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With the continuous development of microgrids (MGs), a hybrid structure consisting of single-phase MGs and three-phase MGs has been widely promoted. When each submicrogrid (SMG) pursues its economic benefit, it can easily cause a three-phase power unbalance for a grid-connected three/single-phase hybrid multimicrogrid (MMG). To address this problem, an optimization model based on the multileader and multifollower game theory is proposed for a grid-connected three/single-phase hybrid MMG in this paper. In the proposed optimization model, the three-phase unbalance constraints are integrated into the utility functions of the leaders and followers to reduce the impact of the unbalance constraints on the benefits of the participants. The performance of the proposed optimization model is verified by a series of tests. The test results show that the proposed optimization model can effectively reduce the three-phase power unbalance factor of the system and improve the profit of the three/single-phase hybrid MMG. [ABSTRACT FROM AUTHOR]

With the proliferation of distributed generation in distribution networks, quickly and smoothly converting to a state of regional autonomy in the case of distribution network failure is one of the main challenges for the stable operation of a multimicrogrid (MMG). To address the aforementioned problem, this paper proposes coordinated control of the passive transition from grid-connected to islanded operation for a three/single-phase hybrid MMG. Under the premise of fully considering the constraints on the tie-line transfer power undertaken by the master power supply (MPS), the following two scenarios regarding safety and emergency are formulated: 1) when the output power of the MPS is in the safe range, the proposed strategy coordinates the energy storage (ES) in each submicrogrid (SMG) to achieve power balance; 2) when the output power is in the emergency range, this paper proposes a three-phase balance method based on a bubble sort to realize the combination optimization of the single-phase source-load-storage (SLS) and a fast power regulation method based on implicit enumeration for the SLS to reduce the tie-line transfer power, which could prevent failure of the mode transition from power overload. The test results verify the effectiveness and feasibility of the proposed coordination strategy. [ABSTRACT FROM AUTHOR]

As the penetration of photovoltaic (PV) generation increases, there is a growing operational demand on PV systems to participate in microgrid frequency regulation. It is expected that future distribution systems will consist of multiple microgrid clusters. However, interconnecting PV microgrids may lead to system interactions and instability. To date, no research work has been done to analyze the dynamic behavior and enhance the stability of microgrid clusters considering the dynamics of the PV primary sources and dc links. To fill this gap, this paper presents comprehensive modeling, analysis, and stabilization of PV-based multiple microgrid clusters. A detailed small-signal model for PV-based microgrid clusters considering local adaptive dynamic droop control mechanism of the voltage-source PV system is developed. The complete dynamic model is then used to access and compare the dynamic characteristics of the single microgrid and interconnected microgrids. In order to enhance system stability of the PV microgrid clusters, a tie-line flow and stabilization strategy is proposed to suppress the introduced interarea and local oscillations. Robustly selecting of the key control parameters is transformed to a multiobjective optimization problem which is solved by genetic algorithm. The proposed damping controller can effectively damp the power oscillations and provide robust control performance under variable operating conditions. Theoretical analysis, simulation results under various scenarios are presented to verify the effectiveness of the proposed scheme. [ABSTRACT FROM AUTHOR]

Summary: With the increasing amount and type of connected microgrids in the near‐term future power networks, how to optimize the operation of multimicrogrids efficiently and reliably has become essential for taking full advantage of the complex systems. In this paper, a multitimescale coordinated optimization strategy for hybrid three‐phase/single‐phase multimicrogrids is proposed. The multitimescale strategy is implemented for day‐ahead economic optimization on a long‐time scale and real‐time tracking optimization on a short‐time scale. With the consideration of the economy of microgrids and three‐phase unbalance constraints in multimicrogrids, a strategy of collecting‐distributing fuzzy modified adaptive particle swarm economic optimization is introduced. In this day‐ahead strategy, a bilayer rolling optimizing structure is designed, where the lower layer conducts economic optimization at all time slots and the upper layer balances the tie‐line power at each time slot based on the results obtained from the lower layer. On this basis, by taking a day‐ahead optimized tie‐line power as baseline values, the real‐time power of energy storage systems is obtained by adopting an improved nondominated sorting genetic algorithm, which achieves distributed real‐time optimization for the multimicrogrid. Simulation results verify that the proposed strategy is feasible. [ABSTRACT FROM AUTHOR]

