The adoption of the virtual synchronous generator (VSG) has attracted wide attention because of the equivalent operating mechanism as a synchronous generator, providing a feasible scheme for the distributed generation connected to utility grid. However, the delivered power and frequency of the VSG may easily oscillate when the dramatic power fluctuation occurred in the distribution generation system. Fortunately, the oscillation can be damped though adjusting the rotating inertia and damping coefficient. Thus, to investigate the influences of parameters perturbation on the active power and frequency for a VSG, the small-signal model is derived and the dynamic performances are analyzed in detail. Then, based on the results of parameters analysis, an adaptive control strategy is proposed in this paper. And an optimal damping ratio can be maintained throughout the whole process of operation to suppress the oscillation of power and frequency. Therefore, the dynamic performances of the VSG are enhanced since the dynamic indexes such as the response time and overshoots are optimized. In the end, a prototype of single-phase VSG has been built and the proposed adaptive control strategy has been verified through experimental results.

A voltage balancer that transfers unipolar dc bus configuration to bipolar dc bus configuration has been widely employed in dc microgrid. Fortunately, unbalanced power flow between positive and negative dc buses can be eliminated through a well-designed voltage balancer. Based on the analysis of a Buck/Boost-type voltage balancer, a deduction method for a series of voltage balancers is proposed in this paper, and is further investigated by applying to other existing voltage balancers. Consequently, several new topologies are proposed for various purpose of improvement with respect to the characters of existing topologies. Furthermore, four new topologies, i.e., Cuk-type, Super-Sepic/Zeta-type, and interleaved Buck/Boost-type voltage balancers have been proposed, which are compared with existing ones in terms of key characters. Finally, the interleaved Buck/Boost topology has been selected as an example for verification and a laboratory prototype is therefore built. The experimental results show a promising effect of current sharing and a good dynamic characteristic of the proposed interleaved average current control strategy based on interleaved sampling while maintaining a balanced power flow between the two dc buses.

This paper provides a comprehensive overview of the microgrid (MG) concept, including its definitions, challenges, advantages, components, structures, communication systems, and control methods, focusing on low-bandwidth (LB), wireless (WL), and wired control approaches. Generally, an MG is a small-scale power grid comprising local/common loads, energy storage devices, and distributed energy resources (DERs), operating in both islanded and grid-tied modes. MGs are instrumental to current and future electricity network development, such as a smart grid, as they can offer numerous benefits, such as enhanced network stability and reliability, increased efficiency, an increased integration of clean and renewable energies into the system, enhanced power quality, and so forth, to the increasingly growing and complicated power systems. By considering several objectives in both islanded and grid-tied modes, the development of efficient control systems for different kinds of MGs has been investigated in recent years. Among these control methods, LB communication (LBcom)-based control methods have attracted much attention due to their low expenses, recent developments, and high stability. This paper aims to shed some light on different aspects, a literature review, and research gaps of MGs, especially in the field of their control layers, concentrating on LBcom-based control methods.

Due to the capacity limitation and the renewable energy's uncontrollability, multiple energy hubs (EHs) are connected by energy routers (ERs) to form a network structure and further build the future energy internet. With concave objective functions and/or nonlinear operation constraints, the centralized optimal dispatch of interconnected EHs is difficult to solve. In order to reduce the complexity of centralized optimal dispatch on large-scale systems and protect the information privacy of different EHs, a hierarchical optimization strategy is put forward for the ER-based energy internet. Specifically, the lower level is the optimal dispatch within EHs, where the dispatch model of EH is further optimized by considering variable dispatch factors, and the information privacy of different EHs is preserved. The upper level is the energy routing control between EHs, where the end-to-end power transmission according to contract path is realized through the controllability of ERs and energy routing protocols. Finally, the effectiveness of the hierarchical optimization strategy and model are verified by simulations.

Bridgeless power factor correction (PFC) converter is popular for reducing the conduction losses of semiconductors. In this paper, a novel bridgeless Cuk PFC converter is proposed. Compared to the conventional Cuk PFC converter, the number of conducting semiconductors in the proposed bridgeless Cuk PFC converter is reduced, contributing to lower conduction losses. Moreover, the conduction losses in proposed converter are further improved compared with the pseudo totem-pole bridgeless Cuk PFC converter. Meanwhile, the total number of component in the proposed converter is less than other bridgeless Cuk PFC counterparts, especially for the big-volume magnetic component and electrolytic capacitor. In addition, all power switches in the proposed converter are common-ground and can be driven by one control signal, availing simple drivers. The theoretical analysis of the proposed converter is presented in discontinuous conduction mode (DCM) with the merits of nature current sharping ability, zero-current switching in semiconductors and easy control. Finally, the simulation and an 100W lab-prototype are built to validate the feasibility of the proposed bridgeless Cuk PFC converter.

With the increasing demand of different voltage levels in industrial applications, multi-port dc-dc converters have been widely employed owing to their low-cost merits. Aiming to provide more multi-port topologies so that engineers can select out a preferred one for the specified application, this paper proposes a novel principle to systematically implement topology derivation by replacing switches in original converters with pulsating current source cells. This principle is simple and effective, with which multiple new integrated multi-port converters having a low number of switches are easily evolved. The advantage of reduced switches is very beneficial for the low power applications with relatively less switches since the overall cost can be effectively improved. And in order to achieve a comprehensive understanding of the proposed converters, an example single-input dual-output converter which integrates the asymmetrical half-bridge flyback converter with the buck converter, is analyzed in detail. It operates similarly with the two separate converters, but with favorable advantages of reduced switches and improved switching operation. Finally, an experimental prototype is built to verify the theoretical analysis.