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A novel scheme is proposed to monitor the operation of capacitors scattered in MV distribution systems. It first codes each capacitor with a distinctive switching character by setting a unique combination of a three-phase switching order and time interval. As a result, the transient of the three-phase reactive power during capacitor switching will appear in a unique way. Then, the reactive power disturbances monitored in the substation are decoded to identify which capacitor is being switchedonandoff. A detailed decoding method is developed to realize this identification without being impacted by the switching interference of loads and other reactive power compensation devices. Moreover, the implementation of the proposed scheme in the field is elaborated, and the resultant three-phase voltage unbalance is analyzed in this paper. Compared with existing methods, this scheme only requires one power quality monitor located at the substation to monitor the operations (energizing or de-energizing) of downstream distribution capacitors without extra communication devices. The operation information is valuable for tackling power quality problems caused by capacitor switching and optimizing the distribution grid operation. [ABSTRACT FROM AUTHOR]

This paper presents a hybrid modulation technique for the three-level neutral-point-clamped converter. A modulation strategy, based on two modulation signals per phase, was presented previously. This strategy completely removes the low-frequency voltage oscillations that appear at the neutral point (NP) in some operation conditions. However, it also has a major drawback: it significantly increases the switching losses of the converter. The proposal in this paper combines such a modulation strategy with sinusoidal pulsewidth modulation (SPWM). The main characteristic of this hybrid modulation is the reduction in switching losses at the cost of some low-frequency voltage oscillations at the NP. The amplitude of these oscillations can be controlled by varying the combination of the two strategies. The performance of the hybrid modulation is analyzed and compared with the original strategies. Power losses and oscillation amplitudes on the dc-link capacitors are evaluated. Experimental results show how the hybrid modulation performs by balancing the dc-link capacitors. [ABSTRACT FROM AUTHOR]

This paper presents the derivation of the three dimensional scaling law for liquid insulators. The case of the parallel plate capacitor geometry was investigated, and it was assumed that the "breakdown voltage" random variable follows Weibull distribution. The deduced scaling law was experimentally verified for fresh and used mineral transformer oil. Good agreement of the obtained results with theoretical expectations confirms validity and applicability of the three dimensional scaling law in the investigated case. Results obtained in this paper indicate that application of the scaling law is more convenient in the case of oil insulators compared to other insulator types, due to mutual independence of discharge processes. [ABSTRACT FROM AUTHOR]

This paper proposes a simple capacitor clamped current-sharing circuit including linear and loop types according to the connection of capacitors for multistring light-emitting diodes (LEDs). The proposed circuit employs interleaved turn-on switches and multicapacitor charge conservation to solve the current imbalance problem caused by voltage drop tolerance and the negative temperature coefficient of LEDs. The operating principle and parameter design of the topologies are analyzed in detail. Based on this analysis, a three-string current-sharing topology has been validated by experiments. Experimental waveforms show that the proposed circuit does not only have good effect on current sharing while the effect is not affected by individual LED short but also has the advantages of low voltage stress, nonmagnetic components, ease of integration, and simple control. [ABSTRACT FROM PUBLISHER]

This paper presents a control scheme of cascaded H-bridge STATCOM in three-phase power systems. Cascaded H-bridge STATCOM has merits in point of switching losses, output harmonics, and the number of circuit components. But every H-bridge cell has isolated dc capacitors. So the balancing problem of capacitor voltages exists. Since STATCOM is often requested to operate under asymmetrical condition by power system faults, capacitor voltage balancing between phase clusters is particularly important. Solving this problem, a technique using zero-sequence voltage and negative-sequence current is proposed. By this scheme, the STATCOM is allowed to operate under asymmetrical conditions by power system faults. The validity is examined by digital simulation under one line and two-lines fault circuit condition. [ABSTRACT FROM AUTHOR]

The detection and characterization of macroscopic cracks inside dielectric materials is an important practical issue. Thus, there is a need to establish evaluation techniques; which can be used to characterize buried cracks; indeed, the knowledge of the geometrical configuration of a hidden crack is a key factor for fatigue crack engineering. Therefore, a microwave method for nondestructive characterization of macroscopic cracks inside dielectric materials is presented in this paper. This nondestructive and noncontact technique is based on the determination of the near-field reflection coefficient of an open-ended rectangular waveguide. The measurements are achieved by means of a microwave six-port-based system that operates at 35 GHz. We show that relatively small defects are detectable and demonstrate that the association of signal processing tools to this characterization method enables the retrieval of the crack profile in an acceptable manner. The reconstruction of a 1-D buried crack profile is performed by means of a multiple-multilayer-perceptron (MLP) approach. Several cases are investigated to demonstrate the capabilities of the method. [ABSTRACT FROM AUTHOR]

