The present paper aims to propose a real-time energy management strategy (EMS) based on two-phase interleaved buck-boost and boost converters for Fuel Cell/supercapacitor hybrid system. The interleaved converter (IC) is chosen to be applied in this work thanks to advantages, which presents compared to conventional DC/DC converter, as low input current ripples, a higher efficiency, a faster transient response, a reduced electromagnetic emission and an improved reliability. The proposed converters control strategies continuously support the EMS, based on frequency distribution to coordinate the hybrid power supply system, under variable load power conditions. In order to implement the proposed controllers, a laboratory test bench is applied to conduct experimental validation of the adopted structure. Experiments FC/SC hybrid system with the developed EMS was performed for variable load and the experiment waveforms of each power source are included. The obtained results suggest that the proposed energy management algorithm and the converters controllers present good performances.

In more electrical aircraft, the embedded electrical network is handling more and more vital functions, being more and more strained as well. Attenuation of switching harmonics is a key step in the network reliability, thus filtering elements play a central role. To keep the weight of the embedded network reasonable, weakly damped high-order filters shall be preferred. Flatness-based control (FBC) can offer both high bandwidth regulation and large signal stability proof. This make FBC a good candidate to handle the inherent oscillating behavior of aforementioned filters. However, this control strategy can be tricky to implement, especially with high order systems. Moreover, FBC is more sensor demanding than classic PI-based control. This paper address these two drawbacks. First, a novel trajectory planning for high order systems is proposed. This method does not require multiple derivations. Then the input sensors are removed thanks to a parameters estimator. Feasibility and performances are verified with experimental results. Performances comparison with cascaded-loop topologies are given in final section to prove the relevance of the proposed control strategy.

It is well known that the Conventional Droop method is commonly used to share real and reactive power between distributed Generation interfaced converters (DICs) based Islanded microgrid. The share of power is done autonomously without communication between Converters. Despite the lot of desirable features the Droop method had, there exist some limitations concerning the accuracy of the reactive power shared between converters when line impedance mismatches exist. This paper presents the droop control law for islanded microgrid, and proposes an online state estimation of the point of common coupling (PCC) voltage, which is then used as a feedback signal for the Droop control to accurately share the power between parallel converters. Thus the proposed method keeps the advantages of the Droop control method to manage the power between distributed generations in autonomous fashion without additional communication links.

Power electronic converters and electric motor drives have become common loads in advanced power systems. Passive LC filters are often used in these systems to reduce the DC-link ripples. These filters are poorly damped for reducing the power losses as well as the size, weight and cost of the system. This may lead to instability phenomena if the load is tightly controlled and absorbs a power exceeding a limit depending on the filter parameters. The purpose of this paper is to present an input impedance shaping method to stabilize DC-link. A matrix filter is put in cascade with load's current controllers. The filter is designed to shape properly input impedance of the load while keeping its performances. Small signal stability of the DC power system is proved using this method. Simulation and experimental results confirm the effectiveness of the proposed stabilizer.

Based on the properties of flatness system, this paper proposes a nonlinear control for a dual active bridge converter for fuel cell applications. This converter is connected to fuel cell via a diode and an LC low-pass filter. The constraint of fuel cell like the maximum power and current slope are taken into account by means of the control of the energy stored in the filter capacitor corresponding to the fuel cell voltage obtained from its static characteristic. The diode and parasitic resistances are modeled as a series resistance connected to the fuel cell and its value is estimated and is used in the control algorithm. The effectiveness of the proposed system is demonstrated via experimental results.

This paper proposes a nonlinear control for a dual active bridge converter (DAB) using properties of flatness system. This converter system is used for a DC microgrid. Losses in the system are modeled as a resistance connected in parallel with the output capacitor. The control algorithm also takes this resistance into account. With a small-scale test bench, bidirectional power flow capability is demonstrated. The effectiveness of the proposed system is demonstrated through experimental results.

