Stray Inductance Research Articles

High Step-Up Converter With Coupled-Inductor

In this study, a high step-up converter with a coupled-inductor is investigated. In the proposed strategy, a coupled inductor with a lower-voltage-rated switch is used for raising the voltage gain (whether the switch is turned on or turned off). Moreover, a passive regenerative snubber is utilized for absorbing the energy of stray inductance so that the switch duty cycle can be operated under a wide range, and the related voltage gain is higher than other coupled-inductor-based converters. In addition, all devices in this scheme also have voltage-clamped properties and their voltage stresses are relatively smaller than the output voltage. Thus, it can select low-voltage low-conduction-loss devices, and there are no reverse-recovery currents within the diodes in this circuit. Furthermore, the closed-loop control methodology is utilized in the proposed scheme to overcome the voltage drift problem of the power source under the load variations. As a result, the proposed converter topology can promote the voltage gain of a conventional boost converter with a single inductor, and deal with the problem of the leakage inductor and demagnetization of transformer for a coupled-inductor-based converter. Some experimental results via examples of a proton exchange membrane fuel cell (PEMFC) power source and a traditional battery are given to demonstrate the effectiveness of the proposed power conversion strategy.

A New Technique for the Measurement of AC Loss in Second-Generation HTS Tapes

The successful application of superconductivity to motors and other power system components depends on several factors. One of these involves characterization and minimization of the ac loss in the superconductor used for fabrication of the component. Previous electrical measurements of ac loss have been complicated by the presence of large, undesirable voltages due to stray inductances in the circuit. Their effect was minimized by the addition of a compensation circuit. We have developed a much simpler circuit that significantly reduces this problem to the extent that no compensation is necessary. We report on measurements of the ac loss of several commercial YBaCuO samples immersed in liquid nitrogen using this circuit. We also propose a definition for characterizing the quality of the tapes.

Measurement of sheet-material electrical properties: extending lumped-element methods to 10 GHz

A procedure for measuring the complex dielectric permittivity /spl epsi//spl circ/ of sheet materials, which uses a lumped-element approach for calculating /spl epsi//spl circ/ is described. Air is used as a standard material to determine the stray capacitance, inductance, and resistance of the sample holder. With a careful determination of these stray parameters, the frequency limit for these measurements can be extended up to 10 GHz. The residual scatter in the data, after the data have been corrected for stray capacitance, resistance, and inductance effects, is typically below 1% for /spl epsi/' and is of the order of 0.001 for tan /spl delta/. The procedure uses a low-cost sample holder and a conventional network analyser.

Evaluation of Large-capacity Self-turn-off Power Devices Application from the Aspects of their Turn-off Characteristics, Applied Circuitry and Structure

The reason why this paper deals with GTO behavior mainly is that the reverse bias safety operating area (SOA) of GTO is narrower than the ones of GCT and IEGT. On the development of large-capacity GTO converter, it is important to evaluate the performance of snubber circuit. This paper is concerned with the spike voltage VDSP during turning-off a GTO, and deals with the design and evaluation of stray inductance for snubber circuit, and shows investigation for transient forward voltage of snubber diode. Especially, the method is described that estimates stray inductance from aspect of snubber circuit structure by electromagnetic field analysis before making prototype. The experimental results of spike voltage VDSP are in approximate agreement with the estimated results. Therefore, investigations on this paper are proper and applicable. The same manner of evaluation is also appropriate to IEGT application, and the development of IEGT converter is easier than in GTO converter because of the gate resistor adjustment for di/dt of main current and a wider SOA.

Circuit analysis of active mode parasitic oscillations in IGBT modules

The susceptibility of multi-chip IGBTs to differential oscillations between chips has been noted experimentally. The authors present a theoretical analysis of such oscillations during the transient active operation at turn off and turn on. They take into account the stored charge within the IGBT, the nonlinear transconductance and capacitances and the basic stray inductance elements found within an IGBT module or capsule. Two small-signal analyses are given. The first of these is based on the characteristic equation and exploits symmetry within the module, if appropriate. The second extends the analysis to asymmetrical designs. It is concluded that the methods are complementary and aid understanding of the operation of such devices. Both will also be of use in the design of future devices, especially in making the choice of the gate resistance.

