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This paper develops a seven-level inverter structure for open-end winding induction motor drives. The inverter supply is realized by cascading four two-level and two three-level neutral- point-clamped inverters. The inverter control is designed in such a way that the common-mode voltage (CMV) is eliminated. DC-link capacitor voltage balancing is also achieved by using only the switching-state redundancies. The proposed power circuit structure is modular and therefore suitable for fault-tolerant applications. By appropriately isolating some of the inverters, the drive can be operated during fault conditions in a five-level or a three-level inverter mode, with preserved CMV elimination and dc-link capacitor voltage balancing, within a reduced modulation range. [ABSTRACT FROM AUTHOR]

In this paper, a 12-sided polygonal voltage space vector generation with common-mode voltage elimination (CME) is proposed for an induction motor drive. An open-end winding configuration is used for the motor. The proposed multilevel structure is achieved by cascading only the conventional two-level inverters with asymmetrical dc link voltages. By appropriately selecting the voltage vectors with identical common-mode voltage from the opposite ends, a pulsewidth modulation (PWM) strategy with zero common-mode voltage variation can be achieved for the entire modulation range with a common dc link requirement for both the inverter systems. Along with the CME, the proposed 12-sided polygonal space vector based multilevel inverter structure has increased modulation range with the absence of 5th, 7th, 17th, 19th, etc., harmonics up to 12-step operation. The bandwidth problems associated with conventional hexagonal voltage space vector structure current controllers due to the presence of 5th and 7th harmonics in the overmodulation region are absent in the present 12-sided structure. So a simple PWM voltage control with linear voltage control up to 12-step operation is possible from the present 12-sided scheme with less current control complexity. [ABSTRACT FROM AUTHOR]

Multilevel inverters are preferred over two-level inverters in high-voltage, high-power applications mainly because low-switching-frequency PWM schemes can be implemented with power devices of low-voltage ratings. Common multilevel inverter structures such as NPC, H-bridge and flying capacitor will produce a hexagonal voltage space vector structure. In the over-modulation range a multilevel inverter with a hexagonal voltage space vector structure will produce high amplitude 5th and 7th harmonic voltages in the output voltages. The maximum phase peak fundamental voltage is 0.637 Vdc in six-step mode operation (where Vdc is the radii of the hexagonal voltage space vector structure). A 12-sided polygonal voltage space vector structure will have a maximum phase peak fundamental voltage of 0.64 Vdc in the linear modulation range itself (where Vdc is the radii of the 12-sided polygonal voltage space vector structure), which is more than the output in six-step operation in the over-modulation range for a conventional multilevel structure. Also with a 12-sided polygonal space vector structure, an additional boost of the fundamental phase voltage is possible in the 12-step operation with the elimination of the 5th- and 7th- order harmonics (6n±1, n=1, 3, 5 ... etc). A multilevel inverter structure with 12-sided polygonal voltage space vector structure is proposed for an induction motor drive. The proposed inverter structure is realised by cascading three conventional two-level inverters. This makes the power bus structure very simple. [ABSTRACT FROM AUTHOR]

Split-phase (six-phase) induction motor stator windings consist of two sets of three phase windings, which are spatially phase separated by 30 electrical degrees. Due to mutual cancellation of the air gap flux for all the 6n ± 1 (n = 1,3,5. . . .) order harmonic voltages, called zero sequence components, large harmonic currents are generated in the stator phases. Only the 12n±1 (n = 0,1,2,3 . . . .)-order harmonic voltage components contribute toward the air gap flux and electromagnetic torque production in the machine. In this paper, a novel scheme is proposed where two six-phase induction motors are connected in series with proper phase sequence so that the zero sequence component voltages of one machine act as torque and flux producing components for the other. Thus, the two six-phase motors can be independently controlled from a single six-phase inverter. A vector control scheme for the dual motor drive is developed and experimentally verified in this paper. [ABSTRACT FROM AUTHOR]

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 open- ended winding induction motor drive, is used to verify the SVPWM generation scheme experimentally. [ABSTRACT FROM AUTHOR]

A scheme for a three-level voltage space phasor generation with common-mode voltage elimination is proposed. An open-end-winding induction motor, fed from both ends by two three- level inverters, which are realised by a cascading two two-level inverter, is used in this configuration. The voltage space vectors of individual three-level inverters, which generate the same common- mode voltage in the inverter pole voltage, are variously grouped. When these voltage space vectors are used to switch individual three-level inverters, it results in zero common-mode voltage across the motor windings. in the proposed scheme, voltage space phasors from individual inverters with zero common-mode voltage in the inverter pole voltage are used for PWM control. For the proposed drive configuration, the DC link voltage requirement is only half when compared to the DC link voltage of a conventional neutral-point-clamped (NPC) three-level inverter. The proposed inverter configuration offers reduced circuit and control complexity when compared to similar schemes with NPC or H-bridge inverter configurations. [ABSTRACT FROM AUTHOR]