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Linear modulation techniques (LMTs) of an asymmetrical six-phase machine (ASPM) with two isolated neutral points synthesize the desired voltage vectors by applying at least five switching states. Different choices of applied voltage vectors, sequences in which they are used, distribution of dwell-times among the redundant switching states give rise to a large number of possible LMTs. It is desirable that these LMTs avoid more than two transitions of a particular inverter leg within a carrier period. Only a subset of existing LMTs of ASPM follows this rule. Through an innovative approach, this article finds a way to account for all possible infinitely many LMTs that follow the rule of at most two transitions per leg. Another important criterion for the selection of an LMT is its current-ripple performance. Therefore, through numerical optimization, this article finds optimal LMTs among the above infinite possible LMTs for all reference voltage vectors in the linear range and for the whole feasible range of a machine parameter. This parameter is related to the leakage inductance of the machine and impacts the current ripple performance of ASPM. An optimal hybrid strategy is proposed with these optimal techniques, which outperforms all existing techniques in terms of the current ripple. The theoretical analysis is validated through simulation in MATLAB and experiments performed up to 3.5 kW on a hardware prototype. [ABSTRACT FROM AUTHOR]

Overmodulation (OVM) techniques of asymmetrical six-phase induction machine (ASIM) achieve higher dc-bus utilization by applying nonzero average voltage in nonenergy transfer plane. This results into unwanted current and associated copper loss. Existing OVM techniques reduce this loss with pulsewidth modulation (PWM) techniques from six-dimensional space vector perspective, which is both conceptually difficult and computationally challenging. The computational complexity of space vector based techniques is reduced by few existing PWM techniques in linear region by splitting the six-phase inverter as two three-phase inverters and modulate these inverters with linear PWM techniques in 30 $^\circ$ phase shifted. This is referred as three-phase inverter based technique in the title. But, three-phase inverter based OVM technique does not exist in the literature due to lack of knowledge of the relationship between six-dimensional space vectors and space vectors of two three-phase inverters. This article first establishes this relation. Based on this relation, an OVM technique is proposed where the reference voltage vectors of two inverters are phase shifted by 30 $^\circ$ but of different magnitudes. The proposed technique achieves THD and WTHD performances similar to space vector based best technique of ASIM with reduced computational complexity, as shown in details. The proposed strategy is validated through experiments and simulations on six-phase induction machine at 4.2 kW. [ABSTRACT FROM AUTHOR]

A three-level three-phase single-stage high-frequency link dc–ac converter is reported in this article for grid integration of photovoltaic sources. The proposed topology employs two three-level neutral point clamp (NPC) half-bridge legs on the dc side. The advantages of using three-level legs over conventional two level are: 1) the three-level legs can be implemented with the devices with lower blocking voltage which are economical; and 2) the low voltage blocking devices have lower on-state drop and lower turn on–off energy losses compared to high voltage blocking devices used in a two-level leg. These help to improve the converter efficiency. The sinusoidal pulsewidth modulation is implemented with the three-level NPC legs. The modulation strategy ensures reduced neutral current drawn by the NPC legs. The inner switches of the NPC legs are zero voltage switched. The turn-on transitions of the outer switches are with zero current. The proposed solution employs two high-frequency transformers to provide galvanic isolation which results in compact, low cost isolated converter solution. The intermediate dc link is pulsating and does not require any filtering. A low-frequency unfolder is employed to generate line frequency ac from pulsating dc. The switching loss of the unfolder is negligible. The proposed topology can support stand-alone load up to $\pm 0.866$ PF. The converter operation is verified on a 2-kW hardware prototype. [ABSTRACT FROM AUTHOR]

In this article, a pulsewidth modulated single-stage high frequency link three-phase dc–ac converter is proposed for grid integration of solar and fuel cell-based energy sources. On the dc side, the converter has three half-bridge legs which are zero-voltage switched over the entire line cycle without using any additional snubber circuit. On the ac side, two diode bridge rectifiers and one neutral point clamped (NPC) T-type three-level inverter are employed. The active switches in NPC inverter are switched either at line frequency or twice of it, incurring negligible switching loss. Modulation ensures soft commutation in the diode bridges. The intermediate three-level dc bus is pulsating and does not require any dc-filter capacitor and thus reduces overall filtering requirements. The high frequency galvanic isolation provides high power density, low-cost converter solution. The converter operation is analyzed in detail and verified on a 2-kW hardware prototype. [ABSTRACT FROM AUTHOR]

