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In the last few years, restrictive grid codes have arisen to ensure the performance and stability of electrical networks, which experience a massive integration of renewable energy sources and distributed generation systems that are normally connected to the grid through electronic power converters. In these codes, the injection of positive-and negative-sequence current components becomes necessary for fulfilling, among others, the low-voltage ride-through requirements during balanced and unbalanced grid faults. However, the performance of classical dq current controllers, applied to power converters, under unbalanced grid-voltage conditions is highly deficient, due to the unavoidable appearance of current oscillations. This paper analyzes the performance of the double synchronous reference frame controller and improves its structure by adding a decoupling network for estimating and compensating the undesirable current oscillations. Experimental results will demonstrate the validity of the proposed decoupled DSRF controller.

Multilevel cascaded H-Bridge converters (CHB) have been presented as a good solution for high power applications. In this way, several control and modulation techniques have been proposed for this power converter topology. In this paper the steady state power balance in the cells of the single phase two cell CHB is studied. The capability to be supplied with active power from the grid or to deliver active power to the grid in each cell is analyzed according to the dc-link voltages and the desired ac output voltage value. Limits of the maximum and minimum input active power for stable operation of the CHB are addressed. Simulation results are shown to validate the presented analysis.

This paper presents a new synchronization scheme for detecting multiple positive-/negative-sequence frequency harmonics in three-phase systems for grid-connected power converters. The proposed technique is called MAVF-FLL because it is based on the use of multiple adaptive vectorial filters (AVFs) working together inside a harmonic decoupling network (HDN), resting on a frequency-locked loop (FLL) which makes the system frequency adaptive. The method uses the vectorial properties of the three-phase input signal in the αβ reference frame in order to obtain the different harmonic components. The MAVF-FLL is fully designed and analyzed addressing the tuning procedure in order to obtain the desired and predefined performance. The proposed algorithm is evaluated by both simulation and experimental results, demonstrating its ability to perform as required for detecting different harmonic components under a highly unbalanced and distorted input grid voltage.

The problem of optimally sizing hybrid energy storage systems (HESS) installed in electric railway systems, considering the effect of regenerative braking is studied in this paper. HESSs combine traditional batteries and newly developed ultracapacitors, taking advantage of the high energy capacity of batteries and of the flexibility and ability to capture high power density of ultracapacitors. A novel mixed integer linear programming formulation that includes the counting of battery cycles is presented. Some particularities of battery operation are included in the model, like the dependence of its performance on the number of cycles and the depth of discharge (DOD). Results are reported first for a illustrative case study, allowing us to perform sensitivity studies for several parameters; results are also reported and for a larger case, closely resembling the problem faced by railway energy systems planners and operators.Index Terms-Electric railway systems, hybrid energy storage sizing, mixed integer linear programming. NOMENCLATUREThis section describes the sets, parameters, and variables used in the paper. A. Sets Set of batteries.Time period set. AC/DC inverter set. DC/DC inverter set. B. ParametersMinimum battery unit (MBU) cost .Daily MBU cost for each battery .Minimum ultracapacitor unit (MUU) cost .

The Andacollo mining district is in the Coastal Cordillera of central Chile, 400 km northnortheast of Santiago. The Andacollo deposits are the products of a complex hydrothermal system and consist of a porphyry copper-gold deposit and peripheral strata-bound manto gold deposits and veins with minor associated base metals. The hydrothermal system was part of the Pacific porphyry copper belt which was generated during development of an Early Cretaceous magmatic arc displaying shoshonitic petrochemical affiliations. Rocks that crop out in the area include a volcanic sequence, the Arqueros and Quebrada Marquesa Formations, consisting of andesitc and dacite flows, volcanic breccias, and pyroclastic rocks of Early Cretaceous age. Intrusive rocks range from diorite to granodiorite in composition and date between 87 and 130 Ma. The porphyry copper-gold deposit is zoned vertically downward from a leached capping through a supergene enrichment blanket to a hypogene sulfide zone. Alteration is characterized by central potassic (K feldspar-biotite), phyllic, and peripheral propylitic zones. Abundant northwest-trending tensional fractures were superimposed on the porphyry copper-gold deposit and surrounding areas during the later stages of the evolving mineralized system. The fractures channeled mineralizing fluids from the central parts of the porphyry copper deposit outward for up to 5 km. Replacement by adularia and sericite took place together with deposition of gold-bearing pyrite and minor amounts of zinc and copper where these fluids encountered permeable dacite flows and andesitc flow breccias. The alteration process caused remobilization of aluminum and alkalies and addition of K20, which attafns values of 12 to 13 wt percent. The Andacollo system is interpreted to be a porphyry coppergold deposit that is transitional outward to distal epithermal, adularia-sericite-type contact metasomatic gold orebodies.

