A current source inverter with advanced external circuit and control method

Abstract

A thyristor-based current-source inverter (CSI) is proposed, employing a standalone voltage-source inverter (VSI) with a small power rating. The VSI, as an external circuit of the CSI, performs three tasks: 1) turning off of thyristors; 2) transfer of reactive load energy; and 3) clamping peak voltages across the load and thyristors. In comparison with conventional thyristor-based CSIs requiring large ac commutation capacitors as well as individual energy recovery and voltage clamping circuits, the proposed CSI system can replace all the complicated auxiliary circuits and bulky ac capacitors with the small VSI. Furthermore, the proposed CSI ensures simple and easy control of the commutation process due to the simple switching operation of the VSI. The VSI operates only during the commutation periods of the load currents and stops working in the noncommutation periods. Thus, the VSI with small power rating can be used for the proposed CSI system. The feasibility of the proposed CSI system is verified by simulation and experimental results.