A solid-state transformer is a three-phase ac/ac converter with a high-frequency transformer. Due to advanced features like high power density, on demand var support and frequency regulation, solid-state transformer is an enabling technology for the modern power distribution system. It can also find application in high-power-density motor drives. The single-stage solid-state transformer considered in this paper is capable of bidirectional power flow and open loop power factor correction. This topology uses a minimum amount of copper and has relatively few semiconductor switches. One major problem in this converter is the commutation of leakage energy which results in power loss, reduction in switching frequency, loss of output voltage, and additional common-mode voltage switching. This paper presents a source-based commutation strategy along with a novel modulation technique resulting in elimination of additional snubber circuits, minimization of the frequency of leakage inductance commutation, recovery of the leakage energy, and soft switching of the output converter. The topology and its proposed control have been analyzed. Simulation and experimental results confirm the operation. [ABSTRACT FROM AUTHOR]

Pulse width modulation (PWM) converters generate switching common-mode voltages (CMVs) across the load terminals. These voltages cause common-mode currents, leading to bearing failure in motor loads and electromagnetic interference problems. This paper presents a generalized carrier-based PWM technique for open-end winding motor drives that completely eliminates switching CMV. The proposed method is applicable to both dual two-level voltage source inverter and dual matrix converter-based open-end winding drives. Detailed analysis shows that the carrier-based method requires significantly less computation compared to the corresponding space vector implementation. This paper also outlines the relationship between the two implementations. The carrier-based method is shown to achieve superior performance in terms of resource requirements and execution time when implemented on a field-programmable gate array-based real-time control platform. Simulation and experimental results have been presented to validate the proposed method. [ABSTRACT FROM AUTHOR]

This paper presents a novel topology for the generation of adjustable frequency and magnitude pulsewidth-modulated (PWM) three-phase ac from a balanced three-phase ac source with a high-frequency ac link. The proposed single-stage power electronic transformer (PET) with bidirectional power flow capability may find application in compact isolated PWM ac drives. This topology along with the proposed control has the following advantages: 1) input power factor correction; 2) common-mode voltage suppression at the load end; 3) high-quality output voltage waveform (comparable with conventional space vector PWM); and 4) minimization of output voltage loss, common-mode voltage switching, and distortion of the load current waveform due to leakage inductance commutation. A source-based commutation of currents associated with energy in leakage inductance (termed as leakage energy) has been proposed. This results in soft-switching of the output-side converter and recovery of the leakage energy. The entire topology along with the proposed control scheme has been analyzed. The simulation and experimental results verify the analysis and advantages of the proposed PET. [ABSTRACT FROM PUBLISHER]

A pulsewidth modulation (PWM) technique is proposed for minimizing the rms torque ripple in inverter-fed induction motor drives subject to a given average switching frequency of the inverter. The proposed PWM technique is a combination of optimal continuous modulation and discontinuous modulation. The proposed technique is evaluated both theoretically as well as experimentally and is compared with well-known PWM techniques. It is shown that the proposed method reduces the rms torque ripple by about 30% at the rated speed of the motor drive, compared to conventional space vector PWM. [ABSTRACT FROM AUTHOR]

Power electronic transformers (PETs) offer the advantage of size and weight reduction compared to line-frequency transformers by operating at much higher frequencies than line frequency. In this paper, a push–pull-based ac/dc PET has been proposed and analyzed. The PET offers bidirectional power flow between single-phase ac and dc, using the dual-active bridge principle. Such a system may find applications in interfacing plug-in hybrid and electric vehicles to the grid. The proposed PET offers advantages of open-loop unity power factor operation, soft switching of secondary-side converter power switches for all operating points, high power density owing to use of a high-frequency transformer, and high utilization factor (UF), compared to previous work. Analysis has been done for power transfer, UF, and soft switching. Simulation and experimental results have been provided to demonstrate the operation of the PET. [ABSTRACT FROM PUBLISHER]