Three-Phase Open-End Induction Motor Drive Interfaced to Higher Voltage DC Bus

Abstract

In applications that require a three phase induction motor to be driven by an inverter from a DC bus input of much higher voltage than needed, the option is to use a step down DC-DC converter before the inverter or use high voltage rating switches in the inverter along with low modulation index. In either case, disadvantages include poor efficiency, high voltage rated switches, etc. In open end winding three phase induction motor drives, the three separated windings are driven by 3-phase inverters from both sides. The arrangement is equivalent to three 1-phase inverters driving each winding separately from the same DC bus in parallel. This paper proposes an inverter scheme for open end induction motor drives, using a 1-phase inverter for each winding supply, but all three inverters being connected in series by their DC bus to the higher applied DC voltage. Unlike existing techniques for interfacing an induction motor drive to a higher voltage DC bus, the proposed scheme requires lower voltage switches with lower voltage bus capacitors to drive the lower voltage motor from a higher voltage DC bus. The series connected DC bus capacitor voltages are shown to remain balanced during normal operation.