Upstream Power Research Articles

Short-Term Multi-Objective Optimal Operation of Reservoirs to Maximize the Benefits of Hydropower and Navigation

Traditional reservoir operation mainly focuses on economic benefits, while ignoring the impacts on navigation. Thus, the economic operation of reservoirs considering navigational demands is of great significance for improving benefits. A navigation capacity evaluation method (NCEM), which evaluates the navigation capacity considering the influence of flow velocity and water level variation on navigation, is proposed to more effectively evaluate the navigation capacity. Based on two-dimensional hydrodynamic numerical simulation, the NCEM accurately calculates the navigation capacity according to detailed flow velocity and water level changes. In addition, a short-term multi-objective optimal operation model considering the upstream and downstream navigation and power generation is established. Then, the Strength Pareto Evolutionary Algorithm (SPEA2) is used to solve the model. To verify the rationality of the method and model, they are applied to the case study of the Xiangjiaba reservoir. The results demonstrate that the method and model can not only provide a series of operation schemes for decision makers of reservoirs, but also direct the ship to pass safely through the approach channel, implying a certain practical value and significance as a reference for the short-term optimal operation of reservoirs in the future.

Hybrid DFT-Spread OFDM-Digital Filter Multiple Access PONs for Converged 5G Networks

In this paper, we propose hybrid discrete Fourier transform (DFT)-spread orthogonal frequency division multiplexing (OFDM)-digital filter multiple access (DFMA) passive optical networks (PONs) for the first time to the best of our knowledge. In this case, digital filtering based on digital signal processing is applied to individual DFT-spread OFDM signals from various optical network units, and a single fast Fourier transform operation and its following data recovery processes are implemented in a pipelined approach in the optical line terminal. The proposed networks maintain all salient features associated with previously reported hybrid OFDM–DFMA PONs. More importantly, they additionally reduce the upstream signal peak-to-average power ratios by less than 2 dB. As a direct result, in comparison with the hybrid OFDM–DFMA PONs, the proposed PONs increase the upstream system power budget by more than 3 dB and reduce the minimum required digital-to-analog converter/analog-to-digital converter quantization bits by at least 1 bit.

Generation maintenance scheduling in virtual power plants

In an active network, as a virtual power plant (VPP), periodic maintenance of distributed generators (DGs) is critically vital for the reliable operation of the power system. To prevent unexpected failure of DGs and avoid deterioration of the grid's reliability, coordination of maintenance scheduling is indispensable. In this study, maintenance management of a VPP is proposed for scheduling the planned outage of DGs, in order to preserve their useful lifespan. In addition to conventional DGs and the upstream power grid, renewable generation including wind turbines and photovoltaic systems, energy storage systems, and curtailable loads are considered as components of the VPP. The proposed maintenance scheduling scheme provides different advantages in viewpoints of cost and reliability. Moreover, risk management is also investigated to lower the risk of maintenance scheduling due to the uncertainty in price in an energy market by adopting the conditional value at risk as a measure of risk. The overall cost is minimised considering the power loss in the grid as well as the security constraints such as DGs operational constraints, voltage magnitude, and transmission lines’ power flow limit. The effectiveness of the proposed scheme is illustrated using numerical studies with short- and long-term scheduling.

Online generalized droop-based demand response for frequency control in islanded microgrids

Frequency stability, as one of the most important issues in the modern power grids, requires more efficient control methods due to the increasing complexity of the power system, high penetration of distributed generation sources as well as high electrical energy consumption. The challenges become more critical in the case of islanded microgrids (MGs), due to existing no traditional ancillary services of the upstream electric power network. Thus, the modern power grids, such as MGs, need advanced regulation methods to keep the generation-consumption balancing. Demand response (DR) is the recently introduced control approach which guarantees continuous contribution of controllable loads in the system frequency control. In this paper, a new online droop-based DR, generalized droop control (GDC), is introduced to apply in islanded MGs frequency control. An artificial neural network is used for online tuning of droop coefficients in the presented GDC framework. The proposed control approach changes controllable active and reactive loads, using a set of equations based on satisfying dynamics. To evaluate the effectiveness of the proposed control method, several scenarios are simulated in which changes of the system frequency and voltage are studied. Results show significant damping of power–frequency fluctuation and a desirable performance of the closed-loop system.

