Soft-Switching System With Safe Connections of Capacitors and Inductors in Three-Phase Two-Level Voltage Source Inverter

This article presents a new soft-switching system for three-phase two-level voltage source inverters. In this system, capacitors are not connected in parallel to the main transistors, and inductors are not connected in series with the auxiliary transistors. Avoiding these types of connections protects the inverter transistors against damage in cases of disturbances in the inverter control system. The control algorithm of the main transistors of the inverter is the same as that of the transistors of an inverter operating with the hard-switching technique because the auxiliary transistors are switched depending on the operation state of the main transistors. The structure and operation principles of the new soft-switching solution are comprehensively described herein. Additionally, the control algorithm and the principles for selecting the elements of the new soft-switching circuits are discussed. The validity of the system operation was verified by performing laboratory tests with a three-phase voltage source inverter (3 kW, 250 V, 12 A, and 3 kHz) supplying an inductive-resistive load or a squirrel cage induction motor, whereas numerical calculations were performed for inverters with a higher rated power. The switching losses of the inverter operating with the proposed soft-switching solution were compared with those of an inverter operating with the hard-switching technique. The proposed soft-switching system increases the inverter efficiency, especially with medium- and high-rated powers.