This paper develops a signal processing, time-frequency analysis-based analytic solution to locate transient capacitor switching disturbances. The flow of transient disturbance energy caused by the capacitor switching is determined by the time and frequency localized phase difference. Cross time-frequency analysis provides time- and frequency-localized phase difference between the transient voltage and current disturbance waveforms which determine the direction of transient disturbance energy flow. The time and frequency localization properties of the proposed scheme allows one to expand the application to complicated power distribution systems without knowledge of system parameters, capacitor size, and configuration. The proposed scheme has been verified by the Electromagnetic Transients Program simulation for all possible spatial locations of the capacitor switching. [ABSTRACT FROM AUTHOR]

Distributed generation (DG) may bring about reliability degradation, instead of reliability enhancement, due to recloser-fuse miscoordination. For the prevention of this reliability degradation, this paper proposes a method to find the threshold value of the DG capacity, beyond which recloser-fuse coordination is lost. Mathematical equations for protective devices are used to set up the protection settings and calculate the threshold value. Three reliability indices—SAIFI, SAIDI, and ENS—are evaluated and compared with the study cases in the reliability test system RBTS bus 2. The results show that the proposed method is effective to prevent the deterioration of system reliability. In addition, a simple modification to the protection system is presented as a preliminary solution. [ABSTRACT FROM AUTHOR]

Capacitor switching transient is one of the most commonly encountered power quality disturbances. Measuring and identifying these transients remains a challenge as the characteristics depend on the system parameters, capacitor ratings and makeup of the connected loads. This paper describes a systematic approach to design an automated system for identifying such transients. It relies on the belief that some of the system and component parameters are either known or can be determined, and thus can be used to develop the necessary pattern for identification and discrimination. However, identification also needs to be robust against uncertainties in these parameters. The proposed method combines the techniques of wavelet transform, rank correlation and fuzzy logic to account for the uncertainties. Dynamic simulations were undertaken to verify the method and to illustrate its robustness when dealing with various uncertain transient characteristics. It is shown to be capable of identifying transients caused by switching of both isolated and back-to-back capacitors. [ABSTRACT FROM AUTHOR]

In this paper, the direct modulation strategy of a three-level inverter with self stabilization of the dc link voltage is extended to a five-level inverter. Therefore, a new modeling and control strategy of a five-level three-phase diode-clamped inverter (DCI) is presented. The obtained modeling shows that modulated multilevel voltages are obtained by combination of eight different three-level functions, which are called modulation functions. Therefore, a space-vector scheme without using a Park transform is explained. Based on this algorithm, the location of the reference voltage vector can be easily determined. Then, the voltage vectors are selected to generate corresponding levels and simultaneously their durations are calculated. More over, the redundancies of different switch configurations for the generation of intermediate voltages are used to limit the deviation of capacitor voltages. Experimental results are given to illustrate the proposed control strategy of the three-phase three-level diode clamped inverter. Then, obtained results for a five-level three-phase DCI with the extended version of the control strategy are presented to show the good performances of the proposed balancing modulation. [ABSTRACT FROM AUTHOR]

In the design of a parallel resonant induction-heating system, choosing a proper capacitance for the resonant circuit is quite important since both output-power maximization and capacitor heat loading should be considered. The temperature rise often blows up the water-cooled capacitors in high-power induction heaters or reduces the lifetime of capacitors significantly. This paper, therefore, presents a method of finding an optimal capacitance that maximizes the output power while considering the capacitor loss at the same time. To count the effect of the capacitor heatup, an equivalent series resistance is included in the model. Based on the equivalent circuit model, the output power and the capacitor loss are obtained as the functions of capacitance, and an optimization technique is applied treating the capacitance as a control variable. The effectiveness of the proposed method is verified by simulations and experiments. [ABSTRACT FROM AUTHOR]

This paper discusses the optimization of series resistance of nonplanar metal-insulator-metal capacitor, i.e., an original 3-D capacitor with a capacitance density of 35 nF/mm², used in very large scale integration. A fully analytical and physically based model of its series resistance versus material and geometrical parameters has been developed, in excellent agreement with both 3-D numerical simulations and experiments. Based on the modeling results, possible design strategies of series-resistance reduction are suggested; showing a reduction of the series resistance by approximately a factor of four, without any degradation of the capacitance density. [ABSTRACT FROM AUTHOR]

This paper presents the small-signal modeling, dynamic analysis, and control design of the asymmetrical half-bridge dc-dc converter that employs a clamp capacitor and a magnetizing inductor to accommodate pulsewidth-modulated operation with asymmetrical duty ratios. The circuit averaging technique is applied to extract the small-signal dynamics of the power stage, and a graphical loop-gain method is used to design the feedback compensation and analyze the closed-loop performance of the converter. The distinctive power-stage dynamics of the converter are addressed and design guidelines for voltage feedback compensation are established. The results of the control design and closed-loop analysis are substantiated by experiments using an experimental converter. [ABSTRACT FROM AUTHOR]