On Outsourced Abatement Services: Market Power and Efficient Regulation

In this paper, we consider competitive polluting firms that outsource their abatement activity to an upstream imperfect competitive eco-industry to comply with environmental regulation. In this case, we show that an usual environmental policy based on a Pigouvian tax or a pollution permit market reaches the first-best outcome. The main intuition is based on the idea that purchasing pollution reduction services instead of pollution abatement inputs modifies for each potential tax rate (or out of the equilibrium permit price) the nature of the arbitrage between pollution and abatement. This induces a demand for abatement services which is, at least partially, strongly elastic and therefore strongly reduces upstream market power. This argument is first illustrated with an upstream monopoly selling eco-services to a representative polluting firm under a usual Pigouvian tax. We then progressively extend the result to permit markets, heterogeneous downstream polluters and heterogeneous upstream Cournot competitors. JEL Codes: Q58, D43

Influence of Deep-Sea Ambient Conditions in the Performance of Pressure-Compensated Induction Motors

AbstractUnderstanding the influence of low temperature and high hydrostatic pressure in the starting performance of deep-sea pressure-compensated (PC) induction motors is essential for sizing of the motor and upstream power systems. This paper presents the observations from experiments carried out on industry-standard 3000-V rated deep-sea PC induction motors of 30- and 60-kW capacities in a hyperbaric chamber. It is identified that the motors consume about 30% of their rated power when started at a pressure of 600 bar and a temperature of 2°C. The results could be used for sizing of deep sea electric motors taking into consideration the increased starting power requirements due to the viscous drag of the PC fluid and to design PC oil viscosity management systems.

Stationarity of I-mode operation and I-mode divertor heat fluxes on the ASDEX Upgrade tokamak

Recent I-mode investigations from the ASDEX Upgrade tokamak are reported. It is shown that neutral-beam-injection heated I-modes can be stationary, which is important in terms of extrapolability towards future fusion devices. Furthermore, detailed studies on the weakly coherent mode are reported. In particular, experimental observations point towards its existence in L-mode, before I-mode starts. Moreover, its impact on density and temperature fluctuations is evaluated. Studies of stationary divertor heat fluxes show that in I-mode, the upstream power fall-off length is between those observed in L-mode and H-mode, and it is connected to the scrape-off layer temperature fall-off length. Moreover, analysis of transient divertor heat loads shows that intermittent turbulent events, observed in the confinement region and linked to the weakly coherent mode, are responsible for a significant part of divertor heat loads.

Nonlinearity Analysis and Multi-Model Modeling of an MEA-Based Post-Combustion CO2 Capture Process for Advanced Control Design

The monoethanolamine (MEA)-based post-combustion CO2 capture plant must operate flexibly under the variation of the power plant load and the desired CO2 capture rate. However, in the presence of process nonlinearity, conventional linear control strategy cannot achieve the best performance under a wide operation range. Considering this problem, this paper systematically studies the multi-model modeling of the MEA-based CO2 capture process for the purpose of (1) implementing well-developed linear control techniques to the design of an advanced controller and (2) achieving a wide-range flexible operation of the CO2 capture process. The local linear models of the CO2 capture process are firstly established at given operating points using the method of subspace identification. Then the nonlinearity distribution at different loads of an upstream power plant and different CO2 capture rates is investigated via the gap metric. Finally, based on the nonlinearity investigation results, the suitable linear models are selected and combined together to form the multi-model system. The proposed model is validated using the measurement data, which is generated from a post-combustion CO2 capture model developed in the go-carbon capture and storage (gCCS) simulation platform. As the proposed multi-linear model has a simple mathematical expression and high prediction accuracy, it can be directly employed as the control model of a practical advanced control strategy to achieve a wide operating range control of the CO2 capture process.

Experimental results of transient testing at the amine plant at Technology Centre Mongstad: Open-loop responses and performance of decentralized control structures for load changes

