Rapid Load Variations Research Articles

STEAM Experimental Facility: A Step Forward for the Development of the EU DEMO BoP Water Coolant Technology

Within the EUROfusion roadmap for the technological development of the European-DEMOnstration (EU-DEMO) reactor, a key point has been identified in the discontinuous operation (pulse-dwell-pulse) of the machine. Water Cooled Lithium Lead (WCLL) Breeding Blanket (BB) Primary Heat Transfer Systems (PHTSs) adopt technology and components commonly used in nuclear fission power plants, whose performances could be negatively affected by the above mentioned pulsation, as well as by low-load operation in the dwell phase. This makes mandatory a full assessment of the functional feasibility of such components through accurate design and validation. For this purpose, ENEA Experimental Engineering Division at Brasimone R.C. aims at realizing STEAM, a water operated facility forming part of the multipurpose experimental infrastructure Water cooled lithium lead -thermal-HYDRAulic (W-HYDRA), conceived to investigate the water technologies applied to the DEMO BB and Balance of Plant systems and components. The experimental validation has the two main objectives of reproducing the DEMO operational phases by means of steady-state and transient tests, as well as performing dedicated tests on the steam generator aiming at demonstrating its ability to perform as intended during the power phases of the machine. STEAM is mainly composed of primary and secondary water systems reproducing the thermodynamic conditions of the DEMO WCLL BB PHTS and power conversion system, respectively. The significance of the STEAM facility resides in its capacity to amass experimental data relevant for the advancement of fusion-related technologies. This capability is attributable to the comprehensive array of instruments with which the facility will be equipped and whose strategic location is described in this work. The operational phases of the STEAM facility at different power levels are presented, according to the requirements of the experiments. Furthermore, a preliminary analysis for the definition of the control strategy for the OTSG mock-up was performed. In particular, two different control strategies were identified and tested, both keeping the primary mass flow constant and regulating the feedwater mass flow to follow a temperature set-point in the primary loop. The obtained numerical results yielded preliminary feedback on the regulation capability of the DEMO steam generator mock-up during pulsed operation, showing that no relevant overtemperature jeopardized the facility integrity, thanks to the high system responsivity to rapid load variations.

Advanced adaptive algorithm controlled single‐phase DSTATCOM operation during weak grid conditions

SummaryThis paper presents the performance of a single‐phase utility‐tied distribution static compensator (DSTATCOM) with nonlinear load operating under weak grid conditions. The DSTATCOM is controlled by a complex kernel risk‐sensitive p‐power (CKRSP) algorithm. Ever‐increasing nonlinearity of the load, rapidly increasing renewable energy system installed capacity, and rising heating loads, especially during the winter season, lead to various power quality issues that worsen during weak grid conditions. An advanced adaptive control scheme, that is, CKRSP, enforces the system to perform various multifaceted operations, including harmonics suppression, handling rapid load variations, voltage sag and swell, and active and reactive power control at the point of common coupling (PCC) during weak grid conditions. The proposed CKRSP algorithm outperforms conventional control algorithms regarding steady‐state error, convergence speed, and accuracy. During weak grid conditions, the proposed system ensures stable DC bus voltage with a reduced second harmonic component. This further assists the CKRSP control in better extracting the fundamental load current component using a smoother loss component of current . The proposed system can handle various power quality issues during weak grid conditions while ensuring the overall system's stability. The laboratory prototype results show that the presented system performs satisfactorily under weak grid conditions per IEEE 519‐2014 standards.

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.

Measurement and analysis of vibrations of electric motors on board container ships

The purpose of this paper is to measure and analysis the vibrations of electric motors on board container ships, in order to reduce the maintenance costs and implicitly in making the optimal decisions. In general, the faults that underlie electric motors are primarily due to mechanical and electrical efforts. Mechanical stresses occur as a result the overloads and rapid load variations. On the other hand, the overcurrents and overvoltages are usually in the close accordance with the power supplies. In this regard the mechanical faults cannot be analyzed by changing the parameters like voltage, current, power, frequency but in practice we can do analysis by used the high-performance testers with intelligent software for measuring the motor vibrations. The MarVib DC650 tester was used in this paper for analysis and measurement the vibrations of electric motors.

