time digital signal controller in the laboratory. The results confirm the effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]