A Medium Voltage AC Drive with Parallel Current Source Inverters for High Power Applications

A power circuit topology suitable for large Medium Voltage AC drive applications is presented. The line side harmonics requirements are met by using an 18 pulse phase-controlled rectifier. The output horsepower of the drive is increased by connecting two inverters in parallel. The low switching frequency used in the inverters makes this approach especially attractive in very high power applications. A new control scheme is proposed to ensure proper current sharing between the two output inverters even when the power switching devices and the two bridges are severely asymmetric. The start up issues and the control response to transient conditions are analyzed and the boundaries of the controllability of the system are discussed. The proposed system is experimentally verified by a 208V, 5 hp laboratory set up.