Flow Characteristics of Preliminary Shutdown and Startup Sequences for a Model Counter-Rotating Pump-Turbine

Pumped Hydropower Storage (PHS) is the maturest and most economically viable technology for storing energy and regulating the electrical grid on a large scale. Due to the growing amount of intermittent renewable energy sources, the necessity of maintaining grid stability increases. Most PHS facilities today require a geographical topology with large differences in elevation. The ALPHEUS H2020 EU project has the aim to develop PHS for flat geographical topologies. The present study was concerned with the initial design of a low-head model counter-rotating pump-turbine. The machine was numerically analysed during the shutdown and startup sequences using computational fluid dynamics. The rotational speed of the individual runners was decreased from the design point to stand-still and increased back to the design point, in both pump and turbine modes. As the rotational speeds were close to zero, the flow field was chaotic, and a large flow separation occurred by the blades of the runners. Rapid load variations on the runner blades and reverse flow were encountered in pump mode as the machine lost the ability to produce head. The loads were less severe in the turbine mode sequence. Frequency analyses revealed that the blade passing frequencies and their linear combinations yielded the strongest pulsations in the system.

An automated strategy for gas turbines off-design predictions with a CFD-based throughflow method

Abstract With the increasing importance of renewable energy sources in the power generation scenario, traditional fossil-fuel power generation systems are subjected to relevant and rapid load variations. Consequently, designers have become more and more interested at predicting the transient behavior of fossil fuel power plants. Tools allowing off-design performance predictions of turbomachines have consequently become desirable even in the first design phases. The paper presents the development of a strategy for gas turbines off-design analyses that exploit a novel CFD-based throughflow method, and its application to a heavy-duty, medium size, F-Class, 4-stage gas turbine designed and manufactured by Ansaldo Energia. The throughflow code is based on the axisymmetric Euler equations with tangential blockage and body forces, and inherits its numerical scheme from a state-of-the-art CFD solver (TRAF code), including real-gas capabilities. The strategy starts from the calibration of the throughflow method in order to match the results of 3D CFD analyses at design point, whereupon the computational framework is frozen and used for off-design simulations. The proposed methodology is fairly general and will be discussed in details in the paper. The analysed operating conditions of the turbine encompass a wide range of expansion ratios and corrected rotational speeds. The feasibility of the procedure is assessed by a detailed comparison with 3D CFD results in terms of span-wise distributions and performance figures. It will be shown how the generality and reliability of the proposed method demonstrates its feasibility for an intensive use in the design of gas turbines. In particular, throughflow predictions can compete with the ones provided by state-of-the-art 3D CFD approaches and can be obtained with a small fraction of the computational time.

Assessment of maximum power point trackers performance using direct and indirect control methods

The direct and indirect control methods are commonly used for maximum power point tracker (MPPT) of photovoltaic (PV) systems. Due to the absence of the literature that assess their performance in a comprehensive way, this work attempts to analyze the effectiveness of both control methods for the perturb and observe (P&O) MPPT algorithm. The MATLAB/Simulink simulation is verified experimentally using a PV array simulator and the dSPACE DS1104 DSP board driving a buck-boost converter. The results show that the indirect method exhibits lower steady-state oscillation and is less sensitive to rapid irradiance change and load variations. It increases the steady-state efficiency by 1.6%. Furthermore, under irradiance and load step changes, the transient efficiency increases by 29% and 30%, respectively. Based on these findings, it is envisaged that the indirect method is more suitable to be used as the controller in conjunction with the MPPT algorithm.