Integrated Design Approach for Medium Power Inverters Optimized for EMC and Thermal Performance

Today’s stale of the an power electronics system require the design engineers ro employ an integrated approach, utilizing IGDTs. heat sink, capacitors and gate driver circuits at their peak performance. While functionality is of course alw ays important, the problem of manufacturahility, cost and electromagnetic compatibility (EMC) are elements that have to he kept into account.In this paper the authors show how electromagnetic interference caused by power electronic circuits can be reduced by the minimization of the total inductance commutation loop of an inverter leg. At the same time special attention is due to the compactness of the inverter especially as regard to the heat sink and the thermal issues. The goal is a proper design and construction of the inverter so tackling EMI directly at the source where most EMI is generated. In this way application of expensive EMI filters can be avoided. Moreover the analysis of the thermal behavior is shown. In order to reach this goal a proper selection and design of the inverter parts have been made and implemented. Specifically, a prototype of converter has been developed to reach the maximum reduction of the stray inductance commutation loop and the maximum compactness using the actual available technology. Experimental results are given to show the validity of this approach.

Novel line conditioner with voltage up/down capability

In this paper, a novel pulsewidth-modulated line conditioner with fast output voltage control is proposed. The line conditioner is made up of an AC chopper with reversible voltage control and a transformer for series voltage compensation. In the AC chopper, a proper switching operation is achieved without the commutation problem. To absorb energy stored in line stray inductance, a regenerative DC snubber can be utilized which has only one capacitor without discharging resistors or complicated regenerative circuit for snubber energy. Therefore, the proposed AC chopper gives high efficiency and reliability. The output voltage of the line conditioner is controlled using a fast sensing technique of the output voltage. It is also shown via some experimental results that the presented line conditioner gives good dynamic and steady-state performance for high quality of the output voltage.

Reduced layer planar busbar for voltage source inverters

Planar busbars are used widely in modern high power inverters and have been shown to provide a good way for minimizing stray inductance and overshoot voltage. Planar busbars, which consist of multilayer copper sheets and dielectric insulators, offer significant advantages such as low impedance, improved thermal characteristic and reduced system cost compared with other interconnection approaches. A common problem of hard switched inverters is stray inductance, which needs to be minimized to reduce the effect of overvoltages. This paper presents a new physical structure for a voltage source inverter with symmetrical planar busbar structure, which minimizes the variation in stray inductance for different switching states. Three-dimensional (3-D) finite element simulations and experimental tests verify the theory.

Microstructure and electric properties of lead lanthanum titanate thin film under transverse electric fields

Polycrystalline lead lanthanum titanate thin film having perovskite structure was fabricated by metalorganic deposition (MOD) on a ZrO2/SiO2/Si substrate at 600 °C for 1 h in O2 atmosphere. Columnar structured ZrO2 buffer layer was also prepared by a MOD process under the same condition. Electrical measurements were conducted on interdigitated electrodes. The crystalline structure and growth behavior of the films have been studied by x-ray diffraction and scanning electron microscopy. It is observed that dielectric response of the film is effected by the cable length used in the measurement and by the values of the ac voltage. Long cable gives rise to an additional resonance peak at high frequency caused by the stray inductance of the contacts and cables. The capacitance and loss tangent over low frequency range shows significant variations due to the trapped charges and space charges in the film. These variations are very dependent on the values of the ac voltage and the length of cable. Meanwhile, the trapped charges and space charges lead to abnormal P–E loops, in which the measured remanent polarization and coercive field increase with increasing frequency.

Low stray inductance bus bar design and construction for good EMC performance in power electronic circuits

Ten years after the publication of the EC Directive 89/336 on electromagnetic compatibility, the impact of this directive on design and lay-out of modern electrical and electronic equipment can be observed. Many research and development studies have proposed and evaluated detailed improvements in the area of component design, component selection, circuit lay-out, shielding and active and passive filtering. New and innovative solutions to minimize noise, especially common mode conducted electromagnetic interference (EMI), in power electronic circuits continue to be developed. In this paper, the authors investigate to what extent EMI caused by power electronic devices in hard switching inverter topologies can be minimized using ultra-low inductive planar busbars. The concept followed in this study is to tackle EMI directly at the source where most EMI is generated; in other words, to reduce the parasitic magnetic energy stored in the inverter DC link to reduce high voltage spikes during switching. A planar busbar was built, tested and analyzed. Measurements show the validity of the theoretical, but simple, design procedure for planar busbars in power converters.

