Minimum Loading Conditions Research Articles

PV Grid-Connected Inverter With DC Voltage Regulation in CCM and VCM Operation to Reduce Switching Losses

In this paper, a photo-voltaic (PV) grid connected inverter (GCI) is employed for multi-functional control (i.e., real power flow control form PV panels, mitigation of current and voltage related power quality (PQ) problems) and the GCI input reference dc voltage is formulated as a function of GCI output currents for loss reduction during low currents through inverter switches. In the latest literature, PV GCI is used for mitigating current related PQ problems, and it is also used for mitigating minor voltage related PQ problems (voltage sag, voltage swell, and voltage imbalance). During voltage sag conditions, GCI output current is high enough to maintain rated voltage at the point of common coupling (PCC) and in this case the reference dc voltage requirement is high. But, during rated grid voltage condition, low power generation from PV, and minimum load condition keeping maximum dc voltage at the input of GCI leads to heavy burden on GCI switches. In the proposed method, in order to reduce losses in GCI, the input dc voltage of GCI is reduced during low GCI output current. The proposed method is validated with MATLAB simulation and hardware experiment by comparing data existing in literature with the proposed method.

Solar Agricultural Sprayer Robot

Abstract: Manual spraying of pesticides and herbicides to crops and weed inhibitors onto the field are quite laborious work to humans. Manual trimming of selected unwanted plants or harvested crops from the field is also difficult. Our project proposes a multipurpose solar powered, flexible, Remote Controlled, semi-automated spraying robot with 4 Degrees of Freedom (DoF) in spatial movement, with an additional plant mowing equipment. The robot is designed to spray pesticide/insecticide directly onto individual lesions minimizing wastage or excess chemical spraying, hence making the system cost effective and also environment friendly. It is designed to cut down undesired plants selectively by remotely controlling the start and stop of the mowing system. Alternatively, it also serves the purpose of maintaining lawns and sports field made of grass. The same system can be used for water spraying and mowing the grass to desired levels, leading to proper maintenance of the field. The robot is designed to move at 1.4m/s, with an effective spraying area of 0.98 sq. m. by the nozzle and an effective cutting area of 0.3 sq. m. by the mower, when stationary. The prototype has a battery back-up of 7.2hrs under minimum load conditions.

Predicting the Impact of Compressor Flexibility Improvements on Heavy-Duty Gas Turbines for Minimum and Base Load Conditions

The increasing importance of renewable energy capacity in the power generation scenario, together with the fluctuating consumer energy demand, forces conventional fossil fuel power generation systems to promptly respond to relevant and rapid load variations and to operate under off-design conditions during a major fraction of their lives. In order to improve existing power plants’ flexibility in facing energy surplus or deficit, retrofittable solutions for gas turbine compressors are proposed. In this paper, two different operation strategies, variable inlet guide vanes (IGVs) and blow-off extraction (BO), are considered for enabling partial load and minimum environmental load operation, and thus to identify implementation opportunities in existing thermal power plants. A typical 15-stage F-class gas turbine compressor is chosen as a test case and some energy demand scenarios are selected to validate the adopted solutions. The results of an extensive 3D, steady, CFD analysis are compared with the measurements coming from an experimental campaign carried out in the framework of the European Turbo-Reflex project. It will be shown how the combined strategies can reduce gas turbine mass flow rate and power plant output, without significantly penalizing efficiency, and how such off-design performance figures can be reliably predicted by employing state-of-the-art CFD models.

Failure analysis of a suspension bridge in Indonesia using the direct analysis method

A 120 m pedestrian suspension bridge recently inaugurated in Pacitan, East Java, Indonesia, suddenly collapsed when it was empty. It was one of the hundreds of similar bridges constructed through a current government project. Although there were no casualties, finding the cause of the failure is essential to ensure the safety of other bridges that have been or are currently being built. Moreover, field investigations showed that the change in the cable orientation between the bridge tower and cable end point of the suspension bridge and the insufficient capacity of the bracing connection in the bridge tower triggered the failure. The analysis is usually conducted through a numerical simulation using a relatively complex non-linear finite-element analysis. However, this research adopted second-order elastic analysis using the direct analysis method of the American Institute of Steel Construction code, a common method for designing steel structures. This method is relatively more straightforward but applicable in proving that the carrying capacity of the bridge tower decreased drastically due to the bracing failure, which is possibly the explanation for the collapsed bridge under the minimum load condition.

