## 1 Introduction  
Distributed generation (DG) technology is characterized by low environmental pollution, high energy utilization rate, and flexible installation sites, which enhances the power supply reliability of the distribution network. Particularly in the case of natural disasters, it ensures the basic energy supply of critical infrastructure and residents in the remote areas [1]. To coordinate the contradiction between DGs' intermittent characteristics and bulk power system, and fully exploit the benefit of DGs, the concept of microgrid was proposed at the beginning of this century [2]. A microgrid consists of distributed renewable resources, energy storage system, and various types of loads. It is capable of operating in either a grid-connected mode or an islanded mode, and handling the transitions between these two operation modes. In an islanded microgrid, the conventional control strategy produces the output voltage deviations from their nominal values as well as the failure of reactive power sharing among DGs connected via different line impedances, thereby affecting the power supply quality and system dynamic performance of microgrids [3; 4]. The hierarchical control structure is an effective way for the coordination of multiple DGs in microgrids [5]. In order to maintain the stability of frequency and voltage, the primary control of a microgrid employs a droop control method that is completely decentralized and only depends on local information without requiring any communication between the DGs. However, the droop control causes deviations of the voltage and frequency from their nominal values. Hence, the secondary control level is necessary to compensate for the deviations caused by the primary droop technique. The tertiary control level is aimed at the economical dispatch and optimized management of power flow in the microgrid. This paper aims to address the voltage restoration and reactive power sharing problem in the secondary control level of an islanded microgrid with multiple inverter-based DGs. In general, the secondary control strategies for microgrids are categorized into three types: centralized [6], distributed [7], and decentralized [8]. Microgrids are characterized by small electrical distances between DGs, lack of static compensation devices, and line impedance mismatch [9], which makes the primary droop control fail to achieve accurate reactive power sharing among the DGs. Such a failure in turn possibly causes DGs overloads and damages the stability of the whole system. The authors of [10; 11] proposed centralized control architectures for voltage restoration and reactive power sharing, in which each DG demands to communicate with a central controller. The centralized manner requires a complicated two-way communication network and any single point failure may cause serious instability of the entire system. For enhancing the scalability and flexibility, a multiagent system (MAS)-based distributed secondary control scheme using only local neighbors' information is more desirable in microgrids. Cooperative secondary controllers by using a multiagent pinning consensus [12], finite-time consensus [13], and distributed averaging proportional integral (DAPI) [14] have been deliberately designed for voltage or/and powering sharing control. Since the objective of most studies is to synchronize the voltages of DGs to nominal values, accurate reactive powering sharing among DGs is impossible. And most recent work does not consider the influence on the consensus algorithm of the potential malicious attacks induced by the communication network. In the MAS-based distributed cooperative control scheme, each DG is considered as an agent that exchanges information with its neighbors through communication networks. Conventional continuous-signal-based communication requires real-time data transmissions between DGs. The continuous-time-based control method can hardly be realized due to the constraints of channel bandwidth and computing resources in practical engineering.