High frequency model of stacked film capacitors

Polypropylene metallized capacitors are of general use in power electronics because of their reliability, their self-healing capabilities, and their low price. Though the behavior of metallized coiled capacitors has been discussed, no work has been carried out on stacked and flattened metallized capacitors. The purpose of this article is to suggest an analytical model of resonance frequency, stray inductance and impedance of stacked capacitors. We first solve the equation of propagation of the magnetic potential vector ( A ) in the dielectric of an homogeneous material. Then, we suggest an original method of resolution, like the one used for resonant cavities, in order to present an analytical solution of the problem. Finally, we give some experimental results proving that the physical knowledge of the parameters of the capacitor (dimension of the component, and material constants), enables us to calculate an analytical model of resonance frequency, stray inductance and impedance of stacked capacitors.

Nuclear magnetic resonance radiation damping in inhomogeneous radio frequency fields: The toroid cavity detector

A theory is presented for radiation damping (RD) in the toroid cavity nuclear magnetic resonance detector, a cylindrically symmetric inhomogeneous-rf field detector in which the magnitude of B1 is inversely proportional to the distance from the cylindrical symmetry axis. The equations of motion of the magnetization components are obtained and discussed. Numerical simulations of conventional- and composite-pulse experiments are presented, along with a discussion of the effects of RD on the evolution of magnetization. Preliminary simulations of RD in the presence of inhomogeneous line broadening are also presented. The signature effect of radiation damping in the TCD is the winding or unwinding of magnetization gratings that has recently been observed by other researchers. The observed magnitude of the effect is linked to the effective filling factor, which currently appears to be limited by the stray inductance of the detection circuit. The results are of interest in connection with recent findings regarding the interaction of RD with the dipolar demagnetizing field.

Electromagnetic considerations in power electronic converters

Electromagnetic effects have an important influence on all aspects of power electronic design. The effects of stray magnetic and electric fields on circuit performance, and the necessity to control the resulting stray inductance and capacitance by good circuit design practices are introduced. Inductors are key components and the pressure to design to meet high-frequency specifications is relentless. Four types of inductors are discussed briefly and their electromagnetic properties are compared and contrasted. High-frequency transformers are discussed in terms of their impact on circuit behavior and their major design issues. The limitations of conventional topologies at multimegahertz frequencies are explored. A circuit example of a half-bridge series-parallel resonant converter working between 1-2 MHz and implemented using hybrid technologies is used to demonstrate how circuit, component and layout design are electromagnetically interdependent.

Recent results of an experimental study on the impact of smoke on digital I & C equipment

A program to assess the impact of smoke on digital instrumentation and control (I & C) safety systems began in 1994, funded by the US Nuclear Regulatory Commission Office of Research. Digital I & C safety systems are likely replacements for today’s analog systems. The nuclear industry has little experience in qualifying digital electronics for critical systems, part of which is understanding system performance during plant fires. The results of tests evaluating the performance of digital circuits and chip technologies exposed to the various smoke and humidity conditions representative of cable fires are discussed. Tests results show that low to moderate smoke densities can cause intermittent failures of digital systems. Smoke increases leakage currents between biased contacts, leading to shorts. Chips with faster switching times, and thus higher output drive currents, are less sensitive to leakage currents and thus to smoke. Contact corrosion from acidic gases in smoke and stray inductance or capacitance are less important contributors to system upset. Transmission line coupling was increased because the smoke acted as a conductive layer between the lines. Permanent circuit damage was not obvious in the 24 h of circuit monitoring. Test results also show that polyurethane, parylene, and acrylic conformal coatings are more effective in protecting against smoke than epoxy or silicone. Common sense mitigation measures are discussed. Unfortunately we are a long way from standard tests for smoke exposure that capture the variations in smoke exposure possible in an actual fire.

A 2-MHz 6-kVA voltage-source inverter using low-profile MOSFET modules for low-temperature plasma generators

This paper presents a 2 MHz 6 kVA voltage-source inverter for low-temperature plasma generators. A new MOSFET module referred to as a "mega pack" is specially designed and fabricated for high-frequency high-power applications. It has a low-profile package equipped with four terminal plates. The main circuit consists of a single-phase full-bridge inverter using the four new modules. The layout of the modules is characterized by two modules, which are placed back-to-back with each other, forming a half bridge. Both device and circuit designs achieve great reduction of stray inductance in the main circuit. A prototype inverter shows stable operation around frequencies as high as 2 MHz.

