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This paper presents a practical approach toward efficient shielding of adjustable speed drives (ASD). The electromagnetic interference problem affects a complex roller rig testing facility that is developed at the Railway Technologies Laboratory of Virginia Tech. The rig uses a slew of sensitive instruments to study the wheel-rail contact mechanics in the railway applications. Eight ASDs run the rig in close vicinity of the sensors, which heavily affects their measurements. System requirements such as heat management, structural rigidity, size, and cost, restrict additional shielding for these drives. In this paper, a two-dimensional finite element analysis is used to find the proper shielding material, optimum thickness, and aperture size that maximize the shielding effectiveness. Based on the simulation results, an enclosure is fabricated for the VT Roller Rig control tower. Simulation results show that steel exhibits the least sensitivity to perforation, especially at frequencies above \text10 kHz. Results also reveal \text23.4\% difference between \text0.5 and \text3 mm thicknesses at \text1 kHz , while the difference is \text3.5\% at \text5 MHz. Moreover, experimental results demonstrate agreement between the simulated and actual performances. Measurements confirm that using \text16 GA off-the-shelf carbon steel sheets with \text80\% perforation, an average shielding effectiveness of \text40 dB is achieved. [ABSTRACT FROM PUBLISHER]

There are two cases that can cause cable overvoltage in a high-speed electric multiple units (EMU) system: one is the seriously rusty rail; the other is pantograph arcing, especially when the train passes through the phase separations. Both cases can endanger the normal operation of the EMU. In this paper, a full analysis is given on the mechanism of the electromagnetic interference, corresponding to the conducted and radiated interference. First, the actual circumstances in which the two kinds of interferences generate are described and the equivalent circuit model is established. Then, the two kinds of interference are analyzed and the induced overvoltage is calculated by means of finite-difference time domain method and piecewise-line technique. Next, based on the analysis mentioned above, a specific transient voltage suppressor (TVS) is proposed to be applied at the terminal of a cable in the train. Finally, the results of theoretical calculation, simulation by Computer Simulation Technology, and measurement are obtained and compared, among which a good agreement is achieved. Thus, the validity of the equivalent circuit model and the suppression effect of the TVS on overvoltage excited by conducted and radiated interference are verified. [ABSTRACT FROM AUTHOR]

The carrier frequency harmonics and significant high-frequency energy of electromagnetic interference (EMI) produced is a major concern in pulse width modulation (PWM) circuit. This paper proposes a chaotic PWM generator for the reduction of EMI. The chaotic CMOS circuit presented is based on a stroboscopic map to realize the chaotic sequence generator, and then, this chaotic frequency generator is used to replace the constant-frequency generator. The main components of the chaotic PWM circuit are chaotic sequence generator for the chaotic triangle waveforms, the chaotic frequency modulation circuit based on one chip. The chaotic PWM generator is fabricated by a 0.35 μ m standard CMOS process. The energy peak of EMC experiment values are all within the limit of CISPR 22. The peak EMI reduction of the proposed chaotic PWM is 12.85 dB. The experiments show the effectiveness of the proposed CMOS chaotic PWM in reducing EMI. [ABSTRACT FROM PUBLISHER]

This paper presents the influence of the pulse width on the thermal burnout effect of a low-noise amplifier (LNA) constructed by a silicon–germanium heterojunction bipolar transistor (SiGe HBT) when it is injected by microwave pulses. Based on the characteristics of microwave pulses and the structure of the SiGe HBT, a theoretical model to predict the impact of the pulse width and power on the thermal burnout effect of the LNA is established by solving the heat conduction equation. The derivation of the theoretical model requires the pulse width less than a microsecond level. Using at least two groups of simulated or measured results to fit the coefficients, the proposed theoretical model can predict the other effect of the pulse width, which can greatly reduce the experimental costs and guide the rational selection of the pulse width in numerical simulations. At last, the theoretical model is verified by numerical simulations and experimental measurements. The results show that within the scope of pulse width (less than the microsecond level) the burnout power threshold can be effectively reduced by increasing the pulse width. [ABSTRACT FROM PUBLISHER]