Solar Agricultural Sprayer Robot

Abstract: Manual spraying of pesticides and herbicides to crops and weed inhibitors onto the field are quite laborious work to humans. Manual trimming of selected unwanted plants or harvested crops from the field is also difficult. Our project proposes a multipurpose solar powered, flexible, Remote Controlled, semi-automated spraying robot with 4 Degrees of Freedom (DOF) in spatial movement, with additional plant moving equipment. The robot is designed to spray pesticide/insecticide directly onto individual lesions minimizing wastage or excess chemical spraying, hence making the system cost effective and also environment friendly. It is designed to cut down undesired plants selectively by remotely controlling the start and stop of the moving system. Alternatively, it also serves the purpose of maintaining lawns and sports field made of grass. The same system can be used for water spraying and mowing the grass to desired levels, leading to proper maintenance of the field. The robot is designed to move at 1.4m/s, with an effective spraying area of 0.98 sq. m. by the nozzle and an effective cutting area of 0.3 sq. m. by the mower, when stationary. The prototype has a battery back-up of 7.2hrs under minimum load conditions

Flow-induced pulsations in Francis turbines during startup - A consequence of an intermittent energy system

Hydraulic turbines are increasingly responsible for regulating the electric grid, due to the rapid growth of the intermittent renewable energy resources. This involves a large increase in the number of starts and stops, which cause severe flow-induced pulsations and fluctuating forces that deteriorate the machines. Better knowledge of the evolution of the flow in the machines during transients makes it possible to avoid hazardous conditions, plan maintenance intervals, and estimate the costs of this new kind of operation. The present work provides an in-depth and comprehensive numerical study on the flow-induced pulsations and evolution of the flow field in a high-head model Francis turbine during a startup sequence. The flow simulation is carried out using the OpenFOAM open-source CFD code. A thorough frequency analysis is conducted on the fluctuating part of different pressure probes and force components, utilizing Short-Time Fourier Transform (STFT) to extract the evolution of the frequency and amplitude of pulsations. Low-frequency oscillations are detected during the startup, which are induced by the complex flow structure in the draft tube. A decomposition is performed on the draft tube pressure signals, and the variations of the synchronous (plunging) and asynchronous (rotating) modes are studied. The plunging mode is stronger at minimum and deep part load conditions, whereas the rotating mode is dominant during the presence of the Rotating Vortex Rope (RVR) at part load. The velocity field in the draft tube is validated against experimental data, and the complex flow structures formed during the startup procedure are explained using the λ2 vortex identification method.

An Integrated Driver With Adaptive Dead-Time Control for GaN-Based Synchronous Buck Converter

This paper proposes a driver integrated circuit (IC) for a GaN-based synchronous buck converter to minimized the dead-time loss of GaN devices and improve converter efficiency. The proposed adaptive control achieves minimized dead-time for any loading condition. A driver IC is fabricated in a 0.18 lm BCD process to verify the concept. The measurement result achieves only 0.7 ns and 0.8 ns dead-time at the minimum and maximum load condition, respectively. The efficiency improves 2.1% at 2 A full load compared to the fixed dead-time control counterpart.

Automatic Generation Control of an Interconnected Power System

ABSTRACT In this Article, Particle Swarm Optimization (PSO) algorithm is used to obtain the controller gain for Automatic Generation Control (AGC) of the representation of an Interconnected Power System (IPS) to meet the growth of electric energy for the sustainable development of most countries. The main task of AGC is to restore primary frequency tuning ability, retrieving the frequency to its nominal value and decrease unscheduled tie-line power flows between neighboring control areas. The new controller is designed using real statistical data of the EPS for maximum and minimum loading conditions of the EPS during Summer and Winter of 2019-2020.The robustness of the suggested controller is verified by applying the proposed controller and study the effect of outage of the largest generation unit in IPS on the grid frequency. The results show that the proposed controller-based PSO gives best dynamic response for a step load change. MATLAB-Simulink software is used for obtaining the results.

Study on Peaking Performance of 330MW Unit under Pure Condensing Condition and Extraction Condition

In this paper, the peaking capacity test is carried out for the 330MW unit to compare the peak shaving performance of the unit under the extraction state. The test content is divided into three parts, respectively (a) operating at minimum output under pure condensing condition, (b) minimum load with maximum steam extraction condition and (c) maximum steam extraction with minimum electric load condition. It can be seen from the test results that the minimum electrical load of the unit under 3 conditions is 128.4 MW, 128.6 MW, and 124.8 MW, respectively. Under the test conditions of industrial steam extraction at about 40t/h, the peak shaving performance of the unit has almost no change, compared with the pure condensing condition.