PWM buck-boost ac choppers for safe commutation

Novel pulse-width modulated (PWM) buck-boost ac choppers solving the commutation problem are proposed for single-phase and three-phase systems. The power circuits of the single-phase and three-phase buck-boost ac choppers use only two and three standard switch modules, respectively, and regenerative dc snubbers are attached directly to standard switch modules to absorb energy stored in line stray inductance. The switching policy for solving the commutation problem is achieved. Compared with previous buck-boost ac choppers, the switching loss is reduced and RC snubbers causing power loss are eliminated. The equivalent circuits of the proposed ac choppers are obtained and the power factor is derived from the equivalent circuits. The proposed ac chopper has the following advantages; improved power factor, low harmonics, sinusoidal input current, fast dynamics, high efficiency, high reliability, and significant reduction of the filter size. Experimental results show that the proposed scheme gives good steady-state performances of the ac chopper and that they coincide with the theoretical results.

Limitations on HTS single flux quantum logic

There is widespread interest in transferring Single Flux Quantum (SFQ) logic from niobium technology to a suitable HTS technology. The higher operating temperature results in increased noise and associated errors. We have developed numerical methods to study noise induced errors and how they depend on circuit parameters. A simple picture holds for all the circuits studied to date. The error probability shows an error function (integrated Gaussian) distribution. The width of the distribution is circuit dependent, but is 1 to 4 times the noise contribution of a single junction, and the noise free (deterministic) margin corresponds to the point where the error probability is 0.5. The distributions are frequently asymmetric, and minimum error rate does not occur for a design centered between the deterministic margins. A stochastic optimizer has been developed that allows us reoptimize circuits for conditions when noise induced margin narrowing is important. We have used this to study the influence of layout induced stray inductance on the feasibility of HTS circuits using the T flip-flop as an example. Stray inductance appears to be as important as junction reproducibility, and significant improvements are needed to allow high operating temperatures.

Highly improved performance of a noise isolation transformer by a thin-film short-circuit ring

One of the typical phenomena observed during operations of transformers in general is the complex resonance phenomena present in high frequency ranges. Noise isolation (or cutout) transformers, which show the best performance among isolation devices, are not exempt from this difficulty, degrading their performance at high frequencies. The source of these resonance phenomena is a number of local spurious resonance circuits composed of various combinations of numerous minute stray capacitances and leakage inductances present in transformers, becoming apparent at higher frequencies. As a countermeasure against this difficulty, a short-circuit ring (made by an aluminum film) is placed near the coils inside a transformer. The effectiveness of this method is demonstrated experimentally by decreased resonance amplitudes and by 20-dB improvement of the overall attenuation level over an extended frequency range.

Automatic voltage regulator with fast dynamic speed

A novel automatic voltage regulator is proposed and analysed. The power circuit is made up of a pulse-width modulated (PWM) buck-boost AC chopper which uses only two standard switch modules. In the AC chopper, the commutation scheme allows dead-time to avoid current spikes from switching and at the same time establishes a current path in the inductor to avoid voltage spikes. The AC chopper uses regenerative DC snubbers attached directly to power semiconductor modules to absorb energy stored in stray line inductances. These DC snubbers enhance the conversion efficiency and feature a very simple structure consisting only of a capacitor. A fast peak voltage detector for fast output voltage control is also proposed. It is shown, via experimental results, that the proposed scheme gives good dynamic and steady-state performances for a high-quality output voltage.

Minimization of the stray inductance in metallized capacitors: Connections and winding geometry dependence

Stray inductance in power electronics capacitors is due to the magnetic field created by the currents in winding and connections. We review different connection schemes that could be used in metallized capacitors. For each of these connections, the stray inductance expression depends of winding geometries. The proposed method to minimize this inductance can be divided in two parts. The first part consists in optimizing the winding geometry for a particular connection. The second is the choice of a low-inductance connection for the previously determined winding. The best results are obtained with large inner and outer radii and through the use of inner annular conductors.