Model predictive control of parallel connected inverters for uninterruptible power supplies

Uninterruptible power supplies have been used in many installations for critical loads that can not afford power failure or surge during operation. It is often difficult to upgrade the UPS system as the load grows over time. Due to lower cost and maintenance, as well as ease of increase system capacity, the parallel operation of modularized small power UPS has attracted much attention in recent years. This paper presents a state space based model predictive controller for controlling two or more parallel connected single phase UPS. In the proposed approach, the controller gains are determined by minimizing a cost function that reduces the output voltage tracking error, the control signals and equal sharing of the load currents among the inverters. The developed system has been evaluated through simulation study and experimental verification. The results under various loading conditions have demonstrated that the system performs well.