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This paper proposes a novel hybrid AC/DC microgrid architecture incorporating a central energy storage system (ESS) for both the AC and the DC sub-grids. To ensure effective operation of the proposed hybrid AC/DC microgrid architecture, a coordinated control strategy between the central ESS and the inter-linking converter (ILC) is proposed in the paper. The proposed central ESS provides voltage and frequency control to the AC sub-grid by measuring voltage and frequency at the point of common coupling (PCC) of the AC sub-grid, while providing DC voltage support to the DC sub-grid by measuring DC sub-grid's PCC voltage. Furthermore, per-unit frequency and the DC sub-grid PCC voltage are utilized to transfer power between the two sub-grids via the ILC. Therefore, two control strategies are coordinating with each other and maintain stable operation. The central ESS eliminates the use of multiple ILCs and complex control schemes for charge and discharge control to maintain same state of charge levels at each ESS. Effectiveness of the proposed coordinated controller is verified by applying various load disturbances, faults, and under different modes of operation in standalone mode operation due to ILC failure.

This paper presents the analysis of release of dark-colored leachate from soil-like material (SLM) mined from three old municipal solid waste dump sites of before its reuse as earth-fill. If SLM is to be re-used in earth-fill, the release of dark-colored leachate can cause coloration of the surrounding water bodies. Laboratory studies (in terms of single batch leaching) were undertaken to quantify the release of color and identify the source/cause of the phenomenon. Influence of repeated washing, heating at various temperature, and aeration of SLM on the intensity of release of color was identified. Correlation of color with total dissolved solids and volatile dissolved solids was also established. The intensity of color of water extract from SLM in platinum cobalt unit (PCU) was found to in the range of 288-712, 465-485 and 740-925 from Delhi, Kadapa and Hyderabad dumpsites respectively. In contrast, the intensity of color in water released from local soils was found to be 25-30 PCU. Organic content present in SLM was identified as the primary cause for the release of color. Results showed that large quantity of water (70-120 ml per gram of SLM) was required to cause significant reduction in the intensity of color. Heating of SLM to 500°C was observed to reduce the color very effectively but short-term aeration of SLM did not reduce color. Good correlation of volatile dissolved solids with color was observed which further confirmed the organic content as the main reason for the release of dark-colored leachate from SLM.

Present study characterizes municipal solid waste incineration bottom ash (MIBA) from three incineration plants in Delhi with an intent to serve the dual objectives: a) assessing the disposal/reuse options for Delhi MIBA, b) evaluating variability in results across the countries (including India) and assessing if is significant enough to influence the fate of MIBA of varied origin. A review on leaching studies of MIBA (50 research papers) was conducted which aided in achieving both the objectives. Delhi MIBA samples were analysed for chemical composition. The two commonly adopted leaching tests i.e., TCLP and EN 12457–2, were conducted and the results were checked against regulatory threshold levels (RTLs) to achieve the first objective. Leaching concentration of the contaminants was compared with the compiled literature and RTLs to accomplish the second objective. The compendium of literature most importantly revealed the physicochemical parameters which are pivotal in determining the fate of MIBA but have been missing from many studies. Ten such parameters were identified: Cr, Cu, Mo, Sb, Cl - , SO 4 2- , Cd, Pb, Ni and Zn and are referred as contaminants of concern (CoCs). Delhi MIBA was found suitable for disposal to non-hazardous waste landfills and unsuitable for unrestricted reuse. CoCs identified in Delhi MIBA were identical to those observed in literature (except Cd, Pb and Zn). The variability in leaching concentration of CoCs, observed from comparative assessment of results, spanned nearly 2 to 3 log 10 magnitudes for Cu, Cr, Pb, Sb and Zn while 1 to 2 log 10 magnitudes for Mo, Cl - and SO 4 2- .

The present study examines the feasibility of using the soil-like material (SLM), less than 4.75 mm size, recovered by the mining of old waste from four municipal solid waste dumps of India as an earth-fill for embankments, low-lying areas, deep pits and as compost for horticulture, agricultural applications. This material constitutes 60−70% of the total excavated waste. The contamination levels of SLM for re-use as earth-fills were analyzed on the basis of heavy metals, organic content, soluble salts, and release of dark-colored leachate. The reuse feasibility of SLM as compost was assessed on the basis of nutrients levels (total organic carbon, nitrogen, phosphorous, and potassium), heavy metals, and physicochemical characteristics. All the obtained results were compared with the values reported in the literature, national and international regulatory guidelines as well as with the background soils. The presence of high levels of organic matter, heavy metals, and soluble salts indicate that the SLM requires treatment before off-site re-use or that specific design measures are must before placing it as earth-fill in embankments, low-lying areas, and deep pits. The study also reveals that the re-use of mined SLM as compost should be restricted to non-agricultural applications due to excess heavy metals after supplementing the total organic carbon.

For achieving sustainability in management of municipal solid waste (MSW), it is important to ensure that residues, remaining after processing of waste in various plants (composting, waste to energy (WTE), landfilling), are reutilised in a safe and useful manner. Such residues constitute more than 25–35% of the total MSW generated in urban areas. This paper examines the feasibility of using soil-sized residues from landfill mining operations as well as from WTE plants in large quantities (bulk) in geotechnical applications relating to earthworks and structural fills. The geotechnical properties of the residues as well as the contaminants of concern in these residues from two waste dumps and three waste-to-energy plants of Delhi have been evaluated and the critical parameters inhibiting their un-restricted bulk reuse have been identified. The role of high soluble solids, high organic content, elevated heavy metals, release of colour and variable pH has been brought out. The design measures and treatment methods that need to be adopted when using these residues in surface fills, shallow fills, deep fills and structural fills have been highlighted.

