ALBERT

Description: Stand-alone power systems based on renewable energy sources are used to replace generators based on fossil fuels. Those renewable power systems also require Energy Storage Devices (ESD) interfaced by a charger/discharger power converter, which consist of a bidirectional DC/DC converter, and a DC bus. This paper proposes a single sliding-mode controller (SMC) for the charger/discharger DC/DC converter to provide a stable DC bus voltage in any operation condition: charging or discharging the ESD, or even without any power exchange between the ESD and the DC bus. Due to the non-linear nature of the power converter, the SMC parameters are adapted on-line to ensure global stability in any operation condition. Such stability of the adaptive SMC is mathematically demonstrated using analytical expressions for the transversality, reachability and equivalent control conditions. Moreover, a design procedure for the adaptive SMC parameters is provided in order to ensure the dynamic response required for the correct operation of the load. Finally, simulations and experimental tests validate the proposed controller and design procedure.

Description: The Holocene, Ahead of Print. 〈br/〉

Description: The Holocene, Volume 29, Issue 2, Page 300-312, February 2019. 〈br/〉

Description: A recent approach to mitigate the adverse effects of photovoltaic (PV) arrays operating under mismatching conditions is the dynamic electrical reconfiguration of the PV panels. This paper introduces a procedure to determine the best configuration of a PV array connected in a series-parallel structure without using complex mathematical models. Such a procedure uses the experimental current vs. voltage curves of the PV panels, which are composed of multiple PV modules, to construct the power vs. voltage curves of all of the possible configurations to identify the optimal one. The main advantage of this method is the low computational effort required to reconstruct the power vs. voltage curves of the array. This characteristic enables one to implement the proposed solution using inexpensive embedded devices, which are widely adopted in industrial applications. The proposed method, and its embedded implementation, were tested using a hardware-in-the-loop simulation of the PV system. Finally, the real-time operation and benefits of the proposed solution are illustrated using a practical example based on commercial devices.

Description: Central Chile is heavily exploited for mineral and water resources, with agriculture and large urban populations all creating intensive landscape use. Few records of past environmental and climate change are available that afford a broader context. To aid in this assessment, we present a 700-year reconstruction from Laguna del Maule (LdM) in the high Andes of central Chile based on sedimentological, geochemical, diatom and pollen analyses. The age model is based on 210 Pb/ 137 Cs and 14 C dating tied into known volcanic eruptions. Sedimentology consists of organic-rich sediments and diatom oozes with several interspersed volcanic-rich facies and two tephra deposits. Sediment geochemistry exhibits increased productivity (high Br/Ti, biosilica) and more dominant oxic conditions (high Fe/Mn) from AD 1300 to 1400 and from AD 1650 to 1850, likely during periods of relatively lower lake levels and better development of littoral environments. However, during this later period, high elevation vegetation was dominant, indicative of regional cooler/wetter conditions. In contrast, sediments deposited from AD 1850 to 1930 evidence decreased productivity and increased anoxic lake bottom conditions. The ‘Little Ice Age’ (LIA) in LdM is characterized by significant variations in lake dynamics and hydrology with cooler/wetter conditions (AD 1570–1700), major environmental changes in the 18th century and ending at ca. AD 1850. LdM record documents the impact of the LIA in the southern hemisphere and stresses the global nature of this climate period. Large changes in lake dynamics and diatoms assemblages during the 20th century could be related to anthropogenic impacts, but recent changes in climate patterns cannot be excluded.

Description: A previous article has presented the members of the asymmetrical interleaved dc/dc switching converters family as very appropriate candidates to interface between photovoltaic or fuel cell generators and their loads because of their reduced ripple and increased current processing capabilities. After a review of the main modeling methods suitable for high-order converters operating, as the asymmetrical interleaved converters (AIC) ones, in discontinuous current conduction mode a full-order averaged model has been adapted and improved to describe the dynamic behavior of AIC. The excellent agreement between the mathematical model predictions, the switched simulations and the experimental results has allowed for satisfactory design of a linear-quadratic regulator (LQR) in a fuel-cell application example, which demonstrates the usefulness of the improved control-oriented modeling approach when the switching converters operate in discontinuous conduction mode.

