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The open-loop control scheme presented in part I of this paper for a dual five-level-inverter-fed induction motor (IM) drive with two dc power supplies maintains dc-link capacitor voltage balancing and common-mode voltage (CMV) elimination throughout the operating range of the drive. The operating limitation of the proposed open-loop control scheme to take corrective action toward the existing unbalance in the dc-link-capacitor voltages is also pointed out in part I of this paper. As a solution to this, a simple closed-loop control scheme, which is based only on the switching-state redundancy, is proposed in this part of the paper. The proposed closed-loop control scheme not only prevents further unbalancing of capacitor voltages but also takes corrective actions to bring back the capacitor voltages in the balanced state. The proposed closed-loop scheme achieves dc-link capacitor voltage balancing and elimination of CMV together in the complete modulation range, including overmodulation of up to the 24-step operation. The proposed control scheme does not affect the output fundamental voltage generated by the inverter, as it effectively utilizes only the availability of redundant switching states of the inverter, and does not call for additional power circuit hardware. The scheme is presented with the simulation studies and experimentally verified with a 1.5-kW open-end winding IM drive. [ABSTRACT FROM AUTHOR]

A current error space phasor based simple hysteresis controller is proposed in this paper to control the switching frequency variation in two-level pulsewidth-modulation (PWM) inverter-fed induction motor (IM) drives. A parabolic boundary for the current error space phasor is suggested for the first time to obtain the switching frequency spectrum for output voltage with hysteresis controller similar to the constant switching frequency voltage-controlled space vector PWM-based IM drive. A novel concept of online variation of this parabolic boundary, which depends on the operating speed of motor, is presented. A generalized technique that determines the set of unique parabolic boundaries for a two-level inverter feeding any given induction motor is described. The sector change logic is self-adaptive and is capable of taking the drive up to the six-step mode if needed. Steady-state and transient performance of proposed controller is experimentally verified on a 3.7-kW IM drive in the entire speed range. Close resemblance of the simulation and experimental results is shown. [ABSTRACT FROM AUTHOR]

The simultaneous elimination of common-mode voltage and DC-link capacitor voltage imbalance is achieved in a five-level inverter scheme for an induction motor drive throughout its operating range. A dual five-level inverter-fed open-end-winding induction motor structure is used for the proposed drive. Initially, the operating limitations of achieving this dual task for the five-level inverter configuration are investigated for a single DC power supply. Subsequently, a switching strategy for a five-level inverter topology with two DC power supplies is proposed to achieve the dual task over the entire speed range of the drive. The proposed drive offers a simple power-bus structure with more redundant switching combinations for inverter voltage vectors, and requires a lower voltage-blocking capacity of the power devices as compared with the conventional single five-level inverter-fed drive. As only the availability of redundant switching combinations for inverter voltage vectors is exploited, the dual task is achieved without disturbing the fundamental component of the inverter output voltage and the scheme does not need any extra control circuit hardware. Experimental verification of the proposed scheme is done on a 1.5 kW induction motor drive in the linear as well as overmodulation range. [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 current-error space-vector-based PWM hysteresis controller is proposed for three-level voltage source inverter fed induction motor drive applications. A hexagonal boundary for the current-error space vector is formed by sensing the current-error space vector along three different axes, which are 120:) apart and are orthogonal to machine phase axes. Only the adjacent inverter voltage vectors forming a triangular sector, in which tip of the machine voltage vector lies, are switched to keep the current-error space vector within the hexagonal boundary. Selection amongst the three nearest voltage vectors is done by a simple region detection logic in all the sectors. Calculation of the machine voltage vector is not needed and information of the same is indirectly derived from the direction of current-error space vector. The controller uses a self-adaptive sector identification logic, which provides smooth transition between sectors (voltage levels), including over modulation region up to 12-step mode of operation. Inherent advantages of current hysteresis controller are retained with the added advantage of adjacent voltage vector selection for hysteresis PWM control. Simple look-up tables are only needed for sector and vector selection, based on the hysteresis controller output, for the proposed hysteresis PWM controller. Experimental verification is provided by implementing the proposed controller on a 1.5 kW open-end winding induction motor drive. The proposed controller can be extended for further levels of multi-level inverters for high-performance drives by constructing suitable look-up tables. [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]

Twenty limbs with varicose veins were subjected to injection compression sclerotherapy. Satisfactory results were obtained in all the cases. The technique and results are presented with the aim that this technique will be practised in more and more centres in India.