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Induction motors, both three and single phase, are used extensively for adjustable-speed drives' applications. These machines are structurally very robust and are a primary source of motive power and speed control where dc machines cannot be used. For closed-loop control of these machines, sensorless speed estimation is usually preferred. Among the current estimation techniques available for speed-sensorless induction motor drives, speed measurement based on rotor-slot-related harmonic detection in machine line current happens to be a prominent one. While these harmonics can be strong in certain kinds of machines, some other machines may exhibit very weak rotor slot harmonics that can be obscured by noise. Skewing, slot shapes and types, structural unbalances, etc., also have a prominent effect on the detectability of these harmonics. This paper attempts to investigate this problem based on the interaction of pole pairs, number of rotor bars, and stator winding. Although the analysis and experimental results have been mainly provided for three-phase squirrel-cage induction motors, single-phase and slip-ring induction motors have also been addressed. Further, it has been shown that eccentricity-related fault detection could also be easily accommodated with this kind of speed detection technique at no or negligible extra cost when certain motors are selected. Index Terms--Eccentricity, fault diagnosis, sensorless speed estimation.

In this paper, a dc–ac buck converter is proposed as a grid-side converter in high voltage dc (HVdc) transmission systems for high-power renewable energy source grid integration. The proposed architecture consists of multimodules of half-bridge voltage source converters (HB-VSCs). The dc terminals of the HB-VSCs are connected in series across the entire dc link (i.e., capacitor tapped), whereas their ac outputs are connected to multiwinding transformers to provide the three-phase terminals for ac grid integration. The proposed grid-connected capacitor-tapped multimodule converter (CT-MC) architecture, inspired from the HVdc shunt tap proposed by ABB, provides a dc–ac conversion with a relatively moderate voltage rating of semiconductor devices. It also provides operation with a lower number of semiconductor devices, gate driver circuits, voltage sensors, and lower total MVA rating of semiconductor devices (67%) compared with the conventional three-phase HB modular multilevel converter, which positively affects the system cost and reduces the computational burden of the employed controller. In this paper, the operational concept and control of the CT-MC are presented along with a capacitor voltage balancing approach. Simulation results are presented during normal and abnormal conditions to show the viability of the proposed architecture. Finally, a scaled down prototype for the CT-MC is employed to validate the converter operation. [ABSTRACT FROM AUTHOR]

Pulsed electric field is a commonly used and effective disinfection method in drinking water treatment applications. In this paper, a transformerless unipolar/bipolar high-voltage pulse generator is presented with well-regulated pulsed output voltage for drinking water treatment via underwater pulsed corona discharge. The proposed high-voltage pulse generator is fed from a relatively low-voltage dc supply. Then, capacitor–diode voltage multiplier centrally fed from a dc–dc boost converter is used to elevate the input voltage to a proper high-voltage level. Finally, a modular multilevel converter is employed to chop the elevated voltage into unipolar or bipolar pulsed output voltage (based on the user selection). The suggested arrangement provides a high-voltage gain with relatively low-voltage components, i.e., neither high-voltage nor series-connected components are needed in the proposed approach. A comparison between the proposed approach and the other Marx-Based pulse generators has been held to show the merits of the proposed approach. A detailed design of the generator passive components and semiconductor devices has been presented. Simulation and experimental results are presented for the unipolar as well as the bipolar pulsed output to validate the proposed concept. [ABSTRACT FROM AUTHOR]

This paper presents an algorithm that enables single-sensor operation of vector-controlled three-phase permanent-magnet-synchronous-motor voltage source inverter (VSI)-based drive systems. The closed-loop operation is performed through measuring only the VSI dc-link current. The measured VSI dc-link current is fed to a space-vector-based lookup table, which reconstructs the motor line currents. Three Luenberger-style observers are used to filter out the reconstructed motor line currents and estimate the rotor position and speed. The effect of observer bandwidth on the accuracy of the motor's estimated parameters is also investigated. The drive system's physical dynamic stiffness is used as a key metric to compare the drive system performance in single-sensor mode and fully sensored mode, in order to find the lowest steady-state speed limit for the single-sensor drive system operation. [ABSTRACT FROM AUTHOR]

Although torque enhancement in multiphase induction machines using harmonic current injection has been addressed in the literature, a detailed assessment of the effect of this enhancement on the design parameters of multiphase machines with different numbers of phases is needed. This paper addresses this topic by performing a detailed comparative study of harmonic injection torque enhancement on multiphase machines with different numbers of phases. Sets of identical dimension and volume rotors differing in their value of the bar skew angle were designed to operate with the various stator designs in order to facilitate the comparative evaluation. A mathematical approach is also introduced to enable the derivation of equivalent multiphase machine parameters based on an existing one. In addition to a detailed finite-element-analysis verification of the results, time domain MATLAB simulations are used to verify the mathematical modeling. The results provide a means to assess the extent to which such harmonic injection may be beneficial by quantifying torque enhancement as well as torque density for various multiphase machines. [ABSTRACT FROM AUTHOR]