Impact of Compressor Flexibility Improvements on Heavy-Duty Gas Turbine for Minimum and Base Load Conditions

Impact of Compressor Flexibility Improvements on Heavy-Duty Gas Turbine for Minimum and Base Load Conditions

Volumetric assessment of fatigue damage in a SiCf/SiC ceramic matrix composite via in situ X-ray computed tomography

To enhance the understanding of matrix cracking and damage progression on the macroscopic scale, within a 0/90° fibre reinforced SiCf/SiC ceramic matrix composite (CMC), X-ray computed tomography (XCT) imaging and analysis have been performed in conjunction with a commercially available in-situ mechanical loading device. CMC test coupons were subjected to tensile cyclic loads and inspected using XCT without removal from the tensile loading device. Attempts to measure and quantify the resulting damage using volumetric image analysis techniques are presented, by characterising the crack network from XCT images acquired at both the maximum and minimum load condition during selected fatigue cycles. The XCT detection of significant crack development within the first loading half-cycle shows good agreement with cumulative acoustic emission energy data recorded under similar test conditions. The results are seen as an important step towards correlating the damage behaviour detected via different NDE and health monitoring techniques.

Parametric study of single-stage gravitational water vortex turbine with cylindrical basin

Gravitational water vortex turbine (GWVT) is one of the emerging micro-hydro power plants because it requires less expertise, low head and reduced setup space for installation. A detailed performance evaluation of the GWVT based on turbine performance curves is yet to be explored. With the help of mathematical expressions along with the experimentation, the present study presents different performance parameters (PPs) such as; rotational speed, torque, brake power and mechanical efficiency of single-stage GWVT under various flow and design conditions. The effect of vortex height, runner position, percentage submergence of blades, notch angle, blades aspect ratio, blades curvature, blades inclination, hub diameter, straight and conical edged blades on the PPs has been investigated. The analytical and experimental results are in a good agreement both qualitatively and quantitatively. The experimental results show that the vortex height and a good vortex shape with fully developed air core are the major parameters in deciding the performance of GWVT. Better performance of GWVT can be achieved at middle of the rotational speed range i.e. between the minimum and maximum load conditions with minimum possible notch angle and hub diameter, using inclined blades of zero curvature fixed near the bottom of the basin.

Experimental dynamic dispatch of a 60 kW proton exchange membrane electrolyzer in power-to-gas application

A 60 kW PEM electrolyzer was modified to have dynamic dispatch capabilities through the use of an external mass flow controller and was subsequently operated and studied in detail as a part of the UC Irvine power-to-gas (P2G) demonstration project. The system operated in load following for both rooftop solar PV output and aggregated wind farm power. The electrolyzer system was able to handle 100% up and down ramps of the electrolyzer stack in sub-second intervals during variable renewable energy load following experiments. Overall system efficiency was improved by imposing a minimum load condition to avoid high parasitic losses at low power conditions, and cycling the system off/on as required and enabled by quick cold start-up capability. Performance was characterized for varying levels of part load and dynamic operation. The gas drying process was found to be a significant source of loss at low power conditions.

Hybrid System that Integrates the Lost Energy Recovery on the Water-Water Heat Pump Exhaust Circuit

Exceeding intermitence and the stochastic character associated with most renewable energy sources in order to maintain the balance between generation and consumption require the most efficient energy storage methods. This balance is important to maintain the quality of the power supply by adjusting the frequency and voltage of the grid. Storage is the capture of the energy produced at a given time for later use. It is known that electricity cannot be stored directly unless it is stored in condenser batteries or in superconducting coils. Other methods of electricity storage presuppose the conversion of these into other forms of energy: mechanical storage, electrochemical storage. The optimization of RES operation and, implicitly, of the energy system implies the choice of a suitable conversion / storage system that must take into account a number of factors, such as: capacity and minimum storage time, loading and unloading conditions, minimum number of cycles download loading, power supply required by the storage system, system lifetime. It is not to be neglected the space required for the installation of the storage systems and their impact on the environment during their exploitation as well as during the post-use and recycling period. There are RES that contain natural storage systems (hydro-electric power plants and biomass and biogas generators). The article proposes an analysis of how to store electricity by approach a Pelton water-water-turbine hybrid system. The heat pump consumes electrical energy for action, producing a thermal effect. By integrating a system with Pelton water storage tank and turbine on the heat pump outlet circuit, the lost hydraulic energy can be recovered. The experimental hybrid system was made to develop HRES optimization models. Hybrid systems may exceed the limits of individual generators in terms of efficiency, economy, reliability and flexibility. An energy storage system can alleviate the problems associated with uncertainties and fluctuations from renewable sources. The large number of random variables and parameters in a hybrid energy system requires optimization to increase the efficiency of hybrid system components to achieve economic and technical benefits.

