Reliability analysis of industrial power systems with sensitive loads

A method for the reliability analysis of power system has been developed that includes the behaviour of the system during a disturbance. The power system is modelled as an electrical network in which branches are removed and inserted by stochastic events, generated by a Monte Carlo simulation. This method considers short circuits followed by an interruption of the protection, in stead of just the removal of a component. By using a maximum-permissable voltage sag as an interruption criterion the method can be used for industrial power systems with sensitive loads. The (correct and incorrect) behaviour of the protection, ageing of components, and the influence of preventive maintenance are also included in the method.An example of the use of the method is given: a power system feeding four industrial plants. The influence of plant voltage solidity and of preventive maintenance in the feeding network are investigated. Both turn out to have considerable influence.     

Reliability of checkpointed real-time systems using time redundancy

Real-time computers are often used in embedded, life-critical applications where high reliability is important. A common approach to making such systems dependable is to vote on redundant processors executing multiple copies of the same task is described. The processors which make up such voted systems are subjected not only to independently occurring permanent and transient failure, but also to correlated transients brought about by electromagnetic interference from the operating environment. To counteract these transients, checkpointing and time redundancy are required, in addition to processor redundancy. This work analyzes the use of time and device redundancy in systems subject to correlated failure. The tradeoffs in checkpoint placement in such a system are found to be considerably different from those for non-redundant systems without real-time constraints. The authors compare fault-tolerant designs and without a rollback capability, accounting for the increased hardware-failure rate due to processor duplication when faults are detected in hardware, and the doubled execution times when detection is implemented in software     

Modeling of power distribution systems for high-performancemicroprocessors

This paper presents approximate techniques for building models and simulating the response of power distribution systems for high-performance microprocessors. Several distributed equivalent SPICE circuit models were built by extracting the appropriate resistance, inductance, capacitance (RLC) component values using a combination of two-dimensional (2-D) and three-dimensional (3-D) quasi-static field solvers. They were used to assess how well such effects as system transfer impedance and transient characteristics can be predicted. The models include the chip, its controlled collapsed chip connection (C4) connections to the package, the power distribution structure in the package, connector and motherboard. It is found that the response of the entire power system can be treated as a second order system, by which the main features of the performance of the power delivery network are assessed. Samples of transient and frequency domain data for typical microprocessors are given and the effects of some design options are discussed, as are the tradeoffs in model complexity versus the gain of useful design information     

Decoupling capacitors for multi-voltage power distribution systems

Multiple power supply voltages are often used in modern high-performance ICs, such as microprocessors, to decrease power consumption without affecting circuit speed. To maintain the impedance of a power distribution system below a specified level, multiple decoupling capacitors are placed at different levels of the power grid hierarchy. The system of decoupling capacitors used in power distribution systems with multiple power supplies is described in this paper. The noise at one power supply can propagate to the other power supply, causing power and signal integrity problems in the overall system. With the introduction of a second power supply, therefore, the interaction between the two power distribution networks should be considered. The dependence of the impedance and magnitude of the voltage transfer function on the parameters of the power distribution system is investigated. An antiresonance phenomenon is intuitively explained in this paper. It is shown that the magnitude of the voltage transfer function is strongly dependent on the parasitic inductance of the decoupling capacitors, decreasing with smaller inductance. Design techniques to cancel and shift antiresonant spikes out of range of the operating frequencies are presented. It is also shown that it is highly desirable to maintain the effective series inductance of the decoupling capacitors as low as possible to decrease the overshoots of the response of the dual-voltage power distribution system over a wide range of operating frequencies. A criterion for an overshoot-free voltage response is presented in this paper. It is noted that the frequency range of the overshoot-free voltage response can be traded off with the magnitude of the response.     

Reliability analysis and redundancy optimisation of a multimodular fault tolerant system

This paper presents the reliability analysis of a multimodular fault-tolerant system having N-modules in parallel. The reliability and MTSF of the system have been calculated and the expression for optimum number of modules has also been obtained with cost constraint in view.     

Reliability analysis of capacity and voltage constrained, optimallyoperated, electric power systems

A method for reliability evaluation of capacity and voltage constrained bulk power systems is suggested based upon contingency analysis. For each contingency and consumer load demand situation assumed, the optimal operation of the power system is established that minimizes the total system consumer curtailment cost. Consumer demands at different nodes may be treated as synchronous or as mutually uncorrelated quantities, depending on the data available. The method uses a version of the decoupled power flow network model that makes its possible to determine optimal generation of both real and reactive powers for the system sequentially. This property makes the method superior to other available approaches for bulk power system reliability analysis. An illustrative example is included     

Modeling and harmonic suppression for power distribution systems

Expansion of voltage distortions along power distribution systems, which is referred to as the harmonic propagation, is pointed out. This is caused by the LC resonances between the distribution line inductances and the power capacitors. This paper presents a modeling and harmonic suppression procedure for power distribution systems. In our proposal, the power distribution system is analyzed based on the modal analysis and it is represented by a reduced-order model. For the harmonic suppression, a series active filter is used and its controller is designed based on the reduced-order model so as to cancel the dominant LC resonances in the power distribution system. Some significant characteristics are verified by experiments using a single-phase power distribution system.     

