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Several drawbacks of the conventional and inverse droop control based decentralized techniques for islanded microgrids are being addressed actively, over the years by various researchers. One of the prominent issues is the inaccurate power sharing (reactive power in the conventional droop and real power in the inverse droop) among the distributed generators (DGs) due to the feeder/line impedances. Virtual impedance (VI) is a popular technique to overcome impedance mismatches but the challenge is in the setting of the appropriate value. This paper presents an adaptive decentralized technique for adjusting the virtual impedance in the controller of a DG, based on its output current, without the need of communication, extra sensors or network parameter/load estimations. The methodology is tested through simulations for a wide variety of cases including unbalanced, harmonic, constant power and induction motor loads, DG plug and play functionality and performance in larger networks (modified 13 and 33 bus systems) under meshed configurations. The range for parameter stability is verified through modelling and small signal eigenvalue analyses. Further, improved power sharing performances using the proposed scheme is validated through implementation on a laboratory experimental setup. [ABSTRACT FROM AUTHOR]

Renewable energy sources are typically interfaced to the main grid at the distribution level, through power electronic converter interfaces. Testing these microgrid systems is a crucial aspect which is gaining increased interest and importance among researchers. This article proposes a system emulator, for testing microgrids, with a special focus on replicating unbalanced network conditions. The proposed system uses a single back-to-back bidirectional converter for real-time emulation, and the user has the option to chose any node of their interest to study the dynamics. This is different from the ones proposed to-date - most of them focus on balanced systems, and use several converters to replicate the dynamics of the microgrid system, in which each converter mimics one entity at a time (source or load). A system with two generators is emulated for different control strategies and types of unbalances in the network. The crucial aspects related to the modelling and control are presented in detail supported by simulations and experimental validation on a prototype developed. [ABSTRACT FROM AUTHOR]

The control algorithms proposed to improve load sharing, stability, and power quality in microgrids need rigorous testing. Real-time emulation is one of the proven approaches to provide realistic testing environments for the development of products and control algorithms. Typically, for microgrid system-level testing, individual component-level (source or load) emulators are employed: hardware test bed clusters. These use multiple converters, increasing control complexity and consuming space. In this article, we propose a flexible microgrid system emulator, based on a single converter for the testing of a complete microgrid, at any node selected by the user. This is unlike the case of emulators proposed in the literature till date, which use a large number of converters to emulate the system dynamics, wherein each converter is used to mimic the behavior of one particular component, such as a single source or a single load. The modeling and control aspects are discussed, and the accuracy of the model developed and the working of the emulator are established through simulations and experiments on a laboratory prototype, respectively, considering the case of a simple two-distributed-generator-based microgrid for various scenarios. [ABSTRACT FROM AUTHOR]

Renewables interfaced through inverters in microgrids, may be controlled using centralized, decentralized or distributed approaches. The decentralized droop control involves mimicking the performance of a synchronous generator of the power system, so as to share load power proportionately amongst parallel connected sources. When the conventional droop control is used, only the fundamental real powers can be shared in proportion to the source ratings, which does not ensure satisfactory performances in the presence of unbalanced/ asymmetrical loads. Several schemes have been worked upon to achieve proportional load power-sharing with power quality aspects: in the presence of harmonic and unbalanced loads. This paper proposes five modifications for the popular virtual conductance vs. negative sequence power (G vs. Q-) approach, aimed at improving the sharing of the unbalanced currents amongst the sources to improve the power quality and microgrid system reliability. The eigenvalue analysis for determining the parameter range for assuring stability and comparisons with fixed virtual conductance values are discussed. The proposed modifications are discussed and demonstrated through simulations on a two inverter-based distributed generator (DG) system, a modified 13 bus system, and using experimental results on a lab-scale microgrid. • The work presented focuses on the power quality of unbalance in islanded AC microgrid systems and proposes five modifications for the popular G vs. Q- approach, aimed at improving the sharing of the unbalanced currents amongst the parallel connected sources. • The proposed modifications are based on local measurements and do not need communication, network and load estimations • The eigenvalue based small signal analysis for determining the parameter range for assuring stability and comparisons with fixed virtual conductance values are presented. • The proposed modifications are discussed and demonstrated through simulations on a two-inverterbased distributed generator (DG) system, a modified 13 bus system, and using experimental results on a lab-scale microgrid. • An overall improvement in the range of 26.0% to 61.0% was observed across the different cases (enhanced unbalanced power-sharing: before and after activating the proposed control). [ABSTRACT FROM AUTHOR]

Generation is shifting from a centralized power generating facility having large synchronous generators to distributed generation involving sources of smaller capacity. Most of these sources require inverters on the front end while being connected to the grid. Lower available kinetic energy, coupled with less short-circuit current ratio compared to large synchronous generators, compromises the transient stability of the microgrid when isolated from the main grid. Sources in the microgrid use droop control to share power according to their capacity without any form of communication. This paper proposes a novel controller for inverters to improve the frequency response of microgrid under disturbances involving large frequency deviations. It also discusses design of various parameters defined for the proposed control. The microgrid, which has two inverters and two synchronous generators, is simulated using Simulink/MATLAB software to test the proposed control strategy. [ABSTRACT FROM PUBLISHER]