Oxy-CFB combustion technology for use in power-generation applications

Implementation of circulating fluidized bed (CFB) boilers in the energy sector has witnessed a steady increase owing to their afforded advantages of operational flexibility in terms of compliance with several low-grade fuels and in-situ DeSOx and DeNOx capabilities. In recent years, the rise in global warming and development of intermittent power-generation technologies have stressed the need for development of techniques to afford high-efficiency low-emission (HELE) power-generation, effective carbon capture and storage, and flexible operation of thermal power plants. To meet these demands, the Future Energy Plant Convergence Research Center (FEP CRC) has investigated oxy-combustion technologies for CFB boilers that use low-grade fuels with calorific values <5000 kcal/kg while maintaining high operational efficiency and low pollutant emission. Of key interest in this study is the operation of the proposed system under rapid load variations over a wide operating range, including an oxy-combustion test with high oxygen concentration more than 40% within oxidants. Efforts in this regard are underway through pilot experiments performed using demonstration-scale facilities and multidimensional numerical simulations. Additionally, studies have been performed to identify materials for use in the said high-efficiency boilers and develop techniques for exhaust-system water recovery. In this paper, the current conclusions from the research activities of FEP CRC will be presented.

A Third-Order Super-Twisting Extended State Observer for Dynamic Performance Enhancement of Sensorless IPMSM Drives

In practice, sensorless drive systems of interior permanent magnet synchronous motors (IPMSMs) are usually working in highly utilized conditions where fast changing uncertain loads, inverter losses, magnetic saturation, and other disturbance exist. These issues can reduce the performance and stability, which become the main vulnerability of sensorless drives. Linear extended state observer (LESO) or quadrature-phase-locked loop is conventionally adopted to estimate the speed and position. Without compensation or adaptive methods, fast changing uncertainties cannot be observed thoroughly. In this article, a third-order super-twisting extended state observer (STESO) is proposed to enhance the dynamic performance of position and speed estimation for IPMSM. Utilizing the high-order extended state and super-twisting algorithm, fast convergence and disturbance estimation can be achieved in STESO. The effectiveness and stability of STESO are analyzed and an optimized parameter selection method is presented. Comparative experimental results between the LESO and STESO verify the effectiveness and improvement of the proposed STESO against rapid speed and load variations.

Design and Control of Coupled Inductor DC–DC Converters for MVDC Ship Power Systems

This paper deals with the design and control aspects of modern ship power systems within the paradigm of an all-electric ship. The widespread use of power electronic converters is central in this context due to the technological advances in automation systems and the integration of the electrical propulsion systems and other components, such as electrical energy storage systems and renewable energy sources. The issue to address in this scenario is related to the request of increased performances in dynamic operation while pursuing advantages in terms of energy savings and overall system security. In addition, the presence of large load changes requires providing robustness of the control in terms of system stability. This paper is focused on medium voltage direct current (MVDC) ship power systems and the design and control of coupled inductor DC–DC converters. The load is handled in terms of a constant power model, which generally is considered the most critical case for testing the stability of the system. The robustness of the design procedure, which is verified numerically against large and rapid load variations, allowed us to confirm the feasibility and the attractiveness of the design and the control proposal.

Fatigue Lifetime Estimation of a Heater in Coal-Fired Power Plants Under a Flexible Operational Framework-Regulating Extraction Steam of High-Pressure Heaters

Although rapid load variation of coal-fired power plants has become a prior objective for improving the operational flexibility, it will cause a lifetime reduction of heaters due to alternating stresses during transient processes. In the paper, among four flexible regulating measures, the dynamic characteristics of thermal parameters were obtained by GSE software, and thermo-mechanical stresses of 1# high-pressure (HP) heater were calculated by Finite Element Analysis, then the fatigue lifetimes of 1# HP heater were estimated and compared. It turns out that the most stressed position is at water chamber baffle, the allowable numbers of cycles at four measures are 5913-9419, and fatigue damage ratios for per cycle are 0.0106-0.0169%. The study can provide a detailed reference for operators to ensure the operational security of coal-fired power plants within flexibility frameworks.