Description: A multiproxy study of a 7 m long sedimentary sequence from Lake La Parra (39°50.948', 1°52', 1014 m a.s.l.) supported by 11 14 C AMS and 210 Pb/ 137 Cs dates provides a robust, high-resolution hydrological and environmental variability record for the last 1600 years of the Las Torcas sinkhole Complex in the Central Iberian Range. The succession of depositional environments in Lake La Parra sinkhole is controlled by both changes in the regional water table and by the balance between sedimentary input through ephemeral creeks and in-lake production of carbonates and organic matter. Although synergetic links with climate are likely, phases of increased sediment delivery to the lake at c . ad 500–700, c . ad 1000, ad 1450–1500, ad 1550–650 and since 1700 till recent times are driven primarily by human impact in the watershed. Prior to c . ad 300, the sinkhole was dry, then became a lake at the end of the Roman Period ( ad 350) when the doline was flooded, and it has not dried out during the last 1600 years. Moderate lake levels with deposition of coarser clastic facies dominated up to the 12th century ( ad 400–1200), and relatively higher levels with deposition of laminated facies during the 13th–15th centuries ( ad 1200–1600). The pattern of palaeohydrological evolution at a centennial scale is roughly coherent with most Iberian lacustrine records; however, the ‘La Parra’ sequence indicates that increased humidity during Iberian–Roman times was restricted to southern Spain and the humid phases of the ‘Little Ice Age’ (‘LIA’) starting and ending earlier in the central Iberian Range compared with the Pyrenean Domain and southern Spain. This new sequence highlights the heterogeneity through space and time of the main dry and wet climatic periods at shorter scales, emphasizing the impact of latitudinal climate gradients on the Iberian Peninsula climate variability.

Description: The Marboré Cirque, which is located in the southern Central Pyrenees on the north face of the Monte Perdido Peak (42°40'0''N; 0.5°0''W; 3355 m), contains a wide variety of Holocene glacial and periglacial deposits, and those from the ‘Little Ice Age’ (‘LIA’) are particularly well developed. Based on geomorphological mapping, cosmogenic exposure dating and previous studies of lacustrine sediment cores, the different deposits were dated and a sequence of geomorphological and paleoenvironmental events was established as follows: (1) The Marboré Cirque was at least partially deglaciated before 12.7 kyr BP. (2) Some ice masses are likely to have persisted in the Early Holocene, although their moraines were destroyed by the advance of glaciers during the Mid Holocene and ‘LIA’. (3) A glacial expansion occurred during the Mid Holocene (5.1 ± 0.1 kyr), represented by a large push moraine that enclosed a unique ice mass at the foot of the Monte Perdido Massif. (4) A melting phase occurred at approximately 3.4 ± 0.2 and 2.5 ± 0.1 kyr (Bronze/Iron Ages) after one of the most important glacial advances of the Neoglacial period. (5) Another glacial expansion occurred during the Dark Age Cold Period (1.4–1.2 kyr), followed by a melting period during the Medieval Climate Anomaly. (6) The ‘LIA’ represented a clear stage of glacial expansion within the Marboré Cirque. Two different pulses of glaciation were detected, separated by a short retraction. The first pulse occurred most likely during the late 17th century or early 18th century (Maunder Minimum), whereas the second occurred between 1790 and ad 1830 (Dalton Minimum). A strong deglaciation process has affected the Marboré Cirque glaciers since the middle of the 19th century. (7) A large rock avalanche occurred during the Mid Holocene, leaving a chaotic deposit that was previously considered to be a Late Glacial moraine.

Description: A fifth-order dynamic continuous model of a linear induction motor (LIM), without considering “end effects” and considering attraction force, was developed. The attraction force is necessary in considering the dynamic analysis of the mechanically loaded linear induction motor. To obtain the circuit parameters of the LIM, a physical system was implemented in the laboratory with a Rapid Prototype System. The model was created by modifying the traditional three-phase model of a Y-connected rotary induction motor in a d–q stationary reference frame. The discrete-time LIM model was obtained through the continuous time model solution for its application in simulations or computational solutions in order to analyze nonlinear behaviors and for use in discrete time control systems. To obtain the solution, the continuous time model was divided into a current-fed linear induction motor third-order model, where the current inputs were considered as pseudo-inputs, and a second-order subsystem that only models the currents of the primary with voltages as inputs. For the discrete time model, the current-fed model is discretized by solving a set of differential equations, and the subsystem is discretized by a first-order Taylor series. Finally, a comparison of the continuous and discrete time model behaviors was shown graphically in order to validate the discrete time model.

Description: The Holocene, Volume 28, Issue 11, Page 1685-1696, November 2018. 〈br/〉