Modeling, analysis and design of resonant free power distribution network for modern microprocessor systems

This paper presents design-oriented analysis of the power distribution network (PDN) for high performance microprocessor systems to realize the resonant free, close to flat output impedance magnitude over a wide frequency range. Based on the frequency domain analysis, closed form design equations and parametric curves relating the system parameters are derived. A systematic method of estimating the optimum parameters of the decoupling capacitors used in a single or multistage PDN is described to realize the output impedance of specified magnitude for the noise-free, and critically damped voltage at the microprocessor core. The design examples and simulation results are discussed to demonstrate the application of the design equations and parametric curves.     

Reliability of industrial packaging for microsystems

Packaging concepts for silicon-based micromachined sensors exposed to harsh environments are explored. By exposing the sensors directly to the media and applying protection at the wafer level the packaging and assembly will be simplified as compared to conventional methods of fabrication.Protective coatings of amorphous silicon carbide and tantalum oxide are suitable candidates with etch rates below 0.1 Å/h in aqueous solutions with pH 11 at temperatures up to 140°C. Si-Ta-N films exhibit etch rates around 1 Å/h. Parylene C coatings did not etch but peeled off after extended exposure times at elevated temperatures. The best diamond-like carbon films we tested did not etch, but delaminated due to local penetration of the etchants.Several glue types were investigated for chip mounting of the sensors. Hard epoxies, such as Epotek H77, on the one hand exhibit high bond strength and least degradation and leakage, but on the other hand introduce large sensor output drift with temperature changes. Softening of the Epo-tek H77 was observed at 70°C.An industrially attractive thin-film anodic silicon-to-silicon wafer bonding process was developed. Glass layers are deposited at 20 nm/s (1.2 μm/min) by electron-beam evaporation and bond strengths in excess of 25 N/mm² are obtained for bonding temperatures higher than 300°C.Through-hole electrical feedthroughs with a minimum line width of 20μm and a density of 250 wires per cm were obtained by applying electro-depositable photo-resist. Hermetically sealed feedthroughs were obtained using glass frits, which withstand pressures of 4000 bar.     

Cryptographic systems using redundancy

The problem of ensuring recoverability of encrypting data in a file storage system is examined. In this situation, the original data (plaintext) are removed from the system after encryption. In the event of errors either in the initial processing or in the storage of the data, the file may be rendered unrecoverable. A model of a file storage system that incorporates errors in these areas is developed. A two-stage coding system involving error-correcting codes and interleaving is introduced. The performance of this system is analyzed for various sizes of encryption blocks and error-correcting codes     

Optimum traffic distribution algorithm for multiple-satellite systems under power constraints

In satellite communications systems, in addition to frequency resources, total satellite transmitting power, (i.e., satellite power) is a crucial radio resource, due to the limited capacity of onboard electric generators. To increase system capacity, satellite power constraints have to be taken into account, as well as the frequency constraints. As one approach to this issue, we propose a traffic distribution algorithm using linear programming, which maximizes the accommodated traffic in a multiple-satellite system under satellite power constraints. The algorithms are applicable to all types of satellite systems with multiple satellites (geosynchronous Earth orbit, medium Earth orbit, low Earth orbit, or a combination of any) to increase system capacity with respect to the total amount of traffic accommodated by the systems. Finally, this paper evaluates the performance of the proposed algorithm by distributing traffic demand on the earth's surface to cells irradiated by spot-beams of a satellite and allocating frequency resources to the cells. By using the algorithm that permits power constraints, the ratio of accommodated traffic in a system was improved 12% compared with the case when no power constraints were used.     

Efficient built-in redundancy analysis for embedded memories with 2-D redundancy

A novel redundant mechanism is proposed for embedded memories in this paper. Redundant rows and columns are added into the memory array as in the conventional approaches. However, the redundant rows and columns are divided into row blocks and column blocks, respectively. The reconfiguration is performed at the row (column) block level instead of the conventional row (column) level. Based on the proposed redundant mechanism, we first show that the complexity of the redundancy allocation problem is NP-complete. Thereafter, an extended local repair-most (ELRM) algorithm suitable for built-in implementation is proposed. The complexity of the ELRM algorithm is O(N), where N denotes the number of memory cells. According to the simulation results, the hardware overhead for implementing this algorithm is below 0.17% for a 1024/spl times/2048-b SRAM. Due to the efficient usage of the redundant elements, the manufacturing yield, repair rate, and reliability can be improved significantly.     