A Multiagent-Based Game-Theoretic and Optimization Approach for Market Operation of Multimicrogrid Systems

This paper proposes a multiagent-based energy market for multimicrogrid systems using game-theoretic and hierarchical optimization approaches. The proposed method is tailored to achieve the optimal operation of smart microgrids in distribution systems. Because of rapid load variations in distribution systems, it is necessary to develop fast optimization algorithms which minimize the power mismatch in and among microgrids. In this paper, a three-level market framework is proposed. The first level comprises a game-theoretic double-auction mechanism for the day-ahead market while the next two levels are optimal rescheduling and intermicrogrid reverse auction model for the hour-ahead and real-time markets, respectively. Using the hierarchical optimization algorithm in a multiagent-based area, it is anticipated to not only minimize the optimization solution time, but also reduce the dependency on the network in grid-connected mode or load shedding in islanded mode. Using this approach, load demand response capabilities along with rescheduling of Distributed Energy Storage Systems and distributed generations could be utilized in all market levels, which will lead to optimal operation of multimicrogrid systems. Agents are developed in DIgSILENT PowerFactory and dynamic data exchange is activated for communication among agents communicating through a data distribution service which utilizes the real-time publish-subscribe communication protocol. The developed framework is applied to the modified 37-bus IEEE distribution test feeder system to validate the effectiveness of this market structure.

Control of Spray Evaporative Cooling in Automotive Internal Combustion Engines

A novel approach is proposed for precise control of two-phase spray evaporative cooling for thermal management of road vehicle internal combustion (IC) engines. A reduced-order plant model is first constructed by combining published spray evaporative cooling correlations with approximate governing heat transfer equations appropriate for IC engine thermal management. Control requirements are specified to allow several objectives to be met simultaneously under different load conditions. A control system is proposed and modeled in abstract form to achieve spray evaporative cooling of a gasoline engine, with simplifying assumptions made about the characteristics of the coolant pump, spray nozzle, and condenser. The system effectiveness is tested by simulation to establish its ability to meet key requirements, particularly concerned with precision control during transients resulting from rapid engine load variation. The results confirm the robustness of the proposed control strategy in accurately tracking a specified temperature profile at various constant load conditions, and also in the presence of realistic transient load variation.

A Variable Current-Limit Control Scheme for a Bi-directional Converter used in Ultracapacitor Applications

In ultracapacitor applications, generally, a bi-directional converter is connected to a DC bus and is designed to compensate rapid load variations on the bus. During transient phases, overloaded DC bus can push the converter out of its operating limits. For providing the necessary power, converters should be put in parallel, while each converter is limited into its optimal operating range. In a boost converter, this operating limit can be related to the inductor current and UC voltage. In this study, a variable current-limit is proposed for inductor current which then determines the operating range of the boost converter. This method will provide stability of the converter during overload transients. An experimental setup consisting of a bi-directional converter, a controllable load/source, and an ultracapacitor is presented, to validate the proposed method. Several scenarii are applied to analyze the performance of the system in overloaded phases and theoretical and experimental results are presented.

Critical investigations on performance of ANN and wavelet fault classifiers

With increasing demands and competitive business environment, the structure of power system has become very complex. Moreover, power system is a dynamic framework due to faults and rapid load variations. Hence, the detection algorithms for faults are potential areas of research. To discuss this issue and to provide the solution methodology for detection of faults and further classification of those in a smart grid is a primary motivation of this manuscript. This paper presents application of supervised learning algorithms based on different neural network topologies for detection and classification of the faults in transmission lines in power system. Different wavelet transforms on different Multi Resolution Analysis levels are applied for detection of the potential features from the voltage waveforms of the Phasor Measurement Units (PMUs). These wavelet transforms are then applied to several neural networks classification engines to classify faults. Binary classification technique is used for definitions of faults. Different faults namely single line to ground, line to line, double line to ground and three phase symmetrical faults are designated as a binary digit. These definitions are employed to train the classification engine. Different plots of confusion and errors are plotted to establish a fair comparison between supervised learning algorithms.

