Distributed Adaptive Virtual Impedance Control for Parallel-Connected Voltage Source Inverters in Modular UPS System

Abstract

AbstractIn this chapter, an average active power sharing control strategy based on distributed concept for the parallel operation of voltage source inverters (VSIs) is proposed to be applied to a modular uninterruptible power supply (UPS) systems. The presented method is named distributed adaptive virtual impedance control (DAVIC), which is coordinated with a droop control method. Low-bandwidth CAN-based communication is used for the requirement of data sharing of the proposed method in the real modular UPS system. Unlike the conventional virtual impedance control techniques, the virtual impedance of a converter module is adjusted automatically by using global information when DAVIC is applied and further to tune the output impedance of the power modules. The adaptive virtual impedance is calculated by using the difference between the active power of a local module and the average active power of all the modules in a modular UPS. The proposed method DAVIC overcomes the drawback of conventional virtual impedance control, since control since an accurate value of the real output impedances of different converter modules is not required. Simulations using PLECS and experimental results on a real commercial modular UPS are presented developed in order to verify the effectiveness of the proposed control methodology. These results have shown that a superior power sharing performance is obtained when using the proposed method.KeywordsDroop controlAdaptive virtual impedanceModular uninterruptible power supply systemPower sharingCirculating current