With the microgrids large-scale interconnect to the power grid, a number of neighboring microgrids in a certain region will form a multi-microgrids (MMGs) system. In the development from microgrid to smart grid, the MMGs will be a new research hotspot after microgrid. The paper analyses the basic structure of the MMGs from many aspects such as voltage grade classification, AC/DC constitutional forms, and phase-sequence constitutional forms. Next the remote-area type, residential-area type, office-building type, industrial-park type and research-study type MMGs are analyzed according to the typical application scenarios. Lastly, based on the research of the four aspects of the planning and design, mode switching, optimal operation and control devices, the key technology of the MMGs is discussed and explored. [ABSTRACT FROM AUTHOR]

In this paper, a novel type of voltage control strategy based on internal model robust and compound control is proposed for three/single-phase hybrid multimicrogrid, which is composed of two parts, feedforward control and internal model robust feedback control. Feedforward control is mainly used to improve the dynamic response and reduce the steady-state error of the system. The objective of the internal model robust feedback control system is to achieve the optimization of control performance, robustness, and the ability to suppress disturbances of the whole system. In order to achieve the goal, the design of the internal model robust feedback controller is transformed into solving a convex optimization problem with linear matrix inequality constraints and linear objective functions. The proposed voltage control strategy is verified by a variety of experimental tests. The experimental results show that the controller can get better voltage output characteristics and robustness in dealing with micro-source output power fluctuations, loads abrupt change or nonlinear loads and unbalanced loads. [ABSTRACT FROM PUBLISHER]

The V/f control adopted by the master power supply has problems of slow dynamic response, poor anti‐interference ability in response to micro‐source output power fluctuations and loads abrupt change. Aiming at problems of the output voltage mentioned above, an improved V/f control strategy based on compound control is proposed in this study. The improved V/f control strategy is composed of two parts, feedforward compensation and robust feedback control. The design of the feedforward compensator is realised by the method of approximate full compensation. The design of the robust feedback controller is transformed into solving a convex optimisation problem with linear matrix inequality constraints and linear objective functions. The designed V/f control strategy is verified by a variety of comparative tests. Test comparisons show that the controller can get better voltage output characteristics, dynamic characteristics and robustness in response to micro‐source output power fluctuations, loads abrupt change or non‐linear loads and unbalanced loads. [ABSTRACT FROM AUTHOR]

In this paper, an islanded medium-voltage (MV) microgrid placed in Dongao Island is presented, which integrates renewable-energy-based distributed generations (DGs), energy storage system (ESS), and local loads. In an isolated microgrid without connection to the main grid to support the frequency, it is more complex to control and manage. Thus, in order to maintain the frequency stability in multiple time scales, a hierarchical control strategy is proposed. The proposed control architecture divides the system frequency in three zones: (A) stable zone, (B) precautionary zone, and (C) emergency zone. In this way, dynamic stability control that copes with disturbances in short-time scale is implemented by microgrid central controller within Zone B and Zone C. Meanwhile, steady-state stability control to solve the peaks and valleys problem of loads and DGs in long-time scale is executed by the microgrid energy management system within Zone A. Furthermore, based on the developed complete small-signal state-space model, sensitivity analysis of the eigenvalues is conducted in order to reveal the dynamic stability margin of the MV microgrid, and to identify the proper range of the control parameters of Zone B. Theoretical analysis, time-domain simulation, and field test results under various conditions and scenarios in the Dongao Island microgrid are presented to prove the validity of the introduced control strategy. [ABSTRACT FROM AUTHOR]