Interaction Between SCR Drives

The main characteristics of reversely switched dynistor (RSD) are infinite series, long lifetime, turning on in microseconds to nanoseconds, high-current rise rate (100 kA/μs), and ability of passing through large current (several kiloamperes). With these advantages, RSD has a great potential of application in repetition rate pulsed power technology and the future HVdc field. To resolve the problem of residual voltage of RSD caused by insufficient precharge, which leads to nonuniform turn-on of RSD, this paper, based on the conduction mechanism of RSD devices, describes precharge circuit design requirements and establishes a second order circuit model to study the resonant triggering circuit of RSD. It is found that reducing precharge inductor can effectively increase precharge current, resulting in reducing the turn-on voltage of RSD. Finally, design for three improved circuit topologies (full-bridge, intense pulsed, and two-step triggering circuit) are presented and experiments show that these improved circuit topologies can enhance the precharge efficiency and reduce the turn-on voltage of RSD.

In this paper, a development of a 6 kW variable DC power supply hardware implementation is presented. The power supply design is based on switched mode power supplies technology. This power supply provides variable output voltages of 10, 20, 30, 40, 50, and 60 V. Effective low cost techniques were employed. The power supply circuit is composed of three main circuits; the input power conversion circuit, the Buck converter power circuit that is controlled by a PWM signal, and the control circuit which includes the logic, isolation and driving circuits. A switching technique is employed based on duty cycle control by which the different outputs are obtained. An insulated gate bipolar transistor (IGBT) is used as a power switch protected by a snubber circuit. A negative feedback is employed to maintain constant output. The snubber circuit is used to dissipate the switching losses and to protect the IGBT switch. A heat sink is used, based on the thermal calculations carried out. The required outputs are obtained by varying the duty cycle and the waveforms at the source are displayed with respect to the switching gate signal. A frequency domain analysis is carried out to show the relative stability of this scheme.

The present paper depicts the application of pulsed gas tungsten arc welding (pulsed GTAW) for aluminium alloy (AA7039) using various Ar + He (Argon + Helium) mixtures as a shielding gas with sinusoidal AC wave. In this investigation, Taguchi method is used to formulate the experimental layout, to analyse the effect of each process parameter on the bead geometry, and to predict the optimum setting for each welding process parameter. The pulsed GTAW process is employed for a high rate of current rise and decay at a high pulse repetitive rate, which is widely used in the joining of precision parts. Zinc is usually added to improve mechanical properties through formation of hard intermediate phase, such as Mg 2 Zn. The main aim of pulsing is to achieve maximum penetration without excessive heat built-up. The use of high current pulses is to penetrate deeply and allow the weld pool to dissipate some of the heat during a proportionately of longer arc period at a lower current. AA7039 is employed in aircraft, automobiles, high-speed trains and high-speed ships due to their low density, high specific strength and excellent corrosion resistance.

DC circuit breakers are the key equipment in maintaining safe and reliable operation of DC system. The presence of stray inductance in each branch of the hybrid DC circuit breaker generates overvoltage due to a high rate of current rise during breaking operation, which brings negative effects to the flexibility and reliability of DC system. The objective of this paper is to investigate the influence of internal stray inductance on overvoltage when the hybrid DC circuit breaker operated. The stray inductance components of main branch, transfer branch and energy consumption branch in hybrid DC breaker were analyzed and the integrated inductance of the three branches were obtained. Based on PSCAD/EMTDC, a 500kV hybrid DC circuit breaker model was established. By changing the size of stray inductance in each branch, the influence rules of stray inductance on overvoltage of circuit breaker during the breaking process were simulated and studied. The results indicate that the increased stray inductance of main branch has no obvious effect on overvoltage of hybrid DC circuit breaker during breaking process. Whereas, for transfer branch, the increased stray inductance results in a decline on overvoltage, which is unfavorable to the establishment of the breaking voltage. And the increased stray inductance of energy consumption branch extends the energy consumption time. This paper provides references for parameter design and insulation coordination of hybrid DC circuit breaker.

With the progress of deep submicron technology, power consumption and temperature related issues have become dominant factors for chip design. Therefore, very large-scale integrated systems like Systems-on-Chip (SoCs) are exposed to an increasing thermal stress. On the one hand, this necessitates effective mechanisms for thermal management. On the other hand, application of thermal management is accompanied by disturbance of system integrity and degradation of system performance. In this paper the authors propose to precompute and proactively manage on-chip temperature of systems based on Networks-on-Chip (NoCs). Thereby, traditional reactive approaches, utilizing the NoC infrastructure to perform thermal management, can be replaced. This results not only in shorter response times for application of management measures and a reduction of temperature and thermal imbalances, but also in less impairment of system integrity and performance. The systematic analysis of simulations conducted for NoC sizes ranging from 2x2 to 4x4 proves that under certain conditions the proactive approach is able to mitigate the negative impact of thermal management on system performance while still improving the on-chip temperature profile.