Most photovoltaic (PV) systems are composed of series and parallel inverters. The electromagnetic interference (EMI) mainly comes from the off–on of inverter switches with pulsewidth modulation (PWM). The output EMI peaks of PV systems would increase markedly due to the interference superposition effect caused by parallel inverters, whose carrier initial phases are in phase or close to each other. In this paper, an auto-screening carrier phase-shift scheme is proposed to weaken the superposition effect of EMI peaks and to get the result of reverse offset at its best. In a PV system, through voltage detections and spectrum estimations of each inverter with a series of phase-shift carriers, a best carrier phase of each inverter is obtained automatically to minimize EMI peaks of the PV system. In order to avoid the conflict that the screening processes of two or more inverters are underway at the same time, a specific frequency signal is output temporarily as an occupancy mark in one of the inverters. The feasibility and effectiveness of the proposed scheme are verified by experimental results in a PV system composed of four parallel single-phase inverters. [ABSTRACT FROM AUTHOR]

Although the dc/dc converter as a common power supply is compatible with the electromagnetic compatibility standard, it may still bring the peak interference generated from one nonlinear load to the other loads. In this paper, a novel filter is designed in a low-voltage buck converter to suppress some extra peak harmonics generated from a nonlinear load, i.e., a pulse width modulation switching circuit. This filter is a variable capacitance filter (VCF) whose active devices are working in the linear areas. The capacitance of the filter is controlled to vary with the change of the switching load's carrier-frequency in the scheme. The impedance of the VCF can not only be matched with the switching load, but also avoid the mismatch effect from the parameter drift caused by the aging of the components. Thus, the VCF can suppress the introductive peak harmonics from the switching load at its carrier-frequency, especially the peak harmonics in the carrier-frequency region when the carrier-frequency modulation is used as the control strategy in the switching load. The feasibility and validity of the VCF are proved by simulations and experiments in a low-voltage buck converter, in which a boost circuit is working as one of its loads. [ABSTRACT FROM AUTHOR]

The aim of this paper is to describe a first- approximation model that predicts the emissions radiated by an induction-machine motor drive. The proposed model can be used in the design stage of an asynchronous motor drive. A three-phase induction machine supplied by a voltage-source inverter is studied; both square-wave and pulsewidth modulations of the power converter are considered. Computer simulations are presented to prove the validity of the proposed model. The applications considered lead to numerical results that are in qualitative agreement with those calculated and/or measured by other authors. [ABSTRACT FROM AUTHOR]

Control schemes applying sinusoidal pulsewidth (sPWM) have been widely employed in power conversion solutions. With the development of the future smart grid, more capabilities of the converters are required introducing additional electromagnetic interference (EMI) control measures. In this article, a MATLAB controllable sPWM generator has been developed to optimize electromagnetic compatibility. The field-programmable gate array running at 100 MHz is capable of producing simultaneous and synchronous control signals for 16 power electronic switches. Six flexible control parameters have been implemented, which allow the controller to be tuned to a large number of applications and investigate several EMI mitigation techniques and investigate the disturbance dependence on operational parameters. As an example, the detrimental dead time effect is shown, with a variation in emissions of 10–20 dB in the frequency range of 50 kHz to 50 MHz. Highest experimentally tested switching frequencies have been recorded at 2 MHz with resulting sinusoidal waveforms from 50 Hz to 250 kHz. [ABSTRACT FROM AUTHOR]

This letter investigates the use of multiple coils for the powering of and the data communication to brain implants. It studies the limits imposed by these coils in terms of biosafety and interference in the communication channels caused by neighboring and misaligned coils. Simulations using the CST Studio voxel head model are used to assess the associated health risks as well as the resilience of the proposed data communication scheme. [ABSTRACT FROM PUBLISHER]