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With the large-scale application of microgrids (MGs), interconnecting nearby MGs to form an MG cluster (MGC) enables a higher utilization of renewable sources. This article presents a pinning-based hierarchical and distributed cooperative control strategy for AC MGC, which includes distributed generation (DG)-layer, MG-layer, and MGC-layer controls. The DG-layer control regulates the local voltage/current of each DG unit. The MG-layer control is performed for each individual MG, managing DG units in a cooperative manner through several sparse communication networks. By representing each MG as an MG agent, the MGC-layer control coordinates MGs based on a higher level peer-to-peer communication network among MG agents. The interaction between MG-layer and MGC-layer is established by pinning some DG units of each MG to communicate with the MG agent. Compared with the existing literature, the contributions of this article are: 1) simultaneously realizing multiple control objectives in the MGC system level including frequency/voltage regulation and active/reactive power sharing; 2) presenting a systematic approach to construct a unified small-signal dynamic model of the MGC system; and 3) performing a detailed small-signal stability analysis to evaluate the system dynamic performance. Time-domain simulation and experiments are carried out to validate the effectiveness of the proposed methods. [ABSTRACT FROM AUTHOR]

This paper presents a two-layer distributed cooperative control method for networked microgrid (NMG) systems, taking into account the proprietary nature of microgrid (MG) owners. The proposed control architecture consists of an MG-control layer and an NMG-control layer. In the MG layer, the primary and distributed secondary controls realize accurate power sharing among distributed generators (DGs) and the frequency/voltage reference following within each MG. In the NMG layer, the tertiary control enables regulation of the power flowing through the point of common coupling (PCC) of each MG in a decentralized manner. Furthermore, distributed quaternary control restores the system frequency and critical bus voltage to their nominal values and ensures accurate power sharing among MGs. A small-signal dynamic model is developed to evaluate the dynamic performance of NMG systems with the proposed control method. Time-domain simulations and experiments on NMG test systems are performed to validate the effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]

Microgrids can be used to restore critical load after a natural disaster, enhancing resilience of a distribution network. To deal with the stochastic nature of intermittent energy resources, such as wind turbines (WTs) and photovoltaics (PVs), forecast information is usually required. However, some microgrids may not be equipped with power forecasting tools. To fill this gap, a risk-limiting strategy based on measurements is proposed. A Gaussian mixture model is used to represent a prior joint probability density function of power outputs of WTs and PVs over multiple periods. As time rolls forward, the probability distribution of WT/PV generation is recursively updated using the latest measurement data. The updated distribution is used as an input of the risk-limiting load restoration problem, enabling an equivalent transformation of the original chance constrained problem into a mixed integer linear programming. Simulations on a distribution system with three microgrids demonstrate the effectiveness of the proposed method. Results indicate that networked microgrids can perform better in uncertainty management relative to stand-alone microgrids. [ABSTRACT FROM AUTHOR]

This paper presents a novel secondary frequency and voltage control method for islanded microgrids based on distributed cooperative control. The proposed method utilizes a sparse communication network where each DG unit only requires local and its neighbors’ information to perform control actions. The frequency controller restores the system frequency to the nominal value while maintaining the equal generation cost increment value among DG units. The voltage controller simultaneously achieves the critical bus voltage restoration and accurate reactive power sharing. Subsequently, the case when the DG unit ac-side voltage reaches its limit value is discussed and a controller output limitation method is correspondingly provided to selectively realize the desired control objective. This paper also provides a small-signal dynamic model of the microgrid with the proposed controller to evaluate the system dynamic performance. Finally, simulation results on a microgrid test system are presented to validate the effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]

The distributed secondary control in a microgrid can be used for complementing the function of the primary droop-based control. However, its dynamic performance may be undesirable and furthermore it may introduce new less-damped modes to the system leading to oscillatory responses. Unfortunately, mechanism analysis of the undesirable dynamic performance and the possible oscillations, and more importantly, stabilization of the microgrid with the distributed secondary control have not been reported. To fill this gap, this paper first develops a unified small-signal dynamic model of the microgrid. Based on the developed model, a small-signal stability analysis is utilized to perform the aforementioned mechanism analysis. A distributed optimal controller is thereafter proposed to enhance the system stability and improve the system dynamic performance. The distributed optimal controller can coordinate multiple distributed generation units in the microgrid and exhibits robust performance under a wide range of operating conditions. Finally, theoretical analysis and time-domain simulation results on a benchmark microgrid system are provided to verify the effectiveness of the proposed methods. [ABSTRACT FROM PUBLISHER]

This paper presents a systematic method to determine the feasible range and optimal value of the virtual impedance of the droop-based control to enhance a microgrid system performance with respect to power decoupling, reactive power sharing, system damping, and node voltage profile. A modified power flow analysis and an augmented small-signal dynamic model of the droop-based controlled microgrid, considering the impact of the virtual impedance, are developed. Subsequently, based on the developed methods, the feasible range of the virtual impedance, which can satisfy all the system performances requirements, is determined and presented. Based on a particle swarm optimization technique, an optimization process is introduced to select a virtual impedance value within the feasible range to achieve the overall optimal microgrid performance. Finally, simulation results in the PSCAD/EMTDC platform are provided to validate the feasibility and effectiveness of the proposed methods. [ABSTRACT FROM PUBLISHER]