We study the problem of optimizing the performance of a system shared by selfish, noncooperative users. We consider the concrete setting of scheduling jobs on a set of shared machines with load-dependent latency functions specifying the length of time necessary to complete a job; we measure system performance by the total latency of the system.Assigning jobs according to the selfish interests of individual users (who wish to minimize only the latency that their own jobs experience) typically results in suboptimal system performance. However, in many systems of this type there is a mixture of “selfishly controlled” and “centrally controlled” jobs; as the assignment of centrally controlled jobs will influence the subsequent actions by selfish users, we aspire to contain the degradation in system performance due to selfish behavior by scheduling the centrally controlled jobs in the best possible way.We formulate this goal as an optimization problem via Stackelberg games, games in which one player acts a leader (here, the centralized authority interested in optimizing system performance) and the rest as followers (the selfish users). The problem is then to compute a strategy for the leader (a em Stackelberg strategy) that induces the followers to react in a way that (at least approximately) minimizes the total latency in the system.In this paper, we prove that it is NP-hard to compute the optimal Stackelberg strategy and present simple strategies with provable performance guarantees. More precisely, we give a simple algorithm that computes a strategy inducing a job assignment with total latency no more than a constant times that of the optimal assignment of all of the jobs; in the absence of centrally controlled jobs and a Stackelberg strategy, no result of this type is possible.

We discuss the implementation of a face verification system on smart card and study the trade-off between performance and computational complexity. In order to establish the system limitations, a study was performed on BANCA and XM2VTS databases. The results of the experiments performed show that the choice of a fixed precision data type does not affect system performance very much but can speed up the verification process. Moreover, the use of less than 8 bits per pixel gray-scale image resolution does not necessarily result in a degradation of system performance. We show that, for both databases, image resolution can be reduced without degrading system performance. However, the actual optimal settings will depend on application scenario.KeywordsFace ImageSmart CardFalse Rejection RateBiometric TemplateFace VerificationThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

Previous work on the discrimination of transducers against reverberation has been extended to include the influence of beamwidth and multiple transmisisons. The directivity index against reverberation is expressed in terms of an ideal searchlight beamwidth that is defined as having a response of unity within the region bounded by its beam and a response of zero elsewhere. This ideal beamwidth is found by considering the total received reverberation power from a specific projector-receiver combination. Two situations are treated: namely, a single transmission and several transmissions. For a single transmission, various transmitting and receiving beamwidths are considered in order to determine the degradation in system performance when transmitting beam dimensions differ from those of the receiving beams. The sensitivity of these results to minor-lobe levels is demonstrated. The findings are then generalized by expressing the multiple-transmission case in terms of an equivalent single transmission. The consequences of the theory are compared with observed sea data and are shown to depend upon reverberation decay rate, and hence upon water depth. Finally, the relation between search rate, beamwidth, and system performance is developed.

Physical Carrier Sensing plays a crucial role in the effectiveness of CSMA-based MAC protocols, yet its properties and impact on the system performance under slow fading channel have not been well understood. We demonstrate that carrier sensing can be highly unreliable even within the "carrier sensing range" and the channel is largely stable during a transmission between slowly moving mobile stations. Then we formulate the carrier sensing outage probability between competing mobile stations and propose a model to estimate the frame error rate and normalized throughput of a saturated IEEE 802.11 DCF single-hop ad-hoc network. Our model is validated via extensive simulations using Qualnet. The numerical and simulation results reveal substantial degradation in system performance with a small amount of carrier sensing outage.

Given the trend towards a user-centric concept in mobile communications, body area networks have received increasing attention within the wireless personal area community. Ultra Wideband (UWB) radio channel propagation model with the inclusion of dynamic body environment is derived and applied to investigate the performance of potential radio systems to be used in body are networks. System-level modelling of potential UWB impulse radio is conducted and system performance is measured using bit error rate (BER) and signal-to-noise ratio parameters corresponding to modulation techniques such as pulse position modulation and bi-phase modulation. Impact of movements on system performance is investigated and degradation in system performance due to movements shows the importance of considering the dynamic channel statistics when designing optimal UWB system for body-centric wireless communications.

