No abstract

The increasing use of electric vehicles connected to the power grid gives rise to challenges in the vehicle charging coordination, cost management, and provision of potential services to the grid. Scheduling of the power in an electric vehicle charging station is a quite challenging task, considering time-variant prices, customers with different charging time preferences, and the impact on the grid operations. The latter aspect can be addressed by exploiting the vehicle charging flexibility. In this article, a specific definition of flexibility to be used for an electric vehicle charging station is provided. Two optimal charging strategies are then proposed and evaluated, with the purpose of determining which strategy can offer spinning reserve services to the electrical grid, reducing at the same time the operation costs of the charging station. These strategies are based on a novel formulation of an economic model predictive control algorithm, aimed at minimising the charging station operation cost, and on a novel formulation of the flexibility capacity maximisation, while reducing the operation costs. These formulations incorporate the uncertainty in the arrival time and state of charge of the electric vehicles at their arrival. Both strategies lead to a considerable reduction of the costs with respect to a simple minimum time charging strategy, taken as the benchmark. In particular, the strategy that also accounts for flexibility maximisation emerges as a new tool for maintaining the grid balance giving cost savings to the charging stations.

The paper outlines orbit and formation control of a long-distance (>100 km) two-satellite formation for the monitoring of the Earth gravity. Orbit control applies to a single satellite and performs altitude control. Here, formation control is formulated as a control capable of altitude and distance control at the same time. The satellites being placed in a low Earth orbit, orbit, and formation control employ the measurements of a global navigation system. Formation control is imposed by long-distance laser interferometry, which is the key instrument for gravity measurement. Orbit and formation control are low-frequency control systems in charge of canceling bias and drift of the residual drag-free accelerations. Drag-free control is the core of the orbit/formation control since it allows the formation to fly drag-free only subject to gravity. Drag-free control being required to have a bandwidth close to 1 Hz, is designed as the inner loop of the formation control. In turn, formation control must not destroy drag-free performance, in which objective demands that formation control be effective only below the 0.2 mHz orbital frequency. Control design is based on a new orbit and formation dynamics, which are compared with the classical Hill-Clohessy-Wiltshire equations. The new dynamic equations are the first step in building the embedded model, which is the core of the control unit. Embedded model derivation is explained only for the orbit control, and briefly mentioned for the formation control. Simulated results are provided. Drag-free results are compared with GOCE experimental data.

In this demo we present TraceME (Traceability Management in Eclipse), an Eclipse plug-in, that supports the software engineer in capturing and maintaining traceability links between different types of artifacts. A comparative analysis of the functionalities of the tools supporting traceability recovery highlights that TraceME is the more comprehensive tool for supporting such a critical activity during software development.

The paper presents the design and some simulated results of the attitude control of a two-satellite formation under study by the European Space Agency for the Next Generation Gravity Mission. The formation spacecrafts, with a distance between them of more than 200 km and orbiting around the Earth at about 300 km altitude, must align their axis to the satellite-to-satellite line with a microradian accuracy (pointing control). This is made possible by specific optical sensors accompanying the inter-satellite laser interferometer. Such sensors allow each satellite to autonomously align after an acquisition procedure. Pointing control is constrained by the angular drag-free control, which, imposed by Earth gravimetry, must zero the spacecraft angular acceleration vector below 0.01 microradian/s 2 in the science bandwidth. This is made possible by ultrafine accelerometers of the GOCE-class, whose measurements must be coordinated with attitude sensors to meet drag-free and pointing requirements. Embedded Model Control shows how coordination can be implemented around the embedded model of the spacecraft attitude and of the formation frame quaternion. Evidence and discussion about some critical requirements is also included.