In this paper, a global optimal study of the efficiency of a cascaded structure with synchronous rectification composed of two sub-converters has been presented, this converter allows obtaining high voltage ratio and consists of two-interleaved boost converter which was chosen as 1stsub-converter and three-level boost converter which was chosen as 2ndsub-converter. An optimal efficiency operation as a function of the intermediate voltage and the branch number of the first converter is studied by the aid of an adaptive losses estimation algorithm to estimate the components losses for each DC/DC converter. The estimated power losses of the two converters are modeled by two estimated resistances. These estimated resistances are used to study and optimize the relation between the intermediate voltage and the global efficiency and also the influence of the number of branches of the interleaved converter on the total global losses. The algorithm is theoretically analyzed, developed and compared with the experimental results. Experimental results allow validating the proposed analysis for maximizing global efficiency.

Computer systems increasingly rely on heterogeneity to achieve greater performance, scalability and energy efficiency. Because heterogeneous systems typically comprise multiple execution contexts with different programming abstractions and runtimes, programming them remains extremely challenging.

Bugs in kernel extensions remain one of the main causes of poor operating system reliability despite proposed techniques that isolate extensions in separate protection domains to contain faults. We believe that previous fault isolation techniques are not widely used because they cannot isolate existing kernel extensions with low overhead on standard hardware. This is a hard problem because these extensions communicate with the kernel using a complex interface and they communicate frequently. We present BGI (Byte-Granularity Isolation), a new software fault isolation technique that addresses this problem. BGI uses efficient byte-granularity memory protection to isolate kernel extensions in separate protection domains that share the same address space. BGI ensures type safety for kernel objects and it can detect common types of errors inside domains. Our results show that BGI is practical: it can isolate Windows drivers without requiring changes to the source code and it introduces a CPU overhead between 0 and 16%. BGI can also find bugs during driver testing. We found 28 new bugs in widely used Windows drivers.

Software vendors collect bug reports from customers to improve the quality of their software. These reports should include the inputs that make the software fail, to enable vendors to reproduce the bug. However, vendors rarely include these inputs in reports because they may contain private user data. We describe a solution to this problem that provides software vendors with new input values that satisfy the conditions required to make the software follow the same execution path until it fails, but are otherwise unrelated with the original inputs. These new inputs allow vendors to reproduce the bug while revealing less private information than existing approaches. Additionally, we provide a mechanism to measure the amount of information revealed in an error report. This mechanism allows users to perform informed decisions on whether or not to submit reports. We implemented a prototype of our solution and evaluated it with real errors in real programs. The results show that we can produce error reports that allow software vendors to reproduce bugs while revealing almost no private information.

Byzantine and rational behaviors are increasingly recognized as unavoidable realities in todaypsilas cooperative services. Yet, how to design BAR-tolerant protocols and rigorously prove them strategy proof remains somewhat of a mystery: existing examples tend either to focus on unrealistically simple problems or to want in rigor. The goal of this paper is to demystify the process by presenting the full algorithmic development cycle that, starting from the classic synchronous repeated terminating reliable broadcast (R-TRB) problem statement, leads to a provably BAR-tolerant solution. We show i) how to express R-TRB as a game; ii) why the strategy corresponding to the optimal Byzantine fault tolerant algorithm of Dolev and strong does not guarantee safety when non-Byzantine players behave rationally; iii) how to derive a BAR-tolerant R-TRB protocol: iv) how to prove rigorously that the protocol ensures safety in the presence of non-Byzantine rational players.

No abstract available.

We present the first protocol that reaches asynchronous Byzantine consensus in two communication steps in the common case. We prove that our protocol is optimal in terms of both number of communication steps and number of processes for two-step consensus. The protocol can be used to build a replicated state machine that requires only three communication steps per request in the common case. Further, we show a parameterized version of the protocol that is safe despite f Byzantine failures and, in the common case, guarantees two-step execution despite some number t of failures (t les f). We show that this parameterized two-step consensus protocol is also optimal in terms of both number of communication steps and number of processes

We present the first consensus protocol that reaches asynchronous Byzantine consensus in two communication steps in the common case. We prove that our protocol is optimal in terms of both number of communication step, and number of processes for 2-step consensus. The protocol can be used to build a replicated state machine that requires only three communication steps per request in the common case.