Flexible operation of combined cycle thermal power plants with chemical absorption post combustion CO2 capture is a key aspect for the development of the technology. Several studies have assessed the performance of decentralized control structures applied to the post combustion CO2 capture process via dynamic process simulation, however there is a lack of published data from demonstration or pilot plants. In this work, experiments on transient testing were conducted at the amine plant at Technology Centre Mongstad, for flue gas from a combined cycle combined heat and power plant (3.7–4.1 CO2 vol%). The experiments include six tests on open-loop responses and eight tests on transient performance of decentralized control structures for fast power plant load change scenarios.The transient response of key process variables to changes in flue gas volumetric flow rate, solvent flow rate and reboiler duty were analyzed. In general the process stabilizes within 1 h for 20% step changes in process inputs, being the absorber column absorption rates the slowest process variable to stabilize to changes in reboiler duty and solvent flow rate. Tests on fast load changes (10%/min) in flue gas flow rate representing realistic load changes in an upstream power plant showed that decentralized control structures could be employed in order to bring the process to desired off-design steady-state operating conditions within (<60 min). However, oscillations and instabilities in absorption and desorption rates driven by interactions of the capture rate and stripper temperature feedback control loops can occur when the rich solvent flow rate is changed significantly and fast as a control action to reject the flue gas volumetric flow rate disturbance and keeping liquid to gas ratio or capture rate constant.

Flexible operation of post-combustion solvent-based carbon capture for coal-fired power plants using multi-model predictive control: A simulation study

Solvent-based post-combustion CO2 capture plant has to be operated in a flexible manner because of its high energy consumption and the frequent load variation of upstream power plants. Such a flexible operation brings out two objectives for the control system: i) the system should be able to change the CO2 capture rate quickly and smoothly in a wide operating range; ii) the system should effectively remove the disturbances from power plant flue gas. To achieve these goals, this paper proposed a multi-model predictive control (MMPC) strategy for solvent-based post-combustion CO2 capture plant. Firstly, local models of the CO2 capture plant at different operating points are identified through subspace identification method. Nonlinearity analysis of the plant is then performed and according to the results, suitable local models are selected, on which the multi-model predictive controller is designed. To enhance the flue gas disturbance rejection property of the CO2 capture plant and attain a better adaption to the power plant load variation, the flue gas flow rate is considered in the local model identification as an additional measured disturbance, thus the predictive controller can calculate the optimal control input even in the case of flue gas flow rate variation. Simulation results on an MEA-based CO2 capture plant developed on gCCS show the effectiveness and advantages of the proposed MMPC controller over wide range capture rate variation and power plant flue gas variation.

An Empirical Analysis of Countervailing Power in Business-to-Business Bargaining

Pricing schemes in business-to-business (B2B) relationships reflect price discrimination and bargaining over rents. Bargaining outcomes are determined by upstream market power and countervailing buyer power downstream. This paper uses a panel of B2B transactions in the UK brick market to study B2B transaction prices. The empirical analysis identifies three effects on prices: nonlinear volume and freight absorption effects; countervailing power effects that arise from buyers’ local commercial significance; and competition effects that are due to the buyers’ local potential suppliers. And it shows that small buyers benefit more from competition than do large buyers because they are not constrained by the suppliers’ capacity.

Anti-Stokes contribution to the SBS Stokes gain in remotely seeded bidirectional NG-PON systems.

We assess the importance of Stimulated Brillouin scattering (SBS) anti-Stokes wave on reflection tolerance in remotely seeded wavelength-division multiplexing passive optical networks (WDM PON). Experimental validation of the extended model for the externally seeded SBS is presented towards assessing the conditions in which the anti-Stokes contribution becomes relevant in the variant scenario of remotely carrier-seeded PON. We identify relevant operating conditions in which the latter can no longer be reliably neglected, and analyze the remote seed power budget implications of such contribution. Considering typical launch powers in PON systems we found that, even for seed launch powers below SBS threshold, non-optimized upstream (US) power spectral density may lead to a considerable anti-Stokes contribution to the SBS gain. In effect, in order to maintain a reference optical return loss (ORL) of 32 dB in such scenario, anti-Stokes wave contribution imposed rigorous remote seed power budget restrictions depending on fiber parameters.

Increased Wind Energy Yield and Grid Utilisation with Continuous Feed-In Management

This paper presents a study to assess how wind turbines could increase their energy yield when their grid connection point is not strong enough for the rated power. It is state of the art that in such situations grid operators impose feed-in management on the affected wind turbines, i.e., the maximum power is limited. For this study a 5 MW wind turbine is introduced in a small grid that has only limited power transfer capabilities to the upstream power system. Simulations of one particular day are conducted with the electric load, the temperature, and the wind speed as measured on that day. This simulation is conducted twice: once with the 5 MW wind turbine controlled with conventional feed-in management, and a second time when its power is controlled flexibly, i.e., with continuous feed-in management. The results of these two simulations are compared in terms of grid performance, and in terms of mechanical stress on the 5 MW wind turbine. Finally, the conclusion can be drawn that continuous feed-in management is clearly superior to conventional feed-in management. It exhibits much better performance in the grid in terms of energy yield and also in terms of constancy of voltage and temperature of grid equipment. Although it causes somewhat more frequent stress for the wind turbine, the maximum stress level is not increased.

