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.

Due to the high R/X ratio and mismatched feeder impedance of low-voltage microgrids (LVMGs), conventional droop method is no longer able to decouple the active and reactive power of distributed generators (DGs) and the power sharing accuracy is degraded. In this paper, a virtual complex impedance based P — 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 (VPS) and point of common coupling (PCC) 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 methods.

Multi-functional grid-tied inverters (MFGTIs) have been investigated recently for improving the power quality (PQ) of microgrids (MGs) by exploiting the residual capacity (RC) of distributed generators. Several centralized and decentralized methods have been proposed to coordinate the MFGTIs. However, with the increasing number of the MFGTIs, it demands a method with improved reliability and flexibility, which are characteristics of distributed framework that has not been introduced into the PQ improvement (PQI) field before. In this paper, we propose a distributed consensus method to undertake the PQI task. The task is proportionally shared among the MFGTIs according to their instant RCs. Besides, most of the existing methods assume that the RCs of the MFGTIs are sufficient for tackling the PQ problem (PQP), which is not always true. In the case of insufficient RC, the active power output of each MFGTI is scaled down by the same factor determined by a proposed leader-follower protocol to make room for the task. In summary, the PQP is dealt with in both cases of sufficient and insufficient RC under the distributed control framework. Finally, simulations and hardware-in-the-loop experiments of an MG consisting of three 10kVA MFGTIs are presented to verify the effectiveness of the proposed methods.

Due to the high resistance/reactance (R/X) ratio of a low-voltage microgrid (LVMG), virtual complex impedance-based P-V/Q-ω 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.

This article proposes a distributed event-triggered control method for multifunctional grid-tied inverters (MFGTIs) in microgrid to improve power quality under denial-of-service (DoS) attack. The proposed method tackles two key challenges. The first is dynamic adjustment of inverter residual capacities responding to variations in the accessible renewable power and the harmonic and unbalanced current. The second is DoS-resistant event-triggered control with the following specific functional requirements in power quality improvement task. 1) Quantitative characterization and adjustability of convergence speed and accuracy. 2) Implementation based on sampled data with adjustable sampling period. 3) Reasonableness of DoS attack descriptions. 4) Guidance on selection of parameters. Theoretical analysis proves that the proposed method achieves adequate harmonic and unbalanced current compensation at the point of common coupling without wasting capacity and ensures fair utilization of all MFGTIs, even under DoS attacks. Simulation results further validate the effectiveness of the method.