A Four-level Inverter Scheme with Reduced Common Mode Voltage for an Induction Motor Drive

Abstract

A four-level inverter configuration for an induction motor is proposed in this paper. The drive used for this scheme is an open-end winding induction motor which can be obtained by separating the neutral connections of any general threephase induction motor. The proposed scheme uses two three-level inverters, with asymmetric DC link voltage, feeding the induction machine from both sides and can generate voltage space vector locations similar to a conventional seven-level inverter. The four-level scheme is based on the use of only those space vector combinations of the seven-level inverter, which generate zero common mode voltage in the machine phase voltages. The proposed four-level inverter scheme requires only two isolated DC links as compared to the conventional diode-clamped four-level inverter scheme, which needs three isolated power supplies. The common mode voltage, in the pole voltages of the proposed four-level inverter, is significantly lower than that of the conventional four-level inverter while the machine phase voltages have zero common mode content. The proposed power circuit bus structure is simple to fabricate when compared to the conventional four-level inverter. A SVPWM scheme is presented, which generates the inverter gate switching signals from sampled amplitudes of reference phase voltages. The proposed four-level inverter scheme is implemented of a 1.5 kW open-end winding induction motor and the experimental results are presented.