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Current harmonics, which are injected in the utility by nonlinear loads, cause major problems that tend to deteriorate the power quality at the mains. To reduce such harmonics, Shunt Active Power Filters (SAPF) are commonly employed. This paper presents a current error space phasor based hysteresis controller for SAPF, which allows precise compensation of harmonic currents produced by nonlinear loads. The proposed controller is self-adaptive in nature and does not require any particular calculation of Point of Common Coupling (PCC) voltage vector (E) because of proper sector change detection logics used. Detailed Modelling and performance analysis of the proposed controller for SAPF with different compensating current generation methods, along with simulation results, is presented in the paper. The controller operation is studied for two different self-adaptive logics for detection of sector changes. Distortion in supply current is further reduced by avoiding the outer hysteresis band and generating the SAPF compensating currents by synchronizing the sector change with supply frequency. The controller keeps the current error space phasor within the hexagonal boundary (fixed band) by applying SAPF voltage vectors which are adjacent to the reference voltage vector (voltage vector at the point of common coupling i.e. E). This leads to the switching of optimal voltage vector unlike the random selection of the voltage vectors in conventional hysteresis controller based schemes. Region detection logic enables switching of SAPF voltage vector which keeps the current error well within the prescribed hexagonal boundary. The versatile nature of the controller is proved by analyzing its performance for three different reference compensating current generation techniques. The performance of controller for SAPF is tested for balanced as well as unbalanced mains voltage and is found to be satisfactory. Effect of dc-link voltage variations on the performance of the controller is also analyzed. Under steady-state and transient conditions controller performance is found fast and precise. Hence the proposed current controller gives generalized solution for any method of reference compensating current generation. The SAPF based on the proposed controller provides adequate compensation for mitigation of harmonics. Detailed theoretical analysis, modelling and simulation studies are presented in the paper and the claimed performance of the proposed controller is evident from the simulation results provided in the paper. [ABSTRACT FROM AUTHOR]

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]

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]

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 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]