This paper presents a distributed average integral secondary control (DAISC) method for modular uninterruptible power supply (UPS) systems-based microgrids. For each UPS unit, the local primary control level encompasses droop control and virtual impedance loops, which is commonly used in parallel inverter systems. In order to provide a fast voltage recovery performance, along with excellent power sharing capability among the parallel UPS modules, a distributed secondary control method based on controller area network (CAN) communication is proposed. In a sharp contrast to the existing distributed secondary control strategies, in which the output voltage and frequency of the modules are not shared through the CAN bus, in the proposed apporach, the inverter modules of the modular UPS share the integral output value of the secondary controller. By using the proposed novel DAISC approach, a better dynamic power sharing performance along with an inherent anti-windup capability of the integral controller is achieved. Simulation results using PLECS and experiments from a modular UPS platform have been developed to verify the feasibility and effectiveness of the proposed distributed secondary control. The results show that good performance of voltage recovery and power sharing of the proposed control method is obtained.