794 IEEE TRANSACTIONS ON POWER ELECTRONICS, VOL. 19, NO. 3, MAY 2004 A Dual Two-Level Inverter Scheme With Common Mode Voltage Elimination for an Induction Motor Drive M. R. Baiju, Student Member, IEEE, K. K. Mohapatra, Student Member, IEEE, R. S. Kanchan, Student Member, IEEE, and K. Gopakumar, Senior Member, IEEE Abstract—Pulse-width modulated (PWM) inverters are known to generate common mode voltages which cause motor bearing currents in the induction motor drives. They also result in leakage currents which act as sources of conducted electromagnetic interference in the drive system. The common mode voltage generated by a conventional three-level inverter can be elimi- nated by switching only the voltage space vectors which do not produce the common mode voltage. This paper presents a PWM switching strategy to eliminate common mode voltage using the open-end winding configuration for the induction motor. The switching strategy presented in this paper, does not generate any alternating common mode voltages in the drive system and hence the electrostatic coupling of the common mode voltage, which results in the bearing currents and the leakage currents, is avoided. The proposed scheme is devoid of neutral point voltage fluctuations and does not require neutral point clamping diodes, when compared to the common mode elimination scheme based on the conventional three-level inverter topology. Also, the present scheme uses a single dc-link with half the voltage compared to the conventional three-level inverter based scheme. Index Terms—Common mode voltage, open-end winding induc- tion motor drive. NOMENCLATURE The dc-link voltage of the neutral point clamped three-level inverter. The pole voltages of INV1. The pole voltages of INV2. The voltage across the phase windings of the induction machine. The combined voltage space phasor for , and . The combined reference voltage space phasor for the dual inverter. The individual reference voltage space phasor for inverter- 1 (INV1). The components of along the - axes. The components of along the - axes. The angle of the combined reference space phasor with the A-phase axis. Manuscript received June 3, 2003; revised December 9, 2003. Recommended by Associate Editor M. G. Simoes. The authors are with the Centre for Electronics Design and Tech- nology, Indian Institute of Science, Bangalore 560012, India (e-mail: kgopa@cedt.iisc.ernet.in). Digital Object Identifier 10.1109/TPEL.2004.826514 I. INTRODUCTION T HE PULSE-WIDTH modulation (PWM) voltage source inverters have enabled efficient and easy control of the adjustable speed induction motor drives and they are widely used in industrial drives. These PWM inverters also cause high frequency, high level, common mode voltages in the system [1] .These alternating common mode voltages result in motor bearing currents by electrostatic coupling through parasitic capacitances [1]–[3]. The inverter generated common mode voltage also causes motor leakage currents which act as sources of Electromagnetic Interference in the drive system [4]. PWM inverter, which does not generate common mode voltage, is suggested as a solution to eliminate the problems associated with the common mode voltage [3]. Reference [5] presents modulation schemes for eliminating the common mode voltage in the conventional neutral point clamped three-level inverter, using only those voltage space vectors which do not generate common mode voltage. This scheme experiences neutral point fluctuations, which is characteristic of neutral point clamped topology. The neutral point fluctuation in this scheme can be controlled, by adding additional hardware to balance the neutral point voltage fluctuation [6]. The open-end winding induction motor, fed by two two-level inverters with half the dc-link voltage (compared to the conven- tional three-level scheme) from both sides, realizes a three-level inverter structure. [7]–[9]. In [7] and [8], isolated power sup- plies are used to suppress the zero sequence currents in the phase windings of dual inverter fed open end winding induc- tion motor drive. In [10], a space vector based PWM technique is employed to suppress the zero sequence currents in the motor phase windings so that the two two-level inverters can be oper- ated with a single dc-link. The PWM scheme in [10], suppresses the zero sequence currents in the machine phase windings, but does not eliminate the common mode voltage generated by the dual inverter. In the present work, a PWM switching strategy is proposed for the dual-inverter fed open-end winding induction motor drive with single dc-link, such that the two inverters do not generate any alternating common mode voltage. As the al- ternating common mode voltage is absent in the proposed drive, the possibility of electrostatic coupling and the associated prob- lems are avoided [1]–[4]. The proposed scheme is based on the open-end winding induction motor configuration with conventional two-level in- verters and hence does not experience neutral point fluctuations 0885-8993/04$20.00 © 2004 IEEE