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Renewable Energy
Effect of Stator Winding Connection of Five-Phase Induction Machines on Torque Ripples Under Open Line Condition
One of the main challenges in designing high-power drive systems is the quality of the developed torque. High-torque-ripple magnitudes result in serious vibration and acoustic noise problems that affect the lifetime of a drive train. Multiphase machines intrinsically offer the torque with higher quality and are also being promoted for their high fault tolerant capability when compared with their three-phase counterparts. During open-phase conditions, the induced nonfundamental sequence current components have a detrimental effect on the machine performance especially under open-loop control. Although optimal current control is usually employed to ensure certain optimization criterion, such as minimizing torque ripples, optimizing flux distribution, or minimizing copper loss, are met, it usually entails a sophisticated current controller. This paper studies the effect of a stator winding connection of a five-phase induction machine on the induced torque ripples. Two possible connections, namely, star and pentagon connections are compared under healthy as well as fault conditions with one-line open. The comparison is conducted using both finite-element simulation and experimental results using a 1.5-Hp five-phase prototype induction machine. The comparison shows that the pentagon connection reduces the machine-induced torque ripples and improves the overall machine performance under fault conditions.
Hybrid Multilevel Converter With Cascaded H-bridge Cells for HVDC Applications: Operating Principle and Scalability
Hybrid multilevel converters are contemplated in an attempt to optimize the performance of voltage source converters in terms of magnitude of semiconductor losses and converter footprint, and to achieve additional features such as dc short circuit proof, which is essential for a high integrity multiterminal HVDC grid. Therefore, this paper considers an emerging hybrid cascaded converter that offers the dc side short circuit proof feature at reduced loss and footprint compared to the existing multilevel and other hybrid converters. Its operating principle, modulation, and capacitor voltage balancing strategies are described in detail. Furthermore, hybrid converter scalability to high voltage applications is investigated. The validity of the modulation and capacitor voltage strategy presented are confirmed using simulation and experimentation. The hybrid cascaded converter is extendable to a large number of cells, making it applicable to high voltage applications, and operation is independent of modulation index and power factor. On these ground, the converter is expected to be applicable for both real and reactive power applications.
A Novel SPLL and Voltage Sag Detection Based on LES Filters and Improved Instantaneous Symmetrical Components Method
The software phase-locked loop and the voltage sag detection algorithm are the two key factors to evaluate the performance of a dynamic voltage restorer, whose dynamic response is usually impacted by phase jump, voltage unbalance, and harmonics of the grid voltage. This paper proposes a novel algorithm based on the combination of least error squares filters and an improved instantaneous symmetrical components method. Hence, a detailed theoretical procedure is first presented. Then, the simulation model is built in MATLAB/SINMULINK. To verify its effectiveness, a series of comparison and analysis have been carried out. Also, a 10-kV/2-MVA prototype is developed with a voltage sag generator platform. Finally, experiments have been done and the results show that the novel algorithm has an improved dynamic response compared with the traditional methods.
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