Abstract:The study was conducted in Lake Tana Basin of Ethiopia to assess potentially irrigable areas for home gardens, water availability, and feasibility of water-lifting technologies. A GIS-based Multi-Criteria Evaluation (MCE) technique was applied to access the potential of surface and groundwater sources for irrigation. The factors affecting irrigation practice were identified and feasibility of water-lifting technologies was evaluated. Pairwise method and expert's opinion were used to assign weights for each factor. The result showed that about 345,000 ha and 135,000 ha of land were found suitable for irrigation from the surface and groundwater sources, respectively. The rivers could address about 1-1.2% of the irrigable land during dry season without water storage structure whereas groundwater could address about 2.2-2.4% of the irrigable land, both using conventional irrigation techniques. If the seven major dams within the basin were considered, surface water potential would be increased and satisfy about 21% of the irrigable land. If rainwater harvesting techniques were used, about 76% of the basin would be suitable for irrigation. The potential of surface and groundwater was evaluated with respect to water requirements of dominant crops in the region. On the other hand, rope pump and deep well piston hand pump were found with relatively the most (26%) and the least (9%) applicable low-cost water-lifting technologies in the basin.

A field-scale experimental study was conducted in Sub-Saharan Africa (Ethiopia and Ghana) to examine the effects of conservation agriculture (CA) with drip irrigation system on water productivity in vegetable home gardens. CA here refers to minimum soil disturbance (no-till), year-round organic mulch cover, and diverse cropping in the rotation. A total of 28 farmers (13 farmers in Ethiopia and 15 farmers in Ghana) participated in this experiment. The experimental setup was a paired 't' design on a 100 m 2 plot; where half of the plot was assigned to CA and the other half to conventional tillage (CT), both under drip irrigation system. Irrigation water use and crop yield were monitored for three seasons in Ethiopia and one season in Ghana for vegetable production including garlic, onion, cabbage, tomato, and sweet potato. Irrigation water use was substantially lower under CA, 18% to 45.6%, with a substantial increase in crop yields, 9% to about two-fold, when compared with CT practice for the various vegetables. Crop yields and irrigation water uses were combined into one metric, water productivity, for the statistical analysis on the effect of CA with drip irrigation system. One-tailed paired 't' test statistical analysis was used to examine if the mean water productivity in CA is higher than that of CT. Water productivity was found to be significantly improved (α = 0.05) under the CA practice; 100%, 120%, 222%, 33%, and 49% for garlic, onion, tomato, cabbage, and sweet potato respectively. This could be due to the improvement of soil quality and structure due to CA practice, adding nutrients to the soil and sticking soil particles together (increase soil aggregates). Irrigation water productivity for tomato under CA (5.17 kg m −3 in CA as compared to 1.61 kg m −3 in CT) is found to be highest when compared to water productivity for the other vegetables. The mulch cover provided protection for the tomatoes from direct contact with the soil and minimized the chances of soil-borne diseases. Adapting to CA practices with drip irrigation in vegetable home gardens is, therefore, a feasible strategy to improve water use efficiency, and to intensify crop yield, which directly contributes towards the sustainability of livelihoods of smallholder farmers in the region.