The wire-bonded interdigital capacitor (WBIDC) is an interdigital capacitor with short circuits across the end of alternate fingers that result in an improved frequency response. This paper presents the analytical and circuital models of the WBIDC, which are useful to design and to incorporate into an electromagnetic or circuit analysis computer-aided design program. Design equations of the WBIDC are also presented. The analytical model and design equations have been validated with numerical analysis and experimental work. [ABSTRACT FROM AUTHOR]

A new method for designing the multilayered filter, diplexer, and triplexer is proposed in this paper. The main structure of the multilayered filter is a parallel-coupled line connected with a capacitor. By properly controlling the coupling coefficient between the parallel-coupled line and the capacitor, the transmission zero will appear at the lower or higher passband's skirt. Moreover, such characteristics can be employed to design the diplexer as well for dual- or quad-band portable telephones. In order to miniaturize the size of the circuit and to improve its performance, multilayered structure and the low-temperature co-fired ceramic technology are employed to design and fabricate the filter. Theoretical analysis and design procedures are also provided. Measurement results of fabricated examples are shown to match well with the electromagnetic simulation, which validate the proposed structure. [ABSTRACT FROM AUTHOR]

A significant problem with neutral-point-clamped three-level inverters is the fluctuation in the neutral-point voltage. In this paper, a capacitor voltage balancing technique for carrier-based three-level pulsewidth modulation (PWM) is developed, with improved voltage control capability at high modulation index. The method incorporates a novel scheme that requires measurements of only the motor currents and capacitor voltages to implement voltage balancing control, and does not need to determine the direction of power flow between the inverter and the motor. [ABSTRACT FROM AUTHOR]

Aluminum electrolytic capacitors are the leading choice for ac variable-frequency drive (VFD) bus filters. Predicting the expected life of these components in this application is complicated by four factors. First, the electrical impedance of aluminum electrolytic capacitors is nonlinear with both frequency and temperature. Second, motor drives produce a spectrally rich ripple current waveform that makes energy loss difficult to compute. Third, the heat transfer characteristic of capacitor banks is dependent on design geometry. Fourth, the expected life of aluminum electrolytic capacitors is extremely sensitive to operating temperature. This paper describes a method for predicting bus capacitor life that addresses these problems by using a multiple component model for capacitor impedance, a motor drive simulation to create ripple current waveforms, a heat transfer model based on bank geometry, and a capacitor life model derived from the device physics of failure. An example is given showing the effect of ac line impedance on the relative expected life. [ABSTRACT FROM AUTHOR]

Supercapacitors, also known as ultracapacitors or electric double-layer capacitors (ELDCs), are electrical energy storage devices, which offer high power density, extremely high cycling capability, and mechanical robustness. Due to their electrical performance, supercapacitors have a high potential to be used in industrial applications. To improve the performance, reliability, and lifetime of these capacitors, charge-balancing circuits are employed. In this paper, different equalization concepts are analyzed and evaluated. In addition, a simulation approach for the design of supercapacitor systems is proposed. As an example, results from an automotive application are presented. [ABSTRACT FROM AUTHOR]

In this paper, critical parasitic couplings in EMI filters are first identified. Based on the understanding of filter parasitics, methods are proposed to improve EMI filter performance by canceling critical couplings. A cancellation inductor is then integrated with capacitors to cancel the mutual coupling between two capacitors and the equivalent series inductance (ESL) of the integrated capacitor. The proposed method is applied to both rectangular and tubular capacitors. Two different integration approaches are also compared. Finally, prototypes are built and tested for both one-stage and two-stage EMI filters. Experimental results show the proposed mutual coupling cancellation technique can drastically improve EMI filter high frequency performance. [ABSTRACT FROM AUTHOR]

This paper describes frequency dependence measurements of fused-silica capacitance standards from 200 to 2000 Hz, using a 1-pF cross-capacitor as the reference. The measured frequency dependence of fused-silica capacitors was found to vary significantly, ranging from a change of less than 0.2 μF/F for one standard to a change of 0.8 μF/F for another over the frequency range. Increasing capacitances with decreasing frequency from 1592 Hz for all tested fused-silica capacitors indicates that dielectric relaxation due to dielectric bulk and/or interfacial defects is the dominant source of frequency dependence. The relative combined standard uncertainty at 200 Hz (the largest in the frequency range) is 0.07 μF/F, which is smaller by about a factor of three than the uncertainty reported previously from the National Institute of Standards and Technology (NIST). [ABSTRACT FROM AUTHOR]