Bi-Level Volt-VAR Optimization to Coordinate Smart Inverters With Voltage Control Devices

Conservation voltage reduction (CVR) uses Volt-VAR optimization (VVO) methods to reduce customer power demand by controlling feeder's voltage control devices. The objective of this paper is to present a VVO approach that controls system's legacy voltage control devices and coordinates their operation with smart inverter control. An optimal power flow (OPF) formulation is proposed by developing linear and nonlinear power flow approximations for a three-phase unbalanced electric power distribution system. A bi-level VVO approach is proposed, where Level 1 optimizes the control of legacy devices and smart inverters using a linear approximate three-phase power flow. In Level 2, the control parameters for smart inverters are adjusted to obtain an optimal and feasible solution by solving the approximate nonlinear OPF model. Level 1 is modeled as a mixed integer linear program (MILP) while Level 2 as a nonlinear program with linear objective and quadratic constraints. The proposed approach is validated using 13-bus and 123-bus three-phase IEEE test feeders and a 329-bus three-phase PNNL taxonomy feeder. The results demonstrate the applicability of the framework in achieving the CVR objective. It is demonstrated that the proposed coordinated control approach help us to reduce the feeder's power demand by reducing the bus voltages; the proposed approach maintains an average feeder voltage of 0.96 p.u. A higher energy saving is reported during the minimum load conditions. The results and approximation steps are thoroughly validated using OpenDSS.

The Challenge of Energy Storage in Europe: Focus on Power to Fuel

Abstract The energy sector in the European market has been changing significantly over the last years. European Union (EU) energy strategy includes the EU low-carbon roadmap milestone, which indicates for 2020, a 20% reduction in carbon emissions, and a 20% EU-wide share for renewables, and by 2030 a 40% reduction in carbon emissions and 30% EU-wide share for renewables. The increased renewable energy sources (RES) penetration and their intermittent energy production have led to the emerging need for energy storage technologies. Especially in the European energy market, large-scale energy balancing with sustainable technologies with product flexibility and cost-effective operation are being investigated. The carbon capture and utilization (CCU) concept, as a means for low-carbon sustainable industries, is integrated in the energy storage technologies. The present paper addresses the integration of power to fuel concept in the energy storage sector with simultaneous emission reduction. Grid management, the scale, and the efficient operation of electrolyzers are the basis for the implementation of Power to Fuel technology. The use of surplus and/or low-cost electricity via water electrolysis to commute captured CO2 from industrial plants to versatile energy carriers such as methane and methanol is being investigated in the present paper. Shadow operation of fossil fuel power plants under minimum load conditions leads to optimized energy dispatch of the power plants and provides product flexibility in terms of electricity, grid services, and chemical production. The produced fuels can be used in highly efficient and well-established power systems and further used in the transportation sector or for covering heat demands. The energy efficiency of the different processes is presented and a comparison is made in terms of cost effective energy storage solutions via the simultaneous grid management optimization, the reduction of carbon dioxide, and the production of valuable chemicals. The cross-sectorial concept of the Power to Fuel is presented for Steel and Power industry for the case of methane and methanol production. A review of the U.S. and European markets is made for the application of Power to Fuel.

Evaluation of Strength of End Structures in Intermediate Rolling Stock of a Train During Train Collision Accidents

This evaluation deals with the structural design standard for rolling stock body structures from the viewpoint of the crashworthiness. Current Japanese Industrial Standard JIS E 7106 Code, which defines the minimum static loading conditions required to provide structural integrity of carbody structures for their normal operation, does not explicitly take the crashworthiness into account. Here, one of the detailed FE models for the end structures of EMUs, designed in accordance with the JIS E 7106 standard, was taken as an example, and numerical analysis was carried out under several irregular loading conditions such as the collision of end structures of intermediate rolling stock in a rake, caused by overriding or train set buckling occurring during train collision accidents. The results of the numerical analyses have shown some points that need to be resolved in terms of the strength of the super structures as well as draw gears around coupling devices.

