Distributed Average Integral Secondary Control for Modular UPS Systems based Microgrids

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 CAN communication is proposed. In a sharp contrast from the existing distributed secondary control strategies, the output voltage and frequency of the modules are not shared through the CAN bus, but instead, the integral output of the secondary controller is shared among the inverter modules of the modular UPS. 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 shown that good performance of voltage recovery and power sharing of the proposed control method is obtained.