Corrective receding horizon scheduling of flexible distributed multi-energy microgrids

The goal of the paper is to provide a comprehensive operational flexibility evaluation of different Multi-energy Microgrid (MEM) options. This is done by incorporating Mixed Integer Liner Programming (MILP) model for annual simulations and expanding it with Receding Horizon Model Predictive Control (RH-MPC) algorithm for short term daily operational analyses. The model optimizes flows of various energy vectors: heat, fossil fuels (natural gas), cooling and electricity, coordinating different microgrid elements with the goal of serving final consumer needs and actively participating in energy markets.The second novelty of the work is in the approach to multi-energy operational flexibility assessment, capturing different technologies, MEM configurations and different modelling concepts. When MEM is connected to the upstream power system its flexibility manifests as capability to alleviate variability and uncertainty in local production of RES and demand. On the other hand, when operating isolated from the rest of the system, the main flexibility indicator is minimum waste of energy while ensuring the satisfaction of all demand needs (electrical and heating/cooling). Following on this, multiple MEM configurations have been analyzed, showing different levels of available flexibility and capability to follow scheduled day-ahead exchange with the rest of the system, but also different amounts of wasted/curtailed energy in off-grid mode. Additionally, detailed analyses are performed concerning algorithm approximations which are often introduced in MEM modelling, such as efficiency of generation units. While these approximations have smaller impact on annual operational flexibility assessment (the difference is around 2–5% in terms of total cost), the result clearly show their significant impact on daily operational flexibility estimates.

Turbulence analysis and multiscale correlations between synchronized flow velocity and marine turbine power production

The correlation between the flow turbulence and the performances of a marine current turbine is studied. First, the incoming flow encountered in the flume tank is characterized in the framework of fully developed turbulent cascades in the inertial range. The Reynolds number, the Kolmogorov dissipation scale and the integral scale, are estimated from flow measurements. The intermittency of the turbulence is characterized in the lognormal multifractal framework, and the influence of the turbulent flow on the turbine power is assessed.The rotor speed control unit characteristics used for the turbine regulation induces non-negligible effects on the turbine behavior under fluctuations loads. Even if the power spectrum does not reveal any scale invariance, a multiscale analysis allows us to show the correlations between the turbulence time series and the power produced. The classical Mean Square Coherency function shows that for scales larger than 10 s, the upstream velocity and power have large correlations. In the framework of the Empirical Mode Decomposition method, such correlations are studied using the time-dependence intrinsic correlation analysis method. This method allows to zoom into time-frequency scales where the flow perturbations induced some modifications in power production.

Physical effects of thermal pollution in lakes

AbstractAnthropogenic heat emissions into inland waters influence water temperature and affect stratification, heat and nutrient fluxes, deep water renewal, and biota. Given the increased thermal stress on these systems by growing cooling demands of riparian/coastal infrastructures in combination with climate warming, the question arises on how to best monitor and manage these systems. In this study, we investigate local and system‐wide physical effects on the medium‐sized perialpine Lake Biel (Switzerland), influenced by point‐source cooling water emission from an upstream nuclear power plant (heat emission ∼700 MW, ∼18 W m−2 lake wide). We use one‐dimensional (SIMSTRAT) and three‐dimensional (Delft3D‐Flow) hydrodynamic numerical simulations and provide model resolution guidelines for future studies of thermal pollution. The effects on Lake Biel by the emitted excess heat are summarized as: (i) clear seasonal trend in temperature increase, locally up to 3.4°C and system‐wide volume mean ∼0.3°C, which corresponds to one decade of regional surface water climate warming; (ii) the majority of supplied thermal pollution (∼60%) leaves this short residence time (∼58 days) system via the main outlet, whereas the remaining heat exits to the atmosphere; (iii) increased length of stratified period due to the stabilizing effects of additional heat; (iv) system‐wide effects such as warmer temperature, prolonged stratified period, and river‐caused epilimnion flushing are resolved by both models whereas local raised temperature and river short circuiting was only identifiable with the three‐dimensional model approach. This model‐based method provides an ideal tool to assess man‐made impacts on lakes and their downstream outflows.

