Search

Numerous critical load applications rely upon a line-interactive uninterruptible power supply system to maintain power during outages as well as during under- and over-voltage utility conditions. When any disturbance occurs at the utility side, the line-interactive uninterruptible power supply system takes over the load within a few milliseconds to avoid interruption. However, during this transition of load, a significant inrush current occurs due to the magnetic saturation of the load transformer. The inrush current phenomenon causes reduced line voltages and sometimes activates the over-current protection of the uninterruptible power supply system. This article proposes a new line-interactive uninterruptible power supply system that eliminates the inrush current phenomenon by connecting a standard current-regulated voltage source inverter to the secondary of the load transformer. During any transient condition at the utility side, the load current is monitored and regulated to achieve a seamless compensation or transition of load. Experimental results are obtained for a prototype during a number of possible irregular utility power conditions to endorse the performance of the proposed uninterruptible power supply system. [ABSTRACT FROM PUBLISHER]

—An improved topology for a low-speed permanent magnet vernier machine, called a dual-stator interior permanent magnet vernier machine, is introduced to significantly increase torque density and power factor. A dual-stator is adopted in the design for more torque and improving space utilization. An interior spoke-type magnet array in the rotor is designed for magnet flux focusing, which can effectively increase useful flux and force flux lines to pass through the entire machine during operation as opposed to two separate torque components as in a normal dual-stator permanent magnet machine. To clearly place the advantages of the proposed topology in perspective, the proposed dual-stator interior permanent magnet vernier machine is compared to a well-known dual-stator surface-mounted permanent magnet vernier machine. This article discusses the operation principle and magnetic field analysis of the proposed machine and reports comparison simulation results taken from the finite-element method. In addition, the stator tooth is optimized for further better performance on torque density and power factor. [ABSTRACT FROM AUTHOR]

This paper describes a new and straightforward approach to estimate the air-gap flux position in induction machines. The proposed scheme is based on the injection of a high-frequency oscillating stator voltage instead of a three-phase high-frequency voltage, thus allowing a reduction in audible noises and torque ripple. The main feature of the proposed approach is that a simple air-gap flux tracking algorithm is developed using the amplitude variation of the high-frequency component of the zero-sequence voltage. Moreover, the zero-sequence voltage is sensed at the output of the inverter rather than at motor terminals. The estimated position is not influenced by load and parameter variation and can be performed at any frequency, including low and zero frequency. An experimental prototype has been implemented showing the performance of the proposed approach. [ABSTRACT FROM AUTHOR]

The optimization of both DC link voltages and switching angles of fundamental switching strategy for the output waveform of a multilevel cascade inverter is investigated in this study. Previous work in the area of fundamental switching for multilevel inverters is highlighted by the pulse width optimization technique, where the switching angle at each voltage level is optimized so that the resulting staircase output voltage has the minimum harmonic content. The DC link voltage of each level, however, is assumed to be the same and constant. As an extension to this work, the optimization of both DC link voltages and switching angles of the staircase output voltage is carried out. Harmonic performance of the proposed switching strategy is simulated and results are compared with that of the previous work. It is confirmed theoretically that substantial improvement in the harmonic minimization can be obtained. In practice, the proposed method is especially suitable for the control of multilevel cascade inverters, the latest development of its kind, where each DC voltage can be self-maintained and independently controlled. The description of the multilevel cascade inverters for applications of AC drives, as well as Static Var Generation, is also given in this article. [ABSTRACT FROM AUTHOR]

Numerous techniques have been reported in the literature to accomplish the task of locating the rotor flux axis for the purpose of direct field orientation. This paper first summarizes the existing sensorless techniques using high-frequency test signal injection to determine the flux spatial location in an induction machine. A novel approach employing balanced and unbalanced excitation is then investigated to track the flux. It is first demonstrated that the rotating flux vector in the machine causes saturation-induced saliency in the phases under normal operating conditions. By employing high-frequency test signals, this saliency is monitored and then used to track the flux in the machine under test. The feasibility of the proposed approach is verified with experimental results. [ABSTRACT FROM AUTHOR]