Decentralized Suppression Strategy of Circulating Currents Among IPOP Single-Phase DC/AC Converters

Abstract

To increase the power rating and improve the reliability of the single-phase power supply system, the input-parallel output-parallel (IPOP) single-phase dc/ac converters (SDACs) are widely used. However, among the IPOP SDACs, there are complicated circulating currents which will increase the current stress on the switching devices and influence the safe operation of the system. But, the detailed quantitative analysis of the circulating currents is not well developed and the corresponding suppression strategies are not very comprehensive. Focusing on these problems, this paper pays attention to the detailed mathematic model and effective suppression strategy of circulating currents among IPOP SDACs. First, the detailed mathematic model of the circulating currents is established. Based on this model, it is found that there are various types of circulating currents existing in the IPOP SDACs, including circulating currents within the single SDAC and circulating currents among the multiple SDACs. At the same time, the influence factors are also analyzed, and it is first revealed that the asymmetry of impedances in different sides will cause circulating currents with different frequencies components including the dc, fundamental, and second frequencies. Second, after the detailed analysis, a decentralized control method composed of the common mode (CM) and differential mode (DM) control is proposed to suppress the complicated circulating currents. The control method is comprehensive and can suppress circulating currents caused by diverse influence factors. All the theoretical analyses are verified by the real-time hardware-in-loop (HIL) tests.