Power loss investigation of series-connected current source inverters

Abstract

Current-source inverters (CSIs) are a type of direct current (DC) to alternating current (AC) converters that generate a defined AC output current waveform from a DC current supply. As the counterpart of voltage source inverters (VSIs), they feature a simple converter structure, low switching dv/dt on the ac-side, and reliable short-circuit protection. These advantages have made CSIs widely used in high power medium voltage drives. Besides, they have also been studied in other applications, such as wind energy conversion systems, superconducting magnetic energy storage (SMES) systems, and microgrid systems. Different topologies of CSIs and modulation schemes have been evolved to tailor various application requirements. For those applications with a higher power rating, two or more CSIs can be connected in series to form series-connected CSIs (SC-CSIs) to increase the power handling capability. To the best of the author’s knowledge, three topologies of SC-CSIs have been developed so far. The first topology referred to as topology A is constructed by connecting several identical CSIs in series. These CSIs are identical in terms of topology, modulation, and control. A multi-winding transformer is employed at the output to provide a clear current path for each CSI and step up the voltage if necessary. In the second topology designated as topology B, the multi-winding transformer is replaced by a phase-shifting transformer, and a phase-shifting modulation scheme is implemented. This topology features an increased DC current utilization, decreased switching losses, and reduced passive components. The third topology denominated as topology C adopts a different arrangement of switches leading to a reduced number of switching devices. A multi-winding transformer is used at the output in this topology. Power losses are an important attribute of SC-CSIs since they have a significant impact on the efficiency of the system. Besides, it is necessary to find out the power loss distribution of inverters to design an appropriate cooling system. However, the power losses and the power loss distribution of these three topologies have not been figured out. [...]