In a network-on-chip (NoC) based system, the NoC is a shared resource among multiple processor cores. Network requests generated by different applications running on different cores can interfere with each other, leading to a slowdown in performance of each application. The degree of slowdown introduced by this interference varies for each application, as it depends on (1) the sensitivity of the application to NoC performance, and (2) network traffic induced by other applications running concurrently on the system. In modern systems, NoC interference is largely uncontrolled, and therefore some applications unfairly slow down much more than others. This can lead to overall system performance degradation, prevent fair progress of different applications, and cause starvation of unfairly-treated applications. Our goal is to accurately model the slowdown of each application executing on the system due to NoC interference at runtime, and to use this information to improve system performance and reduce unfairness. To this end, we propose the NoC Application Slowdown (NAS) Model, the first online model that accurately estimates how much network delays due to interference contribute to the overall stall time of each application. The key idea of NAS is to determine how the delays induced at each level of network data transmission overlap with each other, and to use the overlap information to calculate the net impact of the delays on application stall time. Our model determines the application slowdowns at runtime with a very low error rate, averaging 4.2% over 90 multiprogrammed workloads for an 8×8 mesh network. We use NAS to develop Fairness-Aware Source Throttling (FAST), a mechanism that employs slowdown predictions to control the network injection rates of applications in a way that minimizes system unfairness. Our results over a variety of multiprogrammed workloads show that FAST improves average system fairness and performance by 9.5% and 5.2%, respectively.

This paper documents an investigation into the performance and thermal efficiency of an air-cycle Environmental Control System (ECS) artificially injected with common operational failure modes. A two-wheel bootstrap system is taken from an in-service military fast-jet and installed in a bespoke Ground Test Facility (GTF) at the ECS Research Facility, Loughborough University, UK. The failure modes investigated are bleed air blockages in the intercooler and in the low-pressure water extractor, as well as positional inaccuracy in cycle bypass control valves. The full range of degradation in each fault is considered, allowing the quantification of overall system performance degradation. The performance of the system is found to be insensitive to moderate bleed air blockages (up to 80% by pipe cross-section area), whilst blockages at low pressure are more detrimental to cycle performance than blockages at high pressure. The cycle and/or control system will self-regulate around most degrading-type faults. This particular system is most sensitive to a failure at one bypass valve, where the hardware allows partial redundancy of the valve but the control system does not.

This article presents the development and execution of a Single-Ended Primary-Inductor Converter (SEPIC) multiplier within a Hardware-in-the-Loop (HIL) emulation environment tailored for photovoltaic (PV) applications. Utilizing the advanced capabilities of the dSPACE 1104 platform, this work establishes a dynamic data exchange mechanism between a variable voltage power supply and the SEPIC multiplier converter, enhancing the efficiency of solar energy harnessing. The proposed emulation model was crafted to simulate real-world solar energy capture, facilitating the evaluation of control strategies under laboratory conditions. By emulating realistic operational scenarios, this approach significantly accelerates the innovation cycle for PV system technologies, enabling faster validation and refinement of emerging solutions. The SEPIC multiplier converter is a new topology based on the traditional SEPIC with the capability of producing a larger output voltage in a scalable manner. This initiative sets a new benchmark for conducting PV system research, offering a blend of precision and flexibility in testing supervisory strategies, thereby streamlining the path toward technological advancements in solar energy utilization.

In this paper, the performance of a mixed Terahertz/free-space optical (THz/FSO) wireless transmission system is studied, where the joint effects of channel fading and pointing errors are considered for both THz and FSO links. Employing the semi-blind amplify-and-forward protocol, we derive the cumulative distribution function and probability density function of the end-to-end signal-to-noise ratio. By applying the derived statistics, exact expressions for the outage probability (OP), average bit error rate (BER), and average channel capacity are obtained. In order to attain useful physical insights, asymptotic OP and average BER expressions are also presented. Based on them, the diversity gain is determined, which is shown to depend on channel fading and pointing errors of both links. In addition, by taking into account the hardware impairments, the OP of the non-ideal hardware system is derived. Moreover, the analysis is extended to multi-antenna scenarios and the asymptotic OP is obtained. Finally, illustrative numerical results are plotted and it can be observed that the path loss, channel fading, pointing errors and hardware impairments lead to a considerable degradation in system performance.

The determination of the solution for simultaneous localization and mapping (SLAM) problems has gained significant research momentum in recent times. Although extended Kalman filters have been extensively employed to solve these problems in mobile robots, the performance of the EKF can degrade significantly, if the correct a priori knowledge of process and sensor/measurement noise covariance matrices (Q and R respectively) is not available. Hence, the present paper proposes the development of a new robust solution method for SLAM problems where we employ a neuro-fuzzy system to supervise the performance of the EKF for SLAM problems and take necessary corrective actions by adapting the sensor statistics online, so that the degradation in system performance can be arrested. The free parameters of the neuro-fuzzy system are learned offline, by employing particle swarm optimization in the training phase. The system hence proposed is successfully evaluated by employing it to localize a mobile robot and simultaneously acquire the map of the environment, under benchmark environment situations with varying landmarks and with wrong knowledge of sensor statistics.