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A matrix converter has a topology that inherently exhibits sinusoidal input current waveforms and has small output voltage steps. This paper proposes to integrate the matrix converter with filters, which provide lower electromagnetic interference (EMI), lower common-mode current, lower shaft voltage, and sinusoidal output voltage waveforms. A salient aspect of the proposed integration is its ability to significantly reduce the value of the input EMI filter capacitors and still meet strict EMI regulations. This helps in reducing the ground leakage current, which in the past has been a serious limitation in applying EMI filters with low ground currents for human and cattle safety. Index Terms--AC/AC converter, common-mode voltage, electromagnetic compatibility/electromagnetic interference (EMC/ EMI), harmonics, matrix converters, passive filter.

Many applications involving induction motors that are controlled using variable frequency drives require the ability to stop quickly. These applications include emergency stops, quick stopping of fans, centrifuges, presses, etc. The technique that is widely accepted in the industry for achieving quick stopping makes use of brake resistors in series with a power semiconductor switch. The switch-resistor combination (brake-unit) is applied across the dc bus. The fastest decelerating time achievable depends on the size of the resistors and the switch employed. In this paper, the authors propose a novel method of achieving quick stopping times without the use of any brake-unit. The stopping times achievable depend on the inverter rating, motor parameters, and the inertia of the load. The proposed method uses the concept of achieving large slip condition between the rotating motor and the commanded drive output frequency. Control of current through the motor during the process of stopping is achieved by modifying the V/f pattern. Experimental test results with and without this method on a large inertia motor-load combination show that the proposed stopping method is able to reduce the stopping time significantly compared to normal decelerated stop without the need for a braking unit. Index Terms--Variable frequency drives (VFDs).

The application of variable-frequency drives (VFD's) in industrial and commercial facilities has seen a tremendous increase in the last decade. However, when multiple VFD's are fed from one dedicated power transformer, care should be taken not to drive the transformer into saturation. At one industrial location, nine VFD's rated at 200 hp each, and fed from a single 1500-kVA air-cooled transformer, showed saturation phenomenon, which had the potential of causing serious damage to the transformer. This paper discusses the input ac current waveform asymmetry caused by the interaction of the transformer and the nine 200-hp VFD load fed from it. The term waveform asymmetry is used when the positive half of the input ac current cycle is not equal to the negative half of the input ac current cycle. This results in the existence of dc components along with even harmonics in the input ac current waveform. The various tests and the eventual solution to the waveform asymmetry caused by the VFD's is presented. The value of the inductance in the dc smoothing inductor (dc-link choke), which is included as part of the VFD, was found to contribute significantly to the waveform asymmetry. Experimental results showing the performance of a reconfigured dc-link inductor to reduce its interaction with the power transformer are presented. Index Terms - Harmonic interaction, nonlinear load, variable-frequency drives.

A high-frequency link parallel resonant dc/dc converter (PRC) operating in the lagging power factor mode with the resonating capacitor on the secondary side of the high-frequency (hf) transformer is analyzed for operation in the discontinuous capacitor voltage mode (DCVM) using state-space approach. Converter equations are solved for operation under steady-state condition. Based on the analysis, design curves are obtained for DCVM operation. A method of obtaining the optimum operating point under certain constraints for DCVM operation is developed and is used to present a simple design procedure. Experimental results obtained with a MOSFET based 1 kW PRC is presented to support the theory.

In many applications, it is often needed to extend the speed range of an electric motor. In permanent-magnet ac motors (PMAC), the maximum speed is limited by the available voltage for a given counter electromotive force value. The extension of the speed range can be achieved to some extent by using the field-weakening principle, resulting in constant-power characteristics, but is limited by machine parameters and inverter rating. In an induction-motor-based spindle drive for machine-tool applications, the wye/delta switchover method remains popular for extending the constant-power range without sacrificing the torque capability at higher speeds. Conventionally, the wye/delta method employs mechanical contactors that have limited life and are associated with dead time in the range of tens to hundreds of milliseconds due to mechanical constraints. Power-electronic versions of the contactors have been proposed, but they are rather complicated and involve many switching devices. This paper describes a novel and simple switching technique involving only two three-phase diode bridges and two insulated gate bipolar transistor (IGBT) switches to extend the speed range of ac machines (induction as well as permanent-magnet type). The proposed method requires a center tap to be placed in each phase of the motor with access to the ends and the center tap, making the motor a nine-lead machine. Test results carried out on a nonsalient-type PMAC motor and an induction motor are given to support the idea. [ABSTRACT FROM AUTHOR]