Soil-like material (SLM) was mined from five municipal solid waste (MSW) dumps to assess its potential for reuse in earthwork projects. The contamination levels of SLM (

This paper presents the field test results for 3.3-m-long driven steel pipe single vertical piles, P1 (β=0°), and single batter piles, P2 (β=10°) and P3 (β=20°), for four different eccentri...

Self-governing small regions of power systems, known as “microgrids”, are enabling the integration of small-scale renewable energy sources (RESs) while improving the reliability and energy efficiency of the electricity network. Microgrids can be primarily classified into three types based on their voltage characteristics and system architecture; 1) AC microgrids, 2) DC microgrids, and 3) Hybrid AC/DC microgrids. This paper presents a comprehensive review of stability, control, power management and fault ride-through (FRT) strategies for the AC, DC, and hybrid AC/DC microgrids. This paper also classifies microgrids in terms of their intended application and summarises the operation requirements stipulated in standards (e.g., IEEE Std. 1547-2018). The control strategies for each microgrid architecture are reviewed in terms of their operating principle and performance. In terms of the hybrid AC/DC microgrids, specific control aspects, such as mode transition and coordinated control between multiple interlinking converters (ILCs) and energy storage system (ESS) are analysed. A case study is also presented on the dynamic performance of a hybrid AC/DC microgrid under different control strategies and dynamic loads. Hybrid AC/DC microgrids shown to have more advantages in terms of economy and efficiency compared with the other microgrid architectures. This review shows that hierarchical control schemes, such as primary, secondary, and tertiary control are very popular among all three microgrid types. It is shown that the hybrid AC/DC microgrids require more complex control strategies for power management and control compared to AC or DC microgrids due to their dependency on the ILC controls and the operation mode of the hybrid AC/DC microgrid. Case study illustrated the significant effects of microgrid feeder characteristics on the dynamic performance of the hybrid AC/DC microgrid. It is also revealed that any transient conditions either in the AC or DC microgrids could propagate through the ILC affecting the entire microgrid dynamic performance. Additionally, the critical control issues and the future research challenges of microgrids are also discussed in this paper.

This paper presents the details of an experimental investigation using large-scale inclined pullout apparatus on sheet geosynthetic and geogrid embedded in run-out, I-type, and L-type anchors. The influence of the type of sand on the behaviour of the sheet and the geogrid is also investigated. The results show that in both the sheet and the geogrid, I-type anchor provides approximately 50% and L-type anchor provides 90% higher pullout force than the run-out anchor. The maximum pullout force increases by more than 20% as the inclination of pullout force increases from 0° to 30° for both the sheet and the geogrid.

Stability of geosynthetics along slopes in covers and liners of landfills depends partly on their tensile strength and partly on the efficiency of anchors holding the geosynthetics at berms or the top of the slope. The pull induced in these geosynthetics is in an inclined direction parallel to the slope. But due to difficulty in modelling inclined pullout behaviour experimentally, very few studies have so far been conducted on geosynthetics embedded in anchor trenches. This paper presents details of a device that can perform inclined pullout tests on geosynthetics at variable inclinations. Since geogrids are widely used as veneer reinforcement, inclined pullout tests are conducted on geogrids embedded in run-out, I-type and L-type anchors in sand. The maximum pullout force in the geogrid increases by more than 20% as the pull inclination increases from 0° to 20° in all the three types of anchors. The geogrids exhibit markedly different force-displacement behaviour for the three types of anchors, though the length of reinforcement remains the same. The peak pullout force for the I-type anchor was 1.6–1.7 times higher, and that for the L-type anchor was 2 times higher than that of the run-out anchor at all pullout inclinations.

Coal combustion residue (CCR) has gained considerable acceptance in civil engineering applications, mainly in the cement industry and brick manufacturing. However, despite an increasing application of CCR, a large proportion remains unutilized globally. This research focuses on the feasibility of using fly ash, bottom ash, and their mixtures as a filling material in reinforced soil structures (RSS). The physical, mechanical characterization of the materials, along with the pullout resistance behavior of the interface between the CCR and a uniaxial polyester geogrid was studied. The grain size distribution tests showed the presence of 80% silt particles in fly ash and 7% in bottom ash. All the CCR samples were non-plastic in nature, and direct shear test results revealed that well compacted CCR samples offer similar shear strength as that of natural soils used as backfill in RSS. The leachability tests of CCR were carried out as per EN 12457–4 (2002) for the assessment of environmental risk. The results revealed that the leachable toxic contents in CCR remained quite below than the standard prescribed limits defined by the European Council Decision 2003/33/EC. The interaction coefficient values for a bottom ash-geogrid interface, obtained from the pullout test, match well with the results of natural/conventional fill material. The interaction coefficient value for the fly ash-geogrid interface was the lowest amongst the materials tested i. e 0.28 at 80 kPa, which is greater than the value recommended by JTJ015-91. The finding of the study demonstrated the suitability of using CCR as an economical, environmentally safe and sustainable structural fill material behind RSS.

The paper describes the interface behaviour of bottom ash, obtained from two thermal power plants, and geogrid for possible utilization as a reinforced fill material in reinforced soil structures. Pullout tests were conducted on polyester geogrid embedded in compacted bottom ash samples as per ASTM D6706-01. Locally available natural sand was used as a reference material. The pullout resistance offered by geogrid embedded in bottom ash was almost identical to that in sand. In order to study the influence of placement condition of the material on pullout resistance, test were conducted on uncompacted fill materials. Pullout resistance offered by geogrids embedded in uncompacted specimen reduced by 30–60% than that at the compacted condition.