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Due to the high resistance/reactance (R/X) ratio of a low-voltage microgrid (LVMG), virtual complex impedance-based $P-\dot {V}/Q-\omega $ droop control is adopted in this article as the primary control (PC) technique for stabilizing the system. A distributed event-triggered restoration mechanism (ETSM) is proposed as the secondary control (SC) technique to restore the output-voltage frequency and improve power sharing accuracy. The proposed ETSM ensures that neighboring communication happens only at some discrete instants when a predefined event-triggering condition (ETC) is fulfilled. In general, the design of the ETC is the crucial challenge of an event-triggered mechanism (ETM). Thus, in this article, a static ETM (SETM) is proposed as the ETC at first, where two static parameters are utilized to reduce the triggering frequency. Bounded stability is ensured under the SETM, which means that the output-voltage frequency is restored to the vicinity of its nominal value, and close to fair utilization of the distributed generators (DGs) is achieved. To further improve the power sharing accuracy and accelerate the regulation process, a dynamic ETM (DETM) is then introduced. In the DETM, two dynamic parameters that converge to zero in the steady state are designed, which promises asymptotic stability of the system. Besides, Zeno behavior is excluded in both mechanisms. An LVMG consisting of four DGs is constructed in MATLAB/Simulink to illustrate the effectiveness of the proposed methods, and the simulations correspond with our theoretical analysis. [ABSTRACT FROM AUTHOR]

Hybrid and intermittent characteristics of the distributed energy resources (DERs) bring great challenges to the security control and economic dispatch (ED) of the microgrids. To bypass these hurdles, this article proposes a multiagent system-based integrated design of security control and ED to guarantee the effective and economical operation of the interconnected microgrids. First, a hierarchical control scheme is constructed by two-level unit agents, in which the switching control and dynamic regulation are fully implemented with the corresponding hybrid behaviors based on the differential hybrid Petri-net (DHPN) model. Based on the DHPN model, a novel dynamic ED integrated with security control is proposed to overcome the issues that cannot be solved in conventional models. Furthermore, to reduce the computational complexity and unified the mathematical model of the DERs, the inverter-based power control strategy is converted to a predictive control model which can be decomposed into several subsystems. In the optimization process, all the subsystems are implemented in a fully distributed, communication free, and rolling optimization manner based on the distributed model predictive control (DMPC). The validity of the proposed design is demonstrated according to the simulation results in case studies. [ABSTRACT FROM AUTHOR]

Due to the high R/X ratio and mismatched feeder impedance of low-voltage microgrids, conventional droop method is no longer able to decouple the active and reactive power of distributed generators and the power-sharing accuracy is degraded. In this article, a virtual complex impedance based $P-\dot{V}$ droop method is proposed to decouple the powers and improve the power-sharing accuracy among DGs. With the virtual impedance method, the equivalent impedance between virtual power source and point of common coupling is shaped to be purely resistive. Then, a P — ̇V strategy is adopted to alleviate the effect of mismatched line impedance, where the virtual powers rather than the ordinary P/Q are used in the droop equation. In case the output voltage violates the operation code, a restoration mechanism is proposed to reset ̇V to zero. Compared with existing virtual impedance and Q — ̇V droop methods, the proposed method combines the advantages of both. Besides, a modified P — ̇V strategy is also presented to accelerate the restoration process and improve the active power-sharing accuracy at the same time. Simulation results validate the effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]

At present, more and more communication-based methods are proposed for reactive power adjustment in islanded microgrid (IMG). However, the use of communication data will inevitably cause communication problems, for e.g., delay, packet loss, and communication failure. Among them, the random communication failure (RCF) is common and harmful. To realize the stable operation of IMG and the rational sharing of reactive power under the consideration of this problem, a cyber-physical cooperative hierarchical control strategy is proposed in this article, which include cyber and physical layers in control structure. In these two layers, the main designs are as follows. In the cyber layer, to solve the RCF problem, we have designed the corresponding observer, controller, and prediction compensation part; and to improve the frequency stability, a secondary control method is designed. In the physical layer, to share reactive power reasonably, a reactive power control method based on synchronous voltage regulation is proposed; to suppress the possible disturbance in the data used in the physical layer, a novel sliding-mode controller is designed; and to improve the voltage stability during adjusting power, a voltage compensation strategy is proposed. The effectiveness of proposed methods is finally verified by experiments. [ABSTRACT FROM AUTHOR]

Frequency deviation and powers sharing error exist in a microgrid with multiple droop-controlled distributed generations. To solve the above problems, we propose an event-triggered multistage secondary control. First, to improve the synchronization accuracy, we divide secondary control into multiple stages based on frequency/voltage droop characteristics. The inputs of proportion-integration compensator for these stages are different. The corresponding stage will be activated when the value of frequency/voltage meets a certain “event” (given ranges). Then, we consider the network delay, use a discrete communication scheme to reduce the bandwidth utilization, and further avoid the oversized delay. To stabilize the interloop control with input delay, we derive the robustness criteria. Finally, simulations in RT-LAB confirm the effectiveness of the proposed control strategy. [ABSTRACT FROM AUTHOR]

The distributed cooperative control for frequency and voltage stability and power sharing in microgrid considering the limitation of communication network is concerned in this paper. Two types of novel event-triggered mechanism with distributed architecture are first proposed, which can greatly reduce the communication burdens among power source inverters. Based on the event-triggered schemes, distributed restoration mechanism is constructed, which can restore the frequency and voltage magnitude of microgrid and realize the fair utilization of all power sources with comparative less requirements for the transmission data. Simulation is carried out to verify the effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]

This paper focuses on a multiagent-based distributed coordinated control for radial dc microgrid considering transmission time delays. First, a two-level multiagent system is constructed, where local control is formulated based on local states and executed by means of the first-level agent, and distributed coordinated control law is formulated based on wide-area information and executed by means of the secondary-level agent in order to improve the voltage control performances. Afterward, the research mainly focuses on designing the local controller and the distributed coordinated controller. For the purpose of robust stability, the local control is designed as local state-feedback-based \textH\boldsymbol \infty robust controller. It is worth mentioning that the distributed coordinated control consists of local state feedback control and decoupling coordinated control law that only come from adjacent distributed energy resource units. Moreover, the distributed coordinated controller is designed by means of delay-dependent \textH\boldsymbol \infty robust control method taking into account transmission time delays. Finally, the validity of the proposed control scheme is demonstrated by means of simulation results. [ABSTRACT FROM PUBLISHER]

Since a microgrid consists of various distributed energy resources and local loads, integration of a distributed grid and multiple microgrids leads to an integrated hybrid energy system. This paper focuses on improving profit, economy, security, and dynamic performance of the integrated hybrid energy system by means of developing different areas of management and control strategies upon four-level hierarchical multiagent system. The level 1 agent implements optimal price bidding strategies for high profit of the overall system. The level 2 agent optimizes the energy management strategies for economic operation of each microgrid. The level 3 agent executes coordinated switching control for maintaining security of each microgrid. The level 4 agent facilitates local hybrid control of each distributed energy resource for guaranteeing dynamic performance. Finally, validity of the proposed scheme is tested by means of simulation study. [ABSTRACT FROM PUBLISHER]