Sedimentation Load Analysis Using ANN and GA

Artificial Neural Network (ANN) model is used to predict the suspended sediment load for the survey data collected on daily basis in the river Mahanadi. Genetic algorithm has been used to find the optimal level of process parameters such as water discharge and temperature for a minimum sedimentation load condition. Optimal level of process parameters obtained from the GA has been used in a trained neural network to obtain the sedimentation load condition. A comparative analysis is then made between GA and ANN for achieving minimum sedimentation load with the given process parameters.

Structure and paleoearthquake records of active submarine faults, Cook Strait, New Zealand: Implications for fault interactions, stress loading, and seismic hazard

A new interpretation of active faulting in central Cook Strait, New Zealand, reveals tectonic structures associated with the spatial transition from subduction to continental transform faulting. Marine seismic reflection profiles and multibeam bathymetric data indicate that there are no throughgoing crustal faults connecting the North Island Dextral Fault Belt and the Marlborough Fault System in South Island. The major faults terminate offshore, associated with 5–20 km wide step‐overs and a change in regional fault strike. This structure implies that propagation of strike‐slip earthquake ruptures across the strait is not probable. Faulted sedimentary sequences in the Wairau Basin (Marlborough shelf), correlated to glacioeustatic sea level cycles, provide a stratigraphic framework for fault analysis. A high‐resolution study of the postglacial (<20 ka) vertical displacement history of the Cloudy and Vernon faults reveals up to six and five paleoearthquakes since 18 ka, respectively. These long‐timescale records indicate variable recurrence intervals and possibly variable stress drop, thus conforming to the variable slip model of earthquake behavior. Integration of these data with other submarine and terrestrial paleoearthquake records indicates the presence of clustered earthquake sequences involving multiple faults. Different sequences do not always involve the same faults. It appears that earthquake clustering is driven by fault interactions that lead to specific loading conditions favoring the triggering of earthquakes on major faults in relatively short time intervals. Present‐day regional Coulomb stress distribution has been calculated in two scenarios considered to represent minimum and maximum loading conditions. The models, incorporating secular tectonic loading and stress changes associated with major crustal earthquakes, indicate high stress loading in a large part of central Cook Strait. These conditions may favor the triggering of future damaging earthquakes in this region.

Aerosol optical depth measurements in eastern China and a new calibration method

We present a new calibration method to derive aerosol optical depth (AOD) from the MultiFilter Rotating Shadowband Radiometer (MFRSR) under extremely hazy atmospheric conditions during the East Asian Study of Tropospheric Aerosols: an International Regional Experiment (EAST‐AIRE) and the Atmospheric Radiation Measurement (ARM) Mobile Facility (AMF) deployment in China. MFRSR measurements have been made at Xianghe since September 2004 and at Taihu and Shouxian since March and May 2008, respectively. Aerosol property retrievals from CIMEL Electonique, Paris, Sun and sky radiometers located at each site show that aerosol loading is substantial and highly variable during a given year (averaged daily AOD550 = 0.80 ± 0.14). The conventional application of the Langley method to calibrate the MFRSR is not possible at these sites because there is a dearth of stable atmospheric and low‐AOD conditions. To overcome this limitation of the traditional Langley plot method, highest irradiance values at a given air mass during a given period are used here. These highest values can represent the clear‐sky and minimum aerosol loading conditions. A scatterplot of the AOD estimated by this method with the CIMEL Sun and sky radiometer AOD shows very good agreement: correlation coefficients are on the order of 0.98–0.99, slopes range from 0.93 to 0.97, and offsets are less than 0.02 for the three sites. AOD and Ångström exponents were derived from application of the method to all MFRSR data acquired at the three sites. AOD values at 500 nm are τ500 = 0.99 ± 0.71 (α500–870 = 1.45 ± 0.59) at Xianghe, 0.87 ± 0.54 (1.14 ± 0.31) at Taihu, and 0.84 ± 0.43 (1.15 ± 0.28) at Shouxian. Anthropogenic aerosols appear to dominate in the study region with significant contributions from large dust particles and influence of hydroscopic growth.