Supply Chain Power Configurations and Their Relationship with Performance

To lay the foundation for the study of supply chain power, we study power configurations at the level of interlocking power dyads (IPDs), viewing the simultaneous effect of upstream and downstream power. We build on four key constructs: dependence asymmetry (resource dependence theory), joint dependence (embeddedness perspective), power type differential (based on French &amp; Raven, 1959), and power source asymmetry. We examine the research question of what the relationship is betweenIPDs and the focal firm's operational performance, developing hypotheses based on the dependence asymmetry, joint dependence, power type differential, and power source asymmetry of theoreticalIPDs. A survey of over 600 respondents in China was used to collect data on focal firm perceptions of upstream and downstream power, with cluster analysis yielding eightIPDs. Inferential analysis revealed the importance of joint dependence, dependence asymmetry, power type differential, and power source asymmetry to the operational performance of the focal firm.

Hybrid optical wavelength demultiplexer and power combiner for TWDM PON

In this paper, we have proposed a hybrid optical wavelength demultiplexer and power combiner for a hybrid time- and wavelength-division multiplexing (TWDM) passive optical network (PON), i.e., a single passive optical device that functions as a 1×N wavelength demultiplexer for distributing the downstream signal in multiple wavelengths from the optical line terminal (OLT) to the N optical network units (ONUs), and simultaneously as an N×1 power combiner for collecting the upstream signal in the same wavelength from the N ONUs to the OLT. Through a design example of a 32 channel hybrid optical wavelength demultiplexer and power combiner on the silicon-on-insulator platform, our numerical simulation result shows that the insertion loss and adjacent channel crosstalk of the downstream wavelength demultiplexer are as low as 4.6 and −16.3 dB, respectively, while the insertion loss and channel non-uniformity of the upstream power combiner can reach 3.5 and 2.1 dB, respectively. The proposed structure can readily be extended to other material platforms such as the silica-based planar lightwave circuit. Its fabrication process is fully compatible with standard clean-room technologies such as photo-lithography and etching, without any complicated and/or costly approach involved.

Maximizing hosting capacity of renewable energy sources in distribution networks: A multi-objective and scenario-based approach

Due to the development of renewable energy sources (RESs), maximization of hosting capacity (HC) of RESs has gained significant interest in the existing and future power systems. HC maximization should be performed considering various technical constraints like power flow equations, limits on the distribution feeders' voltages and currents, as well as economic constraints such as the cost of energy procurement from the upstream network and power generation by RESs. RESs are volatile and uncertain in nature. Thus, it is necessary to handle their inherent uncertainties in the HC maximization problem. Wind power is now the fastest growing RESs around the world. Hence, in this paper a stochastic multi-objective optimization model is proposed to maximize the distribution network's HC for wind power and minimize the energy procurement costs in a wind integrated power system. The following objective functions are considered: 1) Cost of the purchased energy from upstream network (to be minimized) and 2) Operation and maintenance cost of wind farms. The proposed model is examined on a standard radial 69 bus distribution feeder and a practical 152 bus distribution system. The numerical results substantiate that the proposed model is an effective tool for distribution network operators (DNOs) to consider both technical and economic aspects of distribution network's HC for RESs.

Reactive Power Dispatch Method in Wind Farms to Improve the Lifetime of Power Converter Considering Wake Effect

In wind farms (WF), the most popular and commonly implemented active power control method is the maximum power point tracking (MPPT). Due to the wake effect, the upstream wind turbine (WT) in WFs has more active power generation than the downstream WT at the wind directions and wind speeds that the WF has wake loss. In the case that WTs support the voltage control by reactive power, the upstream WT's power converter may have shorter lifetime even below the industrial standard. In this paper, based on the analysis of the wake effect, the reactive power capability of the doubly fed induction generator (DFIG) WT, and the lifetime of the DFIG WT's power converter, a reactive power dispatch method is proposed in the WF with DFIG WTs to improve the lifetime of the upstream WT's power converter. The proposed reactive power dispatch method is analyzed and demonstrated by the simulation on a WF with 80 DFIG WTs. It can be concluded that, compared with the traditional reactive power dispatch method, the proposed method can increase the lifetime of the upstream WT's power converter.