This paper describes a general approach to constructing cooperative services that span multiple administrative domains. In such environments, protocols must tolerate both Byzantine behaviors when broken, misconfigured, or malicious nodes arbitrarily deviate from their specification and rational behaviors when selfish nodes deviate from their specification to increase their local benefit. The paper makes three contributions: (1) It introduces the BAR (Byzantine, Altruistic, Rational) model as a foundation for reasoning about cooperative services; (2) It proposes a general three-level architecture to reduce the complexity of building services under the BAR model; and (3) It describes an implementation of BAR-B the first cooperative backup service to tolerate both Byzantine users and an unbounded number of rational users. At the core of BAR-B is an asynchronous replicated state machine that provides the customary safety and liveness guarantees despite nodes exhibiting both Byzantine and rational behaviors. Our prototype provides acceptable performance for our application: our BAR-tolerant state machine executes 15 requests per second, and our BAR-B backup service can back up 100MB of data in under 4 minutes.

We present a framework for transforming several quorum-based protocols so that they can dynamically adapt their failure threshold and server count, allowing them to be reconfigured in anticipation of possible failures or to replace servers as desired. We demonstrate this transformation on the dissemination quorum protocol. The resulting system provides confirmable wait-free atomic semantics while tolerating Byzantine failures from the clients or servers. The system can grow without bound to tolerate as many failures as desired. Finally, the protocol is optimal and fast: only the minimal number of servers - 3f + 1 - is needed to tolerate any f failures and, in the common case, reads require only one message round-trip.

We describe a new architecture for Byzantine fault tolerant state machine replication that separates agreement that orders requests from execution that processes requests. This separation yields two fundamental and practically significant advantages over previous architectures. First, it reduces replication costs because the new architecture can tolerate faults in up to half of the state machine replicas that execute requests. Previous systems can tolerate faults in at most a third of the combined agreement/state machine replicas. Second, separating agreement from execution allows a general privacy firewall architecture to protect confidentiality through replication. In contrast, replication in previous systems hurts confidentiality because exploiting the weakest replica can be sufficient to compromise the system. We have constructed a prototype and evaluated it running both microbenchmarks and an NFS server. Overall, we find that the architecture adds modest latencies to unreplicated systems and that its performance is competitive with existing Byzantine fault tolerant systems.

In this paper we present two protocols for asynchronous Byzantine quorum systems (BQS) built on top of reliable channels-one for self-verifying data and the other for any data. Our protocols tolerate f Byzantine failures with f fewer servers than existing solutions by eliminating nonessential work in the write protocol and by using read and write quorums of different sizes. Since engineering a reliable network layer on an unreliable network is difficult, two other possibilities must be explored. The first is to strengthen the model by allowing synchronous networks that use time-outs to identify failed links or machines. We consider running synchronous and asynchronous Byzantine quorum protocols over synchronous networks and conclude that, surprisingly, "self-timing" asynchronous Byzantine protocols may offer significant advantages for many synchronous networks when network time-outs are long. We show how to extend an existing Byzantine quorum protocol to eliminate its dependency on reliable networking and to handle message loss and retransmission explicitly.

GenVoca is a methodology and technology for generating product-lines, i.e. building variants of a program. The primitive components from which applications are constructed are refinements or layers, which are modules that implement a feature that many programs of a product-line can share. Unlike conventional components (e.g., COM, CORBA, EJB), a layer encapsulates fragments of multiple classes. Sets of fully formed classes can be produced by composing layers. Layers are modular, albeit unconventional, building blocks of programs. But what are the building blocks of layers? We argue that facets is an answer. A facet encapsulates fragments of multiple layers, and compositions of facets yields sets of fully formed layers. Facets arise when refinements scale from producing variants of individual programs to producing variants of multiple integrated programs, as typified byproduct families (e.g., MS Office). We present a mathematical model that explains relationships between layers and facets. We use the model to develop a generator for tools (i.e., product family) that are used in language-extensible Integrated Development Environments (IDEs).