Decoupled circulating- and output-current control of parallel inverter systems

Modern inverter systems often require the operation of multiple parallel inverters. When these are connected to a weak grid or a common filter, stability problems can occur. Also currents, which lead to a bottleneck of the available power, are a known problem of parallel inverter operation. In this paper a method will be presented, which allows to describe any number of parallel inverters as single virtual inverter (VI). By dividing the inverters in pairs and triplets a decoupled control of the circulating currents and the output currents will be possible. The presented control method avoids instabilities due to differing current paths of circulating and output currents. Simulation results and measurements demonstrate the performance and stability of this approach.