Determining optimal redundancy for systems with random lifetimes

The problem of allocating spares to remote machines is examined. No reallocation of the spares between machines is possible, and the life distribution of each spare depends upon the machine on which it is used. The machines are subsystems of a system whose useful life terminates in a finite, but random, amount of time (e.g., from a catastrophe or obsolescence), or when a machine depletes its store of spares. An efficient algorithm determines the allocation of spares that maximizes the minimum probability of a machine depleting its spares before the system's useful life terminates. These results are extended to the case when the spares are divisible. An example illustrates the results     

Finding cyclic redundancy check polynomials for multilevel systems

This letter describes a technique for finding cyclic redundancy check polynomials for systems for transmission over symmetric channels which encode information in multiple voltage levels, so that the resulting redundancy check gives good error protection and is efficient to implement. The codes which we construct have a Hamming distance of 3 or 4. We discuss a way to reduce burst error in parallel transmissions and some tricks for efficient implementation of the shift register for these polynomials. We illustrate our techniques by discussing a particular example where the number of levels is 9, but they are applicable in general     

Reliability and availability analysis of transit systems

This paper presents three newly developed Markov models representing on-surface transit systems. Transit system reliability, steady-state availability, mean time to failure (MTTF) and variance of time to failure formulas are developed. Selective plots are shown for each model. These plots clearly exhibit the impact of various parameters on transit system reliability, steady-state availability, and MTTF.     

Floating redundancy in digital systems

The traditional styles of redundancy such as triple modular redundancy (TMR) use exact functional duplicates to provide increased reliability [NE63]. This need not be the case; a system may be designed using floating redundancy. Floating redundancy improves reliability by using a floating spare that may perform as several module types. The adjective “floating” is used to describe this ability to function as two or more types.This paper outlines some of the results of a study of floating redundancy.     

Reliability analysis of systems with operation-time management

This paper considers the reliability analysis of systems whose operation time is managed with regard to criticality of faults. Several analysis approaches are proposed for the numerical probability analysis of one such operational scenario: FOTM (flight operation time management). The equations derived for the Markov chain based method are novel and their implementation in the tool SPNP (Stochastic Petri Net Program) could help in assessing the risk reduction due to FOTM. The analysis methods are quite general and can be applied to other similar situations where system-failure risk is decreased by operation-time management     

Enhancing peer-to-peer systems through redundancy

Peer-to-peer systems can share the computing resources and services by directly communicating within a widely distributed network. It is important that these systems can efficiently locate, in as few hops as possible, the node storing the desired data in a large system. Thus, it is worth consuming some extra storage to obtain better routing performance. In this paper, we propose redundant strategies to improve the routing performance and data availability on Chord and De Bruijn topologies. Hybrid-Chord combines multiple chord rings and successors, and Redundant D2B maintains successors, to improve the routing performance. The proposed systems can reduce the number of lookup hops significantly (by as much as 50%) compared to the original ones, and have better fault tolerance capabilities, with a small storage overhead     

Reliability modelling and analysis of multiprocessor systems

This paper presents symbolic analytical models to evaluate various reliability measures of a multiprocessor system (MPS). The most commonly used interconnection networks for MPSs, viz. multibus, crossbar and multiport memories, are considered. Simple expressions for system reliability, threshold reliability and multiprocessing reliability are obtained by modelling the MPS as a t-out-of-s system. The methods used are efficient and easy to implement on a computer. Direct numerical computations are also easy. These expressions are also applicable to systems with components of non-identical statistical properties. System availability can be also evaluated by the reliability study.     

Pervasive grid for large-scale power systems contingency analysis

Optimal control and management of power systems require extensive analyses of phenomena that can compromise their operation in order to evaluate their impact on the security and reliability levels of the electrical networks. For complex networks, this process, known as power systems contingencies analysis, requires large computational efforts, whereas computation times should be less than a few minutes for the information to be useful. Even though many architectures based on conventional parallel and distributed systems have been widely proposed in the literature, they are characterized by low extensibility, reusability, and scalability, and so, they require a sensible hardware upgrade when more computational resources are necessary. This event is not infrequent in power systems where the constant growth of the electrical network complexity and the need for larger security and reliability levels of the plant infrastructures lead to the need of more detailed contingency analysis in shorter times. To address this problem, this paper proposes a pervasive grid approach to define a user-friendly software infrastructure for data acquisition from electrical networks and for data processing in order to simulate possible contingencies in a real electrical network. The grid infrastructure adopts a brokering service, based on an economy-driven model, to satisfy the quality of service constraints specified by the user (i.e., a time deadline to simulate the contingencies). This paper also discusses the deployment of the infrastructure on a network of heterogeneous clusters and PCs to compute the contingency analysis of a realistic electrical network. The experimental results obtained demonstrate the effectiveness of the proposed solution and the potential role of grid computing in supporting intensive computations in power systems.