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 eliminated 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 induction 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 theaxes. The components of along theaxes. The angle of the combined reference space phasor with the A-phase axis.

A pulse width modulation (PWM) scheme for multilevel inverters is proposed. The proposed PWM scheme generates the inverter leg switching times, from the sampled reference phase voltage amplitudes and centres the switching times for the middle vectors, in a sampling interval, as in the case of conventional space vector PWM (SVPWM). The SVPWM scheme, presented for multilevel inverters, can also work in the overmodulation range, using only the sampled amplitudes of reference phase voltages. The present PWM technique does not involve any sector identification and considerably reduces the computation time when compared to the conventional space vector PWM technique. The present PWM signal generation scheme can be used for any multilevel inverter configuration. A five-level inverter configuration, using an openended winding induction motor drive, is used to verify the SVPWM generation scheme experimentally.

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