LTE: A procedure to predict power plants dynamic behaviour and components lifetime reduction during transient operation

The liberalization of the European energy markets combined with the rapid spread of unpredictable renewable energy sources have stressed the need of improving the traditional power units flexibility. Fast start-ups/shut downs and rapid load variations have become priority objectives because they guarantee high profits in the short term but cause a lifetime reduction due to thermo-mechanical fatigue, creep and corrosion. To this purpose, in the present work, an innovative procedure, able to predict the power plant dynamic behaviour during load variations, identify the most stressed components and estimate their lifetime reduction is presented and tested. Being combined cycles the most efficient, flexible and widespread technologies, the selected test case is a 380MW combined cycle unit. To predict the plant dynamic performance a dynamic model has been built in Modelica language and several transient conditions investigated. The high pressure steam drum and superheater are the most stressed components. Results show a 52.9% reduction in superheater collectors life if the load variation is 50% faster than the reference case. On the contrary, a 35.8% lifetime increase is observed if the load variation is 50% slower. For the same conditions the high pressure steam drum life is reduced by 31.9% and increased by 16.3%, respectively. Also the superheater tube bank lifetime reduction is computed. The proposed procedure can be considered a valuable innovative tool to assist power plant designers and operators.

Load governor based on constrained extremum seeking for PEM fuel cell oxygen starvation and compressor surge protection

Polymer Electrolyte Membrane Fuel Cells (PEMFC) are extremely sensitive to load variations. A rapid load variation can damage the system in many ways. For this reason, a Load Governor (LG) based on constrained Extremum Seeking (ES) approach has been proposed in this paper. The LG controller ensures that the physical constraints of the system are not violated and the ES controller varies the LG bandwidth parameter to optimize the net power output. The proposed controller has been tested on a Hardware-In-Loop (HIL) emulation test bench, based on a commercial centrifugal compressor and a real time PEMFC emulator. Experimental results show a good performance of the proposed scheme during load variations.

Optimal Voltage Regulation Method for Distribution Systems with Distributed Generation Systems Using the Artificial Neural Networks

With the development of industry and the improvement of living standards, better quality in power electric service is required more than ever before. This paper deals with the optimal algorithms for voltage regulation in the case where Distributed Storage and Generation (DSG) systems are operated in distribution systems. It is very difficult to handle the interconnection issues for proper voltage managements, because the randomness of the load variations and the irregular operation of DSG should be considered. This paper proposes the optimal on-line real time voltage regulation methods in power distribution systems interconnected with the DSG systems. In order to deliver suitable voltage to as many customers as possible, the optimal sending voltage should be decided by the effective voltage regulation method by using artificial neural networks to consider the rapid load variation and random operation characteristics of DSG systems. The simulation results from a case study show that the proposed method can be a practical tool for the voltage regulation in distribution systems including many DSG systems.

Operation Strategy for Solid Oxide Fuel Cell Systems for Small-Scale Stationary Applications

Solid oxide fuel cell micro-cogeneration systems have the potential to reduce domestic energy consumption by providing both heat and power onsite without transmission losses. The high-grade heat produced during the operation of the power causes high thermal transients during the startup/shutdown phases and degrades the fuel cells. To counteract the degradation, the system should not be stressed with rapid load variation during the operation. The analysis will consider an average profile for heat and power demand of a family house. Finally data analysis and power system limitations will be used to develop a viable strategy of operation.

분산전원이 연계된 배전계통에 있어서 ANN을 이용한 최적 전압조정방안에 관한 연구

본 논문은 분산전원이 연계된 배전계통에 있어서 온 라인 리얼타임으로 조정이 가능한 최적 전압조정방안을 제시한다. 가능한 많은 수용가에게 적정한 전압을 공급하기 위하여 최적 송출전압이 결정되어져야 하는데, 여기서는 급변하는 배전계통의 급격한 부하변동과 분산전원의 불규칙적인 출력특성을 고려하기 위하여, 인공 신경회로망(ANN: Artificial Neural Network)을 이용한 최적 전압조정방안을 제시한다. 본 논문에서 제시한 알고리즘을 이용하여 배전 모델계통에 적용한 결과, 제안한 방법이 다수의 분산전원이 연계된 배전계통의 전압조정에 실용적인 방책임을 확인하였다. This paper deals with the optimal on-line real time voltage regulation methods in power distribution systems interconnected with the Distributed Generation(DG) systems. In order to deliver suitable voltage to as many customers as possible, the optimal sending voltage should be decided by the effective voltage regulation method by using artificial neural networks to consider the rapid load variation and random operation characteristics of DG systems. The results from a case study show that the proposed method can be a practical tool for the voltage regulation in distribution systems including many DG systems.